dynamic simulation and exergy analysis for mode switching …ieaghg.org/docs/general_docs/5oxy...

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

国家重点实验室评估

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


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


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


Outline






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


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


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


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


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


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%


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)


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)


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


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


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


Outline






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


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


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



Species concentration


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



After the operation, the furnace outlet temperature increased slightly.

Flue gas temperature


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)



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


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)


Outline






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


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



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)



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


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.


Thank you foryour attention！

dynamic simulation and exergy analysis for mode switching …ieaghg.org/docs/general_docs/5oxy...

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