High Temperature Solid Cycles Research Topics at IC ...Inert Reaction cycle t Elemental sulphur SO2...
Transcript of High Temperature Solid Cycles Research Topics at IC ...Inert Reaction cycle t Elemental sulphur SO2...
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High Temperature Solid Cycles Research Topics at IC:
Reactions of Sulphur during chemical looping
combustion using Iron
Zili Zhanga, Nick Florinb, Paul S. Fennella
a Dept. of Chemical Engineering and Chemical Technology
Imperial College London
Cambridge, September 2013
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Determine the effect and fate of sulphur in chemical looping
combustion system
When sulphur (in the form of H2S) introduced to the system:
-Sulphur products distribution in air and fuel reactor?
-Effect of sulphur on kinetics and long term reactivity of Iron oxide?
H2S
3𝐹𝑒2𝑂3 + 𝐶𝑂 ↔ 2𝐹𝑒2𝑂3 + 𝐶𝑂2 ∆𝐻°1023𝐾 = −44.3𝑘𝐽/𝑚𝑜𝑙
2𝐹𝑒3𝑂4 +1
2𝑂2 ↔ 3𝐹𝑒2𝑂3 ∆𝐻
°1023𝐾 = −238.4𝑘𝐽/𝑚𝑜𝑙
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Detail of closed Fluidised Bed Reactor
Steam
Inlet tubes
Quartz Tube
Supporting Ring
Quartz
Lining Tube
Central Bed Thermal Couple
48.3mm od x 7.13mm wt
Incolloy Tube
504 mm Heating section
304mm
Copper Electrode
Copper Electrode
Half Moon Positioning
Ring
Half Moon Positioning Ring
Flat copper o-ring
Flat copper o-ring
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Investigation of kinetics of Iron oxide reduction with CO in
the presence of H2S
Type of
Experiments
Fe2O3selection
Acid treated
Sand
T P F Reduction
gas
Oxidation
gas
Fe2O3 to
Fe3O4kinetics with
CO0.5g(300-
425µm)
40g(500-
710µm)
723-973K
1bar 2.5 ×Umf
N2+CO+CO2(80-85%, 1-
5%, 15%
N2+Air(82
%, 18%)
Fate and
effect of H2S
addition
773-923K
N2+CO+CO2+H2S(80-
85%, 1-5%,
15%,300-
450ppm)
N2+Air(82
%, 18%)
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Typical cycles profile of Iron oxide reduction with CO in the
presence of H2S at 823 K, 1 barCalibration
&Ambient InputInert Input
Inject Fe2O3
10 redox cycles
*CO,CO2 on the left axes (vol%), all sulphur compounds on the right axes(ppm).
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Detailed look at cycle 4 of Iron oxide reduction with
CO in the presence of H2S at 823 K, 1 bar
Procedure:
Reduction Cycle:
N2 purge 120s
N2+CO2 120s
N2+CO2+CO+H2S 180s
Oxidation cycle:
N2 purge 120s N2+Air 240s
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0
20
40
60
80
100
120
140
0 1 2 3 4 5 6
rate
(1
0-6
mo
l/(g
*s)
)
Inlet mole fraction CO (vol. %)
maximum rate method(used in this work)
extrapolation method
literature results (Bohnet al., 2010)
Determine Rates of the reduction of Fe2O3 to Fe3O4
Left: a typical rate versus conversion graph for the reduction of Fe2O3 to Fe3O4 with
3 vol% CO 15 vol%CO2 at 823K
Right: Comparison of the maximum rate method used in this work with extrapolation
method and literature reference for reduction of Fe2O3 to Fe3O4 at 823KRef: BOHN, C. D., CLEETON, J. P., MÜLLER, C. R., DAVIDSON, J. F., HAYHURST, A. N., SCOTT, S. A. & DENNIS, J. S. 2010. The kinetics of the
reduction of iron oxide by carbon monoxide mixed with carbon dioxide. Aiche Journal, 56, 1016-1029.
0 0.2 0.4 0.6 0.8 10
20
40
60
80
Conversion(X)
r’(m
ol/
(s*g)
Rate,CO2
Rate,CO
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0
20
40
60
80
100
120
140
0 1 2 3 4 5 6
rate
(1
0-6
mo
l/(g
*s)
)
Inlet mole fraction CO (vol. %)
cycle3
cycle4
cycle5
Intrinsic rate constant Ki =565 (s-1), Effectiveness Factor=0.71 (Koverall was derived
using cycle 3-5).
Dependence of overall rate of Fe2O3 reduction on CO vol% at
823K
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Arrhenius plot showing the activation energy based on
overall rate constant k for the reduction of Fe2O3 to Fe3O4
4.00
5.00
6.00
7.00
8.00
0.12 0.14 0.16 0.18
lnk
(s-1
)
103/RT (mol/J)
cycle2, E=50.1 kJ/mol
cycle3, E=64.4 kJ/mol
cycle4, E=64.0 kJ/mol
cycle5, E=60.2 kJ/mol
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0 200 400 6000
3
6
9
12
15
Time (s)
Con
centr
ation (
%)
0
500
1000
1500
2000
2500
3000
Con
cen
tra
tion
(p
pm
)
H2S
SO2
COS
CO2
CO
O2
Reduction Oxidation
0 200 400 6000
3
6
9
12
15
Time (s)
Con
centr
ation (
%)
0
500
1000
1500
2000
2500
3000
Con
cen
tra
tion
(p
pm
)
H2S
SO2
COS
CO2
CO
O2
Reduction Oxidation
The different fates of sulphur before and after completion of
reduction of Fe2O3 to Fe3O4 at 823K, with 3vol%CO,300ppm H2S
*CO,CO2 on the left axes (vol%), all sulphur compounds on the right axes(ppm).
CO and H2S input for 50s (approaching
completion of transition from Fe2O3 to
Fe3O4)
CO and H2S input for 180s (120s after
complete completion of transition from
Fe2O3 to Fe3O4)
No SO2 release SO2 Release
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0
0.2
0.4
0.6
0.8
1
Ine
rt2
cycl
e1
cycl
e2
cycl
e3
cycl
e5
cycl
e8
cycl
e1
0
Inert Reaction cycle
mo
l/m
ol H
2S
inp
ut
Elemental sulphur SO2 release in oxidation
Conversion to COS Conversion to SO2
H2S unreacted
0
0.2
0.4
0.6
0.8
1
Ine
rt2
cycl
e1
cycl
e2
cycl
e3
cycl
e5
cycl
e8
cycl
e1
0
Inert Reaction cycle
mo
l/m
ol H
2S
inp
ut
SO2 release in oxidation Conversion to COS
Conversion to SO2 H2S unreacted
Sulphur product for the reduction of of Fe2O3 to Fe3O4 at 823K
with 3vol%CO, 300ppm H2S for 60s (left) and 180s (right)
Most of H2S was converted into SO2 in the fuel reactor in the 60s case (left),
while in the 180s case (right) most of the H2S was converted into FeS which
was released as SO2 later in air reactor.Elemental sulphur was detected in the downstream trap of the reactor using quantitative XRF analysis after being
dissolved in Toluene solvent.
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Sulphur reaction mechanism with iron
12Fe2O3+CO+H2S8Fe3O4+CO2+SO2+H2O 2Fe2O3+CO+H2S Fe3O4+CO2+FeS+H2O
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0
20
40
60
80
100
0 3 6 9 12
rate
(1
0-6
mo
l/(g
*s))
Cycles
Without H2S
50s, 300ppm H2S
60s, 300ppm H2S
180s, 300ppm H2S
60s, 450ppm H2S
Effect of H2S addition on the overall rate of Fe2O3 reduction at
823 K, 3% CO
• Increasing the residence time of H2S only has significant effect on the
reduction rate if the increase is after complete reduction
• Increasing H2S concentration has an adverse effect on the rate of
reduction.
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y = 0.9188x - 8.8762R² = 0.9994
y = 1.2985x - 8.976R² = 0.952
-12.0
-11.0
-10.0
-9.0
-8.0
-1.50 -1.00 -0.50 0.00
ln r
ate
(1
0-6
mo
l/(g
*s))
ln [CO] (mol m-3)
cycle4
cycle5
cycle8
cycle10
without H2S cycle3
without H2S cycle4
without H2S cycle5
Dependence of overall rate of Fe2O3 reduction on CO vol% at
823 K in the presence of 300 ppm H2S
The linear dependence of rate of reduction on [CO] is still satisfactory. The
rates of reaction in the presence of H2S are in general lower than that without
H2S presence
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Arrhenius plot based on overall rate constant k for the
reduction of Fe2O3 to Fe3O4 in the presence of H2S
A similar activation energy was obtained compared to the case without H2S
presence. The pre-exponential factor, however, was lower when H2S was
present.
5.00
5.50
6.00
6.50
7.00
0.12 0.13 0.14 0.15 0.16 0.17
lnk
(s-1
)
103/RT (mol/J)
cycle4, E=55.5 kJ/mol
cycle5, E=48.8 kJ/mol
cycle8, E=52.7 kJ/mol
cycle10, E=57.0 kJ/mol
without H2S cycle4
without H2S cycle3
without H2S cycle5
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Key Summary and Implications
• A closed-system fluidised-bed reactor has been designed and
constructed for the study of the effect and fate of sulphur in the CLC
cycle
• Experiments concerning Iron oxide reduction agree with the previous
work in Cambridge.
• The study of iron oxide reduction in the presence of H2S showed that
sulphation is nearly reversible.
• Good process control could avoid the production of SO2 in the air
reactor
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Summary and Implications
• The rate of iron oxide reduction started to be adversely
affected by H2S addition when reduction of Fe2O3 to Fe3O4was nearly completed (FeS formation became dominant).
• The linear dependency of rate of reduction of Fe2O3 to Fe3O4for CO was still satisfactory in the presence of H2S.
• Similar activation energies were obtained compared to the
case without H2S presence. The pre-exponential factor,
however, was lower when H2S was present.
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Acknowledgment
This work was financially supported by :
• The EPSRC under the “Joint UK – China Hydrogen Production
Network”. Project reference: EP/G06265X/1
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Thank you!
Q&A
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Sulphur product for the reduction of of Fe2O3 to Fe3O4 at 823K
with 3 vol%CO and 300ppm H2S for 60s (left) and 180s (right)
Most of H2S was converted into SO2 in the fuel reactor in the 60s case (left),
while in the 180s case (right) most of the H2S was converted into FeS which
was released as SO2 later in air reactor.Elemental sulphur was detected in the downstream trap of the reactor using quantitative XRF analysis after being
dissolved in Toluene solvent.
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
Inert1
Inert2
cycle1
cycle2
cycle3
cycle4
cycle5
cycle6
cycle7
cycle8
cycle9
cycle10
Inertcycle
Reac oncycle
mol/molH
2Sinput
H2Sunreacted ConversiontoSO2
ConversiontoCOS SO2releaseinoxida on
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
Inert1
Inert2
cycle1
cycle2
cycle3
cycle4
cycle5
cycle6
cycle7
cycle8
cycle9
cycle10
Inertcycle
Reac oncycle
mol/molH
2Sinput
H2Sunreacted ConversiontoSO2
ConversiontoCOS SO2releaseinoxida on
Elementalsulphur