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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
2
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
3
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
4
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
5
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
6
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)
7
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
8
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
9
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
10
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
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
11
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
12
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
13
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
14
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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