dynamic simulation of a cfb boiler system -...

Thermal Engineering Laboratory

Dynamic Simulation of a CFB

Boiler System

2015. 11. 05, Seoul, Korea

Sang Min CHOI

Thermal Engineering Lab

KAIST

71th IEA-FBC Technical Meeting

Introduction

Dynamic Simulation of a CFB Boiler System

Dynamic Performance Prediction of a CFB Boiler System

3

ü Dynamically changes mass,

energy flow and properties

ü Control system running

ü Dynamically changes mass,

energy flow and properties

ü Control system running

<External environment changes>

Load variation and a change of operating

conditions

<External environment changes>

Load variation and a change of operating

conditions

Dynamic performance

prediction is required

Dynamic performance

prediction is required

▪ Necessity of a Dynamic Model

▪ Modeling Considerations in CFB boiler with drum

ü Operation and Performance of a CFB

Boiler are determined by SG loop and

GS loop

ü These loops has to be considered for

exact performance prediction

ü This model considers gas flow, solid

flow and water-steam flow

SG loopWS loop


Model description


Modeling description (1)

5

▪ Dynamic sub-models of a 340MWe CFB Boiler

Solid-gas circulation loop model<Furnace: ①, ②>

<Return part: ③,④,⑤>

Water-steam circulation loop model(drum-downcoomer-riser tube)

<2’, 2’’>

Heat exchanger model(Convective heat exchanger)

<⑥,⑦,⑧,⑨,⑩>

Dynamic sub-modelsDynamic sub-models

§ The entire CFB boiler is divided into a finite number of dynamic model

(Solid-gas circulation loop model, water-steam circulation loop model, heat exchanger model)

§ Relevant theories, Numerical approach and physical conservation rules are applied in each

dynamic sub-model.



6

▪ Basic concept of heat and mass flow in a discretized heat exchanger

▪ Governing equation

( )uS

t xr frf ¶¶

+ =¶ ¶

1-D unsteady and no diffusion term

Ø Mass balance:

+ ∆ = + Ø Energy balance: + ∆ = + : in-out mass flow, mass transfer, generated mass by reaction

: in-out heat flow, heat transfer, reaction heat

ü Each side is connected in terms of heat

and mass flow

ü Mass-heat flow, heat transfer and heat

reaction are dynamically calculated

+ ∆ = +



7

▪ Transport Phenomena Modules<Solid-gas circulation loop>

Hydrodynamics of

fluidized bed

Bubbling fluidized Bed (Bubble vs. Emulsion)

Core-Annuls model (Core vs. Annulus)

Solid side behavior

Fragmentation, Attrition

Solid volume fraction

Solid-gas mass transfer

Solid circulation rate

Coal combustion

reaction

Devolatilization, Volatile combustion

Char combustion, CO combustion

<Water-steam circulation loop>

Drum loop model

(Astrom, 1999)

Mass and heat balance of drum and

downcommer-riser

Drum level

Discharged steam flow rate

<Heat transfer coefficient>Furnace Cluster renewal model

Cyclone, Loopseal Fitting data from operation data

Heat exchanger tube bank Tube bank heat transfer

▪ Numerical approachü Convergence condition: Mass and Temperature < 10 ü Calculation domain: Furnace (150 × 2), Heat

exchanger (80 × 1), Downcommer-riser

(20 × 1), Drum and Return part (0-D)

ü Time step : 0.5 sec


Model Develop and Dynamic Simulation Process

8

Develop sub-models(Each component)

Develop sub-models(Each component)

Open loop model(CFB Boiler System)Open loop model

(CFB Boiler System)Closed loop model(CFB Boiler System)Closed loop model(CFB Boiler System)

ü Solid-gas circulation loop

ü Water-steam circulation loop

ü Heat exchanger model

ü Each sub model is connected

according to mass and heat

flow (Model scope)

ü Controller is applied to open

loop model

▪ Model Develop Process

▪ Dynamic Simulation Process

Transient response of dynamic sub-models Dynamic behavior of total

boiler system(Open loop) Dynamic behavior of total

boiler system(Closed loop)

Operation simulation according to load level

Check each model validation !

Check control !

Check convergence of total boiler system !

Check with measured data !

Dynamic results


Transient response of sub-models (1)

10

-200 0 200 400 600 800 1000 1200 1400

840

880

920

960

1000

Furnace temperature Cyclone temperature+5 %

+45 °C

+40 °C

305 sec

Solid

-gas

tem

pera

ure [

°C]

Time [sec]

30

35

40

45

50

55 Fuel supply (Input condition)

Fuel

supp

ly [k

g/s]

-200 -100 0 100 200 300 400262

264

266

268

270

+10 %

+2 °C

160 sec

Temperature

Wat

er te

mpe

ratu

re [d

eg C

]

Time [sec]

22

24

26

28

30

32

34

36 Heat duty (Input condition)

Hea

t dut

y [M

W]

-200 -100 0 100 200 300 400384

386

388

390

392

+10 %

Temperature

Stea

m T

erm

pera

ture

[°C]

Time [sec]

35 sec+1.1 °C

14

16

18

20

22

24 Heat duty (Input condition)

Hea

t dut

y [M

W]

=

▪ Solid-gas circulation loop ▪ Economizer

▪ Superheater

=

=

ü Dynamic behavior of each sub-model is

validated time constant which is obtained from

globally simplified lumped system.

ü Difference of response time is showed due to

thermal inertia of each-sub model.


Transient response of sub-models (1)

11

▪ Water-steam circulation loopü Validation of water-steam circulation loop

model was performed by Astrom model.

(small scale 50MWe)

ü Astrom model can be applied to a large

scale boiler.

ü This results show the dynamic behavior of

target boiler in this study.

ü Dynamic behavior of this boiler is similar

to that of the boiler in Astrom.

310

320

330

340

350 Heat duty

Heat

inpu

t [MW

]

250

260

270

280

290

300

Steam flow rate

Steam

flow

rate [

kg/s]

18.0

18.2

18.4

18.6

18.8

19.0 Drum pressure

Drum

press

ure [

MPa]

1200

1220

1240

1260

1280

Circulation rate

Circ

ulatio

n rate

[kg/s

]

-50 0 50 100 150

0.32

0.36

0.40

0.44 Quality

Time [sec]

Qua

lity at

the r

iser e

xit [-]

-0.10

-0.05

0.00

0.05

0.10

Water level

Wate

r leve

l [m]


Open loop model (2)

12

ü Dynamic sub-models are integrated according to the mass flow and the heat transfer as

described in the CFB boiler system of the power plant.


Open loop model (2)

13

-200 0 200 400 600

46

48

50

52

54

Fuel SupplyFuel S

upply

[kg/s

]

Time [sec]

300310320330340350360

Air Flow

Air F

low [k

g/s]

+5 %

-200 0 200 400 600825

850

875

900

925

950

Furnace CycloneSo

lid-G

as Te

mpera

ture [°

C]

Time [sec]

-200 0 200 400 6000.00.51.01.52.02.53.03.54.0

O2 co

ncentr

ation

[%]

Time [sec]

-200 0 200 400 60017

18

19

20

21

22

23

Drum pressure

Drum

Press

ure [M

Pa]

Time [sec]

-0.6

-0.4

-0.2

0.0

0.2

0.4

Water Level Wate

r Leve

l [m]

-200 0 200 400 600

270

300

330

360

Mass F

low ra

te [kg

/s]

Time [sec]

Steam Feed water

-200 0 200 400 600250

300

350

400

450

Water

- Stea

m Te

mpera

ture [°

C]

Time [sec]

P. SH Drum S. ECO

ü Disturbance: Fuel supply

ü Solid-gas temp.

ü Oxygen concentration

ü Water steam temp.

ü Controller is required in drum

pressure, water level and

steam mass flow rate.

ü Require controller


Closed loop model (1)

14

ü In order to simulate real operation situation, controller is applied to the open loop model

ü Several crucially important parameters are chosen in this model.


Closed loop model (2)

15

-1 0 1 2 3 4 5 6

60

40

20

20

19

18

17

-6.3kg/s

795 sec

-0.8MPa

950 sec

Drum pressure Set point

Drum

press

ure [

MPa]

Time [1,000 sec]

Fuel

supply

[kg/s

] Fuel supply

-1 0 1 2 3 4 5 6

Oxygen con. Set point

Oxyg

en co

ncen

tratio

n [%

]

Time [1,000 sec]

Air flow

Air f

low ra

te [kg

/s]-45 sec

400

300200

100

5

2

4

3

2

796 sec

-1 0 1 2 3 4 5 6

0.08

-0.00

-0.08

300

350

250

200

Steam Feed Water Set Steam

-40 kg/s

285 sec

Mass

flow

rate

[kg/s]

Time [1,000 sec]

Water Level Set Level

Wate

r Lev

el [m

]

-1 0 1 2 3 4 5 6200

250

300

350

400

Load

[MW

e]

Time [1,000 sec]

-15 %

ü It is checked that all control variables is controlled to set values

ü Response time of drum pressure is larger than other parameters, so this parameter dominates the

dynamic behavior of the total CFB boiler system


Operation simulation (1)

16

ü Input Condition: Load data (Set value of drum pressure, steam flow rate)

0 2 4 6 8 10 12

150

200

250

300

350Lo

ad [M

W]

Time [hr]

① ② ④③ ⑤

▪ Operation case (trial operation 2011. 9. 18 for 12hr)

( ) = +



17

0 2 4 6 8 10 12200300400500600700800900

time [hr]

FUR out CYC out RH2 in RH1 out SH1 out ECO1 out

CYC out RH2 int RH1 out SH1 out ECO1 out

Gas T

empe

ratur

e [° C

]

(a) Gas temperature0 2 4 6 8 10 12

250

300

350

400

450

500

550

600

time [hr]

SH3 SH2 SH1 CYC ECO2

SH3 SH2 SH1 CYC ECO2

Wate

r-stea

m tem

pera

ture [

° C]

(b) Water-steam temperautre

0 2 4 6 8 10 1215

16

17

18

19

20

time [hr]

Drum

press

ure [

Mpa

](d) Drum pressure

0 2 4 6 8 10 12300

350

400

450

500

550

600

SH3 SH2 SH1

SH3 SH2 SH1

time [hr]

Tube

wall

temp

eratur

e [° C

]

(c) Tube wall temperature

0 2 4 6 8 10 12400

500

600

700

800

900

1000

1100

time [hr]

Steam Feed water

SteamM

ass flo

w [to

n/hr]

(f) Mass flow rate0 2 4 6 8 10 12

40

80

120

160

200

time [hr]

Fuel

supp

ly [to

n/hr]

(e) Fuel supply

▪ Measured data simulation



18

0 2 4 6 8 10 120

500

1000

1500

2000

2500

time [hr]

Solid

circu

lation

rate

[kg/s]

(a) Solid circulation rate0 2 4 6 8 10 12

-0.01

0.00

0.01

0.02

time [hr]Time [hr]

Wate

r lev

el [m

]

(b) Water level

0 2 4 6 8 10 12

Boile

r circ

ulatio

n rate

[kg/s

] Boiler circulation rate

time [hr]

4030

01020

20

1050

15

(d) boiler circulation rate and spary water flow

Spar

y wate

r flow

[kg/s

] Spary water flow

0 2 4 6 8 10 12

200

300

400

500

600

time [hr]

Temp

eratur

e [° C

]

(c) Temperature

RH2 (Gas) ECO2 (Gas) ECO1 (Water-steam)

▪ Unmeasured data simulation


Conclusion


Conclusion

20

ü Through this study, the CFB boiler dynamic model, which is composed of discretized dynamic sub-models

considering the water-steam flow, the gas-solid flow and the tube wall, is developed.

ü This model is based on physical phenomena, heat and mass balance and numerical approach. Especially, the

interaction between the solid-gas circulation loop and the water-steam circulation loop is carefully modeled due to

this circulation loops significantly determine the performance of the CFB boiler with the drum loop.

ü Model was validated as following process; 1) Each dynamic sub-model (Time constant and reference), 2) Open

loop model (Convergence of total boiler system), 3) Closed loop model (Controlled variables), 4) Operation

simulation (Measured data in real plant) → This model can simulate a real situation relatively well even with its

limitations

ü Although current model is developed to a particular CFB boiler, the modeling approach and the simulation strategy

can be extended to the other CFB boiler system with the drum loop.


CFB Boiler Dynamic Simulator

Thermal Engineering Lab


22


Ø The dynamic model is developed to a simulator

Ø The dynamic simulator is developed by MFC programing in

C++



23

Ø This program can simulate the dynamic behavior of a CFB boiler system according

to its load data or operating conditions.

Ø These conditions can be defined as the disturbance according to time by user.

Ø This program is available to Run/Freeze

Ø This program can show visualization :Graph, Result window and Save files

Ø This simulation calculates results for a certain time frame, and then it resumes the

calculations on a preferred day.

Ø Simulation can start from any steady-state, and apply any disturbance.



24

① ②

③ ④ ⑥⑤

1: Main Window, 2: Graph, 3: Time, furnace error, drum error., 4: Input load, 5: Set value, control variables , Manipulated variables 6: Manipulation button


Input window

25

Furnace and back pass geometry Drum loop geometry Convective HE. geometry

Wall type HE. geometry Coal, Limestone, Sand, Air condition Heat transfer condition and Node

① ② ③

④ ⑤ ⑥

Furnace and back pass geometry Drum loop geometry Convective HE. geometry

Wall type HE. geometry Coal, Limestone, Sand, Air condition Heat transfer condition and Node


Controller window

26

①

②

①

②

Ø 1. Controller On: Apply controller, PID value have to input

Ø 2. Controller Off: Not apply controller, Input manual have to input


Simulation Method

27

Ø Simulation method: 1) Auto input, 2) Manual input

Ø Auto input can be defined by load data according to time in

the text window by user

Ø Manual input can be defined by set value and boundary

conditions in the set value window

Auto inputManual input


Simulation of CASE 1

28


Simulation Results

29

Water-Steam temperature Solid-gas temperature Wall temperature

Material Flow Water-Steam Circulation

Gas velocity Water-steam velocity Heat duty

Water-Steam pressure

Water-Steam temperature Solid-gas temperature Wall temperature

Material Flow Drum loop

Gas velocity Water-steam velocity Heat duty

Water-Steam pressure

dynamic simulation of a cfb boiler system -...

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