Vapour-liquid equilibrium in the
monoethylene glycol - methane system
at elevated pressures
Anita Bersås
Chemical Engineering and Biotechnology
Submission date: June 2012
Supervisor:
Hallvard Fjøsne Svendsen, IKP
Co-supervisor:
Even Solbraa, Statoil ASA
Norwegian University of Science and Technology
Department of Chemical Engineering
Abstract
A range of different chemicals are used in natural gas processing. The systems
operate in closed loops, but a small amount of the chemicals are lost due to the
solubility of the chemical in the gas phase. This leads to increased operational
costs, it may cause HSE related problems, and it can lead to operational
difficulties and contamination of downstream processes and products.
A limited number of vapour-liquid equilibrium, VLE, data for processing chemicals in methane are available in the open literature. It is therefore important
to obtain new experimental data to adjust and verify thermodynamic models
used to calculate the concentration of processing chemicals in the gas phase.
Monoethylene glycol, MEG, has been chosen for this work as there exist analytical methods and some literature data for the MEG-methane system. The
plan is to continue the work started in this project to obtain experimental
data for methyldiethanolamine, triethylene glycol and piperazine in addition
to more experimental data for MEG.
The purpose of this work was to develop laboratory equipment and to obtain
experimental data for the solubility of processing chemicals in methane. Two
experimental rigs using analytical techniques with sampling have been used; A
static equipment that apply an isothermal method, and a dynamic equipment
applying a semi-flow isobaric-isothermal method.
The static equipment, where methane is saturated with MEG in a PVT-cell,
has been built and tested as part of this work. An existing dynamic equipment,
where the gas is saturated and condensed in a series arrangement, was modified
for experiments with glycols. Experiments were conducted in the temperature
range from 273.15 to 313.15 K, and for pressures up to 150 bar. The samples
from the experiments were analysed using ATD-GC-FID.
The results from the experiments were compared to an existing model based on
the CPA-EoS. In addition a model based on the SRK-EoS was developed. The
initial results from the SRK-EoS model were significantly higher compared to
the CPA-EoS model and the experimental data. An interaction parameter,
K12 , of 0.35 in the mixing rule was found to improve the agreement between
the developed model and the experimental data.
The experimets showed that the concentration of MEG in methane measured
increases at increasing temperatures. The modelled values show that the concentration of MEG in methane starts to decrease at increasing pressures, before
it passes through a minimum and starts to increase. Further experiments to
determine the pressure resulting in the minimum value will be conducted in
the continuation of this work.
i
ii
Sammendrag
En rekke ulike kjemikalier benyttes i prosessering av naturgass. Systemene
driftes i lukkede sløyfer, men en liten mengde av kjemikaliene tapes på grunn
av løseligheten av kjemikaliet i gassfasen. Dette fører til økte driftskostnader,
det kan gi problemer relatert til HMS, og det kan føre til driftsproblemer og
forurensning av prosesser og produkter nedstrøms.
Et begrenset antall data for damp-væske likevekt er tilgjengelig for prosesskjemkalier i metan i den åpne litteraturen. Det er derfor viktig å skaffe
nye eksperimentelle data for å korrigere og verifisere termodynamiske modeller brukt til å beregne konsentrasjonen av prosesskjemikalier i metan. Monoetylenglykol, MEG, er valgt for dette prosjektet på grunn av at det eksisterer analysemetoder og noen eksperimentelle data for MEG-metan systemet.
Planen er å fortsatte arbeidet påbegynt i dette prosjektet for å arbeide frem
eksperimentelle data for metyldietanolamin, trietylenglykol og piperazin, i tillegg til flere eksperimentelle data for MEG.
Formålet med denne oppgaven har vært å utvikle laboratorieutstyr og å fremskaffe eksperimentelle data for løseligheten av prosesskjemikalier i metan. To
eksperimentelle oppsett som benytter analytiske teknikker med prøvetaking
har vært benyttet: En statisk rigg som benytter en isoterm metode, og en
dynamisk rigg som benytter en semi-strømning, isobar-isoterm metode.
Det statiske utstyret, hvor metan er mettet med MEG i en PVT-celle, har blitt
bygd og testet som en del av dette prosjektet. Et eksisterende dynamisk utstyr,
hvor gassen mettes og kondenseres i serie, har blitt tilpasset for å kjøre forsøk
med glykoler. Eksperimentene har blitt utført i temperaturområdet mellom
273.15 og 313.15 K, og ved trykk opp til 150 bar. Prøvene fra forsøkene har
blitt analysert ved hjelp av ATD-GC-FID.
Resultatene fra forsøkene ble sammenlignet med en eksisterende modell basert
på CPA tilstandsligningen. I tillegg har en modell basert på SRK tilstandsligningen blitt utviklet. De første resultatene fra SRK-modellen var betydelig
høyere sammenlignet med resultatene fra CPA-modellen og de eksperimentelle
dataene. En interaksjonsparameter, K12 , med en verdi på 0.35 ble satt inn
i blandingsregelen, noe som forbedret overenskomsten mellom SRK-modellen
og de eksperimentelle dataene.
Eksperimentene viser at den målte konsentrasjonen av MEG i metan øker
ved økende temperaturer. De modellerte veriene viser at konsentrasjonen av
MEG i metan begynner å avta med økende trykk, før den går gjennom et
minimumspunkt og begynner å øke. Videre forsøk for å avgjøre hvilke trykk
som resulterer i minimumsverdien vil bli gjennomført i fortsettelsen av dette
arbeidet.
iii
iv
Preface
This report is written as part of the master thesis in chemical engineering,
TKP 4900, at the Norwegian University of Science and Technology, NTNU.
The project has been in cooperation with the Gas Treating Technology department at the Statoil Research Centre in Trondheim, and the research group for
Environmental engineering and reactor technology at NTNU. The objective of
the project is to develop equipment, and obtain experimental data, to measure
the concentration of monoethylene glycol in methane at high pressures.
The project has been an opportunity for me to link previous work experience
from Statoil with theory acquired through my studies at NTNU. I have had
my share of problems working with the experiments, but I have learned a lot
through the process of solving the problems along the way.
I greatly appreciate the help from my supervisors in Statoil, Even Solbraa
and Eivind Johannessen, and would like to thank them for giving me this
opportunity. You have been very open to help me with questions along the
way, and I value the time you have used to help me. I would also like to thank
my supervisor at NTNU, Professor Hallvard Svendsen, for his guidance, and
for allowing me to work with this project.
This work would not have been possible without the help from my colleagues
at the Statoil Research Centre. I specially would like to thank Toril Haugum
and Gunhild Neverdal for their help in the lab, and Torbjørn Vegard Løkken
and Andrea Carolina Machado Miguens for their help, follow-up and support.
I also would like to thank the people working in the support organisation
for the lab, T-LAB, for helping me with the building of the new rig and the
modifications done to the existing rig.
I would also like to thank my fellow students and friends at NTNU. Thanks to
Ivar Nesje for your help with computer related questions, and for introducing
me to Latex.
A special thanks to Are - for always being there for me.
I declare that this is an independent work according to the exam regulations
of the Norwegian University of Science and Technology.
Trondheim, June 14, 2012
Anita Bersås
v
vi
Contents
List of figures
ix
List of tables
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Nomenclature
xiii
1 Introduction
1.1 Application of MEG in natural gas processing . . . . . . . . . .
1.2 Aim for the thesis . . . . . . . . . . . . . . . . . . . . . . . . . .
2 Theory
2.1 Thermodynamic framework . . . . . . . . . . . . . . . . . .
2.1.1 Soave-Redlich-Kwong Equation of State, SRK-EoS .
2.1.2 Cubic-Plus-Association - Equation of State, CPA-EoS
2.2 Literature data . . . . . . . . . . . . . . . . . . . . . . . . .
2.2.1 Literature data for the solubility of MEG in methane
2.2.2 Literature data for the vapor pressure of MEG . . . .
2.2.3 Literature data for the solubility of methane in MEG
2.3 Methods for phase equilibrium measurements . . . . . . . .
2.4 Automated thermal desorption gas chromatography . . . . .
2.4.1 Automated Thermal Desorption, ATD . . . . . . . .
2.4.2 Gas chromatography, GC . . . . . . . . . . . . . . . .
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3 Modelling of the solubility of MEG in methane
4 Experimental equipment and HSE
4.1 Chemicals . . . . . . . . . . . . . . . . . . . . . .
4.2 Experimental equipment . . . . . . . . . . . . . .
4.2.1 Dynamic experiments . . . . . . . . . . . .
4.2.2 Static experiments . . . . . . . . . . . . .
4.3 Sample analysis by gas chromatography . . . . . .
4.3.1 Calibration . . . . . . . . . . . . . . . . .
4.3.2 Maintenance . . . . . . . . . . . . . . . . .
4.4 HSE . . . . . . . . . . . . . . . . . . . . . . . . .
4.4.1 HSE for the laboratory at Statoil Research
4.4.2 Chemicals . . . . . . . . . . . . . . . . . .
4.4.3 Dynamic experimental rig . . . . . . . . .
4.4.4 Static experimental rig . . . . . . . . . . .
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5 Results and discussion
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5.1 Dynamic experiments . . . . . . . . . . . . . . . . . . . . . . . . 29
5.1.1 Experiments at 50 bar and various temperatures . . . . . 29
vii
viii
CONTENTS
5.2
5.3
5.4
5.5
5.1.2 Experiments at 273.15 K and different pressures .
5.1.3 Further discussion . . . . . . . . . . . . . . . . . .
Static experiments . . . . . . . . . . . . . . . . . . . . .
5.2.1 Experiments at 50 bar and ambient temperatures
5.2.2 Experiments at 100 bar and 298.6 K . . . . . . .
5.2.3 Further discussion . . . . . . . . . . . . . . . . . .
Analysis by ATD-GC . . . . . . . . . . . . . . . . . . . .
Uncertainty in the experimental data . . . . . . . . . . .
Modelling . . . . . . . . . . . . . . . . . . . . . . . . . .
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6 Further work
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6.1 Dynamic equilibrium experiments . . . . . . . . . . . . . . . . . 47
6.2 Static equilibrium experiments . . . . . . . . . . . . . . . . . . . 47
7 Conclusion
49
Bibliography
52
A Calibration
A.1 Dynamic equipment .
A.1.1 Temperature .
A.1.2 Pressure . . .
A.1.3 Gas volume .
A.2 Static equipment . .
A.2.1 Temperature .
A.2.2 Pressure . . .
A.2.3 Gas volume .
A.3 Gas chromatograph .
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B Matlab source code and results from the calculations
61
B.1 Results from calculations . . . . . . . . . . . . . . . . . . . . . . 61
B.2 Matlab source code, model using SRK-EoS . . . . . . . . . . . . 62
C Estimation of the concentration of MEG in the gas phase
67
D Lists of experiments
71
E Safety analysis for the static equipment
73
F Experimental procedures for the static experiments
77
List of Figures
2.1
2.2
2.3
2.4
2.5
4.1
4.2
4.3
5.1
5.2
5.3
5.4
5.5
5.6
5.7
5.8
5.9
Illustration of phase equilibrium . . . . . . . . . . . . . . . . .
Plot of literature data for the solubility of MEG in methane
[Folas et al., 2007] . . . . . . . . . . . . . . . . . . . . . . . . .
Plot of literature data for the vapour pressure of MEG . . . .
Plot of literature data for the vapour pressure of MEG in the
temperature range from 270 to 350 K . . . . . . . . . . . . . .
Overview of principles used for high pressure phase equilibrium
measurements [Fonseca, 2010]). . . . . . . . . . . . . . . . . .
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Schematic sketch of the dynamic equipment . . . . . . . . . . . 17
Illustration of the flow distributor in the saturation cylinders
[Haugum and Sharifi, 2011] . . . . . . . . . . . . . . . . . . . . 18
Schematic sketch of static equipment . . . . . . . . . . . . . . . 21
Parallels in the experiments at 50 bar and various temperatures
Results from dynamic experiments at 50 bar and different temperatures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Parallels in the experiments at 273.15 K and various pressures .
Results from dynamic experiments at 273.15 K and different
pressures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Results from static experiments at ambient temperature and 50
bar . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Comparison of CPA model and result from static experiments
at ambient temperature and 50 bar . . . . . . . . . . . . . . . .
Results from static experiments at 298.6 K and 100 bar . . . . .
Comparison of CPA-EoS model and result from static experiments at 298.6 K and 100 bar . . . . . . . . . . . . . . . . . . .
Results from modelling of the concentration of MEG in methane
A.1 Results from the temperature calibration of the water baths for
the dynamic test rig . . . . . . . . . . . . . . . . . . . . . . .
A.2 Results from the calibration of the Keller PAA 35X pressure
transmitter from the dynamic test rig . . . . . . . . . . . . . .
A.3 Results from the control of the Ritter TG 1/7 gas clock for the
dynamic test rig . . . . . . . . . . . . . . . . . . . . . . . . . .
A.4 Results from the calibration of the thermocouples in the static
test rig . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
A.5 Results from the calibration of the Keller Leo 3 pressure transmitter from the static test rig . . . . . . . . . . . . . . . . . .
A.6 Calibration curve for the GC . . . . . . . . . . . . . . . . . . .
A.7 Form for quality controls . . . . . . . . . . . . . . . . . . . . .
ix
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x
List of Tables
2.1
2.2
Sources for literature data for the vapour pressure of MEG . . .
Literature data for the solubility of methane in MEG . . . . . .
4.1
4.2
4.3
4.4
Supplier and purity for the chemicals used .
Experimental matrix - Dynamic experiments
Experimental matrix - Static experiments . .
Characteristics for the gas chromatograph .
5.1
5.2
5.3
Results for the concentration of MEG in methane . . . . . . . . 29
The impact of water content in the MEG . . . . . . . . . . . . . 36
Concentration of water in different sources of MEG . . . . . . . 37
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B.1 Results from the calculation of the concentration of MEG in
methane by using the SRK-EoS . . . . . . . . . . . . . . . . . . 61
C.1 Calculations of the fugacity coefficients using the SRK-EoS . . . 68
C.2 Calculations of the Poynting factor . . . . . . . . . . . . . . . . 68
C.3 Calculations of a minimum estimate for yi . . . . . . . . . . . . 69
D.1 List of static experiments . . . . . . . . . . . . . . . . . . . . . . 71
D.2 List of dynamic experiments . . . . . . . . . . . . . . . . . . . . 72
xi
xii
Nomenclature
Latin letters
a0
aij
ai (T )
A
A
b
bi
B
B
C
D
E
fil
fi0
fip
fiv
g(d)hs
g(d)seg
mi
P
Pc
Ps
Pis
R
T
Tc,i
xi
XA
yi
Z
3 2
)
Parameter in the energy term [ bar(m
]
mol2
Non-randomness parameter [−]
Energy parameter [−]
Equation (3.3)
Parameter in the Antoine equation [−]
m3
]
Covolume parameter [ mol
m3
]
Covolume parameter for component i [ mol
Equation (3.4)
Parameter in the Antoine equation [−]
Parameter in the Antoine equation [−]
Parameter in the Antoine equation [−]
Parameter in the Antoine equation [−]
Fugacity for component i in the liquid phase [P a]
Fugacity for pure component i for a given T and P [P a]
Fugacity for pure component i at a pressure different from Pis [P a]
Fugacity for component i in the vapour phase [P a]
Radial distribution function, hard sphere [−]
Radial distribution function, segment [−]
Effective number of segments within the molecule [−]
Pressure [bar]
Critical pressure [bar]
Saturation pressure [bar]
Saturation pressure of component i [bar]
J
]
Gas constant [ mol·K
Temperature [K]
Critical temperature [K]
Mole fraction of component i in the liquid phase [−]
Mole fraction of the compound not bounded at site A [−]
Mole fraction of component i in the gas phase [−]
Compressibility factor [−], equation (3.5)
xiii
xiv
LIST OF TABLES
Greek letters
αi
β
∆AB
AB
γi
ν
νi
ωi
φi
φsi
ρ
Θ
3 2
)
Energy parameter [ P a(m
]
mol2
Association volume parameter [−]
m3
]
Interaction strength between sites A and B [ mol
J
Association energy of interaction between sites A and B [ mol
]
Activity coefficient for component i [−]
m3
Molar volume [ mol
]
m3
]
Molar volume of component i [ mol
Acentric factor [−]
Fugacity coefficient for component i [−]
Fugacity coefficient of saturated component i [−]
Molar density [ mol
]
m3
Poynting factor [−]
Abbreviations
ATD
CPA
EoS
FID
GC
HAZOP
HSE
MDEA
MEG
NTNU
P&ID
PVT
QC
SRK
TEG
VLE
Automatic thermal desorption
Cubic plus association
Equation of state
Flame ionisation detector
Gas chromatography
Hazard and operability study
Health, safety and the environment
Methyldiethanolamine
Monoethylene glycol
Norwegian University of Science and Technology
Piping and instrumentation diagram
Pressure-volume-temperature
Quality control
Soave-Redlich-Kwong
Triethylene glycol
Vapour-liquid equilibrium
Chapter 1
Introduction
A range of different chemicals are used in natural gas processing. The systems
operate in closed loops, but a small amount of the chemicals are lost due to the
solubility of the chemical in the gas phase. This leads to increased operational
costs, it may cause HSE related problems, and it can lead to operational
difficulties and contamination of downstream processes and products.
A limited number of vapour-liquid equilibrium data for processing chemicals
in methane are available in the open literature. It is therefore important to
obtain new experimental data to adjust and verify thermodynamic models used
to calculate the concentration of chemicals in the gas phase. Monoethylene
glycol, MEG, has been chosen for this work, as there are analytical methods
and some literature data available for the MEG-methane system.
1.1
Application of MEG in natural gas processing
Monoethylene glycol, MEG, is a commonly used hydrate inhibitor in natural
gas processing. Gas hydrate formation is a serious problem, because hydrates
can agglomerate and block pipelines and processing equipment. This can lead
to flow assurance failure and can stop the production. It can also leads to
dangerous situations because of pressure build up, and the risk of a sudden
release of hydrate plugs that can damage process equipment.
Hydrates are solids built up by a small gas molecule surrounded by a structure
of hydrogen bonded water molecules. The formation of hydrates is a phase
transition that can take place at high pressures combined with low temperatures in the presence of liquid water.
Monoethylene glycol is a thermodynamic inhibitor that lowers the freezing
point of the gas hydrate. For multiphase pipelines it is common to add a
hydrate inhibitor like MEG to the pipeline, and transport it together with the
multiphase flow to prevent hydrate formation. The hydrate inhibitor is then
regenerated to remove water and salts, before it is circulated back into the
process.
The MEG system is a closed loop, but there are still challenges related to
chemical loss. MEG is lost due to the physical solubility in the gas, and
because of the entrainment of droplets. A lot can be done to minimise liquid
entrainment by correct design of separation equipment, and it is therefore the
solubility of MEG in the gas phase that sets the minimum chemical loss.
1
2
CHAPTER 1. INTRODUCTION
The loss of MEG should be minimised due to a number of process related and
economic reasons. The need for refill to the MEG system leads to increased operational costs. In addition the operational costs may be further increased due
to operational difficulties and contamination of downstream processes. The
monoethylene glycol solved in the gas can adsorb onto the walls of process
equipment, and it can contaminate other processing chemicals downstream.
As MEG is used in the early stages of gas processing, the risk of freeze out
and plugging of downstream low temperature processing equipment and contamination of downstream products is small.
1.2
Aim for the thesis
The purpose of this work is to develop laboratory equipment and to obtain
experimental data for the solubility of processing chemicals in methane. As
previously mentioned it has been chosen to focus on MEG in this work. The
plan is to continue the work started in this project to get experimental data
for triethylene glycol, TEG, and methyldiethanolamine, MDEA, in the longer
run.
For all the processing chemicals mentioned there are a very limited number of
experimental data available. The reason for this is that the experiments are
time consuming and expensive to run [Folas et al., 2007]. The lack of sufficient
data leads to uncertainty in models, and new experimental data is therefore
important to adjust and verify the existing models.
Laboratory experiments have been carried out as part of this work. The two
experimental rigs used will in this work be referred to as a static and a dynamic equipment. Both of the equipment uses an analytical technique with
sampling; The static equipment apply an isothermal method, and the dynamic
equipment apply a semi-flow isobaric-isothermal method. In the static equipment the gas was saturated in a high pressure PVT-cell with variable volume,
while in the dynamic equipment the gas was oversaturated before excess MEG
was condensed at a lower temperature in a series design. Samples from the rigs
were analysed using thermal desorption tubes, ATD, combined with gas chromatography, GC. The same analytical technique has been used by [Folas et al.,
2007]. The static laboratory rig and the appurtenant experimental procedures
have been developed as part of this work. For the dynamic experiments an
existing rig was used and further adapted to experiments with glycols.
The experimental data obtained was compared to two thermodynamic models.
The first model was programed by [Solbraa, 2002] and uses the cubic plus
association, CPA, equation of state. The CPA-EoS model was compared to
a second model developed as part of this work, using Soave-Redlich-Kwong,
SRK, equation of state.
Chapter 2
Theory
2.1
Thermodynamic framework
In this work the phase equilibrium between MEG in liquid phase and methane
in vapour phase has been studied. This is illustrated in figure 2.1. Only the
solubility of MEG in methane has been investigated, as this is the part of the
phase equilibrium that is relevant for the problem to be addressed.
Figure 2.1: Illustration of phase equilibrium
When a system is in phase equilibrium, the fugacity in the vapour phase is
equal to the fugacity in the liquid phase, as shown in equation (2.1) [Prausnitz
et al., 1999, eq.2-47].
fiv = fil
(2.1)
The equation for the fugacity of component i in the vapour phase is shown in
equation (2.2) [Prausnitz et al., 1999, eq.3-34].
fiv = P yi φi
(2.2)
The fugacity of component i in the liquid phase of a mixture, fil , is given by
equation (2.3) [Prausnitz et al., 1999, eq.6-1]. fi0 is the fugacity of pure component i at a given temperature and pressure. The equation for the fugacity
of pure component i at a pressure differenet than the saturation pressure, fip ,
is shown in equation (2.4) [Prausnitz et al., 1999, eq.3-39].
fil = xi γi fi0
fic
=
Pis φsi
exp
3
Z P
Pis
(2.3)
νi
dP
RT
!
(2.4)
4
CHAPTER 2. THEORY
Equation (2.4) is used to correct the fugacity coefficient to the same pressure as
is used for fi0 . By combining equations (2.1), (2.2), (2.3) and (2.4), the equation
for the phase equation can be derived as shown in equation (2.5).
y i P φi =
γi xi Pis φsi
exp
Z P
Pis
νi
dP
RT
!
(2.5)
In this work the Soave-Redlich-Kwong, SRK, and the Cubic-Plus-Association,
CPA, equations of state have been used to calculate the fugacity coefficient,
and hence the concentration of MEG in the gas phase. Presentations of the
SRK- and CPA-EoS are found in sections 2.1.1 and 2.1.2 respectively.
2.1.1
Soave-Redlich-Kwong Equation of State, SRK-EoS
The Soave-Redlich-Kwong Equation of State, SRK-EoS, was developed by
[Soave, 1972]. This is a modified version of the original equation developed by
[Redlich and Kwong, 1949]. The modification was introduced to give better
results for applications to multicomponent vapour-liquid equilibrium, VLE,
calculations, and involved the development of a two-variable dependency for
the energy parameter, a. The parameter a is a function of temperature, T ,
and the acentric factor, ω. The SRK-EoS is shown in (2.6). The information
in this section is taken from [Soave, 1972].
P =
a(T )
RT
−
ν − b ν(ν + b)
(2.6)
The parameters a(T ) and b for component i are given in equations (2.7) and
(2.8) respectively. Parameter a(T ) is referred to as the energy parameter, and
it takes into account that the attractive forces between the molecules in the
gas reduces the pressure in the system. The covolume factor, b, represent
approximately the volume occupied by the gas molecules.
ai (T ) =
bi =
2
0.42747αi R2 TCi
PCi
(2.7)
0.08664RTCi
PCi
(2.8)
The energy parameter ai (T ) is a function of the temperature coefficient αi .
αi is a function of the effective number of segments within the molecule, mi ,
which again is a function of the acentric factor, ωi . The equations for αi and
mi are given in equations (2.9) and (2.10) respectively. The values for ωi were
taken from [DIPPR, 2012].
"
αi = 1 + mi 1 −
s
T
TCi
!#2
mi = 0.48 + 1.574ωi − 0.176ωi2
(2.9)
(2.10)
2.2. LITERATURE DATA
2.1.2
5
Cubic-Plus-Association - Equation of State, CPA-EoS
The Cubic Plus Association Equation of State, CPA-EoS, was developed by
[Kontogeorgis et al., 1996]. It is a combination of the SRK-EoS [Soave, 1972]
and perturbation theory [Huang and Radosz, 1990]. Perturbation theory takes
into account the attractive interactions between species forming hydrogen
bonds. The modification was introduced to evaluate the effect the interactions between molecules may have on the theoretical properties of the fluids.
The CPA-EoS is shown in equation (2.11). The information in this section is
taken from [Kontogeorgis et al., 1996].
a(T )
RT X 1
1 ∂X A
RT
−
+
ρ
−
P =
ν − b ν(ν + b)
ν
X A 2 ∂ρ
A
(2.11)
The energy parameter, a, is defined using the temperature dependency described by [Soave, 1972], see equation (2.12). Temperature independency is
assumed for the covolume parameter, b.
a = a0 1 + c 1 1 −
q
2
(2.12)
TR
Three additional parameters are needed for the association term. The mole
fraction of molecules not bonded at site A, X A , is defined as shown in equation
(2.13). The association strength, ∆AB , is defined in equation (2.14), where the
radial distribution function, g(d), is given in equation (2.15).
!−1
A
X = 1+ρ
X
B
AB
X ∆
(2.13)
B
"
AB
∆
seg
= g(d)
AB
exp
RT
g(d)seg ≈ g(d)hs =
!
#
− 1 βb
2−
2 1−
2.2
2.2.1
b
4ν
b
4ν
3
(2.14)
(2.15)
Literature data
Literature data for the solubility of MEG in methane
The only published data found for high pressure VLE of the MEG-methane
system were published by [Folas et al., 2007]. The reason for the lack of
experimental data is that these experiments are time consuming and expensive
to obtain [Folas et al., 2007]. A summary of the data is presented in figure
2.2.
In addition there is an internal report in Statoil from the work by [Haugum
and Sharifi, 2011]. This report contains results from experiments run on the
dynamic equipment used in this work. The experiments are run at pressures
of 50, 100 and 150 bar, in the temperature range from 273.15 to 303.15 K.
6
CHAPTER 2. THEORY
Figure 2.2: Plot of literature data for the solubility of MEG in methane [Folas
et al., 2007]
As these results are not published the data from the experiments will not be
repeated here, but the experimental points are used for comparison in chapter
5.
2.2.2
Literature data for the vapor pressure of MEG
A literature search showed that a lot of experimental data points are available
for the vapour pressure of MEG. A summary of some of the experimental data
found is included in table 2.1.
The experimental data listed in table 2.1 are plotted in figure 2.3. In figure
2.3 it is difficult to see the data points at low temperatures because of the
scale on the y-axis of the graph. As the experiments in this work are in the
temperature range from 273.15 to 333.15 K, a second graph showing the data
in this temperature range is included in figure 2.4.
Data for the vapour pressure of MEG were needed for the SRK-EoS model to
calculate the concentration of MEG in the gas phase at different temperatures
and pressures. For this calculation the Riedel equation was used, with parameters taken from [DIPPR, 2012]. See chapter 3 for more information. With
the exception of [Kamihama et al., 2012], data from all the sources listed in
table 2.1 are included in the data-pool used to determine the parameters for
the Riedel equation [DIPPR, 2012].
2.2. LITERATURE DATA
7
Table 2.1: Sources for literature data for the vapour pressure of MEG
References
[Joo and Arlt, 1981] a
[Salvi et al., 1990] b
[Kaye and Laby, 1995] c
[Hales et al., 1981] d
[Ambrose and Hall, 1981] e
[Vasiltsova et al., 2005] d
[Petitjean et al., 2009] f
[Kamihama et al., 2012] a
Temperature range
[K]
335
374
332
282
374
303
307
412
-
420
571
471
374
496
337
385
471
Pressure range
[kP a]
No. of points
[−]
0.16 - 18
2.2 - 1092
0.2 - 102
0.0025 - 2.2
2.2 - 202
0.02 - 0.22
0.028 - 3.5
13 - 102
18
28
8
33
27
14
15
17
a
Equilibrium still
Differential PVT apparatus
c
Unknown
d
Transpiration
e
Comparative ebulliometry
f
Static VLE apparatus
b
Figure 2.3: Plot of literature data for the vapour pressure of MEG listed
in table 2.1. The data are compared to calculated vapour pressure (Riedel
equation, [DIPPR, 2012]).
2.2.3
Literature data for the solubility of methane in MEG
Literature data for the solubility of methane in MEG are needed in the SRKEoS model developed, see chapter 3. Only a few points in the pressure range
between 50 and 150 bar were needed for the purpose of the model, but more
data for the solubility of methane in MEG are available in the open literature.
8
CHAPTER 2. THEORY
Figure 2.4: Plot of literature data for the vapour pressure of MEG in the
temperature range from 270 to 350 K. The data are compared to calculated
vapour pressure (Riedel equation, [DIPPR, 2012]).
The data needed were found in [Folas et al., 2007] and [Zheng et al., 1999],
and a summary of some of the experimental data found in these references are
summarised in table 2.2.
Table 2.2: Literature data for the solubility of methane in MEG
Pressure
[bar]
Temperature
[K]
Mole fraction methane
[−]
50
50.2
50.2
59.8
99.8
100.2
100.8
103.0
159.0
283.29
298.33
323.35
323.15
273.25
298.25
323.45
323.15
323.15
0.005950
0.005950
0.006060
0.0066
0.011600
0.011490
0.011460
0.0110
0.0148
Reference
[Folas et al., 2007]
[Folas et al., 2007]
[Folas et al., 2007]
[Zheng et al., 1999]
[Folas et al., 2007]
[Folas et al., 2007]
[Folas et al., 2007]
[Zheng et al., 1999]
[Zheng et al., 1999]
2.3. METHODS FOR PHASE EQUILIBRIUM MEASUREMENTS
2.3
9
Methods for phase equilibrium measurements
There are many experimental methods available for measurements of phase
equilibrium. There is not one specific method that is suitable for the range of
various measurements, and the methods have advantages and disadvantages
that influence the choice of method. Different classifications of the methods
have been presented, but in this work the classification described by [Fonseca,
2010] will be presented. As the focus for this work is on high pressures, techniques for low pressures are not included in this overview. Also the focus of the
overview given here is on analytical methods, as two analytical methods have
been used in this work. A thorough discussion of all the different methods for
high pressure phase equilibrium experiments can be found in [Fonseca, 2010,
ch.3], which is also used as source for the information in this section.
The methods are divided into two groups: Analytical and synthetic methods.
In the analytical methods the composition of the phases in equilibrium is determined by an analytical method, with or without sampling, after equilibrium
is reached. For the synthetic methods the system is synthesised previous to the
experiments, and the exact composition of the system is known. The synthetic
methods are divided in two groups depending on whether there occurs a detectable phase change or not. An overview of the classification of the different
methods are shown in figure 2.5.
Figure 2.5: Overview of principles used for high pressure phase equilibrium
measurements [Fonseca, 2010]).
Analytical methods with sampling can be classified as isothermal, isobaric and
isobaric-isothermal methods. The classification is based on the principle for
how the system reaches equilibrium. An advantage with these methods is the
characterisation of the different phases in the system, but a disadvantage is
that the equilibrium can be disturbed during sampling because of pressure
drop. The most common way to avoid this problem is by applying a variable
volume cell with a moveable piston that can keep the pressure constant. Other
possibilities to minimise the problem are to use a large cell volume compared
to the volume of the sample, or by blocking the contents of the cell from the
sample to be withdrawn.
In isothermal methods the temperature of the system is kept constant during
the experiment. Other properties like pressure and composition vary with
time until the system reaches equilibrium. An advantage is that the point
10
CHAPTER 2. THEORY
where equilibrium is achieved can be observed, because this will be reflected
in constant values for the equilibrium properties.
Isobaric methods measure the boiling temperature for pure components or
mixtures under conditions of constant pressure. The most common isobaric
method is ebulliometry, a method that also can be used for experiments at low
pressures.
In isobaric-isothermal methods one or more fluid streams are continuously
pumped into a thermostated equilibrium cell. The pressure in the system
is kept constant by controlling the inlet and outlet flows. This category of
methods is therefore often called dynamic methods. For continuous flow experiments the separate components in the system are supplied to the cell in a
continuous manner. Another alternative is semi-flow methods where one of the
phases is stationary while the other phase is stable. Often a mobile gas phase
is passed through a stationary liquid phase. In these methods the sampling
process can be carried out without disturbing the phase equilibrium, and the
methods are therefore well suited for trace component experiments where large
sample volumes are needed.
For analytical methods without sampling the two most common alternatives
are spectroscopic and gravimetric methods. A number of spectroscopic methods can be used, including infrared and near infrared spectroscopy. A disadvantage using spectroscopic methods is their inability to perform a complete
characterisation of the composition of the phases, as they are only able to determine the concentration of a particular compound in the different phases.
The alternative of gravimetric methods is based on the monitoring of the condensed phase. Equipment using this method can either have the entire equilibrium cell placed on a balance, or a balance mounted inside the equilibrium
cell. A disadvantage using gravimetric methods is that the densities of the
phases are needed to correct for the buoyancy effects.
Synthetic methods avoid the need for sampling by starting the experiments
with a system with a known composition. Phase behaviour in the equilibrium
cell is observed, measuring properties like pressure and temperature in the
equilibrium state.
For synthetic methods with a phase transition the experiment starts with a
homogeneous phase, before the conditions are altered to provoke the formation
of a new phase. These methods can be divided into two subgroups, visual and
non-visual methods, depending on the detection of the phase transition.
In synthetic methods without a phase transition a number of equilibrium properties are measured to characterise the phase compositions. Properties that
can be measured are temperature, pressure, densities and volumes, and the
measurements can be combined with material balance equations to study the
composition of the phases. These methods can be divided into isothermal and
isobaric methods.
2.4
Automated thermal desorption gas chromatography
The analytical method used in this work is automated thermal desorption
combined with gas chromatography. This section gives an introduction to the
2.4. AUTOMATED THERMAL DESORPTION GAS CHROMATOGRAPHY11
theory for this analytical method. For more details about the equipment used,
see section 4.3.
2.4.1
Automated Thermal Desorption, ATD
Automated thermal desorption, ATD, is a method used for injecting samples
into the gas chromatograph, GC. The method is used for the analysis of trace
levels of organic components. The samples are heated in a flow of inert gas to
extract the compound into the vapour stream, before the sample is analysed
using for example gas chromatography or spectrometry. For most applications
desorption is carried out over two stages to obtain better analytical resolution
and higher sensitivity.
The sampling is performed by passing the gas through an ATD tube, where the
trace component is adsorbed onto an adsorption material inside a metal tube.
For the MEG samples in this work the adsorption material used is Tenax TA.
The ATD-tube is capped to avoid contamination from the air. This makes it
easy to transport the samples, and it is also possible to store samples for later
analysis.
The ATD-tubes are then placed in a tray and inserted into the automated
thermal desorption unit before the analysis is started. During the analysis the
tube is loaded into a temperature controlled environment and connected to a
supply of carrier gas. The tube and the surrounding system is then leak tested
to make sure no part of the sample is lost during desorption. If this test fails,
the sample is not analysed.
If the leak test is passed, the desorption process is ready to start. First the tube
is dry purged in the sampling direction to remove any traces of water that may
be present in the system. Next a prepurge is run, before the primary desorption
is started. In this stage the tube is heated to desorb the sample from the tube.
The sample is carried with the flow of inert gas to a cold trap, where the sample
is adsorbed for a second time. The second adsorption-desorption stage focuses
the sample and concentrates the analytes before transferring the sample to
the analytical system. The cold trap is then rapidly heated in a secondary
desorption stage, during which the sample is injected into the GC.
After the analysis the ATD-tube is heated to 593.15 K while being flushed
with an inert gas, to make sure that any traces of sample have been removed
from the tube. Regular tests are run on random ATD-tubes to check that the
ATD-tube is clean and also that all traces of the samples are removed from
the system.
2.4.2
Gas chromatography, GC
Chromatography aims at separating the different compounds in a mixture. It
is then possible to qualitate and quantitate the different compounds in the
sample. As gas chromatography is a well-known analytical method, only a
short introduction is given in this text. Further information can be found
in numerous publications and textbooks about analytical chemistry and chromatography.
The sample is injected into a flow of carrier gas in an injector. The injector
12
CHAPTER 2. THEORY
is heated to make sure that the entire sample is in vapour phase. The carrier
gas transport the vapour into the column, where the sample molecules are distributed between a stationary and a mobile phase. The carrier gas is the mobile
phase, while the coating of the inside walls of the column act as the stationary
phase. The column is placed in an oven to control the temperature, and depending on the chosen temperature, column composition and properties of the
compounds in the sample, the compounds in the sample travel through the
column at different rates. When the compounds elute from the column, they
enter a detector where an electronic signal is generated. The magnitude of the
signal is recorded and plotted as a function of time in a chromatogram.
The size of the peak in the chromatogram is equivalent to the concentration
of the compound in the sample. If the method and physical conditions are
kept the same, a compound will have the same retention time every time it
is passed through the gas chromatograph. By analysing known amounts of
the compounds of interest, so-called standard solutions, the sample can be
qualified and quantified.
Chapter 3
Modelling of the solubility of MEG in
methane
A good model is necessary to perform reliable calculations for the solubility of
MEG in methane, especially for conditions where experimental data are not
available. This work has used the Soave-Redlich-Kwong, SRK, and the CubicPlus-Association, CPA, equations of state to calculate the concentration of
MEG in the gas phase. For the SRK-EoS a Matlab script was written as part
of this work, and for the CPA-EoS an existing program developed by [Solbraa,
2002] was used to perform the calculations.
The SRK-EoS model developed in this work is set up as an iterative model to
calculate the concentration of MEG in the gas phase, yi . The model uses the
phase equilibrium equation presented in section 2.1, equation (2.5) [Prausnitz
et al., 1999], to update an initial guess for yi . The iteration loop continue
until the change in yi is smaller than the floating-point relative accuracy, eps.
To simplify the calculation it has been assumed that MEG is incompressible,
∂νi
= 0. Equation (2.5) can then be rewritten to the form shown in equation
∂P
(3.1).
y i P φi =
γi xi Pis φsi
νi (P − Pis )
exp
RT
!
(3.1)
A number of parameters needs to be determined to calculate yi , as seen from
equation (2.5). The activity coefficient for MEG in the liquid phase, γi , is assumed to be equal to one, as the liquid phase consists of almost pure MEG. The
value for the molar volume of MEG, νi , was taken from [DIPPR, 2012].
The fugacity coefficients, φ, is in this model calculated by the SRK-EoS. To
be able to calculate the fugacity coefficients, the SRK-EoS has to be written
on its cubic form as shown in equation (3.2) [Soave, 1972]. A, B and Z used
in equation (3.2) is defined in equations (3.3), (3.4) and (3.5) respectively. For
more details on the SRK-EoS, see section 2.1.1.
Z 3 − Z 2 + Z A − B − B 2 − AB = 0
A=
aP
R2 T 2
13
(3.2)
(3.3)
14CHAPTER 3. MODELLING OF THE SOLUBILITY OF MEG IN METHANE
B=
bP
RT
(3.4)
Z=
νP
RT
(3.5)
The Van der Waals mixing rules was used to calculate the parameters a and
b as shown in equations (3.6) and (3.7) respectively. The equations needed
to calculate the parameters ai and bi are given in equations (2.7) and (2.8) in
section 2.1.1.
a=
XX
i
b=
√
xi xj ai aj (1 − kij )
(3.6)
j
XX
i
bi + bj
2
xi xj
j
!
(3.7)
Two fugacity coefficients needs to be calculated. The fugacity coefficient for
MEG at a given temperature and pressure, φi , is calculated using equation
(3.8). Equation 3.8 has been found by using [Soave, 1972, eq.20] as a starting
point, and then changing the equation to adapt for the use of equation (3.6)
as the mixing rule.
A
bi
lnφi = (Z − 1) − ln (Z − B) −
b
B
2
!
P
bi
B
yi aij
−
ln 1 +
P P
b
Z
i
j yi yj aij
i
(3.8)
To calculate the fugacity of MEG at the saturation pressure, φsi , the vapour
pressure, Pis , for the given temperature needs to be determined using the Riedel
equation, see equation (3.9). The parameters A, B, C, D and E needed in the
Riedel equation were taken from [DIPPR, 2012]. φsi can then be calculated
using equation (3.10).
P s = exp A +
lnφsi
B
+ Cln(T ) + DT E
T
A
B
= Z − 1 − ln (Z − B) − ln 1 +
B
Z
(3.9)
(3.10)
Literature data for the amount of methane solved in the MEG at different
pressures, xmethane , is summarised in table 2.2 in section 2.2.3. As the difference
with pressure is much greater than the difference with temperature, it was
decided to use approximate values: 0.6% at 50 bar, 1.15% at 100 bar and 1.5%
at 150 bar. If no experimental data were available in the model, xM EG was set
equal to one.
The Matlab code is included in appendix B together with a table with a summary of the results from the calculations. The results from the modelling and
comparison with experimental data can be found in section 5.5.
Chapter 4
Experimental equipment and HSE
In this work the solubility of monoethylene glycol, MEG, in methane has been
measured. The experiments are conducted in both a dynamic and a static
equipment, in the temperature range from 273.15 to 313.15 K and at pressures
from 50 to 150 bar. This chapter contains detailed information about the
equipment and the procedures used, and a thorough discussion about HSEtopics related to this work.
4.1
Chemicals
The chemicals used in this project are monoethylene glycol and methanol.
Information about the supplier and the purity of the chemicals is summarised
in table 4.1. The water content in the chemicals was measured by coulometric
Karl Fisher titration with a Hydranal Columat AG-H solution.
Table 4.1: Supplier and purity for the chemicals used
Chemical
Monoethylene glycol
Methanol
Supplier
Purity
Water content
[ppm(w)]
VWR International S.A.S.
Lab-scan analytical sciences
AnalaR Normapur, 100%
Analytical reagent A.R.
370
Not analysed
The gas used for the experiments is methane. For the static experiments a 10
dm3 bottle of 3.5 quality methane has been used. The dynamic experiments
consume much more gas compared to the static experiments, and a 50 dm3 gas
bottle of 3.5 quality methane was therefore used for these experiments. The
supplier of the gas was Yara Praxair AS.
4.2
Experimental equipment
Two experimental rigs have been used as part of this work. For the dynamic
experiments an existing rig has been used, but the rig has been modified to
adapt for experiments with glycols. For the static experiments new experimental equipment with appurtenant procedures has been developed. This section
gives an overview of the structure and the operational procedures used for the
experiments. It also contains the experimental matrices outlining the planned
experiments. For more information about calibration of the equipment used
in the rigs, see appendix A.
15
16
4.2.1
CHAPTER 4. EXPERIMENTAL EQUIPMENT AND HSE
Dynamic experiments
In the dynamic experimental setup the gas is saturated and condensed in a
series configuration with continuous gas flow through the rig. According to
the classification for phase equilibrium experiments described in section 2.3,
the method used is a semi-flow isobaric-isothermal analytical method with
sampling. The rig is built for pressures up to 200 bar, and for the temperature
range of 253 to 333 K.
Description of the equipment
The dynamic equipment consists of a series of temperature controlled saturators and condensers, and a sampling system for measuring the MEG content
in the gas. The gas flows from the reservoir to a series of three stainless steel
containers placed in a Julabo FP-45 bath, with a mixture of silicone oil and
water as temperature controlling medium. The stainless steel containers each
have a volume of about 20 cm3 , and the two first containers were filled 23 full
with MEG to act as saturators. The third container was initially left empty to
collect entrained droplets from the saturators. A coil between the saturators
increases the retention period to allow heat transfer between the bath and the
gas.
After leaving the third container in the first water bath the gas passes a Keller
PAA 35-X pressure transducer, before it enters into a new series of three stainless steel containers in a second bath. The temperature in the second bath is
kept 20 degrees below the temperature in the first bath, allowing for excess
glycol to condense out from the gas phase. All three containers in the second
bath is therefore empty, to collect the small amounts of condensed glycol. A
mixture of MEG and water is used as temperature controlling media in the
second bath, to be able to go to temperatures below 273 K.
The gas leaving the last condenser goes through heat traced tubing to a heated
pressure reduction valve to prepare for sampling. The reduction valve is from
the Hoke Milli-Mite 1300 series, and reduces the pressure from experimental
pressure and down to 1 bar.
From the pressure reduction valve the gas goes through heat traced tubing to a
heated three-way valve. Thereafter the gas immediately enters the ATD-tube,
where the glycol in the gas is adsorbed. The amount of gas passing through
the ATD-tube is measured by a Ritter model 1/7 gas clock, before it is sent
to ventilation. The structure of the equipment is shown in figure 4.1.
Experimental procedures
The experimental procedures used for the dynamic equipment is based on the
existing procedures. As these procedures only have been modified and not
developed as part of this work, this section only includes a summary of the
procedures.
Preparations are needed to make the rig ready for a new series of experiments.
The saturation and condensation cylinders are removed from the water baths,
they are cleaned, and the two saturation cylinders are filled with fresh MEG.
It is also important to control the level of temperature controlling media in
4.2. EXPERIMENTAL EQUIPMENT
17
Figure 4.1: Schematic sketch of the dynamic equipment
the water baths. The rig is then assembled, before the desired temperatures
are set. The rig is then pressurised and leak tested. Also the water in the gas
clock needs to be replaced approximately every two weeks, and the water level
is controlled every day at the beginning of an experiment.
At the beginning of an experiment the pressure is adjusted to the pressure for
the experiment. Then the pressure reduction valve is opened, and a small flow
cm3
of gas is flushed through the rig. The flow rate is adjusted to about 250 minute
,
while small corrections are done to keep the pressure constant within ± 0.5
bar. The flow rate is chosen to make sure the residence time is long enough
for the system to reach equilibrium.
Gas is flushed through the rig to replace the gas that has been stagnant in
the rig, before the sampling starts. The volume of the rig is approximately
0.2 dm3 . For 50 bar the amount of gas flushed through the rig is therefore
minimum 10 dm3 . For 100 and 150 bar the amount of gas is minimum 20 and
30 dm3 respectively. As the flow rate is low this is a time consuming process,
but it is important to reduce the number of samples needed to obtain stable
results.
After the gas in the rig has been replaced, a series of minimum five samples
are taken from the rig. The ATD-tubes can adsorb relatively large amounts of
MEG, but there are limitations on how much MEG that can be analysed on
the GC. The number of litres passed through the ATD-tube for each sample
is therefore adjusted according to the expected concentration of MEG in the
gas. The ideal amount of MEG on the ATD-tube varies according to the
method, detector and split factors used for the GC. For this work the ATDtubes contained between 5 and 30 µg of MEG. This corresponds to sampling
between 1 and 7 dm3 of gas.
When starting a new experiment it is important to remember that glycol is
adsorbed to the walls of the tubing and the valves. It can therefore be necessary to flush more than the minimum recommended amount of gas through
18
CHAPTER 4. EXPERIMENTAL EQUIPMENT AND HSE
the rig before starting the sampling. If there is a trend of increase or decrease
in the concentration of MEG through the series of samples taken during an
experiment, this indicates that MEG is being adsorbed or desorbed from the
walls. More gas should then be flushed through the system before the experiment is repeated. When going from experiments with high temperatures and
pressures to experiments with lower expected concentration of MEG in the
gas, it can be necessary to clean the rig with pressurised air to get rid of excess
MEG in the system. A supply of pressurised air can be connected after the
second water bath, and it is recommended to flush through 100 − 300 dm3 of
air through the rig. Samples of the air that has been flushed through the rig
should be analysed on the GC. This way the concentration of MEG left over
in the rig before the start of the new experiment can be documented.
Modifications to the existing equipment
The rig was originally built to measure the water content of high pressure
natural gas as described in [Lø kken et al., 2008]. Later the rig has been
rebuilt to be able to run experiments with glycols.
In the work performed by [Haugum and Sharifi, 2011], efforts were focused
on the investigation of different designs for the distribution of the gas in the
saturators. The aim was to increase the contact area between the gas and the
glycol. This was achieved by distributing the gas through a number of small
holes in the lower part of the saturator, in combination with a layer of steel
mesh between the gas inlet and outlet in each saturator. This design was used
for the experiments in this work, and is illustrated in figure 4.2.
Figure 4.2: Illustration of the flow distributor in the saturation cylinders [Haugum and Sharifi, 2011]
Glycols easily adsorb onto metal and most polymer surfaces. It has therefore
been important to shorten all tubing and reduce the number of valves between
the last condenser and the sampling point. This was done as a part of the work
performed by [Haugum and Sharifi, 2011]. At the beginning of this work the
tubing was changed from Siltek-coated to electro polished tubing to decrease
the degree of adsorption on the tubing walls.
The choice of materials in the valves used is also important to avoid adsorption
of glycol. The pressure reduction valve used in the experiments by [Haugum
and Sharifi, 2011] had a graphite packing. At the beginning of this work it
was discovered that graphite from this packing had leaked into the valve house,
4.2. EXPERIMENTAL EQUIPMENT
19
and was in direct contact with the gas. This was a non-ideal situation, as it
increased the adsorption of MEG in the valve. It was therefore necessary to
replace the pressure reduction valve with a measuring valve from the Hoke
Milli-Mite 1300 series.
As part of the process of removing unnecessary tubing and valves the pressure safety valve, PSV, was moved. Earlier the PSV was placed between the
pressure reduction valve and the three-way valve, but as seen in figure 4.1 it
is now placed between the ATD-tube and the gas clock. This way the PSV
still protects the low pressure equipment, but the dead volume in the tubing
leading to the PSV have been removed from the critical part of the rig where
glycol is still in the gas.
In the process of moving the PSV it was decided to also make an arrangement
to fasten the ATD-tube to the table. The connection between the ATD-tube
and the nuts keeping it in place is only secured with Teflon ferrules. Therefore,
in case of a blocking in or around the ATD-tube, the tube might unfasten. A
device was therefore inserted to lock the tube in place. Also a small shielding
partition was installed between the ATD-tube and the operator of the rig.
This was to protect the operator in case the tube could become unfastened
and move as a projectile.
During the progress of this work a number of cold spots were discovered in the
rig. As discussed in more detail in section 5.1, problems were encountered when
running experiments at temperature above ambient temperatures. The rig was
therefore studied with an infrared camera. In this process it was discovered
that heat was lost through the lids of the water baths. It was therefore decided
to insulate the lids to reduce this heat loss.
The investigation with the infrared camera also revealed that the gas was
allowed to cool down between the two water baths. The tubing connecting
the two water baths was therefore heat traced and insulated, to avoid the
possibility of condensation of glycol in this tubing. Also additional insulation
was added to the part where the gas left the last condenser in the second water
bath.
Further investigations show that there still may be cold spots in the rig. The
discussion of this problem is continued in section 5.1, and possible solutions
are outlined in section 6.1.
Experimental matrix
Planning of the experiments is important to work around the problems with the
adsorption of MEG on the walls of the tubing and valves. To avoid unnecessary
work and uncertainties it is therefore important to run the experiments from
low to high expected concentration of MEG in the gas. An overview of the
planned experimental matrix for the dynamic experiments can be seen in table
4.2.
A detailed discussion about the experiments run as part of this work can be
found in section 5.1. A complete list of all the experiments is included in table
D.2 in appendix D.
20
CHAPTER 4. EXPERIMENTAL EQUIPMENT AND HSE
Table 4.2: Experimental matrix - Dynamic experiments
Chemical
MEG
4.2.2
Gas
Pressure
[bar]
Methane
50
100
150
Condensation temperature
273.15 [K] 293.15 [K] 313.15 [K]
1
4
5
2
6
7
3
8
9
Static experiments
The static experimental rig is designed to run phase equilibrium experiments
where the gas is saturated in a pressure-volume-temperature cell. A sample of
the gas is depressurised, and the amount of the liquid phase solved in the gas
can be quantified. According to the classification described in 2.3, the method
used is an isothermal analytical method with sampling. The rig is designed
for experiments in the temperature range from room temperature to 353.15 K
and for pressures up to 200 bar, and has been built as part of this work.
Description of the equipment
The main component of the rig is the sample cylinder with a movable piston
used as a PVT-cell. The sample cylinder is from Proserv, and has a volume
of 630 cm3 . The compartment above the piston is filled with methane and
approximately 25 cm3 MEG, and the compartment below the piston is filled
with a hydraulic fluid. For these experiments MEG has been used as hydraulic
fluid to avoid contamination across the piston. The PVT cell is heat traced
and insulated to keep a stable temperature inside the cell.
A system for pressurising the PVT-cell is connected to a needle valve in the
bottom of the cell. Hydraulic fluid is taken from a low pressure reservoir
and pumped through the hydraulic system by a Quizix QX-6000 pump. The
Quizix-pump is able to deliver fluid and at the same time keep the pressure
in the system constant. The reservoir is open to the surroundings through a
molecular sieve filter, and is protected by a pressure safety valve, PSV, set at
1.2 bara. The hydraulic system also contain a PSV set at 200 bar, valves to
control the flow of the hydraulic fluid, a pressure transmitter and a temperature
safety system, TSS, to protect the Quizix-pump against temperatures above
323.15 K.
The upper compartment in the cylinder is connected to a sampling system.
The gas sample leaves the top of the cylinder through a needle valve with a
thermocouple inserted into the gas flow. The pressure is reduced to atmospheric pressure through a pressure reduction valve from the Hoke Milli-Mite
1300 series. The gas then flows through a three-way valve before entering an
ATD-tube to collect the glycol in the gas. The amount of gas passing through
the ATD-tube is measured by a Ritter model 1/5 gas clock, before it is sent
to ventilation. All valves and tubing from the needle valve on the PVT-cell
to the ATD-tube are heated to avoid condensation of glycol. The structure of
the equipment is shown in figure 4.3.
4.2. EXPERIMENTAL EQUIPMENT
21
Figure 4.3: Schematic sketch of static equipment
Experimental procedures
The development of the operational procedures for the rig has been an import
part of this work, and a complete version of the procedures is therefore included
in appendix F. There are only Norwegian employees operating the rig, and
therefore only a Norwegian version of the procedures are available.
In the beginning of a series of experiments the upper lid of the cylinder is
opened, and approximately 25 cm3 of the chemical to be studies if filled into
the cylinder. The hydraulic system is filled with the same chemical that is used
in the upper compartment of the cylinder to avoid contamination. Gas is then
filled into the cylinder through the sampling system, before the temperature
and pressure is adjusted to the requested values, and the system is left for
equilibration.
When equilibrium is obtained, samples are taken to analyse the concentration
of the liquid in the gas phase. First the water level in the gas clock is controlled,
and the Quizix-pump is started to keep the pressure stable during the sampling
process. The needle valve on the cylinder and the pressure reduction valve
is opened, and samples are taken in a similar manner as for the dynamic
experiments, see section 4.2.1.
Development of new experimental equipment
The static experimental setup has been built and tested as a part of this
project, and has been designed especially to determine the solubility of process
chemicals in gas at elevated pressure.
The process of planning the rig was started in November 2011 to prepare for
22
CHAPTER 4. EXPERIMENTAL EQUIPMENT AND HSE
this work. The initial drawings for the rig were made by Eiving Johannessen
at the Statoil Research Centre at Rotvoll, and were ready in December 2011.
The work on this project started in January 2012, and one of the first thing
carried out was the hazard and operability study, HAZOP. The building of the
rig started in the middle of January 2012, and the deadline for the mechanical
finish was on March 1st , 2011. The rig was ready to start operation in the
middle of April 2012.
During the building and development phase it has been Eivind Johannessen
that has had the responsibility for the rig. The daily contact with the mechanical and electrical personnel building the rig has been part of this work, including discussions about design and outline of the equipment, and the follow-up
on the development of the build.
Additional work to prepare for the experiments was carried out during the
building phase. Simple tests to check the chemical resistance for the polymer
materials used in the sample cylinder and in the Quizix-pump were performed.
A draft for the operation procedures for the rig, based on the pipeline and
instrumentation diagram, was also written.
At the deadline for the mechanical completion, the electrical work on the rig
was not finished. During the beginning of March the work on the electricity and
signal system was completed, and the development of the monitoring program
in Labview was finished. During this phase the work on this project focused
on putting together all relevant documentation needed for the rig.
The final interdisciplinary control was on March 9th , 2012. After this meeting the last phase of finishing the rig was started. The thermocouples and
the pressure transmitter were calibrated, see appendix A, the Quizix-pump
was tested, the filling and the leak testing of the hydraulic system was performed, the sample cylinder was cleaned, and MEG was filled into the upper
compartment of the cylinder.
The work on the initial tests was then started, beginning with a series of experiments at room temperature. After having verified that the static equipment
worked according to the plan, the work on the rig was finished by adding the
heat tracing and the insulation on the outside of the cylinder.
Experimental matrix
It is important to plan the experiment so that the adsorption of MEG on
the materials in the rig is taken into consideration, as discussed in section
4.2.1. For the work on the static equipment it was most important to look at
the effect of temperature at a given pressure. The experimental matrix was
therefore planned as shown in table 4.3.
For the new static rig it was also important to run initial experiments to
control the functionality of the rig. It was therefore decided to start running
experiments at 50 bar and ambient temperature conditions to test that the rig
worked according to plan, get used to the Quizix pump, and to get to know the
rig. Simultaneously the experiments should investigate elements such as how
long it would take to reach equilibrium, and how many samples were needed
to obtain stable measurements.
4.3. SAMPLE ANALYSIS BY GAS CHROMATOGRAPHY
23
Table 4.3: Experimental matrix - Static experiments
Chemical
Gas
MEG
Methane
Pressure
[bar]
50
100
Condensation temperature
Ambient 313.15 [K] 333.15 [K]
Initial
1
2
3
A detailed discussion about the experiments run as part of this work can be
found in section 5.2. A complete list of all the experiments is included in table
D.1 in appendix D.
4.3
Sample analysis by gas chromatography
The analysis of the samples taken from the experimental rigs were analysed by
a ATD-GC-FID technique. The samples were injected from automatic thermal
desorption, ATD, tubes, and were analysed by a gas chromatograph, GC, with
a flame ionisation detector, FID. A theoretical description for this technique
is found in section 2.4.
The ATD-tubes used are from Perkin Elmer and are coated with Tenax TA.
The characteristics of the GC used are summarised in table 4.4.
Table 4.4: Characteristics for the gas chromatograph
Characteristic
Description
GC type
GC software
Column type
Column stationary phase
Column length
Column inner diameter
Column film thickness
ATD injector
ATD software
Carrier gas
Detector type
Hewlett Packard 6890 from Agilent Technologies
MSD Chem station
WCOT Fused Silica
CP volamine
60 m
0.32 mm
Optimized
Ultra TD 50:50 from Markes International Ltd
Unity
Helium BIP
Flame ionisation detector, FID
4.3.1
Calibration
A calibration of the gas chromatograph, GC, is needed to quantify the amount
of monoethylene glycol, MEG, in the samples from the experiments. For the
calibration a series of standards were made in the laboratory, adapted to the
amount of MEG expected in the samples. The standards were applied onto
ATD-tubes and analysed on the GC to create a calibration curve. Additional
quality controls were run for every third to fifth sample to verify the calibration
curve used. More information and details about the calibration of the GC can
be found in appendix A.3.
24
4.3.2
CHAPTER 4. EXPERIMENTAL EQUIPMENT AND HSE
Maintenance
It is important to carry out regular maintenance to avoid problems with the GC
system. This is particularly important when running samples with challenging
systems such as glycols. When using the adequate column and detector it
is not problematic to detect MEG, but it is difficult to make sure that all
MEG is removed from the ATD-tubes, the injector system, the column and
the detector between each sample. Analysis of the same ATD-tube three times
showed that almost all of the MEG is removed in the first analysis, even for
concentrations up to 50 µg. Regular blank samples are also run both in the
beginning and in the end of a sequence to keep control of this problem. Even
though these controls show that only trace amounts of MEG are left in the
system, these trace amounts create problems with the column and the detector
when glycol samples are analysed over time.
Problems with the FID detector were encountered because the jet that supplies
the gas to the flame was completely blocked. The jet is cleaned every year
during the service carried out by the supplier, but this was not often enough
when running the amount of MEG samples that has been the case for this
project. As this is a common problem, spare parts were found and the jet was
replaced.
The system for desorbing the glycol from the ATD-tube also requires regular
maintenance. When an ATD-tube is loaded, o-rings are used to seal the tube
into place. During the desorption process one of these o-rings is heated, and
the o-rings will therefore be worn over time. At the beginning of the desorption
process the system is leak tested, and worn o-rings will then result in leaks.
If the leak test is not approved, the ATD-tube will not be analysed, and the
sample is lost.
The problems with tube leaks were experienced in this project, and the o-rings
needed replacement. In the process of replacing the o-rings a tubing connection
in the ATD-tube was damaged. The leak was detected, and the tubing was
tightened to stop the leak.
4.4
HSE
A risk evaluation for the experiments performed should be included as part
of the master thesis. As the experiments in this work have not been carried
out in the laboratories at NTNU, the standard risk evaluation used at NTNU
has not been applied. A thorough discussion about the health safety and
environmental topics related to the work in the laboratories at the Statoil
Research Centre at Rotvoll is therefore included in this section. The complete
safety analysis developed for the static equipment is included in appendix
E.
4.4.1
HSE for the laboratory at Statoil Research Centre
A series of courses and approvals are needed to be granted access to the laboratories at Rotvoll. The first part is to complete an electronic course that
gives an overview of the rules and regulations that apply in the laboratories.
The second step is to go for a guided tour in the laboratory together with a
4.4. HSE
25
representative from the organisation responsible for the operation of the lab.
During this tour the topics of waste management, emergency procedures and
exits, safety equipment and general laboratory procedures are discussed. A
tour with the laboratory coordinator for the area where the work in the laboratory will be performed is also needed. This tour focuses on the rules for the
given area, and also includes information about the equipment placed in the
area. In addition the leaders for the department and the laboratory have to
accept the request for access.
Rules, procedures, governing documentation and other information regarding
work in the laboratory are described in the laboratory handbook. This book
is given to all employees, and is a helpful guide in the everyday work in the
laboratories. Any new information regarding HSE or the work in the laboratory is given through an information screen in the lab, and through monthly
HSE meetings for everyone working in the laboratory.
An application is needed to work with chemicals in the laboratory. This application should include information about where the chemical will be used, what
it will be used for, and how large amounts that will be used. Also a detailed
description of the possible health effects from working with the chemical should
be included. The applications are considered by the chemical committee and
the occupational hygienist.
When working with pressurised equipment additional regulations apply. A
training seminar for the use of tubing and fittings is required to be able to
perform modifications or work on the system. As the experiments run as a
part of this work involve pressures up to 150 bar, this course was required for
the work on the equipment used in this project.
An approval to become an operator for the rig was needed both for the dynamic
and static equipment. Before starting the work on the experimental rigs the
operator is trained by the person responsible for the equipment, and approved
by the department leader. Before the operator can be approved to work on
the rig, a list of points must be studied. The points are:
•
•
•
•
•
•
•
•
Get familiar with the documentation for the rig
Go through the flow diagram and procedures for the equipment
Go through the physical layout of the rig
Go through the control system
Understand the risk factors involved
Go through the emergency shut-down procedures for the rig
Carry out an experiment during supervision and guidance
Go through a final discussion about the rig with the department leader
This training is meant to give an overview into the construction, principle,
procedures and documentation for the experimental rig. An important part
of the training is also to get an insight into the risks and safety precautions
relevant for the work.
4.4.2
Chemicals
The main HSE challenges for this work are related to the use of methane at
elevated pressures. Methane is a flammable gas that poses an immediate fire
26
CHAPTER 4. EXPERIMENTAL EQUIPMENT AND HSE
and explosion hazard when mixed with air at concentrations exceeding 5.0%.
Precautions like the use of shut down valves and pressure safety valves were
therefore important, and leak tests were performed after every modification of
the rigs.
Methanol is very flammable and toxic. Inhalation, skin contact or ingestion
can lead to serious, permanent health damage. Ingestion of methanol can
cause blindness, and larger amount can be fatal.
Monoethylene glycol is toxic when ingested, and it can also be adsorbed
through the skin. It has been discussed that MEG may have toxic effects
for the reproductive capacity. The latest information is that large amounts
are needed to be in danger of effects like this.
The use of safety glasses is mandatory in the laboratories at the Statoil Research Centre. In addition nitrile protective gloves were used when working with the chemicals, and all work with methanol was performed in fume
hoods.
4.4.3
Dynamic experimental rig
The main HSE challenges for the dynamic equipment are related to the high
pressures used in the rig. As the gas used is methane, extra precautions are
taken to avoid leak and other problems that can lead to dangerous situations.
A pneumatically controlled shut down valve is installed to block the gas supply
in case of emergencies, and a PSV is installed to protect the low pressure
equipment.
The rig is also heated, both with heater cables and with water baths. The
heater cables used are self-regulating, and will not reach temperatures above
approximately 373 K. The water baths used have internal safety switches that
will shut down the baths incase of a situation where the temperature exceeds
the set safety temperature.
A safe job analysis, SJA, was performed for the modifications done to the
rig. The department leader, the person responsible for the equipment and the
operator were present at the SJA, where the details around the modifications to
be performed were discussed. As described in section 4.2.1, extra precautions
were needed to ensure that the ATD-tube was kept in place when the PSV
was moved.
4.4.4
Static experimental rig
The HSE challenges for the static equipment is similar to the challenges discussed in section 4.4.3. For the precautions related to the work with high
pressures, an additional PSV is needed in the hydraulic system of the rig.
This is because there is a possibility for rapid pressure increases in this system
because of the Quizix-pump. The Quizix-pump has an important, internal
safety function where a safety pressure is set before the pump can be started.
This function also protect against sudden pressure increases.
In addition there is a danger related to the low pressure reservoir in the hydraulic system. The reservoir is made out of glass, so in case of sudden backflows to the reservoir it is a possibility for that the glass may break. A special
4.4. HSE
27
glass flask with a thin plastic coating on the outside of the flask is therefore
used to reduce the risk of loose splinters. A rupture disk design to break at
1.2 bara is also installed in the lid of the flask to protect the reservoir. The
reservoir also has a connection with the surroundings through a molecular sieve
filter to level out any pressure differences.
Many of the safety precautions described in this section were installed as a
result of the discussion at the HAZOP meeting. During the HAZOP meeting
the layout of the rig was divided into two nodes: One for the high pressure
hydraulic system and one for the low pressure sampling system. The key words
for the discussion were:
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
No flow
Composition change
Reverse flow
More flow
More pressure
Less pressure
More temperature
Less temperature
Viscosity
Relief
Instrumentation
Maintenance
Ignition
Safety
Other
For each keyword the possible causes, consequences and safeguards were discussed. Then one or more recommendations were set up where needed, and a
person responsible for taking action was appointed. All the points discussed
during the meeting were summarized in a report for documentation.
28
Chapter 5
Results and discussion
5.1
Dynamic experiments
The results from the dynamic experiments are summarised in table 5.1. More
details and a discussion about the results can be found in sections 5.1.1 and
5.1.2. It should be noted that the result obtained for 313.15 K and 50 bar is
uncertain.
Table 5.1: Summary of results from the dynamic experiments;
The concentration of MEG in methane at different temperatures
and pressure
Temperature
K
Pressure
[bar]
Concentration of MEG in methane
[ppm(mol)]
273.15
273.15
273.15
293.15
313.15
50.0
100.0
150.0
50.0
50.0
0.32
0.43
0.52
2.25
7.52a
a
5.1.1
Uncertain
Experiments at 50 bar and various temperatures
Presentation of the different data points
The parallels in the different series of samples are shown in figure 5.1. This
figure is included to illustrate the scattering of the results, and to show the
trends in the series of samples. The discussion accompanying figure 5.1 explains what points have been excluded from the calculation of the reported
value.
Some of the data points for 273.15 K and 50 bar, shown in figure 5.1a, were
excluded. The sample series from February 10th was not included because not
enough gas was flushed through the system before the sampling started. The
first points in some of the other series were excluded because they showed a
trend of increasing or decreasing concentrations. The rest of the points were
within ±10% of the reported average result. Additional heat tracing was added
to the rig in March. The experiment was therefore repeated on May 18th to
check that the modification did not affect the result.
29
30
CHAPTER 5. RESULTS AND DISCUSSION
(a) T = 273.15 K
(b) T = 293.15 K
(c) T = 313.15 K, before extra heat tracing is added
(d) T = 313.15 K, after extra heat tracing is added
Figure 5.1: Parallels in the experiments at 50 bar and various temperatures.
Figure (c) and (d) show the result for T = 313.15 K before and after additional
heat tracing was added on the tubing between water baths one and two.
For the experiment at 293.15 K and 50 bar, shown in figure 5.1b, a number of
data points were excluded. The four first points were excluded from the series
from February 21st because the series showed an increase in the measured MEG
concentration. For the samples from February 22nd the first six points were
excluded because they were fluctuating more than the rest of the series. The
entire data series from February 24th were excluded because all the samples
deviated from the other points measured. The points that were included in
the averaging were well within ±10% of the reported result.
The first results from the experiment at 313.15 K deviated significantly from
the modelled value. As seen from figure 5.1c the measurements of the concentration of MEG are in the range from 3.2 to 3.9 ppm(m). An estimate of yi
based on a theoretical discussion is presented in appendix C, and the results
from these first experiments were not plausible based on this discussion. Different factors were discussed, but a breakthrough was reached when the rig was
studied through an infrared camera. It was found that heat was lost through
the lids of the water baths, and that the gas was cooled when passing through
5.1. DYNAMIC EXPERIMENTS
31
the tubing between the water baths. The lids were therefore insulated, and
additional heat tracing was added to the tubing connecting the baths.
The experiment at 313.15 K and 50 bar were repeated after the modifications
were completed. For the sample series from March 26th and March 27th the
heat tracing between the water baths was set at 323 and 338 K respectively.
The results from March 26th were lower than the results from March 27th , so
the data points from March 26th were therefore excluded. Set points above 338
K have not been tried, because of the danger of the gas not having enough time
to cool down as it passes through the condensers. The rest of the experiments
at 313.15 K were therefore run with the heat tracing between the baths set to
338 K. It can be advantageous to do more experiments with different set points
for the heat tracing, but as described in section 6.1 there are more pronounces
problems that need to be addressed first.
With the exception of the data series from March 26th , all of the points were
included in the calculation of the reported average result. The sample series
from parallel one on March 27th and parallel two on March 28th show lower
results compared to the other data series. No good explanation has been found
for this observation, and all of the data points from March 27th , March 28th
and March 29th are therefore included. These points are well within ±10% of
the reported average result, but the measured value for yi is still low compared
to the discussion in appendix C.
Comparison of average result with literature data and modelled values
The average results reported at 50 bar and different temperature are summarised in figure 5.2. The figure also includes literature data and the values
modelled by the CPA-EoS model for comparison.
Figure 5.2: Results from dynamic experiments at 50 bar and different temperatures. Literature data and modelled values are included for comparison.
Figure 5.2 show that the results reported in this work generally are too low
32
CHAPTER 5. RESULTS AND DISCUSSION
compared to the literature data and the CPA-model. As mentioned in section
5.5, the values modelled by the CPA-EoS model is uncertain due to the few
number of experimental points available for verification. It will therefore be
to hasty to say that it is the results obtained in this work that have to be
wrong.
There is also an uncertainty related to the data reported by [Haugum and Sharifi, 2011]. The data fit well to the values modelled by the CPA-EoS model,
but as there is an uncertainty in the model this does not necessary mean that
the results are correct. As the experiments were run at the same equipment
as used in this work, it has been possible to study the documentation of the
results in the logbooks. No documentation showing that the rig has been
cleaned between the experiments has been found. When going from experiments with high to low measured concentrations of MEG, this can lead to the
influence of left over MEG from previous experiments. This will result in too
high measurements of the MEG concentration in methane, especially in the
experiments with very small amounts of MEG in the gas phase.
The result for 313.15 K deviates more from the calculated value than the
results for the other temperatures at 50 bar. This reported average result
is therefore marked uncertain in table 5.1. This will be discussed further in
section 5.1.3.
It is therefore difficult to conclude about the quality of the data presented in
this work based on the presentation in figure 5.2. This is why the thorough
discussion about the data points included in the calculation of the reported
average result have been included in the first part of this section. A lot of
time was spent on getting good results at 313.15 K, and this was to be able to
compare the results from the dynamic experiments with the results from the
static experiments. The problems with the experiments run at the dynamic
equipment, together with the deviation between the measured and modelled
values, are the reasons for the decision to build the new static equipment.
Figure 5.2 still clearly show the concentration of MEG in methane increases
at increasing temperature when the pressure is kept constant. This increase
in the MEG concentration is exponential with the increase of temperature. It
is a bit difficult to see this from figure 5.2 because a logarithmic scale is used
on the y-axis, but it can be seen more clearly in figure 5.9 in section 5.5.
5.1.2
Experiments at 273.15 K and different pressures
Presentation of the different data points
The parallels in the different series of samples are shown in figure 5.3. This
figure is included to illustrate the scattering of the results, and to show the
trends in the series of samples. The discussion accompanying figure 5.3 explains what points have been excluded from the calculation of the reported
value. Figure 5.3a is the same as figure 5.1a. The discussion for this figure is
therefore included in section 5.1.1, and will not be repeated here.
For the experiment at 100 bar and 273.15 K, shown in figure 5.3b, a significant
scattering of the results is observed. It should be noted that the sample series
from May 21th and 22th is analysed on the gas chromatograph during a period
5.1. DYNAMIC EXPERIMENTS
(a) P = 50 bar
33
(b) P = 100 bar
(c) P = 150 bar
Figure 5.3: Parallels in the experiments at 273.15 K and various pressures
of problems with the ATD-unit. The sample series from the 16th and 21th
of May are analysed on the ATD-GC-FID used throughout the work with
this project, but the samples from May 22th are analysed on a different ATDGC instrument, with a mass spectrometry, MS, detector instead of a flame
ionisation, FID, detector.
A MS detector is generally less stable than a FID detector. It is not uncommon
with changes in the response through a series of samples when using a MS
detector. Parallels from three different standards were therefore run in the
beginning, in the middle and at the end of the sequence, and quality controls
were run for every third sample.
The GC’s used also have different columns, where the GC-FID has a volamine
column and the GC-MS has a wax column. The units for desorption of
the ATD-tubes were also from different manufacturers. Both detectors and
columns can be used to quantify the amount of MEG in the samples, and the
ATD-GC-MS was calibrated in the same way as the ATD-GC-FID. Not much
work have however been done to compare the accuracy and reliability of the
two set-ups, and the data from this experiment is therefore not included in the
calculations of the reported result from the experiment.
34
CHAPTER 5. RESULTS AND DISCUSSION
It was not ideal to analyse some of the samples on a different GC, but this
was done as a result of the problems with the ATD-unit for the ATD-GC-FID.
During the problem solving period it was not certain that it was possible to
repair the ATD system before after the deadline for this work. The ATD-GCMS was therefore used to try to continue the work on the experiments in the
rigs. After the ATD-GC-FID was up and running again, this GC was used for
the rest of the samples.
All the data points have been included in the calculation of the reported result
for 100 bar and 273.15 K. This has been done because of the scattering in
the results for these sample series. The data points are close to or within the
borders for ±10% of the reported average result, and the data point does not
deviate more from the modelled value than the other results from this work in
figure 5.4. It has therefore been decided not to report this result as uncertain
in table 5.1.
For the experiment at 150 bar and 273.15 K, shown in figure 5.3c, some of the
data points were excluded. The three first points were excluded from the series
from May 29th because the series showed an increase in the measured MEG
concentration. No good explanation has been found for the sudden jump in the
concentration of the fourth sample in the data series from May 30th , and it has
therefore been included in the calculation of the average result reported.
Comparison of average result with literature data and modelled values
The average results reported at 50 bar and different temperature are summarised in figure 5.2. The figure also includes literature data and the values
modelled by the CPA-EoS model for comparison.
Figure 5.4: Results from dynamic experiments at 273.15 K and different pressures. Literature data and modelled values are included for comparison.
Figure 5.4 also show that the results reported in this work give a lower concentration of MEG in methane compared to the literature data and the CPA-EoS
5.1. DYNAMIC EXPERIMENTS
35
model. As discussed in section 5.5, the CPA-EoS model is uncertain due to
the limited number of experimental points available for verification.
As mentioned in section 5.1.1, there is also an uncertainty in [Haugum and
Sharifi, 2011]. This is evident for the result of approximately 2 ppm(m) reported by [Haugum and Sharifi, 2011] for 273.15 K and 100 bar. This represents
a deviation of approximately 300 % from the value calculated by the CPA-EoS
model.
It is therefore difficult to conclude about the quality of the data presented
in this work based on the presentation in figure 5.2, as it was for the results
presented in section 5.1.1.
It can be seen in figure 5.2 that the concentration of MEG in methane increases
when the pressure is increased from 50 to 150 bar. A broader pressure range
has been included in figure 5.2 to show that the concentration of MEG in
the gas phase increases rapidly when the pressure approach 1 bar. The results
from the SRK-EoS model summarised in table B.1 in appendix B indicate that
the minimum value for the concentration of MEG is at a higher pressure than
50 bar for temperatures above approximately 293 K. Due to the limited time
available for this project, it was not enough time to investigate this as part of
this work.
5.1.3
Further discussion
The general trend for the results from the dynamic equipment is that the concentration of MEG in methane measured is lower than literature and modelled
values. This was discussed in sections 5.1.1 and 5.1.2, and was especially noted
for the results at 313.15 K and 50 bar.
One of the factors that may explain the deviation is the retention time. As
the gas is flowing through the equipment during the sampling process, it is
important that the gas has enough time to equilibrate. The procedure used in
cm3
, see section
this work has been to set a flow rate of approximately 250 minute
4.2.1. If the total volume of the high pressure part of the rig is approximated
to be 150 cm3 , this corresponds to the gas using about 30 minutes through
the rig at 50 bar and about 90 minutes at 150 bar. This calculation assumes
ideal gas, and is therefore just a rough estimate. An experiment at 273.15 K
cm3
, but no noand 50 bar were run with a flow rate of approximately 130 minute
ticeable difference could be recorded. It should be noted that the experiments
performed by [Haugum and Sharifi, 2011] are run at a range of different flow
cm3
. It has not been possible to see any clear effects
rates from 250 to 1000 minute
based on the results in the report by [Haugum and Sharifi, 2011].
Another possibility is that there are more cold spots in the rig. The insulation
of the lids for the water baths, and the adding of heat tracing on the tubing between the water baths, lead to a large decrease in the measured MEG
concentration. A likely factor may therefore be that there are still more cold
spots that have not yet been improved. Further investigations around the rig
showed that there may be colder spots at the points where the tubing goes
through the lids of the water baths. The self-regulating heating cable used is
difficult to bend, and it is therefore a length of approximately 5 cm at the entrance and at the exit of each of the water baths without proper heat tracing.
36
CHAPTER 5. RESULTS AND DISCUSSION
Investigations also show that the heating around the pressure reduction valve
and the three-way valve may not be good enough to avoid cooling of the gas.
Possible solutions to this problem is discussed in more detail in section 6.1. As
discussed in this section it is recommended to examine this factor more closely
before trying to run more experiments above room temperature.
Another factor discussed were the level of temperature controlling medium in
the water baths. The level of the medium in the baths was topped up on
a regular basis. This was especially important for the experiments at higher
temperature, as a noticeable change in the level could be seen after just two
to three days.
The level of MEG in the saturators was also discussed as a possible factor.
There is no way to control the level of MEG in the saturators without disassembling the rig. Because the operation of disassembling the rig gradually
damages the connections in the rig and leads to leakages, this was done as
seldom as possible. On the occasions when the rig was opened, it was found
approximately 2 cm3 of the MEG had been transported over to the third saturator in the first water baths. The first and second saturator were still more
than 21 full, and because of the steel mesh inside the saturators this is believed
to not be of a great significance.
Calculations were also performed to investigate how the presence of water
in the MEG would influence the amount of MEG solved in the gas phase.
The calculations were performed using the CPA-EoS, and a summary of the
calculations are included in table 5.2. For the calculations the water content
in the feed were set in the description of the fluid. Then a flash calculation
was performed for 333.15 K and 50 bar, which corresponds to the conditions in
the saturators. The result from this first calculation were then used as input
to a second flash calculation at 313.15 K and 50 bar, corresponding to the
temperature and pressure conditions in the condensers.
Table 5.2: The impact of water content in the MEG. Calculations performed at
333.15 K and 50 bar, and 313.15 K and 50 bar respectively, using the CPA-EoS
model.
Conc. of water in MEG
[mol%]
0.00
0.25
0.50
0.75
1.00
2.00
Calculated conc. of MEG in methane [ppm(m)]
After the saturators
After the condencers
59.97
14.60
59.83
14.51
59.69
14.42
59.54
14.33
59.40
14.24
58.83
13.87
As a result of the discussion about water content, the concentration of water
in different sources of MEG was measured. The analysis was performed using
a coulometric Karl Fisher titration with a Hydranal Columat AG-H solution,
and the results are summarised in table 5.3.
The results from table 5.3 show that the water content in the MEG has in-
5.2. STATIC EXPERIMENTS
37
Table 5.3: Concentration of water in different sources of MEG
Source of MEG
Cons. of water in MEG
[ppm(mol)]
Bottle of MEG, open for 1 day
Bottle of MEG, open for 2 months
Bottle of MEG, open for 1 year
MEG from 1. saturator a
MEG from 2. saturator a
a
343.4
432.9
722.0
2217
4575
Sample taken the dynamic equipment on March 30th , after running
19 experiments since February 10th
creased after a series of experiments. By comparing with the calculations in
table 5.2, it can be seen that the level of water in the MEG is not enough
to influence the measured concentration of MEG in the gas with more than
approximately 1.3 %.
The water probably originates from the gas supply. The gas used for the
experiments is 3.5 quality methane, which can contain up to 10 ppm of water.
When the gas is flushed through the rig some of the water will most likely
be absorbed in the MEG, while some will go with the gas through the rig.
There is no way of detecting water in the sampling method used, so there is
no easy way of controlling this. An option is to use a Karl Fisher titrator set
up for measuring the water content in gas, but this will be a time consuming
process.
A lot of work has been put into trying to obtain good data for 313.15 K.
As explained in section 5.1.1, obtaining these data is important to be able to
compare the results from the dynamic and the static experiments. One of the
aims for this project was to develop and test the new static equipment, and it
was therefore an important goal for this project to be able to run experiments
on both rigs at the same temperature.
5.2
5.2.1
Static experiments
Experiments at 50 bar and ambient temperatures
Presentation of the different data points
The parallels for the experiments at 50 bar and ambient temperature are shown
in figure 5.5. The parallels in the figure are taken from two different experiments, where one was started on April 26th and a new experiment was started
on May 4th .
From looking at the different parallels in figure 5.5, no specific trend of increasing or decreasing concentration can be seen. Samples were taken out from the
first experiment on May 2nd and May 4th , after six and eight days respectively.
For the second experiment sample series were taken out on May 8th , May 9th
and May 11th , after four, five and seven days respectively. As no trend in
the development of the concentration of MEG in the samples is observed, this
indicate that four days is enough time to reach equilibrium for the conditions
38
CHAPTER 5. RESULTS AND DISCUSSION
Figure 5.5: Results from static experiments at ambient temperature and 50
bar
of 50 bar and ambient temperatures.
The degree of diffusion is a function of temperature, and it is therefore expected
that the time to reach equilibrium will decrease at increasing temperatures.
For the experiments in this work the new experiment has been started late in
the week and left over the weekend to equilibrate. It is therefore possible that
the time needed to reach equilibrium can be less than four days.
It should be noted that there were no temperature control for the PVT-cell
during these experiments. As these experiments were performed as part of the
test of the new equipment to see that everything worked according to plan,
the heat tracing and the insulation for the sample cylinder had not been added
yet when these experiments were run. The heat tracing for the sample system
was added, as this was a premise to be able to avoid condensation of MEG in
the tubing during sampling.
The only temperature recorded for these experiments were therefore the temperature in the surroundings of the rig. It was observed that the temperature
in the room varied between 294.6 and 296.1 K, changing with the time of the
day.
Comparison of average result with literature data and modelled values
The result from the experiments at 50 bar and ambient temperature is shown
in figure 5.6. The result is compared to a literature value from [Folas et al.,
2007], and the CPA-EoS and SRK-EoS models.
The uncertainty in temperature is important to keep in mind when looking
at figure 5.6. Because the temperature in the PVT-cell were influenced by
the ambient temperature, it has been difficult to decide which temperature
to use. A temperature of 295 K has been chosen as this is an average of the
5.2. STATIC EXPERIMENTS
39
Figure 5.6: Comparison of CPA model and result from static experiments at
ambient temperature and 50 bar
temperature observed during sampling of the series.
From looking at figure 5.6 it can be seen that the measured concentration of
MEG corresponds to a temperature of approximately 298.5K. It is not likely
that the temperature inside the PVT-cell was that high, but it could be that
heat from the heat tracing of the sample system could heat up the upper part
of the cell.
Compared to the literature data and the modelled values the result from the
static experiment is too high. Taking into account the uncertainty in the modelled value, as discussed in section 5.1, and the uncertainty in the temperature,
it is not possible to say anything about the quality of the result.
5.2.2
Experiments at 100 bar and 298.6 K
Presentation of the different data points
The parallels for the experiments at 100 bar and 298.6 K are shown in figure
5.7. The experiment was started on May 18th , and samples were taken after
4, 7 and 11 days.
It can be seen that the first samples from May 22nd have an increase in the
concentration of MEG through the series of samples. No gas had been flushed
through the system before the sampling started, so this can be explained by
conditioning of the sample system. At 100 bar more gas is available in the
PVT-cell compared to 50 bar. Before the sampling started on May 29th , 5dm3
of the gas was therefore flushed through the system. It can be seen in figure
5.7 that this results in much more stable parallels compared to the parallels
from May 22nd .
The samples from May 25th deviate from the other samples in figure 5.7. No
likely explanation have been found for the scattering of the data observed from
40
CHAPTER 5. RESULTS AND DISCUSSION
Figure 5.7: Results from static experiments at 298.6 K and 100 bar
this data series, other than that the analysis of these samples were performed
during a period with problems with the ATD-GC-FID.
A fourth sample series was taken out on May 30th . These samples were destroyed because of problems with the FID-detector in the GC. It was not
enough gas left in the PVT-cell to run a fifth sample series. To obtain more
data for 100 bar and 298.15 K a new experiment must therefore be started. It
was unfortunately not enough time to do this as part of this work.
Comparison of average result with literature data and modelled values
The result from the experiments at 100 bar and 298.6 K is shown in figure 5.8.
The result is compared to a literature value from [Folas et al., 2007], and the
CPA-EoS and SRK-EoS models.
As can be seen from figure 5.8, the concentration of MEG measured is high
compared to modelled values, but in the same range as the literature data
reported by [Folas et al., 2007]. This may indicate that the CPA-EoS model
calculate a too low value for temperatures around 298 K and a pressure of 100
bar. It is in any case too early to draw conclusions from the result presented
in figure 5.8, as more experiments to test the rig is needed first.
Also for the experiments at 100 bar and 298.6 K there is an uncertainty in
the temperature inside the PVT-cell. As these experiments are the first experiments run with heat tracing and insulation on the sample cylinder, it is
uncertain whether the measured temperature and the actual temperature inside the PVT-cell is the same. The heating cable was set at 298.15 K, but the
temperature measured by the thermocouple that regulates the heat tracing
was approximately 298.6 K.
In addition there is a thermocouple placed in the gas flow, and it measures
temperatures around 300.2 K during the sampling process. It is not certain
5.3. ANALYSIS BY ATD-GC
41
Figure 5.8: Comparison of CPA-EoS model and result from static experiments
at 298.6 K and 100 bar
whether this thermocouple measures the actual temperature in the gas, or
whether the thermocouple is influenced by the heat tracing for the sample
system.
As discussed in section 6.2, modifications to improve the temperature control
in the rig are planned. The first thing that will be tried is to install a Tconnection with a thermocouple at the outlet of the sampling cylinder. This
was the temperature of the hydraulic liquid can be measured as it exits the
cylinder. It is generally easier to measure the temperature in a flow of liquid
compared to a flow of gas, and this may therefore result in more reliable
temperature measurements. In the ideal case, the temperature in the gas and
the hydraulic liquid should be the same. If this is not the case, this issue must
be further discussed. Unfortunately it was not possible to do this modification
as part of this work, as the parts needed were not available at site.
5.2.3
Further discussion
It is still too early to say anything about the quality of the results from the
static equipment, and no data is available to be able to compare with the results
from the dynamic equipment. The further work will therefore be important, as
discussed in section 6.2. An important step further will be to get better control
with the temperature inside the PVT-cell during the experiment, before the
experiments with MEG can be continued.
5.3
Analysis by ATD-GC
The GC analysis is a relatively reliable technique when a good method and
surrounding procedures have been established. The problem is that the response from the GC is influenced by small changes in the system. If changes
are made to the column, the pressure or the flow of the carrier gas, the detec-
42
CHAPTER 5. RESULTS AND DISCUSSION
tor, the split factors or the method, this will influence the response and hence
the results. It is therefore important to keep control over the calibration curve
by running regular quality controls, see appendix A.3 for more details. Also
regular maintenance is important, as discussed in section 4.3.2.
The sample desorbed from the ATD-tube needs to be split in the injector of
the GC, due to the problems with adsorption of MEG in the GC system. A
total split of 7.8:1 has been used for the samples analysed in this work. This
split leads to an increased uncertainty in the analysis, and should be avoided if
possible. Gas clocks have been used to measure the volume of the gas sampled,
and because of uncertainties in the gas clocks it is not recommended to sample
less than 1 dm3 of gas.
The major contribution to the uncertainty in the GC analysis is the manual
work required to prepare the standards and quality controls for the calibration
curve. The standard and quality control solutions are prepared by the operator
in the lab, transferred to the storage containers, and then applied to the ATDtube by using a 10 mm3 glass syringe.
The uncertainty of the series of operations needed is added to the uncertainty
in the GC analysis itself. As mentioned GC analysis is a relatively reliable
method, but there are uncertainties due to factors like contaminations from
MEG in the GC system and differences in the integration of the peaks in the
chromatogram. The overall uncertainty of the methods used are discussed
further in section 5.4.
Attempts to reduce the number of samples to be analysed
In the work conducted by [Haugum and Sharifi, 2011] and [Folas et al., 2007]
the routine was to run two parallels of each of the four standards together with
every sequence of samples. These standards were used to create a calibration
curve, and the samples analysed were reprocessed using this calibration curve
to find the concentration of MEG in the sample. The reason for this routine was
that the GC used when this method was first applied had a mass spectrometry,
MS, detector. As discussed in section 5.1.2, this detector is more unstable
compared to the FID detector. It was therefore necessary to make a new
calibration curve for every sequence of samples that were analysed.
This work aimed at running two experimental rigs simultaneously, and the
number of samples in the GC sequences therefore needed to be reduced. The
analysis of a sample is time consuming, because the ATD-tube needs to be
conditioned after the analysis. During the conditioning the ATD-tube is heated
to 593.15 K for 15 minutes to make sure that any trace of MEG still left
in the tube is removed. The total time needed for each tube is therefore
approximately one hour.
The main action taken to reduce the number of samples to be analysed was to
make one calibration curve that was used for multiple sequences. A calibration
curve was created by analysing two parallels from three to five different over
a period of three days, or until a total of 20 ATD-tubes with standards had
been analysed. To control the calibration curve, and to check for any sudden
changes in the chromatogram, quality controls were run together with the
samples. Experience showed that it was necessary to make a new calibration
5.3. ANALYSIS BY ATD-GC
43
curve approximately once a month, or more often in cases were changes were
done to any part of the GC system. More information about the calibration
of the GC can be found in appendix A.3.
The number of ATD-tubes in a sequence was further reduced by reducing
the number of parallels taken in each sample series. Earlier 8 to 10 parallels
were taken in each sample series, but in this work the number of parallels
was reduced to 5-6. It was therefore more important to make sure that stable
conditions were reached before the sampling began. For the dynamic experiments this was obtained through flushing a minimum of 10, 20 and 30 dm3 of
gas for 50, 100 and 150 bar respectively. For the static experiment a possible
routine for this was investigated as part of the experiments run in this work,
see further discussion in section 5.2.2.
Storage of standards and quality controls
The method for storage of the standard and quality control solutions was
studied as part of this work. In the early experiments performed in this work
it was discovered that the slope of the calibration curve increased from day to
day. Actions were therefore taken to look at this possible problem.
Earlier the standard and quality control solutions were stored in glass containers or graduated flasks at room temperature. Some simple experiments to
investigate the degree of evaporation were therefore performed. One graduated
flask was filled with a methanol solution and stored at room temperature. A
second graduated flask containing approximately the same amount of solution
was stored at the same conditions, but unlike the first flask this flask was kept
open for one minute every day. The opening of the flask was to represent the
need of opening the flask to make standards and quality controls applied to
ATD-tubes. The mass of the flasks was measured over a period of five days,
and the test showed that a notable amount of methanol evaporated from the
second flask.
Methanol is a volatile component, and some evaporation was therefore anticipated, but the degree of evaporation was larger than expected. The error
introduced by the evaporation corresponds to a decrease in the measured concentration for the standard. An error of approximately 6.5% relative to the
concentration of the standard was detected over a period of one week.
After the findings due to the evaporation of methanol it was decided to transfer
the standard solutions to vials just after they were made. The vials used had a
volume of approximately 2 cm3 , and were closed by a crimp lid with a septum.
The vials containing the solutions were also kept in a refrigerator at 277.15
K. When used the vials were stored at room temperature for a minimum of
20 minutes prior to use, for enabling the solutions to reach room temperature.
The samples were then taken directly from the vial by using a syringe, without
the need to remove the lid.
Experience showed that this modification to the procedures was successful.
The results from the quality controls were more stable over time, and when
analysing a standard that had been stored in the refrigerator for two months,
the deviation from the rest of the standards run in the same sequence was
neglectable.
44
5.4
CHAPTER 5. RESULTS AND DISCUSSION
Uncertainty in the experimental data
As the results from these experiments depend on a lot of different measurements, it is difficult to give an accurate value for the uncertainty in the experimental data. The discussion in this section will therefore aim at giving
an argumentation for an estimate for the uncertainty in the reported data.
Because of the very limited number of results available, it has not been attempted to give an estimate for the uncertainty in the results from the static
equipment.
An estimate for the uncertainty in the samples taken from the rig can be
found from figures 5.1 and 5.3 for the dynamic experiments. The figures and
the appurtenant discussion show that almost all of the data points included in
the calculation is within ±10% of the average result reported.
The uncertainty of the GC measurements must be determined by looking at
results from the standards included in the calibration curve and the quality
controls. The standard deviation for the standards analysed were calculated to
find the limits used to evaluate the results from the quality controls, and was
found to be 3.41%. The deviation between the measured and the theoretical
value for the quality controls were in the range of approximately ±5%. See
more information in appendix A.3.
The uncertainty in the measured temperatures, pressures and volumes for the
dynamic experiments can probably be neglected. The calibrations and controls performed as described in appendix A show that there are only small
deviations between the read value and the reference instrument after the calibration has been performed. It is therefore assumed that this uncertainty has
a small influence on the overall uncertainty, compared to the uncertainty in
the equipment and the analysis used.
No comparable value for the uncertainty is reported in the literature. [Folas
et al., 2007] reported that the uncertainty is 25% in the worst case, which
is for the ternary MEG-water-methane system at low temperatures. In the
report by [Haugum and Sharifi, 2011] no value for the overall uncertainty in
the experiments is reported.
Based on the discussion above it is reasonable to assume that the overall uncertainty in the results for the dynamic equipment is in the range between 15
and 20%.
5.5
Modelling
The concentration of MEG in methane was calculated using a SRK-EoS model
developed in this work, and an existing CPA-EoS model developed by [Solbraa,
2002]. The calculations were performed for 50, 100, 150 and 200 bar, in the
temperature range from 273-333 K. The results from the calculations are
shown in figure 5.9, together with literature and experimental data for comparison. The concentration of MEG in methane calculated by the SRK-EoS
model is also summarised in table B.1 in appendix B.
The calculations with the SRK-EoS model have been performed with two different interaction parameters, K12 , in the mixing rule. The first calculation
5.5. MODELLING
45
(a) P = 50 bar
(b) P = 100 bar
(c) P = 150 bar
(d) P = 200 bar
Figure 5.9: Results from modelling of the concentration of MEG in methane.
Literature and experimental data are included for comparison.
was performed with K12 set equal to zero. This resulted in very high values
for the concentration of MEG in methane. The K12 was then fitted to the
experimental data available from this work and to the literature data. From
figure 5.9 it can be seen that a K12 of 0.35 gives a relatively good fit with the
experimental data available.
When using K12 of 0.35 the concentration of MEG calculated is higher than
for the CPA-EoS model. This deviation is small at low temperatures, but
increases at higher temperatures and pressures. Higher values for K12 were
tried, and when K12 was set equal to 0.42 the calculations from the SRK-EoS
corresponds very well with the results from the CPA-EoS model. This results
in a better fit with the experimental data at low pressures, but when using a
K12 -value of 0.35 the results give an acceptable fit for low pressures. At the
same it gives a better fit than the CPA-EoS model for higher pressures, when
compared to the data reported by [Folas et al., 2007].
The CPA-EoS model is not necessary correct, as discussed in the comparison
between the average reported result and modelled values by the CPA-EoS
model in sections 5.1 and 5.2. The CPA-EoS model used for the calculations
46
CHAPTER 5. RESULTS AND DISCUSSION
in this work has been run with a K12 -value of 0.134, as reported in [Folas et al.,
2006]. As mentioned in the introduction, section 1.2, the background for the
work with this project is to obtain more experimental data to verify the results
from the models.
Chapter 6
Further work
The vapour-liquid equilibrium studied in this work has been for the monoethylene glycol - methane system. Some experimental data have been obtained,
but more work is needed to finish the experimental matrices planned for this
project, see sections 4.2.1 and 4.2.2. The plan is to continue the work started
in this project to study the vapour-liquid equilibrium for the triethylene glycol - methane, methyldiethanolamine - methane and methyldiethanolamine carbon dioxide systems in the longer run.
6.1
Dynamic equilibrium experiments
An important challenge for the dynamic equipment is to further investigate
the problems with cold spots in the rig. This is discussed in more detail in
section 5.1, and has been an important reason for the limited number of results
obtained in this work. Two possible solutions should be investigated: a) To
change the heater cables used to more flexible solutions, or b) to put the rig
into a climate chamber . Initial investigations show that there are possibilities
for placing part of a heating cable in contact with liquid, and this may be
able to solve the problem with the cold spots at the entrances and exits of the
water baths. It is also possible to apply the self-regulating cable used in layers
without harming the cable, so this may solve the problems with the cold spots
around the valves. The option of placing parts of the rig in a climate chamber
has not been investigated further.
Before the problem with the cold spots is solved, it is not possible to use the rig
for experiments above room temperature. It is important to obtain data in the
temperature range between 298 and 313 K to be able to compare the results
from the dynamic and the static experiments. It is therefore recommended
that the problem with the cold spots is solved before the experiments continue.
Alternatively it should be discussed whether the equipment is suited for the
type of experiments planned.
6.2
Static equilibrium experiments
For the static equipment all parts of the rig now work according to plan. The
rig is therefore ready to start running experiments, but there are still some
issues from the initial experiments that should be sorted out.
The most important thing is to investigate whether the temperature measured
on the outside of the PVT-cell is the same as the temperature inside the
47
48
CHAPTER 6. FURTHER WORK
cell. This uncertainty results in a large uncertainty in the experimental data,
as the concentration of MEG in methane is very dependent on temperature.
Investigations have been started to look for a possible solution. One option is
to install a thermocouple mounted in a T-connection just after the outlet of
the hydraulic part of the sample cylinder.
The discussion in section 5.2.1 indicates that the system needs four days or
less to reach equilibrium. For all the experiments performed as part of this
work it has been waited for four days or more before the first sample series
have been taken out. It is therefore recommended that later experiment should
investigate this further. A good idea can be to start a new experiment on a
Monday, and then take out samples every day for the rest of the week. It
was planned to do this as part of this work, but the experiment could not be
carried out as planned due to problems with the GC used.
When the initial uncertainties have been sorted out, more experiments with
MEG should be run. It will be very interesting to see how the results from
the static rig compare to the experimental data from the dynamic rig. This
comparison will be important in the determination of whether the experimental
work should be continued in both of the rigs, or whether one rig should be
chosen because of better results.
It will also be very interesting to do more experiments to see how fast the rig
can react to changes in the concentration of MEG. Only an increase in the
concentration has been studied in this work, so it will be interesting to see
how fast the concentration in the sampling system decreases when going from
a higher to a lower concentration of MEG in the gas phase. This has been
one of the problems with the dynamic equipment. The static equipment have
therefore been designed to minimise this problem by using the minimum number of valves and the minimum length of tubing possible, without increasing
the risks involved.
In the longer run the plan is to continue the experiments for other processing
chemicals. Important chemicals that will be prioritised are triethylene glycol,
TEG, and methyldiethanolamine, MDEA. One of the challenges when changing to different chemicals will be that the concentration of the components in
methane will be lower than it is for MEG.
Another problem can be the choice of materials used in the packing materials
in the PVT-cell and the Quizix-pump when running experiments with MDEA.
Previous experience shows that MDEA damage the commonly used materials
after a relatively short period of time. This may result in problems with leaks,
and it can also harm the equipment. Further investigation is therefore needed
to select the proper materials to be used, and to replace the parts in question
in the cylinder and in the pump.
Chapter 7
Conclusion
A static equipment where methane is saturated with MEG in a PVT-cell has
been built and tested. An existing dynamic equipment where the gas is saturated and condensed in a series arrangement was modified for experiments
with glycols. The samples from the experiments were analysed using ATDGC-FID.
Experimental data were obtained in the temperature range from 273.15 to
313.15 K, and for pressures up to 150 bar, and the results were compared to
an existing model based on the CPA-EoS. In addition a model based on the
SRK-EoS was developed. The initial results from the SRK-EoS model were
significantly higher compared to the CPA-EoS model and the experimental
data. An interaction parameter, K12 , of 0.35 in the mixing rule was found
to improve the agreement between the developed model and the experimental
data.
The experiments show that the concentration of MEG in methane increases
at increasing temperatures. The modelled values show that the concentration of MEG in methane starts to decrease at increasing pressures, before it
passes through a minimum and starts to increase. Further experiments to determine the pressure resulting in the minimum value will be conducted in the
continuation of this work.
49
50
Bibliography
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compounds L. The vapour pressures of 1,2-ethanediol (ethylene glycol) and
bis(2-hydroxyethyl)ether (diethylene glycol). J. Chem. Thermodynamics,
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DIPPR (2012). Design Institute for Physical Properties, DIPPR database.
Folas, G. K., Berg, O. J., Solbraa, E., Fredheim, A. O., Kontogeorgis, G. M.,
Michelsen, M. L., and Stenby, E. H. (2007). High-pressure vapor-liquid
equilibria of systems containing ethylene glycol, water and methane: Experimental measurements and modeling. Fluid Phase Equilibria, (251):52–58.
Folas, G. K., Kontogeorgis, G. M., Michelsen, M. L., and Stenby, E. H. (2006).
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Fonseca, J. M. S. (2010). Design , Development and Testing of New Experimental Equipment for the Measurement of Multiphase Equilibrium. PhD
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Hales, J., Cogman, R., and Frith, W. (1981). A transpiration-g.l.c. apparatus
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Haugum, T. and Sharifi, Z. (2011). MEG solubility in nitrogen and methane.
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Huang, S. H. and Radosz, M. (1990). Equation of state for small, large, polydisperse, and associating molecules. Industrial & engineering chemistry research, 29:2284–2294.
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Kamihama, N., Matsuda, H., and Kurihara, K. (2012). Isobaric Vapor−Liquid
Equilibria for Ethanol + Water + Ethylene Glycol and Its Constituent Three
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Kaye, G. and Laby, T. (1995). Tables of Physical and Chemical Constants.
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Kontogeorgis, G. M., Voutsas, E. C., Yakoumis, I. V., and Tassios, D. P.
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Thermodynamics of Fluid-Phase Equilibria. Prentice Hall PTR, 3. edition.
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An Equation of State. Fugacities of Gaseous Solutions. Chemical Reviews,
pages 233–244.
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on PVT Properties of Ethylene Glycols (C2H2OH)2 and (CH2OD)2.
Pressure and Isotope Dependence of Liquid-liquid Phase Separation of
(Ch2OH)2/CH3NO2 and (CH2OD)2/CH3NO2 Solutions. J.Phys. Chem.,
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Domanska, U. (2005). Thermodynamic Properties of Mixtures Containing
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Zheng, D., Ma, W., and Wei, R. (1999). Solubility study of methane, carbon dioxide and nitrogen in ethylene glycol at elevated temperatures and
pressures. Fluid phase equilibria, (July 1998):277–286.
Appendix A
Calibration
For the experimental rigs the temperature elements and the pressure sensors
were calibrated, and the gas clocks were controlled. The results from the
calibrations for pressure and temperature were used to find a linearization
used to update the calibration files in Labview.
The gas chromatograph was calibrated on a regular basis to be able to obtain
accurate measurements of the glycol content in the samples. Calibration curves
were established, and daily quality controls were run together with the samples
to check the current calibration curve.
A.1
A.1.1
Dynamic equipment
Temperature
The dynamic test rig has temperature measurements in the two water baths, in
connection with the heat traced tubing and in the gas clock. The temperature
reading in the water baths were calibrated, because the temperature in the
second water bath is used as the experimental temperature. The temperature
elements to control the heat tracing were not controlled, as the temperature in
these lines does not directly influence the results. It is important that the lines
are heat traced to avoid condensation problems, but a temperature deviation
is accepted. The thermometer in the gas clock was checked against the new
thermometer in the gas clock for the static equipment, but no calibration was
performed. This thermometer requires manual readings of the temperature on
a scale with 0.5 K intervals, and it therefore has limited accuracy.
The temperature in the water baths were set in the control unit, and the actual
temperature was logged in the Labview program. It was not possible to change
the calibration for the set point of the water bath, but the calibration was used
to correct the temperature logged in Labview.
The calibration was performed by selecting 5 points in the operating range
used in the experiments. A set point was entered in the control panel for the
water bath, and a reference was placed inside the liquid in the water bath. The
reference element used was of the type STS-100 A 901 from Ametek Calibration
Instruments. The result was noted when both the bath temperature and the
reference temperature were stable. After measuring all 5 points, the results
were summarised in a graph. A linearization for the points was found, and the
equation for the linearization was entered into the calibration file in Labview.
53
54
APPENDIX A. CALIBRATION
The results from the calibration of water bath 1 and 2 are summarised in figure
A.1.
(a) Water bath 1
(b) Water bath 2
Figure A.1: Results from the temperature calibration of the water baths for
the dynamic test rig
A.1.2
Pressure
The pressure in the dynamic test rig is measured by a PA 35X pressure transmitter from Keller. The pressure transmitter was removed from the rig and
mounted in a separate rig for the calibration, using nitrogen gas from an external bottle. A Druck DPI 610 Pressure Calibrator was used as a reference.
The calibration started at low pressures, gradually increasing the pressure
up to about 210 bara. Afterwards the pressure was decreased back down to
atmospheric pressure, noting points both on the way up and on the way down.
The results are summarised in figure A.2.
A.1.3
Gas volume
The gas volume of the samples from the dynamic test rig is measured by a
Ritter TG 1/7 gas clock. The gas clock is from 2003, and does not have a
valid calibration from the manufacturer. It was therefore controlled against a
Chandler Engineering model 2331D gasometer. The gasometer is new, and it
has a measuring principle that give reliable values for volume differences, but
it is not approved as a reference instrument.
The control was performed by connecting the gas clock to the gasometer,
and the gas used was air. The cylinders in the gasometer were filled with
air, and the pressure was adjusted to atmospheric pressure. Then the gas
was transported to the gas clock by manually decreasing the volume of the
gasometer cylinders. The results from the control are shown in figure A.3.
The results show that there are points both over and under the linearization
line. The maximum deviation was ± 2.6%, but the average deviation was
-0.6%. This indicates that the gas clock does not give a consistent deviation
in one direction, and it is therefore not possible to use a correction factor
A.2. STATIC EQUIPMENT
55
Figure A.2: Results from the calibration of the Keller PAA 35X pressure
transmitter from the dynamic test rig
to take this into account. The volume readings from the gas clock are also
dependent on the water level in the gas clock. It was therefore decided that
2.6% uncertainty of the gas clock must be accepted.
A.2
A.2.1
Static equipment
Temperature
The static test rig has temperature measurements in the sample outlet from
the sample cylinder, on the outside of the sample cylinder, in connection with
the heat traced tubing and in the gas clock. In addition there is a temperature
safety system to protect the Quizix-pump against temperatures that exceeds
323 K.
The temperature readings in the sample outlet from the sample cylinder and on
the outside of the sample cylinder were calibrated, because these temperatures
are used to determine the experimental temperature. The thermocouples used
to control the heat tracing of the sample line and the temperature safety system
were not controlled, as a deviation is accepted for these measurements. The
thermometer in the gas clock was new, and it requires manual readings of the
temperature on a scale with 0.5 K intervals. It therefore has limited accuracy,
and was not controlled.
The calibration was conducted by placing the thermocouples in a dry bath
together with the reference. The bath and reference used were of the types
ATC-650 B and STS-100 A 901 respectively, and both were delivered by Ametek Calibration Instruments. Set points were entered in the control unit for the
bath, the temperature was logged in the Labview program and the reference
temperature was displayed in the panel of the bath. The results were noted
when the bath temperature, the measured temperature in Labview and the
reference temperature were stable.
56
APPENDIX A. CALIBRATION
Figure A.3: Results from the control of the Ritter TG 1/7 gas clock for the
dynamic test rig
After measuring a series of points in the range from 298 to 393 K, the results
were summarised in a graph. A linearization for the points was found, and the
equation for the linearization was entered into the calibration file in Labview.
The results from the calibration of the thermocouples are summarised in figure
A.4.
(a) Water bath 1
(b) Water bath 2
Figure A.4: Results from the calibration of the thermocouples in the static
test rig
A.2.2
Pressure
The pressure in the static test rig is measured by a LEO 3 pressure transmitter
from Keller. An external test bench used for calibrations were connected directly to the pressure transmitter, using nitrogen gas from an external bottle.
A Druck DPI 610 Pressure Calibrator was used as a reference.
A.3. GAS CHROMATOGRAPH
57
The calibration started at low pressures, gradually increasing the pressure up
to about 120 bar. For the experiments planed in this work it was enough with a
calibration valid up to 120 bar, which was the limit of the external test bench.
In the longer run it will be necessary to do a new calibration valid up to 200
bar. The results from the calibration are summarised in figure A.5.
Figure A.5: Results from the calibration of the Keller Leo 3 pressure transmitter from the static test rig
In addition there are pressure transmitters in each of the cylinders in the
Quizix pump. These pressure transmitters have been calibrated by the supplier of the pump, and have not been controlled as part of this work. By
comparing the pressure readings from the transmitters in the pump with the
pressure transmitter in the rig, it has been seen that there is a 0.1 - 0.5 bar
pressure deviation, where the pressure transmitters in the pump measure a
lower value for the pressure. The pressure noted for the experiments is the
pressure readings from the Keller pressure transmitter in the rig, as this has
been calibrated as part of this work.
A.2.3
Gas volume
The sample gas volume in the static test rig is measured by a Ritter 1/5
gas clock. This gas clock was bought for this rig, and was calibrated by the
manufacturer in March 2012. No further control of the gas clock was therefore
performed.
A.3
Gas chromatograph
A calibration of the gas chromatograph, GC, is needed to quantify the amount
of monoethylene glycol, MEG, in the samples from the experiments. For the
calibration a series of standards were made in the laboratory, adapted to the
amount of MEG expected in the samples.
The standards were made by diluting a small amount of MEG in methanol.
58
APPENDIX A. CALIBRATION
The desired amount of MEG was added to a measuring cylinder, and the mass
of MEG was determined using a scale with ±0.00001g resolution. The MEG
was then diluted, mixed and transferred to storage containers.
To obtain an accurate calibration of the GC, the standards were applied onto
ATD-tubes. A setup has been put together where the ATD-tube is continuously flushed with helium as carrier gas. A given volume of the standard is
taken out using a 10 mm3 syringe. The standard is then added to the ATDtube through a septum, and the tube is flushed for three minutes to evaporate
the methanol introduced together with the standard.
A calibration curve is created by analysing two parallels from three to five
different standards together with samples from the experiments. This process
is repeated over a period of three days, or until a total of 20 ATD-tubes with
standards have been analysed. The quality of the chromatograms was then
controlled, before the resulting calibration curve was created in the software
for the GC. One of the calibration curves used in this work is included in
figure A.6. This calibration curve was used from the middle of April to the
second half of May, a period where most of the experiments in this work
were conducted. For the experiments with glycols it is experienced that the
chromatogram changes slightly over time, and it is therefore necessary to create
a new calibration curve approximately once a month.
Figure A.6: Calibration curve for the GC
To control the calibration curve, and to check for any sudden changes in the
chromatogram, quality controls are run together with the samples. The quality
control, QC, is prepared in the same manner as the standards, and in this work
it has been run a QC for every three to five samples. A graph is used to follow
the development of the QCs, and the form used for the calibration curve in
figure A.6 is shown in figure A.7. The vertical lines in figure A.7 represent the
border lines used to evaluate the quality controls.
The value plotted in the QC form in figure A.7 is the deviation between the
measured and theoretical value for the quality control sample. The standard
A.3. GAS CHROMATOGRAPH
59
Figure A.7: Form for quality controls
deviation for the standards used to make the calibration curve is calculated,
and is used as border values for the quality controls. As long as the QCs is
within the borders of ± 2 standard deviations the QC is ok. When the QC is
outside ± 2 standard deviations, the alarm border is crossed. This indicates
that a new calibration curve will need to be made very soon. If one or more
of the quality control samples are outside ± 3 standard deviations, the action
border is crossed and the calibration curve is no longer valid.
60
Appendix B
Matlab source code and results from
the calculations
The concentration of MEG in methane was calculated using the Soave-RedlichKwong Equation of State, SRK-EoS, combined with the Van der Waals onefluid mixing rules. The Matlab code used to perform these calculations was
written as a part of this work, and the source code is included in section
B.2. The main file is called SRK.m, and this file uses the function Psat.m
to calculate the vapour pressure of MEG. The theoretical background for the
model is described in section 2.1. For a description of the development of the
model, see section 3.
B.1
Results from calculations
The results from the calculations are shown in table B.1. A figure summarising
the results from the calculations can be found in figure 5.9 in section 5.5.
Table B.1: Results from the calculation of the concentration of MEG in
methane by using the SRK-EoS. The values reported in the table have been
calculated using an interaction parameter K12 of 0.35.
Temperature
[K]
50 bar
Pressure
100 bar 150 bar
200 bar
273.1
278.1
283.1
288.1
293.1
298.1
303.1
308.1
313.1
318.1
323.1
328.1
333.1
0.529
0.865
1.388
2.187
3.390
5.168
7.760
11.481
16.751
24.117
34.284
48.152
66.852
0.600
0.948
1.473
2.251
3.386
5.020
7.340
10.588
15.082
21.224
29.524
40.617
55.290
1.114
1.673
2.476
3.615
5.207
7.407
10.409
14.461
19.870
27.018
36.369
48.488
64.054
61
0.803
1.233
1.865
2.780
4.084
5.919
8.468
11.967
16.714
23.083
31.541
42.657
57.127
62APPENDIX B. MATLAB SOURCE CODE AND RESULTS FROM THE CALCULATIONS
B.2
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
Matlab source code, model using SRK-EoS
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
% Function t o c a l c u l a t e t h e c o n c e n t r a t i o n o f MEG i n methane ,
% u s i n g SRK−EoS
% Anita Bersas 2 7 . 0 5 . 2 0 1 2
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
clear a l l
clc
clf
% Component 1 = MEG and component 2 = methane !
% Inputs :
Tvector = 0 : 1 : 6 0 ;
Pvector = 5 0 : 5 0 : 2 0 0 ;
C = 2;
% [ grC ]
% [ bara ]
% Number o f components [ −]
% C r i t i c a l P r o p e r t i e s : Tc Pc w . Source : DIPPR
Tc = [ 7 2 0 1 9 0 . 5 6 4 ] ;
% C r i t i c a l temperature
v e c t o r [K]
Pc = [ 8 . 2 0 0 0 0 E06 4 . 5 9 9 0 0E+ 0 6 ] ; % C r i t i c a l p r e s s u r e v e c t o r
[ Pa ]
w = [ 0 . 5 0 6 7 7 6 1 . 1 5 4 7 8E− 0 2 ] ;
% A c c e n t r i c f a c t o r v e c t o r [ −]
vMEG = 5 . 5 9 0 8 0E−05;
% Molar volume MEG [mˆ3/ mol ]
R = 8.314;
% U n i v e r s a l g a s c o n s t a n t [ J/mol K]
% Matrix w i t h b i n a r y i n t e r a c t i o n p a r a m e t e r s
K = o n e s (C, C) ;
K( 1 , 2 ) = 0 . 3 5 ;
K( 2 , 1 ) = K( 1 , 2 ) ;
% I n i t i a t e counting v a r i a b l e s .
% i t c o u n t s number o f i t e r a t i o n s
i t = zeros ( length ( Tvector ) , length ( P v e c t o r ) ) ;
% A l l o c a t e space for matrices
R e s u l t = o n e s ( length ( Tvector ) , length ( P v e c t o r ) ) ;
R e s u l t p h i = o n e s ( length ( Tvector ) , length ( P v e c t o r ) ) ;
Poynting = o n e s ( length ( Tvector ) , length ( P v e c t o r ) ) ;
for f = 1 : length ( Tvector )
T = Tvector ( f ) + 2 7 3 . 1 5 ;
% Change u n i t t o [K]
f o r g = 1 : length ( P v e c t o r )
P = P v e c t o r ( g ) . ∗ 1 E5 ;
Tr
Pr
=
=
T. / Tc ;
P . / Pc ;
% Change u n i t t o [ Pa ]
% C alcu late reduced temperature
% C alcu late reduced pressure
% C a l c u l a t e p a r a m e t e r s a and b f o r SRK−EoS
% E q u a t i o n s from [ Soave1972 ]
B.2. MATLAB SOURCE CODE, MODEL USING SRK-EOS
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
m = 0 . 4 8 0 + 1 . 5 7 4 . ∗w− 0 . 1 7 6 . ∗w . ˆ 2 ;
E q u a t i o n 15
a l p h a = (1+m. ∗ ( 1 − ( ( Tr ) . ˆ ( 0 . 5 ) ) ) ) . ˆ 2 ;
E q u a t i o n 13
a i = 0 . 4 2 7 4 7 . ∗ a l p h a . ∗ Pr . / ( Tr . ˆ 2 ) ;
63
%
%
b i = 0 . 0 8 6 6 4 . ∗ Pr . / Tr ;
% Guess a v a l u e f o r y1 (MEG c o n t e n t i n methane )
y ( 1 ) = 0 . 0 0 0 0 0 1 ; % [ −]
dy = 0 . 1 ;
% Set i n i t i a l value for d e l t a
while abs ( dy ) > eps
y ( 2 ) = 1−y ( 1 ) ;
% C a l c u l a t e non−randomness parameter a i j and A
f o r the mixture :
a i j = zeros (C, C) ;
A = 0;
f o r i = 1 :C
f o r j = 1 :C
aij (i , j ) =
( ( a i ( i ) ∗ a i ( j ) ) ˆ ( 0 . 5 ) ) ∗(1−K( i , j ) ) ;
A = A + y ( i ) ∗y ( j ) ∗ a i j ( i , j ) ;
end
end
% Calculate B f o r the mixture
b i j = zeros (C, C) ;
B = 0;
f o r i = 1 :C
f o r j = 1 :C
b i j ( i , j ) = ( b i ( i )+b i ( j ) ) / 2 ;
B = B + y ( i ) ∗y ( j ) ∗ b i j ( i , j ) ;
end
end
% Zˆ3 − Zˆ2 + (A−B−Bˆ2)Z − AB = 0 (SRK)
COEFF = [ 1 −1 (A−B−Bˆ 2 ) −A∗B ] ;
Z = roots (COEFF) ;
% Choose t h e g r e a t e s t r o o t , t h a t i s f o r t h e
vapour p h as e
z = max( Z ( imag ( Z )==0)) ;
% C a l c u l a t e t h e f u g a c i t y o f MEG
l n p h i = b i ( 1 ) /B∗ ( z −1) − log ( z−B) −
A/B∗ ( 2 ∗ ( ( ( y ( 1 ) ∗ a i j ( 1 , 1 ) ) +(y ( 2 ) ∗ a i j ( 1 , 2 ) ) ) /A)−b i ( 1 ) /B) ∗ log (1+B/
p h i = exp ( l n p h i ) ;
% S a t u r a t e d system : Find Phi ˆ s
% Function Psat .m c a l c u l a t e s t h e s a t u r a t i o n
p r e s s u r e o f MEG
64APPENDIX B. MATLAB SOURCE CODE AND RESULTS FROM THE CALCULATIONS
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
[ Psat1 ] = Psat (T) ;
Trs =
T. / Tc ( 1 ) ;
% Reduced t e m p e r a t u r e [ −]
Prs =
Psat1 . / Pc ( 1 ) ; % Reduced p r e s s u r e [ −]
% C a l c u l a t e new p a r a m e t e r s f o r SRK−EoS . P i s
r e p l a c e d by PsatMEG , and p a r a m e t e r s a r e f o r
pure MEG ( not m i x t u r e )
% E q u a t i o n s from [ Soave1972 ]
ms = 0 . 4 8 0 + 1 . 5 7 4 . ∗w( 1 ) −0.176.∗w( 1 ) . ˆ 2 ; %
E q u a t i o n 15
a l p h a s = (1+ms.∗(1 − sqrt ( Trs ) ) ) . ˆ 2 ;
%
E q u a t i o n 13
a i s = 0 . 4 2 7 4 7 . ∗ a l p h a s . ∗ Prs . / ( Trs . ˆ 2 ) ; %
Equation 8
b i s = 0 . 0 8 6 6 4 . ∗ Prs . / Trs ;
%
Equation 9
As = a i s ;
Bs = b i s ;
% Zˆ3 − Zˆ2 + (A−B−Bˆ2)Z − AB = 0 (SRK)
COEFFs
=
[ 1 −1 +(As−Bs−Bs ˆ 2 ) −As∗Bs ] ;
Zs
=
roots (COEFFs) ;
% Choose t h e g r e a t e s t r o o t , t h a t i s f o r t h e
vapour p h as e
zs
=
max( Zs ( imag ( Zs )==0)) ;
% C a l c u l a t e t h e f u g a c i t y o f MEG, s a t u r a t e d
system
% E q u a t i o n 10 i n [ Soave1972 ]
l n p h i s = ( zs −1) − log ( zs−Bs ) −
As/Bs∗ log (1+Bs/ z s ) ;
p h i s a t = exp ( l n p h i s ) ;
% C a l c u l a t e new v a l u e f o r y
gamma1 = 1 ;
% Assume a c t i v i t y c o e f f i c i e n t
f o r MEG i s e q u a l t o 1
% C o n c e n t r a t i o n o f methane i n MEG a t P = 50 ,
100 and 150 b a r r e s p e c t i v e l y
% Data from [ F o l a s e t a l . , 2 0 0 7 ] and [ Zheng e t
a l . , 1999]
i f P == 50E5
x1 = 1 −0.006;
e l s e i f P == 100E5
x1 = 1 −0.0115;
e l s e i f P == 150E5
x1 = 1 −0.015;
else
x1 = 1 ; % Assume pure MEG i f d a t a not
available
end
B.2. MATLAB SOURCE CODE, MODEL USING SRK-EOS
ynew =
gamma1∗ x1 ∗ Psat1 ∗ p h i s a t /P/ p h i ( 1 ) ∗ ( exp (vMEG∗ ( ( P−Psat1 ) / (R∗T) ) ) )
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
65
% Update g u e s s o f y1
dy = y ( 1 ) − ynew ;
y ( 1 ) = ynew ;
i t ( f , g )=i t ( f , g ) +1;
% Update c o u n t i n g v a r i a b l e
end
R e s u l t ( f , g ) = y ( 1 ) ; % Save r e s u l t i n a m a t r i x
Resultphi ( f , g ) = phi ;
Poynting ( f , g ) = ( exp (vMEG∗ ( ( P−Psat1 ) / (R∗T) ) ) ) ;
end
end
% Convert r e s u l t s t o u n i t used i n g r a p h s (ppm( mol ) )
R e s u l t s = R e s u l t . ∗ 1 E6 ;
% Convert answer t o ppm( mol )
TvectorK = Tvector + 2 7 3 . 1 5 ; % Convert u n i t t o K
save r e s u l t K R e s u l t s R e s u l t p h i Poynting % Save v a r i a b l e s t o
file
% Cre a t e f i g u r e
figure (40)
hold on
plot ( TvectorK , R e s u l t s ( : , 1 ) , ’ k− ’ , ’ l i n e w i d t h ’ , 2 )
plot ( TvectorK , R e s u l t s ( : , 2 ) , ’ k−− ’ , ’ l i n e w i d t h ’ , 2 )
plot ( TvectorK , R e s u l t s ( : , 3 ) , ’ k : ’ , ’ l i n e w i d t h ’ , 2 )
xlabel ( ’ Temperature
[K] ’ , ’ f o n t w e i g h t ’ , ’ b o l d ’ , ’ f o n t s i z e ’ , 1 6 , ’ f o n t a n g l e ’ , ’ i t a l i c ’ )
ylabel ( ’ S o l u b i l i t y o f MEG i n methane
[ ppm(m) ] ’ , ’ f o n t w e i g h t ’ , ’ b o l d ’ , ’ f o n t s i z e ’ , 1 6 , ’ f o n t a n g l e ’ , ’ i t a l i c ’ )
legend ( ’ P r e s s u r e = 50 bar ’ , ’ P r e s s u r e = 100 bar ’ , ’ P r e s s u r e =
150 bar ’ , ’ l o c a t i o n ’ , ’ n o r t h w e s t ’ )
axis ( [ 2 7 0 330 0 7 0 ] )
set ( gca , ’ f o n t s i z e ’ , 1 2 )
print ( f i g u r e ( 4 0 ) , ’−dpng ’ )
hold o f f
164
165
166
167
168
169 % Move f i g u r e t o d i f f e r e n t f o l d e r
170 [ SUCCESS,MESSAGE,MESSAGEID] =
m o v e f i l e ( ’ ∗ . png ’ , ’C: \ U s e r s \ Anita \ Documents \ Masteroppgave \ Report \ F i g u r e s ’ ,
171
172 % Write r e s u l t s f o r y i t o l a t e x code t o i n s e r t
report
173 a r r = R e s u l t s ;
174 f = fopen ( ’ R e s u l t s . t x t ’ , ’w ’ ) ;
175
176 for row = 1 : 5 : length ( a r r )
177
f p r i n t f ( f , ’ %3.1 f ’ , TvectorK ( row ) ) ;
178
f p r i n t f ( f , ’ & %3.3 f ’ , a r r ( row , 1 : end ) ) ;
179
f p r i n t f ( f , ’ \\\\\ n ’ ) ;
180 end
Matlab/SRK.m
t a b l e in
66APPENDIX B. MATLAB SOURCE CODE AND RESULTS FROM THE CALCULATIONS
1 %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
2 % Psat .m
3 % Function t o c a l c u l a t e t h e s a t u r a t i o n p r e s s u r e o f MEG ( 1 )
and methane ( 2 )
4 % Created by Anita Bersas
02.05.2012
5 %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
function [ PsatMEG ] = Psat (T)
% Riedel equation
% C o e f f i c i e n t s from DIPPR
% Psat = exp (A + B. /T + C. ∗ l o g (T) + D. ∗ (T. ˆE) ) / 1 0 0 0 ; % [ kPa ]
% Component 1 = MEG
A1 = 8 . 4 0 9 0 e +01;
B1 = −1.0411 e +04;
C1 = −8.1976;
D1 = 1 . 6 5 3 6 e −18;
E1 = 6 ;
PsatMEG = exp (A1 + B1/T + C1∗ log (T) + D1∗ (TˆE1 ) ) ; % [ Pa ]
%
%
%
%
%
%
% Component 2 = methane ( not used i n t h i s c a l c u l a t i o n )
A2 = 3 . 9 2 0 5E+01;
B2 = −1.3244E+03;
C2 = −3.4366;
D2 = 3 . 1 0 1 9E−05;
E2 = 2 ;
% PsatC1 = exp (A2 + B2/T + C2∗ l o g (T) + D2∗(TˆE2) ) / 1 0 0 0 ; %
[ kPa ]
Matlab/Psat.m
Appendix C
Estimation of the concentration of MEG
in the gas phase
A theoretical estimation for yi has been calculated to be used as a basis for
the discussion of the results from this work. The estimation is based on a
simplification of equation (3.1).
y i P φi =
γi xi Pis φsi
νi (P − Pis )
exp
RT
!
(3.1)
As mentioned in chapter 3 the activity coefficient for MEG in the liquid phase,
γi , can be assumed to be equal to one, as the liquid phase consists of almost
pure MEG. Based on the literature data presented in section 2.2.3 the concentration of MEG in the liquid phase can also be assumed to be equal to one. If
the temperature is such that the saturation pressure is below 1 bar, then φsi is
close to unity [Prausnitz et al., 1999]. Based on the literature data in section
2.2.2 this corresponds to a temperature of approximately 473 K for MEG. It
is therefore no problem to assume that φsi is equal to one in the temperature
range of interest for this work. These terms can therefore be cancelled as
shown in equation (C.1). By setting the Poynting factor equal to Θ as defined in equation (C.2), equation (3.1) can be simplified to the form shown in
equation (C.3).
y i P φi = γi
xi Pis φsi
νi (P − Pis )
exp
RT
νi (P − Pis )
Θ = exp
RT
yi =
Pis Θ
P φi
!
(C.1)
!
(C.2)
(C.3)
Equation (C.3) show that yi is a function of the ratio between Pis and P . Two
main factors will influence yi : a) The Poynting factor Θ, and b) the fugacity
coefficient φi . If Θ is larger than one or φi is smaller than one, this will lead
to an increase in the estimation of yi . On the other hand, if Θ is smaller than
one or φi is larger than one, the estimation of yi will decrease.
67
68APPENDIX C. ESTIMATION OF THE CONCENTRATION OF MEG IN THE GAS PHASE
Calculations performed by the SRK-EoS model developed in this work show
that Θ is larger than one and that φi is smaller than one. The calculations for
Θ and φi are summarised in tables C.1 and C.2 respectively.
Table C.1: Calculations of the fugacity coefficients using the SRK-EoS
Pressure
Temperature
[K]
273.1
278.1
283.1
288.1
293.1
298.1
303.1
308.1
313.1
318.1
323.1
328.1
333.1
Calculations with Kij = 0
50 bar 100 bar 150 bar 200 bar
Calculations with Kij = 0.35
50 bar 100 bar 150 bar 200 bar
0.244
0.261
0.278
0.295
0.312
0.328
0.345
0.361
0.378
0.394
0.410
0.426
0.441
0.420
0.438
0.456
0.473
0.490
0.507
0.523
0.539
0.554
0.569
0.584
0.598
0.612
0.077
0.086
0.097
0.107
0.118
0.130
0.142
0.155
0.167
0.181
0.194
0.208
0.222
0.029
0.034
0.040
0.046
0.053
0.060
0.067
0.076
0.084
0.093
0.103
0.113
0.123
0.013
0.016
0.019
0.023
0.027
0.031
0.036
0.041
0.047
0.053
0.060
0.067
0.075
0.208
0.224
0.241
0.257
0.274
0.290
0.307
0.324
0.341
0.357
0.374
0.391
0.407
0.117
0.129
0.142
0.155
0.169
0.183
0.198
0.212
0.227
0.243
0.258
0.274
0.289
0.073
0.082
0.092
0.102
0.113
0.125
0.137
0.149
0.162
0.175
0.189
0.203
0.217
Table C.2: Calculations of the Poynting factor
Temperature
Pressure
[K]
50 bar
100 bar
150 bar
200 bar
273.1
278.1
283.1
288.1
293.1
298.1
303.1
308.1
313.1
318.1
323.1
328.1
333.1
1.131
1.128
1.126
1.124
1.122
1.119
1.117
1.115
1.113
1.111
1.110
1.108
1.106
1.279
1.273
1.268
1.263
1.258
1.253
1.248
1.244
1.240
1.235
1.231
1.227
1.224
1.447
1.437
1.428
1.419
1.411
1.403
1.395
1.387
1.380
1.373
1.366
1.360
1.354
1.636
1.622
1.608
1.595
1.582
1.570
1.558
1.547
1.536
1.526
1.516
1.507
1.497
As the discussion above suggest, a minimum estimate of yi can be calculated
by using equation (C.4). The results from this calculation is summarised in
table C.3.
Pis
yi =
P
(C.4)
69
Table C.3: Calculations of a minimum estimate for yi
Temperature
Pressure
[K]
50 bar
100 bar
150 bar
200 bar
273.1
278.1
283.1
288.1
293.1
298.1
303.1
308.1
313.1
318.1
323.1
328.1
333.1
0.197
0.338
0.565
0.927
1.491
2.355
3.655
5.581
8.390
12.427
18.147
26.147
37.193
0.099
0.169
0.283
0.463
0.745
1.177
1.828
2.791
4.195
6.213
9.074
13.073
18.596
0.066
0.113
0.188
0.309
0.497
0.785
1.218
1.860
2.797
4.142
6.049
8.716
12.398
0.049
0.084
0.141
0.232
0.373
0.589
0.914
1.395
2.098
3.107
4.537
6.537
9.298
70
Appendix D
Lists of experiments
This appendix gives an overview of all the experiments run as part of this work.
The lists of experiments give more details about how each of the experiments
are run. Lists of the experiments from the static and dynamic experiments
are shown in tables D.1 and D.2 respectively. Comments are added where
additional information is needed to understand the development in the experiments.
Table D.1: List of static experiments run as part of this work
Date
02.05.2012
04.05.2012
08.05.2012
09.05.2012
11.05.2012
18.05.2012
22.05.2012
25.05.2012
29.05.2012
30.05.2012
Temperature
[K]
Pressure
[bar]
No. of days
[−]
No. of samples
[−]
Average result
[ppm(m)]
Ambient
Ambient
Ambient
Ambient
Ambient
298.15
298.15
298.15
298.15
298.15
50
50
50
50
50
50
100
100
100
100
6
8
4
5
7
7
4
7
11
12
3
3
5
5
5
5
5
6
6
6
4.408a
3.430b
4.465c
4.990
4.539
5.391d ,f
7.479e,f ,g
6.874h
7.498
-i
a
Started first experiment 26.04.2012
Colder in the room than usual
c
Started new experiment 04.05.2012
d
Started new experiment 11.05.2012
e
Started new experiment 18.05.2012
f
The concentration increased through the sampling sequence, indicating that it was not
flushed enough gas through the sampling system before starting the sampling. The average
result is therefore the result from the last sample.
g
The samples were analysed on a ATD-GC-MS instead of the ATD-GC-FID normally used,
because of problems with the ATD-GC-FID
h
Analysed during a period with problems with the ATD-GC-FID
i
The samples were destroyed during the GC-analysis due to problems with the FID-detector
b
71
72
APPENDIX D. LISTS OF EXPERIMENTS
Table D.2: List of dynamic experiments run as part of this work
Date
10.02.2012
13.02.2012
16.02.2012
17.02.2012
21.02.2012
22.02.2012
24.02.2012
27.02.2012
28.02.2012
09.03.2012
12.03.2012
13.03.2012
14.03.2012
26.03.2012
27.03.2012
27.03.2012
28.03.2012
28.03.2012
29.03.2012
14.05.2012
14.05.2012
16.05.2012
16.05.2012
18.05.2012
18.05.2012
21.05.2012
22.05.2012
29.05.2012
30.05.2012
a
A
B
A
B
A
B
A
B
A
B
Temperature
[K]
Pressure
[bar]
No. of samples
[−]
Average result
[ppm(m)]
273.15
273.15
273.15
273.15
20
20
20
20
40
40
40
20
20
40
40
40
40
40
40
273.15
273.15
273.15
273.15
273.15
273.15
273.15
273.15
273.15
273.15
50
50
50
50
50
50
50
50
50
50
50
50
50
50
50
50
50
50
50
50
100
50
100
50
50
100
100
150
150
4
6
10
8
9
10
5
8
8
6
7
4
6
9
5
5
5
5
5
5
5
6
6
5
5
8
6
6
6
0.310a
0.320
0.328
0.323
2.243
2.283
2.113
2.213
3.360
3.726
3.801
3.395b,g
4.872c,g
7.174d
7.256
7.742
7.647
7.291
7.672
0.993e,g
1.087e,g
0.598f ,g
0.487
0.324
0.309
0.421
0.379g
0.507h
0.536
Not flushed enough gas through the system before the sampling started
Tried to see what happened when decreasing the temperature. Flushed 15
dm3 gas before sampling.
c
Tried to continue the experiment after decreasing the temperature. After
insulating the lids of the water baths.
d
After insulating the lid of the water baths and added heat tracing on the
tubing between the water baths
e
Too high temperature on the heat tracing between the water baths (343.15K)
f
Samples showed decreasing concentration, indicating carry over from previous
experiment
g
This experiment is not included in the calculation or discussion of the results
h
The samples were analysed on a ATD-GC-MS instead of the ATD-GC-FID
normally used, because of problems with the ATD-GC-FID
i
The concentration increased through the sampling sequence, indicating that it
was not flushed enough gas through the sampling system before starting the
sampling. The average result is therefore the result from the last three
samples.
b
Appendix E
Safety analysis for the static equipment
A risk evaluation for the experiments performed should be included as part
of the master thesis. As the experiments in this work have not been carried
out in the laboratories at NTNU, a standard risk evaluation used at NTNU
has not been used. To document that the necessary health, safety and environmental precautions have been taken, the safety analysis performed for the
static experimental rig is included instead. More detailed and complementary
information about HSE regarding the work with this project can be found in
section 4.4.
It has been decided to include the safety analysis for the static equipment as the
development of the equipment, and hence the preparation of the appurtenant
HSE documentation, has been part of this work. As all the safety documentation at Statoil’s laboratories at Rotvoll should be available in Norwegian,
only a Norwegian version is available. The rig is in the safety analysis referred
to as the trace components rig, or ”sporkomponentrigg” as it is denoted in
Norwegian. This is the term used for the rig in the laboratory.
73
SIKKERHETSANALYSE
Utstyr: Sporkomponentrigg
Krav til utstyr ved Laboratoriet i Trondheim
•
•
•
•
•
•
Mulighet for å gjøre utstyret strømløst uten bruk av verktøy, dvs nødstoppbryter eller mulighet for å
trekke ut kontakt.
Laboratorieutstyr der giftige eller brennbare gasser benyttes uten tilsyn eller forbruket er over 5 liter
pr. time, skal være overvåket med gass-spesifikk deteksjon og utstyrt med automatisk avstegning
mot flaske/gasslager. Utstyr plassert i avtrekkskap eller under avtrekkshette er ikke pålagt deteksjon
og automatisk nedstegning.
Generelt vernebrillepåbud i laboratoriet.
Utstyr i fareklasse 2 hvor kombinasjon av høyt trykk og volum kan utløse store energimengder skal
utstyret/riggen sikres mot bevegelse og utstyres med manometer.
Trykkpåkjent utstyr skal være godkjent/CE-merket i hht myndighetskrav, se labhåndbok
Bærbar fallalarm obligatorisk mellom kl 17-07 samt på helger og helligdager
Trykksatt volum:
Type
Volum væske
Volum gass
Trykk (bara)
Trykktest
Lekkasjetest (oppgi
tillatt lekkasjerate)
Annet
Barrierer:
Type
Nødbryter
Detektor, alarmer
Automatisk
nedstengning
Ex klassifisering
Rensing av
avløp/utslipp
Automatisk
trykkavlastning
ved nødstopp
Temp-, nivå-,
massestrøms- og
trykkovervåkning
Sikkerhetsventil
Annet
Relevans
(Ja/Nei)
Ja
Ja
Ja
Ja
Ja
Relevans
(Ja/Nei)
Ja
Ja
Ja
Kommentar
0 – 600 ml
0 – 600 ml
200
Utstyr er trykktestet av leverandør (se dokumentasjon i
driftspermen)
Vil bli testet ifm med oppstart
Kommentar
HC detektor i rommet
Temperaturovervåkning på væskeretur til pumpe. Ved for høy
temperatur vil oppvarming slås av.
Nei
Nei
Nei
Ja
Temperaturovervåkning på væskeretur til pumpe. Logging av trykk
og temperatur
Ja
200 bar på høytrykksiden og 1,2 bar på lavtrykksiden
Tilkoblinger:
Type
Vann
Strømtilførsel,
(400V, 230 V,
UPS, prioritert, etc)
Gasstilførsel
(forskyningskilde,
trykk)
Ventilasjon
Kjøling (isvann,
nettvann, luft, etc)
Lufttilførsel (trykk-,
instrumentluft)
Annet
Relevans
(Ja/Nei)
Nei
Ja
Ja
Kommentar
230 V
Metan eller nitrogen flaske. Naturgass fra stempelsylinder
Ja
Nei
Ja
Automatisk avstengning av gassflaske og styring av pumpe
Stråling (laser, røntgen, radioaktivitet, annet):
Type
N/A
Kommentarer
Kjemikalier:
Formel/
navn
MEG
Mengde
Maks 800 ml
TEG
Maks 800 ml
MDEA
Maks 800 ml
Giftig
KreftReproduksjons- Etsende
fremkallende
skadelig
Brannfare/
Merknader
LEL-verdi
Ikke
Fareklasse
brannfarlig. Xn=Helseskadelig
LEL:3,2%v/v R22 =Farlig ved
svelging
Ikke
brannfarlig
LEL:0.9%v/v
R36= Irriterer
øynene
Husk: egne regler ved bruk av flussyre
Gass:
Formel/
navn
Metan
Maks 120 Ndm³
Nitrogen
Naturgass
Maks 120 Ndm³
Maks 120 Ndm³
Mengde
Giftig
Kreftfremkallende
Oksygenfortrengende
Etsende
Brannfare/
LEL-verdi
LEL 5,0%v/v
Merknader
R12= Ekstremt
brannfarlig
Ikke brannfarlig
LEL: 5,0%v/v
R=60= Kan
skade
forplantning.
R48/20=
Farlig. Alvorlig
helsefare ved
lengre tids
påvirkning ved
innånding.
R12= Ekstremt
brannfarlig
Driftsbetingelser, max og min verdier:
Type
Maksimum
Temperatur (°C)
120
Trykk (bara)
200
Rotasjonsshastighet
(rpm)
Massestrøm
5 Nl/min
(Nl/h, m3/h,etc)
Personlig verneutstyr:
Type
Relevans
(Ja/Nei)
Hansker
Ja
Støvfilter
Nei
Åndedrettsvern
Nei
Ansiktsskjerm
Nei
Bærbar detektor
Nei
Hørselvern
Nei
Vernesko
Nei
Hjelm
Nei
Bekledning
Nei
Fallalarm
Ja
Operatørs kompetanse:
Type
Minimum
Erfaring
Opplæring
Tilstrekkelig
Opplæring labvakt
Nei
Minimum
Romtemperatur
0
Kommentar
0
Kommentar
For arbeid mellom kl. 17 og 07, samt i helger og på helligdager
Kommentar
Kjennskap til arbeid med trykksatt utstyr
Spesielle forhold knyttet til prosess/utstyr:
Fare forbundet
Aktualitet
Kommentar
med:
Eksoterm/
Nei
endoterm rx
OverflateJa
Isolert varmekabel på prøveflaske og tilhørende rør
temperatur
Varmgang
Nei
Vedlikeholdsrutiner
Nei
(intervaller)
Løfteutstyr
Nei
Fareklasse 1
Deltakere på sikkerhetsanalysen: Toril Haugum, Eivind Johannessen og Anita Bersås
Sikkerhetsanalyse utført 06.03.2012
Oppdateringer (vurderinger, dato og endring):
Appendix F
Experimental procedures for the static
experiments
As the development of the operational procedures for the static experiments rig
has been an import part of this work, a complete version of the procedures is
included. There are only Norwegian employees operating the rig, and therefore
only a Norwegian version of the procedures are available. A summary of the
experimental procedures for the rig is given in section 4.2.2.
A draft for the procedures for the static experiment was written before the rig
was built. The task of writing the procedures was one of the actions resulting
from the HAZOP meeting. Previous experience with equipment operated at
elevated pressures and the piping and instrumentation diagram, P&ID, was
used as a basis for the preparation of the procedures.
When the rig was ready for operation the draft for the procedures was used
as a starting point. As the operator started operating the rig parts of the
procedures were modified, mostly details such as volumes and flow rates.
The rig is in the procedures referred to as the trace component rig, or ”sporkomponentrigg” as it is denoted in Norwegian. This is the term used for the rig in
the laboratory.
77
Skrevet av Anita Bersås, våren 2012
Prosedyrer for sprokomponentsriggen:
Forsøksgjennomføring:
-
Fylle væske på prøvesiden av stempelsylinderen, se prosedyre C punkt 1 - 4.
Koble til stempelsylinderen, se prosedyre C punkt 5 - 8.
Fylle hydraulikkvæske, se prosedyre A.
Fylle gass, se prosedyre C punkt 9 - 25.
La forsøket stå til det er oppnådd likevekt.
Prøvetaking ved hjelp av ATD-rør, se prosedyre D.
Etterfylling av gass og innstilling til nytt forsøk, se prosedyre E.
Kjøre ferdig forsøksserie med et kjemikalium.
Bytte av kjemikalium og klargjøring til ny forsøksserie, se prosedyre B.
Huskeliste for situasjoner som krever ekstra oppmerksomhet:
A
x
Før fylling av nytt kjemikalium på hydraulikksiden må de to rørstykkene i forbindelse med
sikkerhetsventilen PSV001 demonteres og skylles gjennom, se nærmere beskrivelse i «Prosedyre
for tømming av væske fra hydraulikksystemet og trykkavlastning av riggen før avkobling av
stempelsylinder».
x
Det må alltid være nok væske i reservoaret til å dekke filteret for å unngå å dra luft inn i Quizix pumpa.
x
Hvis det er væske på prøvesiden av stempelsylinderen er det viktig å aldri fylle mer enn om lag
550 ml hydraulikkvæske på baksiden av stempelet for å unngå å presse væsken på prøvesiden ut
i prøvetakingssystemet. Følg derfor med på «Cummulative Volume» i Pumpworks. Hvis
stempelet i stempelsylinderen er helt i bunnen kan det være lurt å nullstille det kummulative
volumet før en begynner et forsøk eller en skylleprosedyre.
x
Vær veldig forsiktig med å åpne «Filling valve» i Pumpworks hvis det er trykk i quizix -pumpa!
Ventilene på pumpa åpnes brått, og selv om det er bare små volum væske det er snakk om bør
en slik operasjon tenkes nøye gjennom. Se om det er mulig å slippe ut trykket først ved å åpne
«Delivery valve» og slippe hydraulikkvæske sakte tilbake til reservoaret ved å åpne ventil
20V0002 og 20V0003.
Prosedyre for skylling med, og fylling av, væske på hydraulikk-siden:
1. Kontroller at ventilene 20V0002 og 20V0003 er åpne, og at ventilene inn til hydraulikksiden og
forsøksdelen av stempelsylinderen er stengt.
2. Fyll 400 ml væske i beholder 20TX0001. Som hydraulikkvæske brukes den samme komponenten
som benyttes i forsøksdelen av stempelsylinderen.
3. Koble fra retur av hydraulikkvæske like før den føres tilbake til glassflasken, og plasser utløpet i
et begerglass for oppsamling.
4. Fyll quizix-pumpen med væske (beskriv fra brukermanual s. 3-8 og 3-9).
a. Sett sikkerhetstrykket i pumpen til 100 psi.
b. Sett strømningsraten til 50% av maksimal strømningsrate, dvs. 25 ml/min for QX-6000.
5.
6.
7.
8.
9.
10.
11.
12.
13.
14.
15.
16.
17.
c. Sett operating mode til mode 1 (Independent Constant Rate) for pumpesylinder A.
d. Hvis sylinderen står i Max Retract posisjon, gå videre til punkt e. Hvis ikke må
fylleventilen (fill valve) åpnes, leveringsventilen (deliver valve) stenges og retningen
settes til retract. Start pumpesylinderen for å sette i gang fylleprosessen.
e. Når pumpesylinderen står i Max Retract posisjon stenges fylleventilen og åpnes
leveringsventilen. Kontroller at sylinderretningen er satt til extend. Start
pumpesylinderen.
f. Når Max Extend er nådd, stenges leveringsventilen for deretter å åpne fylleventilen.
(OBS! Her er det viktig å gjøre dette i riktig rekkefølge). Start pumpen, og vent til
pumpesylinderen når Max Retract og stopper.
g. Gjenta punkt e og f til alle luftbobler er fjernet og det kun er væske i pumpesylinderen
(kontroller dette ved å sette utløpsslangen ned i væske for å se om det kommer ut
bobler). Avslutt med Retract stroke.
h. Gjenta punkt c til g for hver pumpesylinder. Avslutt ved at alle pumpesylindrene er fylt
av væske og i Max Retract posisjon.
Still inn quizix-pumpen for å gi en jevn strømningsrate på 20 ml/min, start pumpen og la væsken
sirkulere gjennom pumpen til nivået i væskereservoaret er på om lag 150 ml. Væskenivået må til
enhver tid være over 150 ml for å dekke filteret på innløpsslangen til quizix-pumpen. Hvis deler
av filteret kommer i kontakt med luft vil det komme luft inn i pumpen.
Stopp quizix-pumpen, og sjekk om den sirkulerte væsken inneholder spor av forurensninger i
form av partikler eller lignende (visuell inspeksjon). Tøm den sirkulerte væsken i beholder for
avhending av organisk avfall uten halogener. Dersom det er partikler i væsken må punkt 5-7
gjentas flere ganger til det ikke er spor av partikler igjen i den sirkulerte væsken. Hvis det ikke er
tegn til partikler kan en fortsette til punkt 8.
Koble retur av hydraulikkvæske tilbake til original plassering på glassflasken.
Fyll væske i beholder 20TX0001 til væskenivået er om lag 700 ml.
Løsne røret fra ventilen inn til hydraulikksiden av stempelsylinderen. Legg et papir under for å
samle opp eventuelt søl.
Lukk ventil 20V0003.
Still inn quizix-pumpen for å gi en jevn strømningsrate på 5 ml/min og start pumpen.
Pass på det løse røret. Når det kommer væske i stedet for luft ut gjennom det løse røret,
stoppes quizix-pumpen og det løse røret skrus fast.
Åpne ventilen inn til hydraulikksiden av stempelsylinderen.
Still inn quizix-pumpen for å gi en jevn strømningsrate på 20 ml/min, start pumpen og fyll om lag
500 ml inn på hydraulikksiden av stempelsylinderen. Trykket i systemet vil da øke på grunn av at
ventilen på forsøksdelen av stempelsylinderen er stengt.
Stopp quizix-pumpen. Åpne begge «delivery valve» på pumpa for å trykkavlaste den samtidig.
Åpne ventil 20V003 forsiktig for å redusere trykket i systemet. La ventilen stå åpen til trykket er
tilbake ved atmosfærisk trykk og det har sluttet å dryppe hydraulikkvæske tilbake til reservoaret.
Det vil da fortsatt være 100-300 ml hydraulikkvæske igjen i stempelsylinderen (det er ikke nok
trykk igjen over stempelet til å skyve det helt ned).
Trykktesting av systemet:
a. Steng ventil 20V0003 og ventilen på hydraulikksiden av stempelsylinderen. La ventil
20V0002 være åpen.
b. Start logging i labview! Hvis du planlegger å la riggen stå i lengre perioder ved
trykktesting kan det være lurt å tenke over hvor ofte labview skal lagre loggedata! En
anbefaling kan være å logge hvert 5. sekund eller sjeldnere ved trykktesting.
c. Still inn pumpen til ønsket trykk, og trykk start. Vær obs på at dette er et lite volum, så
pumpen kan fort være uheldig å komme til et for høyt trykk. Sett derfor
sikkerhetstrykket til pumpa like over det trykket du ønsker.
d. Stopp pumpa når den når ønsket trykk. La begge delivery valves stå åpne.
e. La systemet stå i noen timer. Trykket vil mest trolig variere litt med temperatur, og
erfaring tilsier at trykket går litt opp og ned. Det er derfor ofte vanskelig å si om en har
en lekkasje eller ikke, så et tips kan være å se over alle koblingene for å se etter
eventuelle væskedråper. Et annet tips er å prøve å gjøre det samme, men med stengte
delivery valves på pumpa. Da bør trykksensor PIT001 og trykksensorene inne i pumpa
vise om lag det samme trykket etter en periode.
f. For å kontrollere at nåleventilen på prøvesiden av stempelsylinderen: Gjenta punkt a-e
over, men la ventilen på prøvesiden av stempelsylinderen være stengt og ventilen på
hydraulikksiden av stempelsylinderen være åpen.
18. Kontroller at ventil 20V0002 og ventilen inn til hydraulikksiden av stempelsylinderen er åpne, og
at ventilen 20V0003 og ventilen inn til forsøksdelen av stempelsylinderen er stengt.
19. Gjenta punkt 13-16 en ekstra gang.
B Prosedyre for tømming av væske fra hydraulikksystemet og trykkavlastning av riggen før avkobling
av stempelsylinder:
Før prøvesiden av systemet trykkavlastes:
1. Slå av quizix-pumpen, og kontroller at ventil 20V0002, 20V0003 og at ventilen på prøvesiden av
stempelsylinderen er stengt.
2. Åpne ventilen på hydraulikksiden av stempelsylinderen, og åpne ventil 20V0003 forsiktig. Følg
med på trykksensoren og vent til trykket har nådd atmosfærisk trykk.
3. Steng ventilen på hydraulikksiden av stempelsylinderen.
4. Åpne ventil 20V0002 forsiktig, og vent til trykket igjen har nådd atmosfærisk trykk.
Trykkavlastning av prøvesiden av riggen:
5. Kontroller at ventil 20V0007 er åpen mot ventilasjon.
6. Kontroller at ventil 20V0006 er åpen mellom riggen og 20V0007.
7. Kontroller at ventil 20V0005 er stengt.
8. Åpne ventilen på prøvesiden av stempelsylinderen og ventil 20V0005 gradvis for en kontrollert
reduksjon av trykket i stempelsylinderen.
9. Steng ventilen på prøvesiden av stempelsylinderen når trykket i nne i stempelsylinderen har
nådd atmosfærisk trykk.
10. Snu ventil 20V0007 frem og tilbake flere ganger for å fjerne trykket i røret frem mot gassflasken.
11. Kontroller at flaskeventilen på gassflasken er stengt.
12. Åpne reguleringsventilen på gassflasken for å trykkavlaste reguleringsventilen.
13. Snu ventil 20V0007 frem og tilbake flere ganger for å fjerne trykket i røret frem mot gassflasken.
14. Steng reguleringsventilen.
Avkobling av stempelsylinderen:
15. Kontroller at trykket i stempelsylinderen er ved atmosfærisk trykk.
16. Kontroller at begge ventilene på stempelsylinderen er stengt.
17. Kontroller at ventilene 20V0002, 20V0003 og 20V0005 er åpne, og at ventilene 20V0006 og
20V0007 er åpen mot ventilasjon.
18. Løsne tilkoblingen på prøvesiden av stempelsylinderen.
19. Løsne tilkoblingen på hydraulikksiden av stempelsylinderen. Hold et papir i nærheten av
koblingen når dette gjøres for å unngå søl.
20. Løsne stempelsylinderen fra festet som holder den fast i bordet.
Åpning og vasking av stempelsylinderen:
21. Åpne ventilen på prøvesiden av stempelsylinderen.
22. Åpne prøvesiden av stempelsylinderen ved hjelp av en C-nøkkel.
23. Vask denne siden av stempelsylinderen grundig med varmt vann. Skyll med destillert vann, og
avslutt med å skylle med det kjemikaliumet som skal benyttes i riggen for å fjerne alle rester av
vann. Husk også å vaske lokket til stempelsylinderen.
24. Monter på plass lokket igjen, og steng nåleventilen igjen.
25. Gjenta punkt 16-19 for hydraulikksiden av stempelsylinderen.
Skylling av rør i forbindelse med sikkerhetsventil 20PSV001:
26. Kontroller at ventil 20V0002 og 20V0003 er åpen.
27. Skru løs de to rørlengdene i forbindelse med sikkerhetsventilen 20PSV001.
28. Skyll rørene med varmt vann. Skyll med destillert vann, og avslutt med å skylle med det
kjemikaliumet som skal benyttes i riggen for å fjerne alle rester av vann.
29. Skru rørene tilbake på plass.
C
Prosedyre for å fylle gass og væske på prøvesiden av stempelsylinderen ved bytte av
kjemikalium:
Fylling av væske:
1. Åpne ventilen på prøvesiden av stempelsylinderen.
2. Åpne prøvesiden av stempelsylinderen ved hjelp av en C-nøkkel.
3. Fyll 20 ml kjemikalium direkte ned i stempelsylinderen.
4. Monter på plass lokket igjen, og steng nåleventilen igjen.
Monter inn stempelsylinderen i riggen:
5. Skru fast stempelsylinderen i festet som holder den fast i bordet.
6. Koble til hydraulikksiden av stempelsylinderen.
7. Koble til prøvesiden av stempelsylinderen.
8. Fyll væske på hydraulikksiden av stempelsylinderen, se «Prosedyre for skylling med, og fylling
av, væske på hydraulikk-siden».
Fylling av gass: (se ekstra godt over punkt 23-26 pga usikker på akkurat dette).
9. Kontroller at ventilen på hydraulikksiden av stempelsylinderen er stengt.
10. Kontroller at ventil 20V0007 er åpen fra gasstilførsel og mot stempelsylinderen.
11. Kontroller at ventil 20V0006 er åpen fra gasstilførsel og mot stempelsylinderen.
12. Kontroller at ventil 20V0005 og ventilen på prøvesiden av stempelsylinderen er stengt.
13. Åpne flaskeventilen på gassflasken.
14. Åpne reguleringsventilen og øk trykket gradvis til om lag 10 bar.
15. Åpne ventilen på hydraulikksiden av stempelsylinderen og 20V0003.
16. Åpne ventil 20V0005 forsiktig og slipp gassen inn på stempelsylinderen.
17. Still inn trykket til like under ønsket trykk ved hjelp av reguleringsventilen. Pass på at trykket er
om lag 1-2 bar under ønsket trykk, så kan quizix-pumpen fininnstille trykket (se punkt 23-26).
18. Noter volum i 20TX0001 og nullstill akkumulert flow i 20PX0001
19.
20.
21.
22.
Steng ventilen på prøvesiden av stempelsylinderen.
Steng ventil 20V0005.
Steng reguleringsventilen og flaskeventilen på gassflasken.
Vri ventil 20V0007 slik at den er åpen mellom stempelsylinderen og ventilasjon. Vri ventil
20V0007 frem og tilbake flere ganger for å trykkavlaste frem til flaskeregulatoren. Husk også å
avlaste selve flaskeregulatoren. Avslutt med å sette 20V0007 stilt mot ventilasjon.
23. Kontroller at ventil 20V0002 og 20V0003 er stengt.
24. Still inn quizix-pumpen til å holde ønsket trykk og start denne.
25. Åpne ventil 20V0002 gradvis, slik at quizix-pumpen rekker å opprettholde trykket.
26. Åpne ventilen på hydraulikksiden av stempelsylinderen gradvis, slik at quizix-pumpen rekker å
opprettholde trykket.
27. Juster trykket til akkurat ønsket trykk, og steng ventilen på hydraulikksiden av
stempelsylinderen.
28. Kjør pumpen til det er samme trykk i begge kamrene i pumpa og i rørsystemet frem til
stempelsylinderen.
29. Åpne begge «delivery valve» på pumpa.
30. Åpne ventil 20V0003 forsiktig for å trykkavlaste hydraulikksystemet.
Nå er forsøket klart til å stå og vente til det har innstilt seg likevekt.
D
Prosedyre for sampling med ATD-rør:
Innstilling av riktig strømningshastighet:
1. Sjekk at Quizix-pumpa er stilt inn på å holde konstant trykk, og at ventil 20V0002 og ventilen på
hydraulikksiden av gassylinderen er åpne.
2. Kontroller at ventil 20V0007 er åpen mot ventilasjon.
3. Koble til et «dummy» ATD rør til 20V0006. ATD røret skal settes inn slik at de to inngraverte
ringene står inn mot ventil 20V0006.
4. Sett ventil 20V0006 slik at den er åpen mot ATD røret.
5. Åpne ventilen på prøvesiden av stempelsylinderen.
6. Åpne ventil 20V0005 veldig forsiktig til gassuret viser ønsket strømningshastighet.
Prøvetaking:
7. Sett ventil 20V0006 slik at den er åpen mot ventilasjon.
8. Bytt ut «dummy» ATD røret med et kondisjonert ATD rør.
9. Sett ventil 20V0006 slik at den er åpen mot ATD røret.
10. La gassen strømme gjennom ATD røret til ønsket gassvolum er nådd. Antall liter gass som
sendes gjennom ATD-røret vil variere med forventet konsentrasjon av sporkomponenten, og fra
erfaringer med forsøkene.
11. Sett ventil 20V0006 slik at den er åpen mot avtrekk.
12. Bytt til et nytt kondisjonert ATD rør, og gjenta punkt 8-10 til ønsket antall paralleller er nådd.
Det anbefales å ta minimum 5 paralleller.
Husk å notere ned tidspunkt, nummeret på ATD-røret og start- og stoppvolum i skjema for
prøvetaking for hver av parallellene.
E
Prosedyre for etterfylling av gass:
Tømming av væske fra hydraulikksiden av stempelsylinderen:
1. Slå av quizix-pumpen, og kontroller at ventil 20V0002, 20V0003 og at ventilen på prøvesiden av
stempelsylinderen er stengt.
2. Åpne ventilen på hydraulikksiden av stempelsylinderen, og åpne ventil 20V0003 forsiktig. Følg
med på trykksensoren og vent til trykket har nådd atmosfærisk trykk.
3. Steng ventilen på hydraulikksiden av stempelsylinderen.
4. Åpne ventil 20V0002 forsiktig, og vent til trykket igjen har nådd atmosf ærisk trykk.
Fylling av gass:
5. Kontroller at ventil 20V0007 er åpen fra gasstilførsel og mot stempelsylinderen.
6. Kontroller at ventil 20V0006 er åpen fra gasstilførsel og mot stempelsylinderen.
7. Kontroller at ventil 20V0005 og ventilen på prøvesiden av stempelsylinderen er stengt.
8. Åpne flaskeventilen på gassflasken.
9. Åpne reguleringsventilen og øk trykket gradvis til trykket i rørsystemet er like over trykket som
er inne i stempelsylinderen. Dette er viktig for å hindre tilbakeslag av gass fra stempelsylinderen
og inn i regulatoren.
10. Åpne ventilen på hydraulikksiden av stempelsylinderen.
11. Åpne ventil 20V0005 forsiktig og slipp gassen inn på stempelsylinderen.
12. Still inn trykket til like under ønsket trykk ved hjelp av reguleringsventilen. Pass på at trykket er
om lag 1-2 bar under ønsket trykk, så kan quizix-pumpen fininnstille trykket (se punkt 17-20).
13. Steng ventilen på prøvesiden av stempelsylinderen.
14. Steng ventil 20V0005.
15. Steng reguleringsventilen og flaskeventilen på gassflasken.
16. Vri ventil 20V0007 slik at den er åpen mellom stempelsylinderen og ventilasjon.
17. Kontroller at ventil 20V0002 og 20V0003 er stengt.
18. Still inn quizix-pumpen til å holde ønsket trykk og start denne.
19. Åpne ventil 20V0002 gradvis, slik at quizix-pumpen rekker å opprettholde trykket.
20. Åpne ventilen på hydraulikksiden av stempelsylinderen gradvis, slik at quizix-pumpen rekker å
opprettholde trykket.
Nå er forsøket klart til å stå og vente til det har innstilt seg likevekt.