Development of 2nd generation oxyfuel CFB technology
– laboratory and pilot scale combustion experiments in
high oxygen concentration
VII Liekkipäivä, 30.1.2014, Tampere
Heidi Saastamoinen and Toni Pikkarainen
VTT Technical Research Centre of Finland
Content
Introduction to O2Gen – project
Experimental work and preliminary results:
Bench scale BFB
Pilot scale CFB
What next
2
O2Gen
Optimization of Oxygen-based CFBC Technology with CO2 capture
Project under EU 7th FP
started 10/2012, duration 3 years
total budget 11.9 M€ (EU contribution 6.6 M€)
Consortium contains 11 partners
4 companies and 7 research organisations
from Spain (5), Finland (3), France (1), Italy (1) and Poland (1)
3
O2Gen
Optimization of Oxygen-based CFBC Technology with CO2 capture
The project objective is to demonstrate the concept of the 2nd
generation oxyfuel combustion that reduce significantly (around
50%) the overall efficiency penalty of CO2 capture into power
plants, from approximately 12 to 6 %-points.
The efficiency improvements will be achieved by
the use of higher O2 concentrations in oxyfuel combustion reducing
the flue gas recirculation and energy penalty (also enabling boiler
size reduction and thus cost reductions)
integration of ASU (air separation unit) and CPU (CO2 processing
unit) with the power plant reducing energy penalties
more efficient oxygen production, and CO2 purification and
compression steps
As a result, conceptual design for 600 MWe scale 2nd generation
oxygen-fired CFB power plant will be created
4
O2Gen
Optimization of Oxygen-based CFBC Technology with CO2 capture
Motivation:
Decrease the costs of CCS and making the way to towards competitive
commercialization of oxy-CFB based CCS technology
5
Fluidised bed test facilities
Bench scale BFB and pilot scale CFB
http://www.vtt.fi/img/research/ene/combustion/VTT.html
6
Fuel impulse tests
Objectives and test matrix
Objectives in fuel impulse tests are to solve how high O2 concentrations
affect the
•
char reactivity of coal
•
emission (NO, CO, SO2) formation
Test
Spanish Anthracite 1
Spanish Anthracite 2
Spanish Anthracite 3
Spanish Anthracite 4
Spanish Anthracite 5
Spanish Anthracite 6
Spanish Anthracite 7
Spanish Anthracite 8
Polish Bituminous coal
Polish Bituminous coal
Polish Bituminous coal
Polish Bituminous coal
Polish Bituminous coal
Polish Bituminous coal
Polish Bituminous coal
Polish Bituminous coal
1
2
3
4
5
6
7
8
Fraction, mm
0.5-2
0.5-2
0.5-2
0.5-2
4-8
4-8
4-8
4-8
0.5-2
0.5-2
0.5-2
0.5-2
4-8
4-8
4-8
4-8
Gas composition for both prim and sec
O2 feed (%)
CO2 feed (%)
5
15
30
50
5
15
30
50
5
15
30
50
5
15
30
50
95
85
70
50
95
85
70
50
95
85
70
50
95
85
70
50
T
850
850
850
850
850
850
850
850
850
850
850
850
850
850
850
850
prim, (CO2+O2), Nl/min sec, (CO2+O2), Nl/min
5
5
5
5
5
5
5
5
5
5
5
5
5
5
5
5
5
5
5
5
5
5
5
5
5
5
5
5
5
5
5
5
7
Bench scale fuel impulse tests: O2 responses
• When the oxygen concentration in
primary and secondary gas
increases combustion rate
increases
• Combustion of volatiles, char
gasification and combustion occur
almost simultaneously in high
oxygen combustion, whereas in
low concetrations and with larger
particles these phases separate
• Combustion of bituminous coal
occurs faster compared to
anthracite due to higher volatile
content of fuel
8
Bench scale fuel impulse tests: Temperature, CO
• Peak temperature increases along with the increase in oxygen concentration
• Char gasification in CO2 environment increases CO formation
• CO formation is controlled by feeding secondary gas
• The less oxygen is fed
• the more CO forms
• the longer CO forms
9
Fuel impulse tests: Nitrogen emission formation
NO formation:
• The rate of NO formation increases
along with the increase in oxygen
feed.
• Formation of NO strictly follows the
increase in temperature.
• There no significant change in total
amount of N released although the
rate of NO formation increases
• In 50% oxygen feed N2O
formation increases and NO
formation decreases
10
CFB-pilot tests
Anthracite-petcoke blend
Limestone Fuel power Ca/S total Bed temp. Feed gas O2 Primary gas O2 Secondary gas O2 Primary gas
type
kW
mol/mol
ºC
% wet
% wet
% wet
share-%
55
3.1
889
21
21
21
79
2.8
873
28
28
28
121
2.6
918
42
42
42
118
2.6
856
42
42
42
70
121
2.7
817
42
42
42
121
2.7
863
42
48
29
118
2.5
853
42
37
55
Estrella
Fuel
blend
Anthracite/Petcoke
70/30 w-%
Test Mode
# air/oxy
1
air
2
3
4
oxy
5
6
7
Test matrix with anthracite/petcoke blend contained 7 tests:
Test 1: air reference, medium temperature
Test 2: oxyfuel 28% (ref. to 1st generation design), medium temperature
Tests 3-5: oxyfuel 42% (ref. to 2nd generation design), 3 temperature levels
Test 6-7: Oxyfuel 42%, oxygen staging (prim. O2 share 60...80%)
Total feed gas flow and prim./sec. gas share (fluidisation conditions)
were constant
Also Ca/S-ratio (limestone calcium to fuel sulphur ratio, mol/mol) was
kept as constant as possible
11
CFB-pilot tests
Unburned carbon (UBC) losses
940
1.8
UBC to fly ash
UBC to bottom ash
1.6
Bed temperature
920
UBC [% LHV]
900
1.2
1.0
880
0.8
860
Temperature [ºC]
1.4
0.6
840
0.4
820
0.2
800
0.0
Test 1
Test 2
Test 3
Test 4
Air
Oxy 28%
Oxy 42% - high
T
Oxy 42% medium T
Test 5
Test 6
Test 7
Oxy 42% - low Oxy 42% - high Oxy 42% - low
T
prim. O2
prim. O2
In all tests UBC losses were low, <1.6 % of fuel LHV
The lowest UBC was measured from high temperature, high-O2 test 3, as expected
12
CFB-pilot tests
SO2 formation and capture – tests at medium temperature
SO2 emission [mg/MJ]
Calcium utilisation [%]
Ca/S total [mol/mol]
SO2 retention [%]
4.0
100
94.6
97.6
99.0
98.7
99.1
3.5
3.1
80
3.0
2.8
2.6
2.7
2.5
2.5
60
40
31
35
38
37
39
1.5
20
0
2.0
94
40
17
21
14
Test 1
Test 2
Test 4
Test 6
Test 7
Air
Oxy 28%
Oxy 42%
Oxy 42% - high
prim. O2
Oxy 42% - low
prim. O2
Ca/S total molar ratio
SO2 emission, Ca utilisation, SO2 retention
120
1.0
Lower SO2 emissions and better sulphur capture in high-O2 oxyfuel conditions (at ~860ºC)
Also at 28% oxyfuel conditions the sulphur capture was better than in air-firing
13
CFB-pilot tests
SO2 formation and capture – high-O2 oxyfuel conditions
SO2 emission [mg/MJ]
Calcium utilisation [%]
Bed temperature
SO2 retention [%]
940
160
920
120
900
100
98.2
99.0
98.7
99.1
880
91.3
863
856
80
853
840
60
817
40
38
38
20
0
860
820
34
37
39
Ca/S total molar ratio
SO2 emission, Ca utilisation, SO2 retention
918
140
800
31
17
140
21
14
Test 3
Test 4
Test 5
Test 6
Test 7
Oxy 42% - high T
Oxy 42% medium T
Oxy 42% - low T
Oxy 42% - high
prim. O2
Oxy 42% - low
prim. O2
780
Clear effect of temperature (tests 3-5), temperatures >850ºC were favored
O2-staging had no significant effect (tests 4 and 6-7)
14
CFB-pilot tests
SO2 formation and capture – calcination/carbonation
Bottom ash
46
30
43
25
40
20
37
15
34
10
31
5
28
0
CaCO3 [%]
CaO [%]
CaSO4 [%]
Ca utilisation
Test 1
Test 2
Air
Oxy 28%
0.42
13.77
15.64
30.5
4.17
18.28
23.38
35.1
Test 3
Test 4
Test 5
Oxy 42% high T
0.83
19.99
25.12
37.6
Oxy 42% medium T
1.67
20.08
27.84
38.1
Oxy 42% low T
32.50
2.08
19.08
34.0
Test 6
Test 7
Calcium utilisation [%]
Mass share [%]
35
25
Oxy 42% Oxy 42% high prim. O2 low prim. O2
2.50
1.67
18.69
19.35
24.99
26.22
36.9
39.3
At low temperature and high CO2 partial pressure, CaCO3 is not calcined to CaO (direct sulfation to CaSO4)
From the bottom ash analysis it can be seen that poor sulphur capture in test 5 was due to slow direct
sulfation of CaCO3 (main part remained as CaCO3)
15
CaCO3 – CaO equilibrium
1
Equilibrium curve according to Marion et al.
0.9
Test 1 Air
Test 2 Oxy 28%
0.8
CO2 partial pressure [atm]
Test 3 Oxy 42% - high T
0.7
Test 4 Oxy 42% - medium T
Test 5 Oxy 42% - low T
0.6
Test 6 Oxy 42% - high prim. O2
0.5
Test 7 Oxy 42% - low prim. O2
0.4
CaCO3
CaO
0.3
0.2
0.1
0
700
725
750
775
800
825
850
875
900
925
950
975
Temperature [°C]
16
CFB-pilot tests
Formation of nitrogen oxides
NO emission [mg/MJ]
N2O emission [mg/MJ]
Bed temperature
940
80
78
918
920
70
69
900
889
873
50
54
880
863
856
40
853
860
840
30
817
24
20
16
10
9
0
820
21
20
14
12
Temperature [ºC]
Emissions [mg/MJ]
60
18
15
800
8
5
780
Test 1
Test 2
Test 3
Test 4
Air
Oxy 28%
Oxy 42% - high
T
Oxy 42% medium T
Test 5
Test 6
Test 7
Oxy 42% - low T Oxy 42% - high Oxy 42% - low
prim. O2
prim. O2
NO and N2O emissions were clearly higher in air-firing
In high-O2 tests:
NO was higher and N2O lower than in 28% oxyfuel at comparable conditions
NO increased and N2O decreased with increasing temperature
O2-staging had relatively small effect on NO or N2O
17
Next
Second set of bench scale tests
Temperature changes (750ºC & 950ºC) in high oxygen
concentration combustion
Model for bench scale combustor under development
Target: to obtain parametres for pyrolysis, char gasification, char
combustion and reactions of nitrogen species
Particle model approach for bench scale results
Bench scale modelling results will be implemented to one
dimensional CFB furnace model for pilot scale CFB
validation of the model with the data from air-firing and oxy-firing
tests under widened operation range (O2 concentration 21...42 %)
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ACKNOWLEDGEMENT
The research leading to these results has received funding from the
European Union Seventh Framework Programme FP7/2012 under grant
agreement no 295533.
Projects’ website:
www.o2genproject.eu
More about VTT’s combustion research and services:
http://www.vtt.fi/img/research/ene/combustion/VTT.html
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