simulation studies on oxy-cfb boiler dynamics and ... · simulation studies on oxy-cfb boiler...
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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 !