dynamic simulation and exergy analysis for mode switching …ieaghg.org/docs/general_docs/5oxy...
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Dynamic simulation and exergy analysis for mode switching process in a 35MWth
oxyfuel pilot plant
Wei Luo, Qiao Wang, Zhaohui Liu, Chuguang Zheng
5th Oxy-fuel Combustion Research Network Meeting
Wuhan, China
Oct. 29, 2015
State Key Laboratory of Coal Combustion, Huazhong University of Science and Technology
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Outline
Overview of study on mode switching process
Model development and validation of 35 MWth oxy-fuel test facility
Dynamic simulation and analysisof mode switching process
Exergy analysis of different mode switching strategies
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09:3009:1008:5008:3008:1007:50
Flue-gas flow
O2 from ASU
Recycled flue-gas flow
Flue-gas recycle damper
Intake air damper
Oxidant flow
Air flow
14.2 14.4 14.6 14.8
0
20
40
60
80
100
Valve
ope
ning
(%)
Time (h)
Air vale Recycle valve Stack valve Main oxygen valve Primary oxygen valve Secondary oxygen valve
Transition operation
Background
Air Mode Oxy-fuel ModeTransition
Simultaneous operation Experimental study-TWO strategies of mode switching process Step and step
Vattenfall 30 MWth 3Babcock & Wilcox 30 MWth 1
1. McCauley et al., GHGT9, 2009 ; 2. Uchida et al., 2nd OCC, 2011 ; 3. Frank Kluger et al., GHGT-10, 2011; 4. Zheng et al., 3rd OCC, 2013
Mode Switching Process
Callide 30 MWe 2 HUST 3MWth 4
-Valves and dampers operate at the same time-Process is more stable
-Sequence run step by step-In case of jam, the step will stop
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Background Simulation study
5 10 15 20 25 30 35
0
20
40
60
80
100
Valve
ope
ning
(%)
Time (Min)
Recirculation valve Stack valve Air valve Main oxygen valve Primary oxygen
Transition operation
HUST 3MWth 1
QUESTION: The efficiencies of these two methods haven’t been evaluated yet.
-Develop a dynamic model based on a 35 MWth Oxy-fuel pilot plant-Conduct the simulation of the mode switching process-Evaluate the efficiency with exergy analysis
TARGET and STEPS:
1. Luo et al., Energy Procedia, 2015
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Outline
Overview of study on mode switching process
Model development and validation of 35 MWth oxy-fuel test facility
Dynamic simulation and analysisof mode switching process
Exergy analysis of different mode switching strategies
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Roadmap for Oxy-fuel R&D in China
Fundamental Study
300kWt small pilot studyBurner development
Data collection and OptimizationThermal Design
3MWt large pilot study7000T/a full chain validationASU-CPU couplingFGC and drying
35MWt pilot plant0.1 million ton captureASU-power generation integration and optimization
200 - 600MWe full demo.Millions ton CCS
2020
2014
2010
2005
1995
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New Features of 35 MWth Pilot Plant
3 MW1 35MWCoal preparation system No Intermediate storageBoiler island Tube bank Drum; WaterwallGas cleaning system Bag filter,scrubber,condenser Bag filter,scrubber,condenser,GGHFlue gas recycle system Dry Dry and wet
Air
Flue GasOxygenAir/Cold Recycle Flue GasWater
Cooling Tower
`
Primary Air
Secondary Air
OFATube
bank 1Tube bank
3
Tube bank 2
Air Separation Unit
Primary Fan Recycle Fan
CompressionPurification
Unit
Induced Draft Fan
CondenserScrubber
Stack
Bag Filter
Flue gas Preheater
Induced Draft Fan
Coal Bunker
CoolingTower
Pump
3MW full chain system 35MW pilot plant
Coal preparation system Boiler island Gas cleaning system Flue gas recycle system
1. Luo et al., International Journal of Greenhouse Gas Control, 2015
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Model Development
Flue gas recycle system
Scrubber Condenser
Boiler island
PA
SAOFA
Ash Filter
The process model mainly consists of boiler island, gas cleaning system and flue gas recycle system.
Modeling Tool: Aspen Plus and Aspen Dynamics
Oxygenfrom ASU
CoalfromCPS
Flue gasto
StackGas cleaning system
Ambient air
Ambient air
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Model Description
System Device ModelBoiler island Burner Rstoic
Drum User-defined Drum ModelWater wall (gas side) User-defined Radiation
ModelSuperheater/Economizer Heater/HeatX
Gas cleaning system Ash Filter Split ModelScrubber Split ModelFlue gas condenser Split Model
Flue gas recycle system
Pipes Pressure drop modelValves Valves ModelFans Compressor Model
Model description
1. Astrom et al., Automatica, 2000 ; 2. Kim et al., International Communications in Heat and Mass Transfer, 2005
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Model Input Coal property
Cad Had Sad Nad Oad Mad Vad FCad Aad Qad(kJ/kg,HHV)
57.48 3.29 0.68 0.86 5.59 1.31 22.67 45.23 30.79 22390
Transformed components (required for dynamic model)
Basic inputs needed in the simulation
C14H10 C12H10 O2 N2 S H2O Ash High heat value (kJ/kg)
55.28 0.04 6.76 0.86 0.68 5.59 30.79 22550
Coal flowrate (t/h) 4.38 SO2 scrubber efficiency 0.90
Air/Oxygen excess ratio 1.05 Fan isentropic efficiency 0.85
Recycle ratio 0.716 Oxygen purity 0.99
Total feedwater flowrate (t/h) 32 Oxygen pressure (KPa) 50
Feedwater temperature (°C) 108 Oxygen temperature / (°C) 15
Property methods
Proximate and ultimate analysis of coal (Air dried basis, wt%)
Gas side Peng-Robinson Water side SteamNBS
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Steady State Model ValidationMass Balance
Flue gas composition Test Model Difference %
O2 (%) 3.1 3.1 0
CO2 (%) 15.3 15.0 -1.9
NO (ppm) 165 175 6.1
CO (ppm) 365 380 4.2
SO2 (ppm) 1022 1062 3.9
Flue gas composition Test Model Difference %
O2 (%) 2.8 2.8 0
CO2 (%) 81.0 80.6 -0.5
NO (ppm) 300 312 4.0
CO (ppm) 651 686 5.3
SO2 (ppm) 1559 1653 6.0
Air Mode
Oxy Mode
The Differences between Test and Modelwere less than 2%
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Steady State Model Validation Energy Balance in Air-mode
Tg : Gas temperatureTw: Water temperatureQ : Heat duty
T1 T2 T3 T40
200
400
600
800
Tem
pera
ture
(Wat
er s
ide)
(C)
Tem
pera
ture
(Gas
sid
e) (C
)
Test Model
0
100
200
300
400
500
600
Qw Qhsh Qlsh Qeco0
4
8
12
16
20
Test Model
Heat
dtu
y (M
W)
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Steady State Model Validation Energy Balance in Oxy-mode
Tg : Gas temperatureTw: Water temperatureQ : Heat duty
T1 T2 T3 T40
200
400
600
800
Tem
pera
ture
(Wat
er s
ide)
(C)
Tem
pera
ture
(Gas
sid
e) (C
)
Test Model
0
100
200
300
400
500
600
Qw Qhsh Qlsh Qeco0
4
8
12
16
20 Test Model
Heat
dtu
y (K
W)
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Dynamic Model validation (1)
Heat load step change
0 5 10 15 20 25 304.2
4.4
4.6
4.8
Test Model
Coal
flow
rate
(t/hr
)
Time(min)
0 5 10 15 20 25 30650
700
750
800
850
Gas
tem
pera
ture
(C)
Time(min)
400
410
420
430
440
450
Coal flowrate Gas temperature
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Dynamic Model validation (2)
16 17 18
0
20
40
60
80
100
Valve
ope
ning
(%)
Time (h)
Primary oxygen valve Secondary oxygen valve Primary air damper Secondary air damper Stack damper Pramary RFG damper Secondary RFG damper
0 1 2
0
20
40
60
80
100
Simultaneous operation
Valve
Ope
ning
(%)
Time (h)
Primary oxygen valve Secondary oxygen valve Primary air damper Secondary air damper Stack damper Pramary RFG damper Secondary RFG damper
Valve opening Gas flowrate
Test
Model Model
Test
Mode Switching Process
16 17 180
10
20
30
40
Gas
flow
rate
(t/h
)
Time (h)
Secondary gas Secondary RFG Primary oxygen Secondary oxygen Primary gas
0 1 20
10000
20000
30000
40000
Gas
Flo
wrat
e (k
g/hr
)
Time (h)
Secondary gas Secondary oxygen Primary oxygen Secondary RFG Primary gas
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Outline
Overview of study on mode switching process
Model development and validation of 35 MWth oxy-fuel test facility
Dynamic simulation and analysisof mode switching process
Exergy analysis of different mode switching strategies
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Mode Switching Strategies
Basic control requirements for combustion and flue gas system(1) Flue supply stable(2) Furnace draft stable(3) Primary gas pressure stable
Control requirements for mode switching process(1) Boiler outlet oxygen concentration :2 ~5%(2) Oxygen concentration in primary gas :15~21%, target value 18%(3) Oxygen concentration secondary gas: 21~35%, target value is 29%
Optimized control requirements(1) The fluctuation of primary gas volume:less than 5% in one operation(2) The oxygen concentration fluctuation in primary gas, secondary gas and boiler inlet gas:
less than 3% in one operation
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Mode Switching Strategies
Operating devicesStep by step strategy Simultaneous strategy
Phase I Phase II
Secondary recycle damper
Secondary oxygen valve
Secondary air damper
Stack damper
Primary oxygen valve
Primary recycle damper
Primary air damper
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Mode Switching Process Simulation
Valve opening
Simultaneous operationStep and step
After 30 minutes’operation, all the valves and dampers reached the same opening
0.0 0.5 1.0 1.5
0
20
40
60
80
100
Valve
Ope
ning
(%)
Time (h)
Stack damper Secondary RFG damper Pramary RFG damper Secondary air damper Primary air damper Secondary oxygen valve Primary oxygen valve
0.0 0.5 1.0 1.5
0
20
40
60
80
100
Valve
Ope
ning
(%)
Time (h)
Stack damper Secondary RFG damper Pramary RFG damper Secondary air damper Primary air damper Secondary oxygen valve Primary oxygen valve
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Mode Switching Process
Species concentration
Simultaneous operationStep and step
After the transition operation, CO2 concentration continued to increase due to flue gas recycle and reached 80%.
The final oxygen concentration in primary and secondary gas meet the control requirement.
0.0 0.5 1.0 1.50.0
0.2
0.4
0.6
0.8
Conc
entra
tion
(km
ol/k
mol
)
Time (h)
CO2 O2 SO2 PO2
0.0 0.5 1.0 1.50.0
0.2
0.4
0.6
0.8
Conc
entra
tion
(km
ol/k
mol
)
Time (h)
CO2 O2 SO2 PO2
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Mode Switching Process
After the operation, the furnace outlet temperature increased slightly.
Flue gas temperature
Simultaneous operationStep and step
0.0 0.5 1.0 1.50
200
400
600
800
Tg1 Tg2 Tg3 Tg4
Tem
pera
ture
(C)
Time (h)0.0 0.5 1.0 1.5
0
200
400
600
800
Tg1 Tg2 Tg3 Tg4
Tem
pera
ture
(C)
Time (h)
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Mode Switching Process
After the operation, the steam temperature remained stable.From above results, it was indicated that both strategies could achieve successful
mode switching process. The difference in efficiency?
Water-steam temperature
Simultaneous operationStep and step
0.0 0.5 1.0 1.50
100
200
300
400
500
Tw1 Tw2 Tw3 Tw4
Tem
pera
ture
(C)
Time (h)0.0 0.5 1.0 1.5
0
100
200
300
400
500
Tw1 Tw2 Tw3 Tw4
Tem
pera
ture
(C)
Time (h)
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Outline
Overview of study on mode switching process
Model development and validation of 35 MWth oxy-fuel test facility
Dynamic simulation and analysisof mode switching process
Exergy analysis of different mode switching strategies
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Exergy Calculation
Exergy calculation principles Material exergyEx = Ech + Eph + Emix
Energy exergyEx = W
Heat exergyEx = (1-T0/T) ·Q
,( )och i ch iE F E= •∑
[ ( ) ( )] [ ( ) ( )]o o o oph i i i i o i i i iE F H F H T F S F S= • − • − • • − •∑ ∑ ∑ ∑
[ ( )] [ ( )]mix i i o i iE F H F H T F S F S= • − • − • • − •∑ ∑
Program using ACM and embed into Aspen Dynamics 11. Luo et al., Fuel, 2015
Exergy calculation method Calculation range
Total exergy destruction Boiler island
Exergy in Exergy out Exergy destruction
Gas cleaning system Exergy in Exergy out Exergy destruction
Gas recycle system Exergy in Exergy out Exergy destruction
Exergy_destruction = Exergy _in – Exergy_out
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Exergy Destruction Results (1/3)
The exergy destruction increased as the mode switching proceeded;The total exergy destruction in simultaneous control is smaller.
0.0 0.5 1.0 1.50.50
0.55
0.60
0.65
0.70
0.75
Exer
gy d
estru
ctio
n (x
108 G
J/h)
Time (h)
Simultaneous Step by step
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Exergy Destruction Results (2/3)
The exergy destruction in boiler island was much greater than that in other two systems. Thus, the variation tendency of exergy destruction in boiler island dominated the total exergy destruction.
0.0 0.5 1.0 1.50.0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
Boiler island Gas cleaning system RFG system
Exer
gy d
estru
ctio
n (x
108 G
J/h)
Time (h)
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Exergy Destruction Results (3/3)
The comparison of detailed exergy analysis in boiler island indicated that the greater exergy destruction under step by step strategy resulted in higher total exergy destruction.
0.0 0.5 1.0 1.50.0
0.5
1.0
1.5
2.0
Exer
gy (x
108 G
J/h)
Time (h)
Exergy_in Exergy_out Exergy_destr
SimultaneousStep by step
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Conclusion
Both step-by-step and simultaneous strategies could achieve successful mode switching process.
The exergy analysis results indicate that simultaneous mode switching strategy has lower exergy destruction.
The dynamic model based on the pilot plant could simulate the process very well, which provides a good platform for other study like control system design, operation optimization.
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Thank you foryour attention!