Simulation studies on oxy-CFB boiler dynamics and controldynamics and control

3rd Oxyfuel Combustion Conferencey

Jari Lappalainena, Hannu Mikkonena, Mikko Jegoroffa, Andres Sanchez-Biezmab, Jenö Kovacsc, Antti Tourunena

a VTT, FinlandVTT, Finlandb Endesa, Spainc Foster Wheeler Energia Oy, Finland

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Overview

Background and motivation Modelling Simulation results Conclusions

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EU Project: Flexi burn CFB

The Flexi-Burn CFB concept: High efficiency Circulating Fluidized Bed (CFB) power plant with CCS capable of air/oxy operation with a wide range of fuels including biomass

CIUDEN30 MW

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Motivation

Development of a novel boiler plant concept begins with steady state modeling Dynamic modeling is the logical next step

Targets To provide information on dynamic behavior of the integrated

systemy To verify feasibility of the process concept and its control

strategies from different perspectives To provide data and test bench for the development ofTo provide data and test bench for the development of

advanced high level controls

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APROS - simultaneous accuracy and comprehensiveness in dynamic modeling

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Modeling principles

First-principles models Pressure flow solution, realistic fluids (flue gas, water, O2, CO2) Main process units and streams modeled to provide the p p

characteristic dynamic features of the system Realistic flow path lengths and volumes (pipes, ducts, tanks,..) Pressure increase and loss elements (pumps, fans, pipes, valves, ..)(p p , , p p , , ) Heat exchangers Circulating fluidised bed (1D) Turbine sections, electrical network,

Control loops, ramping calculations, most important interlockings,and other supporting calculations included

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Modeling scope

SU

ASU ASU-Boiler interface

Boiler

AS

Circulating fluidised bed Flue gas path and recirculation Water steam path LE

R

Water steam path Turbine island CPU

BO

IL

OLS

CP

U

CO

NT

RO

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Model use

Typical simulation studies Load changes Mode changes between air/oxy-firingg y g Various disturbance situations

Comparison and analysis of air/oxy-firing Special features of oxy firing Special features of oxy-firing

e.g. effect of high flue gas recirculation on boiler behavior and related control needs

D l t f l l t l Development of upper level controls

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Si l ti l 1 L d hSimulation example 1: Load change

Electric power 100 % → 40% → 100 %

Ramping rates app. 3%/min

Manipulated variables: Fuel feed, Pressure before HP turbine, Oxidant flows GOX flows to oxidants Flow from feed water tankOxidant flows, GOX flows to oxidants, Flow from feed water tank, Feed flows to LP & HP eco

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Si l ti l 2 M d h f i tSimulation example 2: Mode change from air to oxy

Constant fuel feed

Manipulated variables:

Air flows ramped (20 min) Air flows ramped (20 min)

Oxygen flows to oxidants ramped (20 min)

RFG flows ramped (20 min)RFG flows ramped (20 min)

Minor set point changes in Turbine pressure, Flow from feed water tank, Feed flows to LP & HP eco

Flue gas O2 control OFF

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Si l ti l 2 M d h f i tSimulation example 2: Mode change from air to oxy

270Turbine inlet

300Electric power

60CO2 to storage

6Flue gas O2

260

265

s; b

ar 280

290

MW 30

40

50

kg/s 3

4

5

ol%

0 2000 4000250

255

kg/s

0 2000 4000

250

260

270M

0 2000 40000

10

20

k

0 2000 40000

1

2

m

flowpres

Time, s Time, s Time, s Time, s

30

35GOX to Oxidants

200

250Oxidant flows

250

300Total gas flows

60

70Flue gas conc.

10

15

20

25

kg/s

100

150

200

kg/s

100

150

200

kg/s

20

30

40

50

mol

%

RFGAirGOX

0 2000 40000

5

10

Time, s

0 2000 40000

50

Time, s

0 2000 40000

50

Time, s

0 2000 40000

10

20

Time, s

1Oxdt2Oxdt

1Oxdt2Oxdt

GOXCO2H2O

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Si l ti l 2 M d h f i tSimulation example 2: Mode change from air to oxy

Concentrations of the oxidant streams

Primary oxidant Secondary oxidant

P i id t CO2 P i id t H2O S d id t CO2 S d id t H2O

30

40

50

60Primary oxidant gas CO2

mol

%

10

15

20Primary oxidant gas H2O

mol

%

30

40

50

60Secondary oxidant gas CO2

mol

%

10

15

20Secondary oxidant gas H2O

mol

%

0 1000 2000 3000 40000

10

20

Time, s

m

0 1000 2000 3000 40000

5

Time, s

m

Primary oxidant gas O2 Primary oxidant gas N2

0 1000 2000 3000 40000

10

20

Time, sm

0 1000 2000 3000 40000

5

Time, s

m

S d id t O2 S d id t N2

20

21

22Primary oxidant gas O2

mol

%

40

60

80Primary oxidant gas N2

mol

%

26

28

30

32Secondary oxidant gas O2

mol

%

40

60

80Secondary oxidant gas N2

mol

%

0 1000 2000 3000 400018

19

Time, s

m

0 1000 2000 3000 40000

20

Time, s

m

0 1000 2000 3000 400020

22

24

Time, s

m

0 1000 2000 3000 40000

20

Time, s

m

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Si l ti l 2 M d h f i tSimulation example 2: Mode change from air to oxy

ASU-Boiler interface

40

60Flows in the ASU-boiler interface

g/s

GOX flow from ASU

0 500 1000 1500 2000 2500 3000 3500 40000

20

Time, sk

40Flows in/out of GOX buffer (kg/s)

Momentary O2 demandO2 flow to boiler

0 500 1000 1500 2000 2500 3000 3500 40000

10

20

30

kg/s

O2 from LOX tankvented GOX valve1

Time, s

0.135

0.14

0.145GOX header pressure

MP

a

0 500 1000 1500 2000 2500 3000 3500 40000.125

0.13

Time, s

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Conclusions (1/2)

A dynamic model of CCS capable power plant (ASU+CFB+CPU) was developed using the APROS simulation platform

The model provided excellent base to study dynamic behavior of the oxyfuel CFB power plant, and to develop and optimize control strategies, upper level controls, and p p , p p g , pp ,operational practises

Control system has a central role to enable the operation of the integrate in a safe and effective way Controlling of the flue gas O2 content is more complicated in the oxy firing Controlling of the flue gas O2 content is more complicated in the oxy-firing

mode because of the flue gas recirculation O2 content of the oxidants has strong influence to the boiler behavior. There are

new risks for the boiler shut down in situations like fuel feed stop, lack of i l ti t d t t diti l i fi i b ilrecirculation gas, etc. compared to traditional air-firing boilers.

The process islands can be only temporarily operated independently (no large buffer volumes between the process areas) Careful coordination is required to manage transients – both planned operations q g p p

and disturbances

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Conclusions (2/2)

Very tight coupling of the ASU, boiler and CPU processes (e.g. by heat integration) can make the operation more vulnerable to disturbances. Economical reasons encourage to look for agility and flexibility by control technology means.

Also the future development of oxyfuel CCS concepts calls for dynamic simulation

e.g. development of the second generation of oxyfuel CFB power plant concept with significantly higher efficiency

FP7 project: O2GEN 2012-2015, coordinated by CIRCE

Further development of submodels for ASU, boiler and CPU needed

Integration of different simulation tools, e.g. ASPEN and APROS, provides interesting option for future dynamic studies

Acknowledgements for FLEXI BURN CFB:Acknowledgements for FLEXI BURN CFB:The research leading to these results has received funding from the European Community’s Seventh Framework Programme (FP7/2007-2013) under grant agreement n° 239188.

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Thank You !