The Oxyfuel Process with Circulating Fluidised Bed ...
Transcript of The Oxyfuel Process with Circulating Fluidised Bed ...
Hamburg University of Technology
The Oxyfuel Process with Circulating Fluidised Bed Combustion and Cryogenic Oxygen Supply
September 13th 2013 – 3rd Oxyfuel Combustion Conference
C. Günther
M. Weng
A. Kather
Institute of Energy Systems
Hamburg University of TechnologyInstitute of Energy Systems
• Huge bandwidth of possible fuels
• Emission reduction by primary measures
▸ Low combustor temperatures and air staging reduce significantly the amount of NOx produced during combustion
▸ SO2-emissions can be reduced by in-situ desulphurisation
• Oxyfuel Next to the flue gas the circulated solids can be used as a heat sink for the process (in contrast to pulverised coal firing)
Potential to reduce the amount of flue gas recirculated
Advantages of Circulating Fluidised Bed Boilers
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Hamburg University of TechnologyInstitute of Energy Systems
Available Heat Sinks for Oxyfuel Processes
PC:
CFBC:
TO2
TFG-Recirculation
Tadiabat
TCoal Q
TO2
TFG-Recirculation
TCC
TCoal CHEQCCQ
EHEQTSolids-
Recirculation
2/3
1/3
?
?
CC – Combustion ChamberEHE – External Heat Exchanger CHE – Convective Heat
Exchanger
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Hamburg University of TechnologyInstitute of Energy Systems
• Link of EBSILON and ASPEN via ProgDLL allows the simultaneous execution of both software applications
Input CO2 Processing Unit• Composition
• FlowOverall Process CO2 Processing Unit
Process Evaluation• Transferred heat quantities
• Gas compositions• Efficiencies
• etc.
Input Overall Process• Power requirements
• Cooling demand• Steam demand
• CO2 purity
Software and Simulation
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Hamburg University of TechnologyInstitute of Energy Systems
Process Scheme
Air
Vent gas
Air Separation Unit (ASU)
N2
O2
FuelInerts
FG-Recirculation
H2O
FG-Drying
CO2-Liquefaction
Nearly pure CO2
Ash
FG-Recirculation
Goal
Identification of main influencing variables on feasibility and efficiency of the process under realistic boundary conditions
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Hamburg University of TechnologyInstitute of Energy Systems
• State-of-the-art power plant with EHE (460 MWel,gross – about 1000 MWth)
• South American hard coal (El Cerrejón – Burnout 99 %)
• CC-outlet: 880 °C
• EHE-outlet: 550 °C
• Steam parameters: 275 bar / 54 bar; 560 °C / 580 °C (SH/RH)
• Feed water temperature: 290 °C ; FG outlet temperature (CHE) 340 °C
• Temperature of recirculation (beneficial as hot as possible, limited by available fans)
▸ To CC: about 340 °C; To EHE: about 150 °C (preheated to 290 °C)
• Oxygen ratio 1.15 - Oxygen purity 95 volume-%- 2 % air ingress at the convective heat exchangers- 0.5 % air ingress at the electrostatic precipitator
Basic Assumptions I
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Hamburg University of TechnologyInstitute of Energy Systems
CC- Cross Sectional Area
▸ Reduction of the FG-Recirculation leads to a smaller cross sectional area of the CC and the CHE (u0=const.)
▸ Same effect for higher velocities leading to:
▸ Less available space for heat transferring areas walls and additional equipment in the combustor (e.g. wing walls)
▸ Differences to Lagisza depend on simulated coal and u0
30 40 50 60 7050
100
150
200
250
300 4 m/s5 m/s6 m/s
Cros
s Se
ctio
nal A
rea
of th
e CC
in m
²
FG - Recirculation in %
Area of Lagisza (27,6 m x 10,6 m)
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Hamburg University of TechnologyInstitute of Energy Systems
Air Case
▸ About 32,5 % of the heat are transferred in the CHE
▸ Approximately 28,5 % are transferred in the CC (wing-walls with ribbed tubes and platen superheater)
▸ Remaining heat is transferred in the EHE (39 %)
Oxyfuel Air
30 40 50 60 700
102030405060708090
100
CHE
CC
Tran
sfer
red
Heat
Qua
ntitie
s in
%
FG - Recirculation in %
EHE
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Hamburg University of TechnologyInstitute of Energy Systems
30 40 50 60 700
102030405060708090
100
CHE
CC
Tran
sfer
red
Heat
Qua
ntitie
s in
%
FG - Recirculation in %
EHE
Oxyfuel – Convective Heat Exchanger (CHE)
▸ Temperatures:TCHE, in = 880 °C, TCHE, out = 340 °C
▸With a decreasingFG-recirculation there is less massflow through the CHE
▸ Leading to less heat transferred in the CHE
Oxyfuel Air
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Hamburg University of TechnologyInstitute of Energy Systems
Oxyfuel – Combustion Chamber (CC) II
▸ A decrease in the FG-Recirculation leads to a smaller cross-sectional area (u0=const.)
▸ Reduction of heat transferring area (wall and equipment)
▸ Less heat can be withdrawn out of the CC
▸More heat has to be transferred in the EHE
30 40 50 60 700
102030405060708090
100
CHE
CC
Tran
sfer
red
Heat
Qua
ntitie
s in
%
FG - Recirculation in %
EHE
Oxyfuel Air
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Hamburg University of TechnologyInstitute of Energy Systems
Oxyfuel – External Heat Exchanger (EHE) I
▸ The amount of heat transferred in the EHE increases with a reduction of the FG-Recirculation
▸ The theoretical minimum of FG-Recirculation is about 35 %
▸ The whole recycled FG is necessary to fluidise the EHE
▸ CC O2-Conc.in the CC nozzle floor exceeds limits hot-spots in the bed
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102030405060708090
100
CHE
CC
Tran
sfer
red
Heat
Qua
ntitie
s in
%
FG - Recirculation in %
EHE
Oxyfuel Air
Min
imum
Flu
idis
atio
nof
EHE
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Hamburg University of TechnologyInstitute of Energy Systems
Oxyfuel – External Heat Exchanger (EHE) II
▸ The restricting limit for the range of operation of the Oxyfuel-CFB is the state-of-the-art of the EHE
▸Geometrical arrangement around the boiler is limited
▸ Design of Loop-Seal and EHE
▸Minimum for the FG-Recirculation > 60 %
30 40 50 60 700
102030405060708090
100
CHE
CC
Tran
sfer
red
Heat
Qua
ntitie
s in
%
FG - Recirculation in %
EHE
Oxyfuel Air
Min
imum
Flu
idis
atio
nof
EHE
Geo
met
rie a
ndD
esig
n
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Hamburg University of TechnologyInstitute of Energy Systems
Oxyfuel – External Heat Exchanger (EHE) III
▸Minimum for the FG-Recirculation ≈ 60 %
▸ Changes in the transferred heat due to Oxyfuel conditions:
▸ CHE ≈ 25 % (- 7,5 %-pt.)
▸ CC≈ 22 % (- 6,5 %-pt.)
▸ EHE≈ 53 % (+14 %-pt.) + 1/3
30 40 50 60 700
102030405060708090
100
CHE
CC
Tran
sfer
red
Heat
Qua
ntitie
s in
%
FG - Recirculation in %
EHE
Oxyfuel Air
Min
imum
Flu
idis
atio
nof
EHE
Geo
met
rie a
ndD
esig
n
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Hamburg University of TechnologyInstitute of Energy Systems
30 40 50 60 700
102030405060708090
100
Volu
met
ric G
as C
once
ntra
tions
at t
he
Entra
nce
of th
e G
PU in
vol
.-% (d
ry)
FG - Recirculation in %
0102030405060708090100
O2 C
once
ntra
tion
at th
e No
zzle
Flo
or
of th
e CC
in v
ol.-%
(dry
)
Oxyfuel – Selected Flue Gas Concentrations
▸ Due to air ingress there is a maximum for the CO2 concentration of 80 %
▸ For lower recycle rates the CO2 concentration decreases due to an increase in residual oxygen
▸ The O2 concentration in the flue gas increases accordingly
▸ The O2 concentration at the CC nozzle floor in-creases for decreasing FG-Recirculation
CO2
O2
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Hamburg University of TechnologyInstitute of Energy Systems
• Assumptions
▸ Live steam parameter: 275 bar, 560 °C
▸ Reheat: 54 bar, 580 °C
▸ Condenser pressure: 45 mbar
▸ ASU: 236 kWh/tO2,pure (adiabatic compression)
• Calculated efficiencies for comparisons
Air Case PC: ηel,net ≈ 44.2 %
Air Case CFBC: ηel,net ≈ 43.3 %
Oxy-PC: ηel,net ≈ 34,1-35,0 %
Oxy-CFBC: ηel,net ≈ 34,1 % - 34,4 %
Oxyfuel – Efficiencies I
Δη = 0,9 %-pts.
Δη = 0 - 0,6 %-pts.
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Hamburg University of TechnologyInstitute of Energy Systems
30 40 50 60 7047,5
48,0
48,5
49,0
49,5
50,0
Elec
tric
Gro
ss E
fficie
ncy
in %
FG - Recirculation in %
33,0
33,5
34,0
34,5
35,0
35,5
Elec
tric
Net E
fficie
ncy
in %
Oxyfuel – Efficiencies II
▸ For the chosen design the efficiency is at34,4 % and by this comparable to PC-firing
▸ Slight demand increase for ASU and GPU
▸ The loss for higher recirculation is due to CC-Compressor
▸ The electrical demand for the EHE fan is dominated by the CC-compressor for higher FG-Recirculation
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Hamburg University of TechnologyInstitute of Energy Systems
• The efficiencies of the CFBC are comparable to those of pulverised coal combustion, as long as no secondary flue gas treatment is necessary
▸ Efficiency loss in the order of 8 to 10 %-pts
• Primary goal Reduction of FG-Recirculation seems realisable, but is limited by:
▸ The fluidisation of the CC and EHE,
▸ Arrangement of the boiler,
▸ Design of Loop-Seal and EHE,
▸ The solids entrainment
Summary
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Hamburg University of TechnologyInstitute of Energy Systems
The Project
COORETEC-Cooperative Project: ADECOS ZWSF„Oxyfuel-Process with Circulating Fluidised Bed Boiler“
Duration: 1st January 2010 - 31st March 2013
Institutes: IET TU Hamburg HarburgIFK Universität StuttgartVWS TU Dresden
Industry Partners: EnBW Kraftwerke AGE.ON Energie AGRWE Power AGVattenfall Europe Generation AG & Co. KGLinde AGDoosan-Lentjes
Thank you for yourattention!!
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