Sulphur impacts during
pulverised coal combustion
in oxy-fuel technology for
carbon capture and storage
Terry Wall and Rohan Stanger
Chemical Engineering, University of Newcastle,
2308, Australia
Outline
•General sulphur impacts
•Pilot-Scale experiments
•Sulphur Thermodynamics
•Control and Mitigation
….. For pulverised coal fired oxy-fuel
Updated from
Stanger, R and T Wall, Sulphur impacts during pulverised coal combustion in oxy-fuel
technology for carbon capture and storage. Progress in Energy and Combustion Science,
2010. 37(1): p. 69-88
Sulphur Impacts in Oxy-fuel CCS
Slagging & Fouling
Higher
COS
SCR –H2S
SO&
3 formation
Combustion
SNCR – NH4(SO3)2
ASU
O2
CO2 purity
CO2
Compression
ESP
FF
Coal
Handling
Sequestration
Site
(Pipeline, Truck, Ship)
Transport
Recycle
H2SO4 corrosion
Enhanced ESP – SO3 coating
FF – SO3 competes for Hg sites
Deep Geological Storage
HEX – acid dew point
pH & porosity
Cooling - H2SO4
Process factors for SOx in Oxy-fuel:
comparison with Air firing
•
Higher Feed O2 and CO2 rather than N2% (to reproduce furnace heat transfer)
– Lower volumetric flow
– Longer residence times for gas and solids
– Higher dust loading
– Different thermal profile
•
Flue Gas Recirculation – and N2 omission from oxidant
– Higher SO2 concentration
– Higher Acid Dew Point
– Wet or dry recycle
– Use/placement of FGD
– Direct or Indirect FGC
•
CO2/H2O atmosphere
– Different thermal profile
– Different diffusion rate
– Higher Acid Dew Point (H2O0
Pilot Work with Oxy-fuel with recycle
SO2
emissions
•
•
•
•
•
•
Chalmers, 100kW 2009
IFK, 20 & 500kW 2008
Callide/IHI, 1.2MW, 2005
CANMET, 300kW 2001
IHI, 1.2MW 1993-6
IFRF, 2.5MW, 1994
SO3
emissions









S
balance
Fly ash
capture






Conclusions
•
Higher SO2 concentration in oxy-fuel (ppm)
•
Less SO2 “emitted” in oxy-fuel (mg/MJ)
•
Sulphur balanced NOT CLOSED, ie S is “lost” (not accounted for)
•
Sulphur in Ash + condensate cannot account for residual-S
Condensate


S BALANCES: Lost-S example
Fleig, D., K. Andersson, D. Kuhnemuth, F. Normann, F. Johnsson, and B. Leckner,
The Sulphur Mass Balance in Oxy-fuel Combustion of Lignite- An Experimental
Study, in IEA 1st Oxy-fuel Combustion Conference. 2009: Radisson Hotel, Cottbus,
Germany.
Literature Conclusions about Lost-S
•
“Although the mass balance of sulphur could not be closed completely, it is
supposed ...... that the condensation of sulfate or sulfite in the duct where the gas
temperature was low enough and the absorption of sulphur in ash resulted in the
reduction of SO2 emissions from the stack on O2/recycled flue gas combustion”
Kiga, T., S. Takano, N. Kimura, K. Omata, M. Okawa, T. Mori, et al., Characteristics of pulverized-coal combustion in the system of
oxygen/recycled flue gas combustion. Energy Conversion and Management, 1997. 38(Supplement 1): p. S129-S134.
•
“it does not seem that the removal of SO2 through condensation is very
significant..... ......the sulphur present in the ash cannot be the only explanation for
the lower conversion of fuel-S into SO2”
Croiset, E. and K. V. Thambimuthu, NOx and SO2 emissions from O2/CO2 recycle coal combustion. Fuel, 2001. 80(14): p. 2117-2121.
•
“Sulphur mass flow in in the ash is higher in oxy-fuel.... Sulphur mass flow in
condenser water is low.... Clarify the gap in the mass balance.... Gap being Air 69%, OF35 dry 21-27%, OF43 wet 8-17%”
Fleig, D., K. Andersson, D. Kuhnemuth, F. Normann, F. Johnsson, and B. Leckner, The Sulphur Mass Balance in Oxy-fuel Combustion
of Lignite- An Experimental Study, in IEA 1st Oxy-fuel Combustion Conference. 2009: Radisson Hotel, Cottbus, Germany.
IHI Pilot Plant for Callide/IHI tests
Oxy-fuel combustion flowchart
PAF
Ash Deposits
Sampling
Electrical
heater
positions
SO2/ SO3
Furnace
Radiative
Section
Pulverized
coal
~160°C
~500°C
Gas
cooler
Air
heater
Gas
cooler
Bag
filter
Stack
IDF
Convective section
~800°C Equal velocity
aspiration sample
Temperature
Fly Ash
of transport
lines ?
Bottom Ash
Air
Electrical Steam gas Water spray
heater
heater
tower
Direct FGC
for primary
feed gas
FDF/GRF
O2
Pilot SO2 Results
Example: Callide/IHI results
500
2500
400
SO2,
mg/MJ
SO2, ppm
2000
1500
1000
OXY
500
300
200
100
25-30% less
AIR
0
0
0
0.2
0.4
0.6
0.8
1
Fuel-S, % db
Oxy-fuel concentration higher
0
0.2
0.4
0.6
0.8
Fuel-S, %
but produces LESS total SO2
Higher concentration acts as driver for secondary products
1
Pilot SO3 Results
Example: Callide/IHI results
70
160
60
150
Oxy Fired
o
Acid Dew Point, C
Measured Oxy Fired
SO3, ppm
50
40
30
20
O
AIR to
XY →
140
SO3 estimate
130
∆Hloss
Air Fired
120
SO3 measured
110
10
Measured Air Fired
0
500
1000
1.94%
2.13%
HHV
HHV
HHV
100
0
0
0.86%
1500
SO2, ppm
IHI/Callide Coal A-Air
ANL-Air [17]
IHI/Callide Coal A-Oxy
ANL-Oxy [17]
IHI/Callide Coal B-Air
CANMET-Air [13,30]
IHI/Callide Coal B-Oxy
CANMET-Oxy [13,30]
IHI/Callide Coal C-Air
IVD Stuttgart-Air [31]
IHI/Callide Coal C-Oxy
IVD Stuttgart-Oxy [31]
2000
0.2
0.4
0.6
Fuel-S, %
0.8
1
Pilot Ash Results – Callide/IHI
1.2
Fly Ash
1.2
1
Air
Oxy
0.8
Coal C
0.6
0.6
0.4
0.4
0.2
0.2
0
0
0.2
Oxy Fired
0.8
S as SO3,
% (ad)
S as SO3, %
1
Coal C
Air Fired
0.4
0.6
Fuel-S, %
0.8
1
0
Bottom Ash
Fly Ash
Deposit
Radiative
Deposit
Convective
Little SO3 in Bottom Ash and Radiative Deposits for other
coals
In-flame measurements
IVD - Stuttgart
SO2
H2S
SO2+H2S
6000
30
O2
30
6000
(SO2+H2S)max
18
AIR-BLOWN COMBUSTION_LAUSITZ
12
2000
(SO2+H2S)max
0
0.5
1
1.5
Distance from Burner [m]
2
18
OF27_3000 COMBUSTION_LAUSITZ
12
2000
6
0
0
4000
2.5
6
0
0
0
0.5
1
1.5
Distance from Burner [m]
2
2.5
O2 [vol%]
4000
SO2, H2S [ppm]
24
O2 [vol%]
SO2, H2S [ppm]
24
Effects on corrosion in the boiler
Fuel-S 0.68 % daf
Fuel-S 1.93 % daf
•
Corrosion rate in oxy-fuel is an issue in Oxy-fuel USC development
•
Boiler corrosion may dictate SOx control
Impacts of High S/High Cl coals on high temperature corrosion- a brief note
Robin Irons, E.ON
IEA 1st Oxyfuel Combustion Conference, Cottbus, 2009
Interaction of Fly Ash & SO2
Okazaki measurement/modelling of CaSO4
decomposition
In-furnace desulphurisation with limestone – applicability to fly ash capture?
1.
Fixed Bed Reactor
→ Limestone sulphur capture kinetics & diffusivity
2.
Drop Tube Furnace
1212°C
High temperature
limit for capture
→ CaSO4 decomposition
vs SO2 concentration
3.
•
•
Modelling
1170°C
→ pore diffusion with shrinking core model
→ SO2 diffusion through calcined limestone
→ No direct sulphation
→ 4-6 increase in desulphurisation efficiency
Increase of η due to inhibition of CaSO4 decomposition
Increase of η due to recirculation of flue gas
Modelling Basis
1.2 O2-Fuel ratio,
Ca/S = 5,
8s residence time
10µm limestone particle
Oxy with 0.84 recycle rate
Limestone Desulphurisation Experiments
performed in drop-tube furnace
Calcining inhibited by CO2
O2/CO2
Indirect sulphation
Air
3000ppm SO2
Direct Sulphation
3000ppm SO2
1050°C
3s residence time
BUT …. Calcium in fly ash is expected to be sintered, glassy & non-porous
Mechanism of Highly Efficient In-Furnace Desulfurization by Limestone under O2/CO2 Coal
Combustion Atmosphere
Chuanmin Chen, and, Changsui Zhao
Industrial & Engineering Chemistry Research 2006 45 (14), 5078-5085
Measurements of SO2 with Fly Ash
Fly Ash Capture in Oxy-fuel -IVD
Radiative (>1150°C)
Convective (1150 → 450°C)
Ca/S
Fe/S
3.17
0.83
3.96 1.28
1.03 0.90
2.98 0.38
• No evidence of SO2 transformation in radiative section
• Convective SO2 transformation is coal specific
Patrick Monckert, Bhupesh Dhungel, Rene Kull, and Jorg Maier. Impact of Combustion Conditions on Emission
formation (SO2, NOx) and Fly Ash. in 3rd MEETING of the OXY-FUEL COMBUSTION NETWORK 2008.
Yokohama Symposia, Yokohama, Japan: IEA Greenhouse Gas R&D Programme.
Catalytic Oxidation of SO2 to SO3
Conversion of SO2 to SO3, %
The Effect of Temperature & Fe2O3 in Fly Ash
Fly ash + temperature
Fly ash + Fe2O3 mixtures
Marier, P. and H. P. Dibbs, The catalytic conversion of SO2 to SO3 by fly ash and the
capture of SO2 and SO3 by CaO and MgO. Thermochimica Acta, 1974. 8(1-2): p. 155-165.
Mass Balance & Thermodynamics
Theoretical Mass Balance – Callide/IHI
4000
Measured Air
Measured Oxy
SO2,
ppm (dry)
3000
Difference due
to the formation
of secondary
sulphur
products
2000
1000
0
0
0.2
0.4
0.6
Fuel-S, %
0.8
1
Theoretical Mass Balance- Callide/IHI
4000
Oxy - recycle with no gas treatment
Theoretical SO2, ppm
Oxy - recycle with full gas treatment
Oxy - recycle with primary treatment only
Air Fired
3000
2000
Effect of
Recycle
1000
Effect of Lower Flow Rate
0
0
0.2
0.4
0.6
Fuel-S, %
0.8
1
ASHY PRODUCTS- Thermodynamic shift
in S-species
SO
Gases
SO2
SO3
O2S(OH)2
Liquids and molten solutions
Oxy-fuel combustion
Air combustion
Na2SO4 (slag)
K2SO4 (slag)
CaSO4 (slag)
Na2SO4 (salt)
K2SO4 (salt)
H2SO4 (H2O)6
Na2SO4
MgSO4
Solids
CaSO4
K2SO4
Fe2(SO4)3
1500 1400 1300 1200
1100 1000
900
800
700
Temperature °C
600
500
400
300
200
100
GASEOUS PRODUCTS- Sulphur Products & Effects
Convective Fouling
Acid dew point
Fly Ash Capture
Corrosion in
compression
In-flame
reduction
products
Cooling Flue Gas
1.0
H2SO4
SO2
Equilibrium
0.8
SO3
0.5
Kinetics “frozen”
with cooling ???
0.3
0.0
0
500
1000
Temperature,oC
1500
SO2 Conversion to SO3
10
SO3
9
8
Fuel-S
Air
Oxy
%, db
ppm
ppm
Coal A
0.24
2
7
Coal B
0.57
9
18
Coal C
0.88
3
11
AIR -
SO2 SO3
Conversion, %
7
↑
1000°C used to
estimate SO3
conversion for
acid dew point
OXY -
6
5
(Okkes, Verhoff
& Banchero
methods)
4
3
2
IHI Pilot- 1.2 MW t
(Callide study)
1
IVD Pilot- 0.5 MWt
(Maier et al )
0
0
500
1000
Temperature, C
1200
1500
Control Strategies
Mitigation Options
Air
Separation
Unit
O2
Soot Blowing
N2
CO2
compression
Low S Coal
Coal
Handling
ESP
Limestone
Sulphur
Scrubber
Transport
(pipeline, truck, etc)
Sequestration
Site
Sulphur removal in
compression circuit
Condenser/
Cooler
Recycled Flue Gas
Sulphur
Scrubber
Deep Geological Storage
Control Strategies
•
SO2 limited -
low sulphur coals
•
SO2 removed -
•
•
•
Soot-blowers
Flue Gas above acid dew point
Corrosion resistant materials
FGD (85-98% capture)
Limestone addition (<50% capture)
High calcium coals (5-10% capture)
Direct Cooling/Caustic wash (Linde, Air Liquide)
In compression (Air Products)
In purification
Conclusions – Pilot-Scale Sulphur
• Higher SO2 in Oxy-fuel
• Higher SO3 & acid dew point
• Fly Ash & Bottom Ash appear to be unaffected in
limited current measurements tho’ theoretically this is
expected
• Oxy-fuel Deposits higher in S
Conclusions- Sulphur Impacts
• Sulphur Impacts throughout oxy-fuel CCS
• Oxy-fuel SO2 - higher conc (ppm), lower emissions
(mass/energy)
• SO2 Concentration driver for S products
• SO3 conversion ~thermodynamics 1000°C
Focussing questions…..
SULFUR HAS MULTIPLE IMPACTS AND CONTROL OPTIONS
THERE IS LITTLE DATA, SOME OF WHICH DISAGREES WITH THEORY
DATA
• Can we be sure of data unless S balances?
• Do we need to measure heterogeneously and homogeneously condensed S?
ACID DEW POINT (ADP)
• No direct measurements, can we rely on ADP/SO3/H2O correlations?
ASH/DEPOSITS
• Do we need to understand differences with air firing?
OPTIMUM S REMOVAL, WHERE/EXTENT?
• POWER PLANT - Based on corrosion or ADP?
• COMPRESSION - Based on transport and storage, and removal during
compression?
• Is any FGD required?
• Note that S removal is associated with gas drying/cooling
Thank you for your attention
Sulphur Impacts
Furnace
Convective Pass
corrosion, slagging
corrosion, fouling
SCR
fouling, catalytic formation- SO3
ESP
higher performance
Heat Exchange
Compression
acid dew point
H2SO4
CO2 Purity
SO2
Transport
corrosion, H2SO4
Storage
Corrosion, injection (pH zone)
In-flame Sulphur Products
10
10
9
9
8
8
OXY/AIR
Concentration Ratio
OXY/AIR
Concentration ratio
(Thermodynamics at 1500°C)
7
6
COS
SO3
5
4
3
SO3
7
H2S
6
5
COS
4
SO2
3
2
2
SO2
1
1
H2S
0
0
0.8
0.9
1
Equivalence Ratio
1.1
1.2
0.8
0.9
1
1.1
Equivalence Ratio
ONCE THROUGH
WITH RECYCLE
(O2/CO2 vs O2/N2)
(~69% recycle, 28% O2 IN, 5% O2 OUT)
1.2
SO2 in Compression
High
Low
H2O
H2O
Scenario
Scenario
– 500ppm
– 50ppm
Storage
- 3% O2,O2,
100ppm
SO2,
50ppm
H2O,
CO2CO2
balance
For Aquifer
EOR Storage
- 100ppm
100ppm
SO2,
500ppm
H2O,
balance
(Dynamis Project recommendations for Pre-combustion capture)
Temperature, °C
Limestone Addition
SO2, ppm
* Assumes max Ca/S = 2
Limestone Addition
* Assumes max Ca/S = 2
In-furnace measurements - IVD
Patrick Monckert, Bhupesh Dhungel, Rene Kull, and Jorg Maier. Impact of Combustion Conditions on Emission
formation (SO2, NOx) and Fly Ash. in 3rd MEETING of the OXY-FUEL COMBUSTION NETWORK 2008.
Yokohama Symposia, Yokohama, Japan: IEA Greenhouse Gas R&D Programme.