Institute of Combustion and Power Plant Technology
Prof. Dr. techn. G. Scheffknecht
Pilot scale
combustion testing
Installation and Operation
of R&D test facilities under oxy-fuel
conditions
Joerg Maier
[email protected]
University Stuttgart
4th APP OFWG Capacity Building Course, Tokyo, Japan 2012
Institute of Combustion and Power Plant Technology
Prof. Dr. techn. G. Scheffknecht
Institute of Combustion and Power
Plant Technology - IFK (former IVD)
Universität Stuttgart
1
Outline
• 0.5 MWth Unit Retrofit
Oxy-fuel
fuel Burner Development
• Oxy
• Test Results and Experiences
•
•
•
•
NO formation and reduction
S behaviour
Corrosion, slagging
gg g and fouling
g
Modelling
• Ongoing/Future R&D topics
3
Example of Emission Reduction
(Reunion of Germany)
1982 - 1999: old federal states
1990 - 1999: new federal states
Dust
in millon tons
0.25
Sulphur dioxide
in millon tons
2.0
Nitrogen oxide
in millon tons
0.8
1982
84
86
88
90
92
94
96
1999
4
2
IFK 0.5 MWth Unit Retrofit for Oxy-Fuel
operation
under the requirement to keep availability for air firing
0.5MWth Unit
Modifications for Oxyfuel Combustion Conditions
Condensers
Oxygen supply
Flue gas
recycle duct
FD fan
Coal feeding
g
Bypass
ID fan
Bottom
ash
SCR
APH
ESP
stack
6
3
Pf-fired 0.5 MWth Test Facility
(15 years operation)
coal + primary air
additional fuel +
conveyor air
burner
secondary air, flue gas recirculation
vertical
ti l
furnace
SP 1
SP 2
SP 3
SP 4
SP 5
to stack
SCR Catalyst
ESP
SP 6
fabric
filter
slag and ash
Φ > 100 µm
fly ash
(1 fraction)
fly ash
(3 fraction)
fly ash
(1 fraction)
7
Oxy-fuel Mode Integration
Infrastructure
O2/ CO2 Supply Infrastructure
Preparation:
• Negotiations with providers:
commissioning of tanks, lines,
product prices, installations,
maintenance, …
• Permission procedures:
City of Stuttgart and
University authorities
• Engineering:
work safety aspects, construction and
ground works,climatic constraints, …
8
4
Infrastructure
O2/ CO2 Supply Infrastructure
Consumption (planned):
• Oxygen: 72,000 m3N
• Carbon dioxide: 48 tons
Tank capacities:
• Oxygen: 6,000 m3N
• Carbon dioxide: 5 tons
Modifications for Oxyfuel Combustion
CO2
O2
gas distribution
0.5MWth
others
storage tanks
20kWth
consumers
5
Air-Oxyfuel Test Facility (500kWth)
Infrastructure
Concerned area of the major changes for the
adaptation for the new burner design
level no.
1
2
3
4
5
CO2
Air/
Flue gas
Air
Coal
feeding
Burner
windbox
Gas
distribution
O2
FD/ RG fan
Storage
tanks
Inflame
Measurements
•Gas emissions
•Gas temperature
•Heat Flux
•Radiation etc.
23
24
25
By-passes
Bottom
ash
SCR
ESP
16
17
18
19
20
22
Stack
APH
11
12
13
14
15
21
O2 CO2
Ai
Air
6
7
8
9
10
26
ID fan
Continuous gas
emission
measurements
27
28
29
30
31
Sampling
•Ash, HCL, SO3
11
O2/recyled flue gas
0.5MWth Unit Modifications for Oxyfuel Combustion Conditions
re-circulation
ventilator
O2 injection system
(MFC, injector)
duct for
re-cycled
flue-gas
Venturi orifice
to furnace
12
6
Topics of first Oxyfuel-Tests
• Start-up/shut-down procedure
• Identification of air-inleakage
air inleakage
• Max. CO2 concentration
• Switch from air to oxyfuel operation
• Parameter optimisation (variation of O2-injection,
injection,
recycle rate, …)
• Definition reference flame definition (air/oxyfuel)
• Start of test programmes
13
Switch from once-through to re-circulation mode (I)
Lausitz lignite
100
80
100 flap open
O 2 in vol.-% dry
CO 2 in vol.-% dry
80
start of O2 injection
and
CO2 as carrier gas
60
60
40
FGR flap
position
in %
40
flap for flue-gas
re-circulation (FGR) opened
air combustion
20
0
18:09
20
0 flap closed
18:29
18:49
Time
19:09
LA_OXY_1_20980-21450
14
7
Shift from Air to Oxyfuel of the 30MW Pilot Plant
Behaviour of flue gas concentrations
Approx. 60 min
Source: Vattenfall, Alstom Cottbus 2009
15
Conclusions from 0.5 MW Retrofit Test
Facility
• Switching from air to oxy-fuel combustion, achievable
in short time interval (~30 minutes).
( 95% dry).
• High CO2 concentration achievable (~95%
• Operation under oxy-coal combustion with different
ranks of coals achieved successfully.
• Burner adjustments required and successful
implemented
• O2-concentrations at the burner inlet ducts up to 100%
• High flexibility of recycle rate (40-90%)
• Additional safety measures required
More than 1500h successful Oxyfuel operation
16
8
Burner adjustments and further
burner developments
17
Development of Low NOx Oxyfuel burner
Performed Investigations at the electrically heated 20 kW
test facility:
•Determination of optimum oxygen injection method (pure or
premixed
O2 concentrations in the different gas streams
Total
combustion gas
Carrier stream
Primary stream
Secondary
stream
21%
21% / 5% / 5%
21% / 23% / 100%
21% / 23% / 5%
27%
27% / 5% / 5%
27% / 30% / 100%
27% / 30% / 5%
39%
39% / 5% / 5%
39% / 43% / 100%
39% / 43% / 5%
•Determination of optimum burner operation mode; swirl,
momentum, velocity
•Determination of optimum parameters for oxy-fuel operation
using high volatile Brown Coals (Stoichiometric ratio, oxygen
excess, oxygen content in combustion gas)
•Staging at the oxyfuel combustion
9
Development of Low NOx Oxyfuel burner
Investigations at the 500 kW semi-technical test facility:
Comparison of two different burner designs
• Flame characterisation and ignition optimisation under recycled
conditions
diti
• Optimum O2 injection method
• Impact of recycle rate on flue gas momentum,
flame stabilisation, internal recirculation
• Staging at the oxyfuel combustion
• Emission behavior
Actual burner
Inflame
Measurements
•Gas emssions
•Gas temperature
New burner design
Continuous gas
emssion
measurements
secondary gas stream
(optionally swirled)
primary gas stream
and fuel
gas probe with nine drillings
19
Integration of the new burner design
Implementation of:
• new primary line for the new burner
• 4 new secondary lines for the new burner
• oxy-fuel staging
• Second source of oxygen injektion
20
10
Integration of the new burner design
Previous burner installation (previous burner) with
one primary and one secondary lines.
Current burner installation (new burner) with:
• one primary
• four different measured and controlled
secondary lines
• one oxygen line
21
Example of O2-Injection Modes
Pre-mixing (total)
Individual Pre-mixing
Direct injection
Source: Alstom Cottbus 2009
22
11
Test Results and Experiences
•
•
•
•
•
NO formation and reduction
S behaviour
Slagging and fouling
Corrosion
Modelling
23
Electrically heated test reactor (20kW)
Experiment Conditions
Air & 27% O2/73%
CO2
Coals
Klein Kopje, Lausitz
Oxidant flow through
burner
Constant for all cases
[6.7 m³/h]
λoverall
1.15
λ (burner stoichiometry)
0.75, 0.85, 0.95
T1
1, 2 and 3 seconds
1
24
12
NOx reduction potential during staged combustion
Klein Kopje Coal
350
Air_3 sec
300
Air_2 sec
250
27% Oxy_3 sec
200
27% Oxy_2 sec
Un-staged
Combustion
NOx [mg/MJ]
400
150
100
50
0
0.7
0.75
0.8
0.85
0.9
0.95
1
1.05
1.1
1.15
1.2
Burner Stoichiometry
Parameters
Optimum
Effect
Burner Stoichiometry
0.75-0.85
Oxygen deficiency, encouraging
formation of N2
Residence time in reduction zone
2-3 seconds
Longer time available for
conversion of NOx precursors to
N2
Temperature
Shift of coal-N towards gas phase
25
Fate of recycled NO - Summary
Reduction of recyclled NO [%]
Air_KK
27% O2_KK
Air_LA
27% O2_LA
Air_NG
Oxy_NG
120
100
99 100
95
91
98 96
91
92
80
8381
85 88
72
79
60
49 47
40
53
59
50
39 38
13
20
0
0.75
0.85
0.95
Unstaged
Stoichiometric Ratio
• Reduction dependent on combustion mode (burner stoichiometry and residence
time in reduction zone).
• Generally higher reduction for oxy-coal combustion.
• For the coals investigated: for a particular combustion condition, percentage
reduction during oxy-coal combustion is almost similar.
• Combustion modification can take care of recycled NOx accumulation.
26
13
Conclusions from 20 kW furnace
¾ NOx emission rate is lower during oxy-coal combustion with
oxygen partial pressure between 21-27% (un-staged
combustion).
¾ Oxidant staging is applicable for oxy-coal combustion.
¾ Recycled NOx can be reduced by combustion modification,
with ~60% reduction during un-staged combustion and
~100% during staged combustion (λ1=0.75 and T1=3 sec) for
all coals tested.
¾ CO in the near burner region is higher during oxy-coal
oxy coal
combustion indicating enhancement of water-shift and CO2
shift reactions.
27
Test Results and Experiences
•
•
•
•
•
NO formation and reduction
S behaviour
Slagging and fouling
Corrosion
Modelling
28
14
Set-up and description of 20 kW once through furnace
• SO2 Injection: up to 6000
ppm via the secondary stream
of the burner
• In-flame measurements
H2S/SO2, staged/unstaged
• SO2 measurements outlet
rediative section T=1150°C
• SO2/SO3 measurements
outlet of convective section
T= 350°C
29
SO2 and H2S formation concentrations in an
Air and Oxyfuel environment
H2S
SO2+H2S
O2
SO2
30
6000
SO2+H2S]max
0
0.5
1
4000
18
12
2000
6
0
0
30
24
O 2 [ v o l% ]
12
2000
O2
SO2+H2S]-mass balance
S O 2, H 2S [ppm ]
S O 2, H 2S [ppm ]
18
SO2+H2S
SO2+H2S]max
24
4000
H2S
1.5
2
Distance from Burner [m]
Air- Blown Combustion,
λ1=0.75
2.5
O 2 [v o l% ]
SO2
6000
6
0
0
0
05
0.5
1
15
1.5
2
25
2.5
Distance from Burner [m]
OF27 Combustion,
λ1=0.75
30
15
Measuring SO3 - Methods
• Controlled condensation method (CCM): discontinuous sampling; selective
condensation of H2SO4 in a tempered (85-95°C) glass coil
out
in
H2SO4 condenser
• Continuous SO3 monitor working on a wet-chemical principle1: The analyser
should be further tested under oxy-fuel conditions (tested by EOn in the UK2)
1
Jackson, P. J.; Hilton, D. A.; Buddery, J. H. Continuous measurement of sulphuric acid vapour in combustion gases using a portable
automatic monitor. J. Inst. Energy 1981, 54, 124–135.
2 Couling,
D. Impact of Oxyfuel Operation on Emissions and Ash Properties based on E.ON’s 1MW CTF. Presented at the IEAGHG
Special Workshop on Oxyfuel Combustion, London, January 2526, 2011.
31
Correlation of SO3-Moisture and Acid dew point
Acid dew
w point temperature(°C))
• Considerable increase of acid dewpoint due to high SO3 and H2O concentrations
• Increase by 20-40°C will influence operation of low temperature units
air
Moisture content of flue gas (%Vol)
(Scheffknecht et al 2009)
32
16
Correlation of SO3-Moisture and Acid dew point
Acid dew
w point temperature (°C))
Similar increase of SO3 concentration at a SCR catalyst, but much less effect
on dew point temperature under oxy-fuel conditions.
SO3 content (mg/Nm3)
(Spörl et al 2011)
33
Measuring SO3
• Measuring SO3 is difficult, due to high reactivity
• SO3/H2SO4 can be absorbed byy
• filter materials
• fly ash on sample filter
• Carefull choice of construction materials for sampling system
• Sampling system must be carefully heated above sulfuric
acid dewpoint
34
17
Test Results and Experiences
• NO formation and reduction
• S behaviour
• Corrosion, slagging and
fouling
• Modelling
35
Corrosion under oxy-fuel
• Corrosion risk
• Tests at IFK
• Results
36
18
Identification of corrosion risk
Source: Takashi Kiga, Experimental study Results on corrosion issues in oxy-fuel combustion process, Special Workshop on Oxyfuel Combustion,
Addressing SO2/SO3/Hg and Corrosion Issues, London, Jan. 25th – 26th, 2011
37
Tests at IFK
short-term tests
up to 100 h
long-term tests
CO2
Air
C l
Coal
feeding
G
Gas
distribution
Burner
windbox
O2
FD/ RG fan
Storage
tanks
O2 CO2
Air
Stack
By-passes
APH
SCR
ESP
ID fan
Bottom
ash
Real fly ash
Gas composition: SO2,
CO2, H2O, O2, NOx
source: Stein-Brzozowska et al, [GSB6]
19
Lignite fly ash deposit, end of radiative zone
S
concentration
oxy-fuel
air
S
In both cases Fe-rich molten phases
More S in oxyfuel and bigger fraction of smaller particles noticed
Enrichment at the particles surface
39
SEM-MAP – Ca + S + O / Ca + C + O
Ca+S+O
Ca+C+O
- Close relation between sulfates and carbon on the particle surface
- Carbon content increased by exposure time
40
20
S
BSE
MAE and O
S
concentration
MAE and O
N1-A_350C_750h_3
BSE
N1-O_35
50C_750h_1
oxyy-fuel
air-ccase
Alloy N1 after 350h at 750°C
• higher growth of oxide-scale under oxy-fuel conditions;
• internal oxidation was noticed already in the pre-exposed state;
• no sulphur-front recognized
41
Results of the 500kW facility- SO3 and Deposits
•
Clear tendencies that under Oxyfuel conditions the SO3
concentration are higher
•
Impact of Oxyfuel conditions on SO2/SO3 conversion rate
needs further clarification
•
Verification of data according to pilot scale measurements
(30MW plant Schwarze Pumpe)
•
Indications that beside sulfatization carbonization on the particle
surface of deposits occurs under Oxyfuel conditions
•
Carbonatisation of sulfates can enhance the release of Sulphur
Components which promotes sulphur corrosion mechanism
42
21
Test Results and Experiences
• NO formation and reduction
• S behaviour
• Corrosion, slagging and
fouling
• Modelling
43
Program Code AIOLOS
Numerical Modeling and Simulation, combined Simulation
(Furnace and Steam Side)
Two Phase
Flow
Turbulence
Burnout air
Burner level 3
HomoHomogene
geneous
Reaktionen
Reactions
Pulverized
Coal
Combustion
Radiation
Burner level 2
Heat
Transfer
Optical
Properties
Chemical
Reactions
HeteroHeterogene
geneous
Reaktionen
Reactions
Burner level 1
44
22
Detailed Coupled Simulation
AIOLOS
3D g
geometry
y
boiler
DYNAMIK
Measurement data
Process data
Furnace Simulation
Tube
wall
Iterations
Temperature velocity
concentrations
Heat fluxes
Temperatures
Results for
the whole system
with high
spatial resolution
3D geometry Heat
exchanger
Water/Steam
Process
Simulation
Iterations
Temperature
pressure
material stress
45
Current Model Developments for Oxy-Fuel
•
Model developments for Oxy-fuel combustion
• Development of mathematical models for heterogeneous char
conversion under Oxy-Fuel
Oxy Fuel conditions
conditions, including enhanced gasification
reactions
• Mathematical models for turbulent gas phase reactions:
• gas phase combustion, NOx formation and destruction
• Development of mathematical models for radiative heat transfer in CO2enriched atmospheres
• Validation of new modelling approaches with experimental results
• Combined coupled approach to furnace and steam generation
simulation
•
Simulation and optimization of oxyfuel-combustion
(0.5MWth, 30MWth,….
46
23
Extended chemical reaction models
» Gas phase reactions:
(1)
(2)
(3)
(4)
CnHm + n/2 O2
C nH m + n H 2O
H 2 + ½ O2
CO + H2O
→
→
↔
↔
n CO + m/2 H2
n CO + (m/2 +n) H2
H 2O
CO2 + H2
» implementation of additional reactions and considering equilibrium
reactions enables accounting for chemical effects of specifically high O2
and CO2 levels in the oxidizing atmosphere during oxy
oxy-fuel
fuel combustion
» including reverse reaction of (3) is particularly required for correct
prediction of local flame temperatures since equilibrium is shifted
towards educts in high temperature flames
47
Extended chemical reaction models
» Char burnout reactions:
(1) C + ½ O2 →
(2) C + CO2 →
(3) C + H2O →
CO
2 CO
CO + H2
(char oxidation)
(Boudouard reaction)
(water-gas-shift reaction)
» gasification reactions (2) and (3) may have major impact in O2-lean
regions due to higher partial pressures of CO2 and H2O compared to
conventional air-firing
» at ambient pressure and typical combustion temperatures the reactions
(2) and (3) may be considered irreversible since the equilibrium is shifted
towards the product side
48
24
Simulation results / Validation
» Test case: 500 kWth reactor, Lausitz lignite,
O2 direct injection @ burner, total [O2] = 21%
Axial plots showing:
• very good agreement after
~ 0.5 m
• improved CO prediction
• deviations at near burner
region
Æ delayed ignition
Æ late O2 consumption
• overall good accuracy
49
Ongoing/Future R&D Topics at IFK
•
Experimental Oxy-fuel combustion topics:
• Rank of coal (bituminous, lignite, hard coals…)
• Slagging, Fouling, (impact of higher SO2, H2S, CO2, HCl etc.)
• Corrosion high-low temperature (Deposits, HCl, SO2, SO3, H2O…)
• Fly ash quality and utilisation (EN 450 …)
• Component development and test (burner, …)
• Emissions (Hg, fine dust, etc)
• Flue gas cleaning (SCR, Additives…)
• Particle removal and impact to particle removal systems ( ESP and Bag
Bagfilter performance)
• Biomass (co-)combustion
•
•
Oxy-fuel: CFB
Improvement and validation of CFD models
50
25
Biomass (co)-firing under oxy-fuel Æ Bio-CCS
In order to keep
• Global temperature rise
• Safe CO2 levels
Below 2°C
Below 450 ppm
Given
• Growing population
• Increasing energy demand
• Energy mix
Atmospheric
carbon
Organic
carbon
measures beyond CCS
need to be considered
Bio-CCS
Geological
Storage
51
Bio-CCS (or BECCS)
(Koornneef, ECOFYS, 2010 in Dixon et al, IEA, 2012)
52
26
Bio-CCS technologies
•
Biochemical production of biofuels
• Biomethane
• Bioethanol
•
Thermochemical production of biofuels
• Hydrogen
• SNG
• BtL
•
Biomass combustion for electricity and/or heat production
•
•
•
•
•
Biomass co-firing
g ((direct/indirect)
/
)
100% Biomass combustion (CHP plants and CFB boilers)
Biomethane/Bio-SNG
Biomass-based IGCC (BIGCC)
Industrial applications (Fuel substitution, pulp and paper, etc.)
(EBTP/ZEP, 2012)
53
Vattenfall Oxy-fuel Pilot Plant
54
27
Road Map Vattenfall
Source: Vattenfall IEA Cottbus 2009
55
28