ASIA-PACIFIC JOURNAL OF CHEMICAL ENGINEERING
Asia-Pac. J. Chem. Eng. (2017)
Published online in Wiley Online Library
(wileyonlinelibrary.com) DOI: 10.1002/apj.2071
Research article
Process development unit experimental studies of a splitflow modification for the post-combustion CO2 capture
process
M. Stec,*
A. Tatarczuk, L. Więcław-Solny, A. Krótki, T. Spietz and A. Wilk
Institute for Chemical Processing of Coal, Zamkowa 1, 41-803 Zabrze, Poland
Received 23 June 2016; Revised 7 October 2016; Accepted 10 January 2017
ABSTRACT: A process development unit (PDU) for amine-based post-combustion carbon capture located at Clean Coal
Technologies Centre in Zabrze, Poland, was used to validate split-stream configuration. A PDU having capacity up to
100 m3n/h was designed to test the amine scrubbing carbon capture process from flue gases or mixtures of technical gases.
Flexible process flow sheet of the unit allowed investigation of the split flow process.
The split-flow flowsheet modification was compared with a standard system for chemical absorption-based CO2 capture.
The tests were conducted using well-accepted baseline solvent: 30 wt% aqueous monoethanolamine solution. The flow sheet
modification resulted in a decrease of reboiler heat duty by ~1.6% and an increase in CO2 recovery by ~1.2 p.p. Split-flow
process modification was examined together with standard process flow sheet, and vast number of process parameters
recorded during the trials have been presented. The explanation of beneficial effects of split-flow designs have been shown
together with detailed analysis of experimental trials carried out using PDU for amine-based post-combustion carbon capture.
This paper is also a valuable source of experimental data useful during validation of models. Copyright © 2017 Curtin
University of Technology and John Wiley & Sons, Ltd.
KEYWORDS: post-combustion carbon capture; split-flow; MEA
INTRODUCTION
Carbon capture from flue gases is gaining interest in the
European Union because of current council
obligations[1] concerning reduction of greenhouse gas
emissions. To fulfil council liabilities, it is necessary
to develop technically feasible CO2 separation
processes allowing the reduction of greenhouse gases
from fossil fuel power plants. Amine-based flue gas
scrubbing is the most promising technology that may
be used in CO2 separation processes. The main
advantage of this process is simplicity of incorporation
into existing power plants.[2,3] However, amine-based
CO2 separation processes add a serious energy penalty,
reducing the efficiency of the power plant.[4,5]
Therefore, current research concentrates on
examination of energy-saving design approaches[6,7]
and on solvent developments.[8–10]
This paper deals with the results of tests of the splitflow modification of amine scrubbing flowsheet.
*Correspondence to: Marcin Stec, Institute for Chemical
Processing of Coal, Zamkowa 1, 41-803 Zabrze, Poland. E-mail:
[email protected]
Splitting the flow of the solvent is advantageous and
can reduce energy consumption of the process[11] and
increases CO2 recovery.[12] Description and modelling
of the split-flow process have been well established.
The numerous papers deal with energy considerations,
capital costs,[13] evaluation of different split flow
configurations[14] or thermodynamic aspects of the
flow splitting.[15] In contrast, studies describing
experimental implementation of the split-flow process
are scarce[16] or not based on post-combustion carbon
capture.[12] This conjuncture encouraged the authors
to present the results of tests carried out at a process
development unit (PDU) for amine-based postcombustion carbon capture located at Clean Coal
Technologies Centre in Zabrze, Poland.
A PDU having a capacity of up to 100 m3n/h was
designed to test the amine scrubbing carbon capture
process from flue gases or mixtures of technical gases.
The PDU (Fig. 1) incorporates a novel process flow
sheet introducing both concepts: split flow process
and rich split, therefore the results are a valuable
material for model validation. Flexible configuration
of the PDU allows straightforward changes in process
flow sheet therefore tests of conventional as well as
novel flow sheets are possible. This feature of the
Copyright © 2017 Curtin University of Technology and John Wiley & Sons, Ltd.
Curtin University is a trademark of Curtin University of Technology
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Asia-Pacific Journal of Chemical Engineering
M. STEC ET AL.
Figure 1. Overview of the process development unit for amine-based post-combustion
carbon capture at Clean Coal Technologies Centre in Zabrze, Poland.
PDU makes comparisons between configurations
effortless.
This paper deals with the detailed description of four
tests: two tests for standard process flow sheet and two
tests carried out with split-flow arrangement. Process
conditions were selected to make the comparison
between standard and split-flow flow sheets possible.
It should be noted that the tests shown in this paper
represent an initial attempt to prove profitability of
the split-flow configuration, and future work is still
required to draw final conclusions; however, the results
are encouraging. In the next step, similar comparisons
will be conducted, but using the optimal operating
conditions for each concept. Vast number of the pilot
plant process parameters are included, making this
paper a valuable source of data for model validation.
The tests presented in this paper were carried out
using 30 wt% monoethanolamine (MEA) aqueous
solution considered baseline solvent for pilot plant
studies of the post-combustion carbon dioxide capture
by reactive absorption.[17]
Split-flow process analysis
A literature review on description of the split-flow
process is outlined in the succeeding paragraphs.
The concept of the flow splitting was first suggested
by Shoeld[18] in a patent aiming to remove H2S from
fuel gases using sodium phenolate. Shoeld suggested
splitting the streams of both lean and rich amine and
claimed that such modification reduces steam usage
by 50% as compared with conventional single flow
process.
Shoeld’s idea has been improved by several
authors.[19–21] Despite the differences in various splitflow modifications, there is one common feature
present in every split-flow configuration. Because of
semi-lean amine drawn off the middle of the stripper,
the amount of the solvent remaining in the stripper
for further regeneration is lower, therefore it can be
regenerated to a higher extent than for conventional
process. Resulting lean amine has a lower CO2 content
and can be fed to the top of the absorber to ‘polish’ the
gas.[12] Semi-lean amine recycled to an intermediate
stage of the absorber is used to absorb the bulk of
CO2. Additionally, semi-lean amine, which is cooled
before being fed to the column, acts as an interstage
absorber cooling. The more optimal temperature profile
obtained makes better absorption of CO2 possible.[15]
In split-flow designs, lean amine is fed to the stripper
at various heights (Fig. 2). Forcing the lean solvent at
different column heights changes temperature and
concentration in the stripper, bringing together the
operating and the equilibrium line.[11] According to
the Second Law of Thermodynamics, in order to
reduce heat consumption of the process, it is necessary
to reduce driving force.[15] Therefore, split-flow
designs are advantageous in terms of the reduction of
heat consumption.
A comprehensive analysis of the heat reduction
potential of the split-flow designs, based on exergy
losses, was presented by Amrollahi et al.[22]
The flow sheet of the PDU shown in Fig. 2 contains
also rich split modification suggested by Eisenberg and
Johnson.[23] One of the streams of the lean amine is
routed directly to the amine stripper bypassing heat
Copyright © 2017 Curtin University of Technology and John Wiley & Sons, Ltd.
Asia-Pac. J. Chem. Eng. (2017)
DOI: 10.1002/apj
Asia-Pacific Journal of Chemical Engineering
SPLIT-FLOW FOR CO2 CAPTURE PROCESS
Figure 2. Flow sheet of the process development unit. Symbols G and L are used to note the location of the gas and liquid
sampling points.
exchangers. This stream is heated by condensing steam
in the column, which would normally be lost from the
stripper. Reducing the losses of the steam and heating
of a portion of amine reduce the overall energy
requirements of the process.
Simulations of CO2 removal in split-flow processes
confirm beneficial character of split-flow modifications.
The reduction of the reboiler heat duty by 5–18% than
for conventional process was claimed by Bae et al.[24]
Cousins et al.[25] presented simulations of rich split
and split-flow modifications where the reduction of
the reboiler heat duty over standard process reached
10.3% and 11.6%, respectively.
EXPERIMENTAL
Chemicals
Concentrated ethanolamine (MEA, CAS: 141–43-5,
technical grade) was obtained from Brenntag NV.
Aqueous solution of ethanolamine was prepared on-site
using mains water.
The following additives were used in minor
quantities: Silpian W-3 purchased from Silikony
Polskie Sp. z o.o. as antifoaming agent, potassium
metavanadate (KVO3, CAS: 13769–43-2) as a
corrosion inhibitor and hydrazine hydrate solution
(H4N2 H2O, CAS: 7803–57-8) as an antioxidant.
The PDU uses 30 wt% MEA aqueous solution as
solvent.
Process development unit description
The overview of the PDU for amine-based postcombustion carbon capture is shown in Fig. 1.
In Fig. 2, the process flow sheet of the PDU is
introduced. The PDU allows CO2 separation from gas
streams. Either flue gas fed by blower or mixture of
technical gases can be treated. The CO2-rich gas
(volumetric flow up to 100 m3n/h) is fed into the
pretreatment scrubber where the temperature of the
gas is set and gas is saturated with water. The
pretreatment scrubber acts therefore as a direct contact
cooler using water as cooling medium. To avoid
excessive amine degradation while testing the process
on flue gases, the activated coal SOx adsorber is located
downstream of the scrubber. In case of absence of the
SOx due the usage of a mixture of gases instead of
the flue gases, the adsorber is bypassed. The CO2-rich
gas enters the absorber at the bottom. The absorber is
built of three sections. Middle section, where gas
contacts counter-currently with semi-lean amine, top
section where lean amine is fed and water wash section
above the lean solvent inlet. The water wash section,
where make-up water is added, acts as a cooler and
prohibits the increase of amine concentration in the
solvent. Packing parameters and dimensions of the
absorber are given in Tab. 1.
Carbon dioxide from CO2-rich gas is absorbed into
the liquid phase. The rich solvent is pumped into the
stripper through rich lean and rich semi-lean heat
exchangers. The rich solvent is heated to higher
temperatures through hot solvents leaving the stripper.
Such split-flow configuration is based on the invention
proposed by Shoeld.[18] In Fig. 2, an additional line of
rich solvent, bypassing heat exchangers, can be
noticed. Using this line, a small portion of rich solvent
remains unheated and enters the top of the stripper.
This modification, known as ‘rich split’, was suggested
by Eisenberg and Johnson.[23] In conclusion, the rich
amine can be fed to the stripper by means of three feed
Copyright © 2017 Curtin University of Technology and John Wiley & Sons, Ltd.
Asia-Pac. J. Chem. Eng. (2017)
DOI: 10.1002/apj
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Asia-Pacific Journal of Chemical Engineering
M. STEC ET AL.
points: as unheated or heated either with semi-lean or
lean solvent.
The solvent in the bottom of the stripper is heated
using electrical heating element. Energy delivered to
the solvent is spent on its regeneration. A portion of
the solvent is drawn from the intermediate section
(semi-lean solvent) of the stripper and fed to the
absorber at some mid-column feed point. Because of
the side draw, remaining amine flow to the reboiler is
lower, resulting in lower lean amine loading. Lean
amine is pumped back to the absorber and enters the
top of the column, as for conventional process flow
sheet. Further details regarding construction, packing
and dimensions of the stripper are given in Table 1.
Pan-type liquid distributors are used in the absorber
and stripper, to achieve optimum mass transfer for the
entire operating range of a column and to ensure equal
distribution of liquid over the entire bed cross section.
Product CO2 saturated with water vapour is collected
from the top of the stripper. The remaining part of the
water is removed in the condenser installed
downstream of the column, and almost pure CO2 is
obtained.
Effects of foregoing modifications will be described
in detail in consecutive sections. The analyses
presented in this paper were carefully selected from a
database of trends registered in the supervisory control
and data acquisition system. The tests were recognised
as valuable when the steady-state period lasted at least
2 h. For balancing or performance estimation, the
average of each parameter from the steady-state period
was used for further calculations.
For additional details concerning the PDU as well as
other facilities located at Clean Coal Technologies
Centre in Zabrze, Poland, refer to Lajnert and
Latkowska and Śpiewak et al.[26,27]
Gas and liquid analysis
Gas and liquid analyses are the most important and
sophisticated measurements, therefore will be
described in detail.
Gas analysis is conducted on-line by using an
ULTRAMAT 23 gas analyser. The measuring principle
of the instrument is based on the molecule-specific
absorption of bands of infrared radiation. Prior to
feeding the gas to the analyser, it is dedusted and
cooled to separate the water vapour. The CO2
concentration from the instrument is given directly as
volumetric percent. Output signal error of the analyser
does not exceed 1% of the current value indicated.
Liquid samples of rich, semi-lean and lean amine are
collected during the steady state, before the trial is
stopped. The liquid samples are further analysed to
determine the amine concentration and CO2 loading.
The concentration of the solvent is checked by
titration, and CO2 loading is estimated based on the
density of the solvent using correlations given by
Hartono et al.[28] Additionally, the density method
was checked titrimetrically using the method of
Weiland and Trass,[29] and the agreement was
satisfactory. The accuracy of the CO2 loading
determination is ±0.01 molCO2/molMEA.
RESULTS AND DISCUSSIONS
Experimental data
In this section, the measurement results of the test cases
are presented. Cases 1 and 2 should be analysed
together as presenting the comparison of standard and
flow sheet process, for reboiler heating element power
set to 33.0 kW, inlet gas volumetric flow ~100 m3n/h.
Similarly, cases 3 and 4 are the same comparison for
the reboiler heating element power set to 29.7 kW
and gas volumetric flow ~95 m3n/h. Pressure in the
absorber was held constant during the tests and was
~35 kPa gauge. Minor differences between parameters
in tests 1–4 result from process fluctuations that are
unavoidable in a pilot-scale plant. The split-flow rates
were selected using a 50–50 distribution, i.e.
volumetric flows of the semi-lean and lean streams
are equal, and their total equals to the lean amine flow
in the standard configuration.
Table 1. Column size, packing heights and packing materials at the process development unit for amine-based
post-combustion carbon capture.
Column
Diameter (mm)
Packing height(mm)
Surface packing (m2/m3)
Packing material
Absorber
273
Stripper
273
1400
1200
2000
320
320
480
1600
1000
1000
660
622
700
700
700
360
620
Cylindrical ring 5 mm; VFF GmbH
Berl saddles 10 mm; VFF GmbH
Novalox saddles 13; VFF GmbH
Sulzer CY
Sulzer CY
Sulzer CY
Interpack #2; VFF GmbH
Interpack #1; VFF GmbH
The packing elements location is shown in Fig. 2 and enumerated from top to bottom of the columns.
Copyright © 2017 Curtin University of Technology and John Wiley & Sons, Ltd.
Asia-Pac. J. Chem. Eng. (2017)
DOI: 10.1002/apj
Asia-Pacific Journal of Chemical Engineering
SPLIT-FLOW FOR CO2 CAPTURE PROCESS
The gas for the separation process using PDU was
prepared as a mixture of CO2 (concentration:
12.30 vol%) and nitrogen (concentration: 87.7 vol%).
Such CO2 concentration is typical for flue gases from
coal-fired power plant. Lack of oxygen, which is the
next typical component of the flue gases, do not affect
the analysis, as it is mainly responsible for oxidative
degradation of the solvent. Detailed specification of
the gas at the absorber inlet is given in Table 2.
Prior to feeding the gas into the absorber, it is
saturated with water in the pretreatment scrubber using
water wash. Generally, the pretreatment scrubber is
intended to dedust and cool flue gases; however,
presented experiments were conducted using technical
gases, therefore such operations were not required.
The gas is treated in the absorber, contacting amine
solvent counter currently. The solvent absorbs CO2,
treated gas (CO2-lean gas) is vented to the atmosphere
and CO2-rich solvent is pumped to the stripper. The
operation conditions of the experiments, including
solvent flows, temperatures and solvent loadings are
presented in Table 4.
The conditions and composition of CO2-lean gas
collected from the absorber, together with conditions
of CO2 leaving the stripper, are summarised in
Table 3.
In every case, CO2 leaving the stripper is cooled to
25°C, and water is removed in the condenser installed
downstream of the stripper. Water collected in the
separator is afterwards pumped back to the absorber
to avoid excess water losses from the solvent.
On the contrary, water vapour leaving the absorber
with CO2-lean gas is not returned to the process,
therefore water balance is disturbed. Fortunately,
partial pressure of water vapour at the outlet of the
absorber is not high, thanks to moderate temperatures
of CO2-lean gas stream.
However, to maintain the concentration of the
solvent constant, the levels in the bottom of the
absorber and stripper are carefully controlled, and
water is added in case of level deviations.
Table 2. Gas conditions and composition at the
absorber inlet.
Case
Process variable
Conditions
Volumetric flow (m3n/h)
Mass flow (kg/h)
Pressure (kPa gauge)
Temperature (°C)
Composition (vol%—dry)
Nitrogen
Carbon dioxide
1
2
3
4
100.4
133.6
34.8
17.3
99.2
132.1
38.6
15.4
95.0
126.4
38.3
15.2
94.8
126.2
38.1
15.2
87.7
12.3
Table 3. Gas conditions and composition at the
absorber and the stripper outlets.
Case
Process variable
CO2-lean gas leaving
absorber
Pressure (kPa gauge)
Temperature (°C)
CO2 concentration
(vol%—dry)
CO2 leaving stripper
Pressure (kPa gauge)
Temperature (°C)
1
2
3
4
29.99
37.9
1.17
29.99
41.1
1.00
29.98
36.2
1.11
30.00
38.8
0.95
45.02
97.9
45.01
99.2
44.99
95.3
44.98
94.9
The reboiler heat duties shown in Table 4 are gross
values, therefore include heat losses to the ambient.
The losses depend on many parameters, and its
estimation is not straightforward; however, for
comparable pilot plant, the authors claim than an
average value of 10% of the reboiler heat duty could
be an acceptable simplification for the heat loss.[30]
Absorber operating lines
Figures 3 and 4 show a comparison between absorber
operating lines for standard and split-flow process flow
sheets and equilibrium curves. The equilibrium curves
are plotted based on experimental data taken from Jou
et al.[31] Temperature in the absorber varies along the
column height from 40°C to 60°C for a typical test,
and the equilibrium data for this temperature range
are presented in Figs 3 and 4.
The experimental data for the CO2 partial pressure is
available at three points of the absorber: at the inlet, in
the middle section (between the lower and middle
packing sections) and at the outlet (downstream of the
washing section); straight lines were used to connect
experimental data, but these lines serve only to join
the data points.
Despite the semi-lean amine loading being higher
than the lean amine loading for the standard case, the
slope of the operating lines for both process flow sheets
remain similar for the lower section of the absorber.
This fact is clearly visible in Fig. 4, where the operating
lines almost overlap for higher partial pressures of CO2
(lower section of the absorber), which in terms of
driving force means the same CO2 absorption
capabilities.
On the contrary, the driving force for the top section
of the absorber in split-flow process is much higher
than for the standard process flow sheet. This is
expected because the lean solvent loading for split-flow
process is lower than for standard process flow sheet.
To summarise, the CO2 recovery in the lower part of
the absorber remains similar for both process flow
Copyright © 2017 Curtin University of Technology and John Wiley & Sons, Ltd.
Asia-Pac. J. Chem. Eng. (2017)
DOI: 10.1002/apj
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Table 4. Operation conditions of the experiments. The temperature at the absorber inlet is always 40°C for the
solvent.
Case
Process variable
CO2 recovery (%)
Reboiler heat duty (MJ/kgCO2)
Absorber pressure (kPa gauge)
Stripper pressure (kPa gauge)
L/G (kg/kg)
MEA concentration (% mass)
Overall rich amine mass flow (kg/h)
Rich amine mass flow—top stripper inlet (kg/h)
Rich amine mass flow—middle stripper inlet (kg/h)
Rich amine mass flow—bottom stripper inlet (kg/h)
Lean amine mass flow (kg/h)
Semi-lean amine mass flow (kg/h)
Rich amine loading (molCO2/molMEA)
Lean amine loading (molCO2/molMEA)
Semi-lean amine loading (molCO2/molMEA)
Rich amine temp. at absorber outlet (°C)
Rich amine temp. Top stripper inlet (°C)
Rich amine temp. Middle stripper inlet (°C)
Rich amine temp. Bottom stripper inlet (°C)
Lean amine temperature (°C)
Semi-lean amine temperature (°C)
Reboiler heating element power (kW)
1
2
3
4
91.68
5.36
29.99
45.02
5.07
30
677.0
59.4
14.3
603.2
648.2
—
0.41
0.27
—
54.6
54.6
—
102.0
110.5
—
33.0
92.84
5.37
29.100
45.03
5.09
30
672.1
59.3
262.1
350.7
320.1
331.5
0.42
0.23
0.33
52.5
52.5
97.0
105.5
111.5
107.6
33.0
91.94
5.11
29.101
45.04
5.43
30
686.0
59.2
22.3
604.5
652.2
—
0.43
0.30
—
53.0
53.0
—
101.0
109.8
—
29.7
93.17
5.03
29.100
45.03
5.39
30
680.9
59.3
270.2
351.3
321.2
331.8
0.42
0.24
0.34
51.9
51.9
95.9
103.3
110.7
106.4
29.7
sheets, as the driving force is also at a similar level.
However, the split-flow process becomes beneficial in
the top part of the absorber where the gas is contacting
the solvent having very low loading. Thanks to
increased driving force in the upper part of the column,
overall CO2 recovery is higher for the split-flow
process when comparing cases 1, 2 and 3, 4.
The discussion can be reframed in terms of chemical
potential differences. Because the goal of the absorber
is to uptake CO2 from the flue gas into the solvent,
the relevant driving force is the chemical potential,
which includes both pressure and temperature aspects.
What has occurred with the split-flow system is that
the chemical potential driving force is reduced in the
Figure 3. Comparison of absorber operating lines for cases 1
and 2 to equilibrium curve.
Figure 4. Comparison of absorber operating lines for cases 3
and 4 to equilibrium curve.
Copyright © 2017 Curtin University of Technology and John Wiley & Sons, Ltd.
Asia-Pac. J. Chem. Eng. (2017)
DOI: 10.1002/apj
Asia-Pacific Journal of Chemical Engineering
SPLIT-FLOW FOR CO2 CAPTURE PROCESS
As shown earlier, the split-flow process increases
CO2 recovery as compared with the standard process.
The advantage of split-flow designs would reveal more
significantly for systems where the lean solvent loading
is very low. The split flow designs are particularly
preferred when high quality CO2-lean gas is
required.[12]
Absorber temperature profiles
Figure 5. Absorber temperature profiles for cases 1
(standard) and 2 (split-flow process).
lower half of the absorber and increased in the upper
half of the absorber. In net, this evening out of the
chemical potential difference results in a reduced
average driving force, which lowers the entropy
production of the system. It also results in more
effective use of the upper half of the absorber, which
was not used optimally in the standard set up.
It should be noted here that comparisons between
standard and split-flow process were carried out for
constant power delivered to the process.
Figure 6. Absorber temperature profiles for cases 3
(standard) and 4 (split-flow process).
Figures 5 and 6 show absorber temperature profiles for
standard and split-flow processes. The presence of the
pronounced temperature increase is common for every
case. This temperature bulge[32] can be explained by
the fact that during absorption, the heat is released,
causing the temperature increase.
It can be noticed that the temperature bulge for splitflow process is less prominent (Fig. 5). This is an
intercooling effect caused by the injection of cool
semi-lean solvent. The semi-lean solvent is fed into
the absorber at 40°C and cools the interior of the
absorber. Other possible factor that affects the
temperature drop would be lower heat released during
absorption in the lower part of the absorber with splitflow designs, caused by higher loading of the semi-lean
amine. Both reasons together cause temperature
decrease below semi-lean solvent inlet for split-flow
process. However, a more careful analysis, including
measurement of loading of the solvent at a location
inside of the absorber, would be necessary to quantify
the influence of the second factor.
The opposite effect occurs in the top section of the
absorber where the temperature increase can be noticed
for the split-flow process (Figs 5 and 6). The lean
solvent fed into the top inlet of the absorber has the
same temperature either for the standard or the splitflow process, but the amount of the liquid and its
loading differs. The loading of the lean solvent is lower
for split-flow designs, therefore the amount of CO2
absorbed in the upper part of the column presumably
increases. Higher CO2 absorption causes higher heat
release, and together with the lower liquid load of the
upper part of the absorber, thus lower heat capacity,
causes the temperature increase.
The temperature drop in the lower section of the
absorber for case 4, shown in Fig. 6, is less prominent.
This was probably a result of higher heat release during
the absorption that diminished the intercooling effect.
Feeding the solvent, having different loadings, at
various heights of the absorber causes the temperature
profile of the column for split-flow process to be
uniform and slightly lower on average than for the
standard process flow sheet. Lower average
temperature of the absorber is in favour of higher
driving forces for the absorption process and also
increases the absorption capacity of the solvent.[33] It
must be mentioned that overcooling the absorbent
Copyright © 2017 Curtin University of Technology and John Wiley & Sons, Ltd.
Asia-Pac. J. Chem. Eng. (2017)
DOI: 10.1002/apj
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Asia-Pacific Journal of Chemical Engineering
M. STEC ET AL.
would be detrimental because the mass transfer kinetics
is affected by increasing viscosity, and decreasing
temperature leads to a lower CO2 absorption reaction
rate constant.[34,35] Aroonwilas et al. have suggested
that the ~40°C is the optimal temperature for CO2
absorption in 20% MEA solvent in terms of masstransfer efficiency.[34] In presented tests, the reduction
of temperature by splitting the flow caused only
favourable effects, therefore it can be concluded that
the mass transfer kinetics has not been affected.
generation: Development of a technology for highly
efficient zero-emission coal-fired power units
integrated with CO2 capture, and the results presented
in this paper were obtained during the research project
entitled ‘Development of technologies for separation
and purification of process gases with regard to their
further
development’
(IChPW
No.
11.16.010.001.001), financed by the Ministry of
Science and Higher Education.
REFERENCES
CONCLUSIONS
The effects of splitting the flow of the solvent being
injected into the absorber have been described in detail.
Split-flow modifications in absorber are intended to
even out CO2 absorption driving force and to lower
the energy demand of the process.
The reduction in the reboiler heat duty for split-flow
process during trials presented in this paper is
observed. Therefore, the split-flow modifications give
the savings in terms of reboiler duty. Apart from the
reboiler heat duty reduction, the increase in CO2
recovery is also observed with split-flow design. In
the presented tests, the flow sheet modification resulted
in a decrease of reboiler heat duty by ~1.6% and an
increase in CO2 recovery by ~1.2 p.p. Split-flow
process improvement showed advantages for the
experimental conditions evaluated here because with
minor increase in process complexity, noticeable
increase in process efficiency was perceived.
Presented results are encouraging, but future studies
on the split-flow modification are required in order to
be able to conclude definitively as to the advantages
of the split flow over the standard process. Future
studies should target on comparing the configurations
in the optimal conditions. Besides the process
comparison, a complete economic assessment should
be conducted, because, in the end, the decision on the
implementation of the split-flow process will be
determined by the overall economics of the system.
It can be expected that split-flow modification
coupled with a new solvent would drastically decrease
the energy demand and increase the CO2 recovery of
the amine-based post-combustion CO2 capture process.
Acknowledgements
The authors would like to thank the anonymous
reviewers for their helpful and constructive comments
that greatly contributed to improving the final version
of the paper. The results presented in this paper were
obtained during research co-financed by the National
Centre of Research and Development in the framework
of Contract SP/E/1/67484/10—Strategic Research
Programme—Advanced technologies for energy
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