SO3 Control in Oxyfuel Applications
B. Dhungel, C. Ellul, J. R. Gibson and F. D. Fitzgerald
Overview
 Background on sulphur related issues during oxyfuel combustion
 Description of the test facility, SO3 measurement equipment and test programme
 Results on sulphur balance
 Results on SO3 and SO2 reduction by the injection of sorbents
 Conclusions
1
25 January 2011 | IEAGHG Special Workshop on Oxyfuel Combustion
Furnace Exit SO 2 (vppm dry) (mg/MJ)
Sulphur Related Issues during Oxyfuel Combustion
Oxyfuel Firing (ppm)
Air Firing (ppm)
Air Firing (mg/MJ)
Oxyfuel Firing (mg/MJ)
Burner Stoichiometry
 SO2 concentration (ppm) during oxyfuel combustion is generally higher – levels up to 3-5 times have been
measured
 Arises from dilution effect caused by elimination of N2
 SO2 in mg/MJ is however lower than air-firing and has been attributed to:

More retention of sulphur by the ash

Removal with condensate during dry flue gas recycle

Unknown conversion of SO2 to SO3
 Sulphur balance across the system is required to optimise configuration of oxyfuel combustion system
25 January 2011 | IEAGHG Special Workshop on Oxyfuel Combustion
2
Sulphur Related Issues during Oxyfuel Combustion
IVD
Callide- Coal A
Callide- Coal B
Callide- Coal C
SO3- Oxy [ppm]
20
16
12
8
4
0
0
4
8
12
16
20
SO3- Air [ppm]
 SO3 concentration has been reported to be 2-5 times higher during oxyfuel combustion
 Water vapour content is approximately 3 times higher during oxyfuel combustion with wet flue gas recycle
 For an oxyfuel combustion plant that gives similar performance as air-firing plant, the H2SO4 dew point
temperature will be higher
 Raises the concern of low temperature corrosion
Research Needs:
 Detailed investigation on SO3 formation during oxyfuel combustion
 Means to reduce SO3 during oxyfuel combustion
3
25 January 2011 | IEAGHG Special Workshop on Oxyfuel Combustion
TSB Project: SO2/SO3 in Carbon Capture Applications and its Mitigation
TSB Funded Project in collaboration with E.ON Engineering, IEA-GHG and
University of Leeds, with additional sponsorship from Vattenfall AB
Doosan Power Systems Objective:
Experimental investigation on a 160 kW t
Emission Reduction Test Facility (ERTF)
focusing on:
 Sulphur balance across the system
 Investigate the formation of SO3 under
oxyfuel conditions
 Investigate the SO3 reduction potential
by injection of dry pulverised sorbents
4
25 January 2011 | IEAGHG Special Workshop on Oxyfuel Combustion
160 kW t Emission Reduction Test Facility (ERTF)
 Water cooled refractory lined
furnace
 5m long and 0.5m in diameter
 Down fired with scaled down
Doosan Power Systems Mark 3 Low
NOx burner
 Flue-gas recycled after ESP (wet)
 CO2/O2 used for primary stream
(similar to dry recycle)
5
25 January 2011 | IEAGHG Special Workshop on Oxyfuel Combustion
Modifications to Enable Dry Sorbent Injection
Air supply
during air-firing
Rospen Loss in Weight Feeder for
Sorbent Injection
CO2 from tank
CO2 to sorbent
feeder
CO2 and Air Supply Pipelines for
Sorbent Transport
CO2 to coal
feeder
25 January 2011 | IEAGHG Special Workshop on Oxyfuel Combustion
6
Controlled Condensation Sampling Train for SO3 Measurement (Method 8B)
 Flue gas pulled through
temperature controlled quartz lined
probe
Clean Air Engineering
 Dust separated using an ultra
pure quartz filter
 SO3 condensed in a condenser
tube packed with glass wool
 Condenser tube temperature
controlled by water bath
 Temperature of water bath is
maintained sufficiently higher than
moisture dew point
 Avoids moisture condensation
and hence possible interference
with SO2
 SO2 collected in impringers with
3% H2O2
 Moisture may be determined by
increase in weight of the impingers
7
25 January 2011 | IEAGHG Special Workshop on Oxyfuel Combustion
Test Overview
 Air-Firing and Oxyfuel Firing
 Medium Sulphur Bituminous Coal
 2 In-furnace sorbents
 2 post combustion sorbents
 Baseline Measurements (Air/Oxy): Without sorbent injection
 Establish baseline SO3, Sulphur balance
 Compare with sorbent injection measurements
 In-furnace sorbent injection (Air/Oxy):
 Verify if in-furnace sorbents are efficient in reducing SO3 during oxyfuel
combustion
 Optimise sorbent feed rate
 Post combustion sorbent injection (Air/Oxy):
 Verify if post combustion sorbents are efficient in reducing SO3 during
oxyfuel combustion
 Optimise sorbent feed rate
8
25 January 2011 | IEAGHG Special Workshop on Oxyfuel Combustion
Measurement Programme
X: Continuous measurement
O2 and CO2 in primary &
secondary FGR as required
X: Wet chemical method
X: Isokinetic Sampling
Temp, SO2, O2, CO, NO
Sorbent
SO2, O2 NO,
CO Analyser
Chiller
FURNACE
O2, CO2,
NO,CO,
SO2
Heated Line
SO2,O2,
CO, NO,
H2O
Solid
Sampling
SCR
(Catalyst
Removed)
SO2,O2,
CO, NO,
H2O
ESP
ESP
SCR
Solid
Sampling
SO3,
SO2, H2O
ESP Bin
Ash
25 January 2011 | IEAGHG Special Workshop on Oxyfuel Combustion
9
Sulphur Balance (Without Sorbent Injection)
S-Coal
S-FGR
2
2
S-Ash
Discrepancy
4
32
100%
S-SO2
80%
19
17
18
ESP Exit
68
81
94
ESP
Inlet
82
97
Furnace
Exit
40%
79
96
100
60%
Furnace
Exit
ESP
Inlet
ESP Exit
20%
0%
Input
Air-Firing
Input
Oxyfuel Firing
 Discrepancy in sulphur balance of approximately 5% during air-firing, baseline condition
 Discrepancy in sulphur balance of approximately 20% during oxyfuel firing baseline condition
 Result indicate that most of the ‘missing’ sulphur is within the furnace
10
25 January 2011 | IEAGHG Special Workshop on Oxyfuel Combustion
Sulphur Balance (With In-Furnace Sorbent Injection)
Air-Firing
Oxyfuel Firing
 Discrepancy in sulphur balance increases from 5% to approximately 20% during air-firing tests with sorbent
injection
 Discrepancy in sulphur balance remains constant at approximately 20% during oxyfuel firing tests with sorbent
injection
 Indication that when SO2 capture potential in a system is high, the discrepancy in sulphur balance also
increases
25 January 2011 | IEAGHG Special Workshop on Oxyfuel Combustion
11
Carbon Balance
C-Coal
C-FGR
C-Transport CO2
C-CO2+CO
2
98
98
98
-4
-4
0%
Input
-20%
2
Furnace
Exit
ESP
Inlet
ESP Exit
36
20%
35
103
40%
103
103
100
80%
60%
2
29
100%
Discrepancy
C-Ash
Furnace
Exit
-4
ESP
Inlet
Air-Firing
ESP Exit
Input
Oxyfuel Firing
 Discrepancy in carbon balance is seen to be <5% for both air-firing and oxyfuel combustion
 Indication that there is no systematic error on calculation method for Carbon and Sulphur
balance
25 January 2011 | IEAGHG Special Workshop on Oxyfuel Combustion
12
SO3 Reduction by Sorbent Injection during Oxyfuel Firing
SO3 Reduction [%]
100
75
50
Sorbent A
Sorbent B
25
Oxyfuel Firing
Sorbent C
Sorbent D
0
X:S Molar Ratio
Sorbent A & B : In-Furnace Sorbents, Sorbent C & D: Post Combustion Sorbents
 SO3 reduction up to 95% was achieved by the injection of sorbents during oxyfuel and air-firing
 Results indicate that sorbent injection at the flue gas duct is more effective in SO3 reduction
 Formation of SO3 is known reach maximum value after the furnace, the location where post
combustion sorbents are injected
 Furthermore, in-furnace sorbent injection is unlikely to reduce SO3 formed at the SCR
13
25 January 2011 | IEAGHG Special Workshop on Oxyfuel Combustion
SO3 Reduction during Air-Firing and Oxyfuel Firing
Reduction-Air
Reduction-Oxy
SO3 Reduction [%]
100
75
50
25
Sorbent A
0
X:S Molar Ratio
 In general, the SO3 reduction efficiency for all of the sorbent tested is seen to be
comparable to Air-Firing
 Higher mass of sorbent is required to achieve same X:S molar ratio, as the concentration
of sulphur species is more during oxyfuel firing
14
25 January 2011 | IEAGHG Special Workshop on Oxyfuel Combustion
SO2 Reduction
Sorbent A
Sorbent B
Sorbent C
Sorbent D
SO2 [mg/MJ]
1600
1200
800
400
Oxyfuel Firing
0
X:S Molar Ratio
Sorbent A & B : In-Furnace Sorbents, Sorbent C & D: Post Combustion Sorbents

In-furnace sorbent injection shows steady decrease in SO2 with increase in sorbent injection
 After initial reduction, SO2 concentration is seen to remain almost constant with increase in
sorbent injection for post combustion sorbents
 This could be due to:
 Limited residence time for the post combustion sorbent to react with SO2
 Temperature at which the post combustion sorbents were injected
25 January 2011 | IEAGHG Special Workshop on Oxyfuel Combustion
15
Concluding Remarks
 All of the 4 sorbents were effective in reducing SO3 during air-firing and oxyfuel
firing, with SO3 reduction up to 95%
 Post combustion sorbents were seen to be more efficient in reducing SO3; the
location at which SO3 formation is maximum
 Demonstrated that sorbent injection is a viable option for reduction of SO3 during
oxyfuel combustion
 Discrepancy in sulphur balance was seen to be higher during oxyfuel combustion
 ‘Missing’ sulphur appears to be lost in the furnace
 Results also indicate that the discrepancy in sulphur balance increases as the sulphur
capture potential of the system increases.
16
25 January 2011 | IEAGHG Special Workshop on Oxyfuel Combustion
Acknowledgements
Vattenfall AB
17
25 January 2011 | IEAGHG Special Workshop on Oxyfuel Combustion