Dynamic modelling of a supercritical coal fired po er plant integrated coal fired power plant integrated

with post-combustion CO2 capture

3rd Post Comb stion Capt re Conference (PCCC3)3rd Post Combustion Capture Conference (PCCC3)8-11th September 2015

Stefanía Ósk GarðarsdóttirChalmers University of Technologyy gy

Division of Energy Technology

Background• There is a need for dynamic modeling of power plants with CO2

capture– Dynamic models are useful for improving design operation– Dynamic models are useful for improving design, operation

and control of new and existing plants– Dynamic power plant modelling has been done to some

extent but often some important characteristics are left out (e.g. feedwater heaters, steam drum level…)

Aim

• Develop a simplified representation of a supercritical coal-fired l tpower plant

• Construct a dynamic model of a coal fired power plant according to y p p gthe simplified design

• Link the power plant model with a model of a post combustion CO• Link the power plant model with a model of a post-combustion CO2capture (PCC) system from previous work– Identify effects of PCC on the power plant dynamics

Steam cycle simplification• Starting point: Existing detailed steady-state model of

Nordjyllandsvaerket power plant constructed in Ebsilon Professional‒ Detailed model validated against plant data‒ Detailed model validated against plant data

Power plant model overview

FGD Stack

Water

Steam

Air

Flue gas

Fuel

Econ.

Superh2

Reheat2VHP HP IP LP1 LP2

W.Wall

Reheat1

Superh1

Comb.Load set point

To VHP and HP spray

FWH

Boiler

Dynamic process modeling

• Dynamic power plant model constructed in Dymola accordingconstructed in Dymola according to simplified design– Based on Modelica language

(aca sal eq ation based(acausal equation based modeling)

– Components from Modelon’sThermalPower library, the Modelica standard library and custom made componentscustom made components

Dynamic model evaluation• Steady-state results in Dymola compared with plant data• Main input to the model is the load curve

ar]

t [M

W]

Pres

sure

[ba

ener

ator

out

puG

e

Power plant model – example of results

• Boiler dynamics – Transition from full load to 70% part load m

ber [

kg/s

]

kg/s

]

from full load to 70% part load

• Load change implemented by mbu

stio

n ch

am

wat

er w

alls

[k

Load change implemented by ramping down fuel feed rate

flow

from

com

am fl

ow fr

om

• Dynamics on gas side very fast compared with the water side Fl

ue g

as f

Stea

CO2 absorption model

• Rate-based model originally developed by Åkesson et al.developed by Åkesson et al. (collaboration with ModelonAB)– 30 wt% MEA assumed non30 wt% MEA, assumed non-

volatile and degradation not accounted for

• Chemical reactions atChemical reactions at equilibrium, influence of reaction rates on mass transfer accounted for by using anaccounted for by using an enhancement factor

System model overviewTo stack Pure CO2

FGD

Water

Steam

Air

Flue gas

Fuel

Solvent

Econ.

Reheat2

Control signal

Superh2

Reheat2

Reheat1

Superh1

VHP HP IP LP1 LP2LP_CCS

W.Wall

Comb.Load set point

FWH

Boiler

To VHP and HP spray

Integration of PCC unit• Steam extracted from an

additional extraction point in the LP turbine section

• Extraction pressure maintained at ~3bars in the

To stack Pure CO2

maintained at 3bars in the load range tested by throttling steam between LP turbine stages

 

turbine stages• Steam extraction to PCC

system affects e.g. mass From reheat

To feedwater heaters

flows in FWH system– Effective control of water levels

in tanks and heat exchangers of

VHP HP LP_CCS LP1

To reheat

LP2IP

importance

Preliminary resultsTransition from full load to 70% part load- load change implemented by ramping down fuel feed rate

[kg/

s]

w [k

g/s]

[kg/

s]

te [%

]

Fuel

inpu

t

Flue

gas

flow

Fuel

inpu

t

Cap

ture

rat

Preliminary results

°C]

W]

l inp

ut [k

g/s]

tem

pera

ture

[°

tor o

utpu

t [M

W

Fuel

Reb

oile

r

Gen

erat

Similar trends, small effects of PCC system?

Preliminary results

kg/s

]

S bi li i i

l inp

ut [k

g/s]

e st

eam

flow

[kSteam turbine limitations –minimum flow and changes in steam quality

Fuel

LP tu

rbin

e

Next steps

• Continue with model and scenario development– Some adjustments are feasible e g updating mass transfer andSome adjustments are feasible, e.g. updating mass transfer and

liquid hold-up correlations, possible improvements in heat transfer calculations in boiler components

• Collaboration study with Norwegian University of Science and Technology (NTNU)

Ai i t i ti ti ff t f i t ti PCC it ith l d– Aiming at investigating effects of integrating PCC unit with coal and gas fired power plants on the power plant dynamics

– How will the power plants ability to operate flexibly be affected?

Summary

• A simplified steam cycle was designed using the existing Nordjyllandsvaerket coal fired power plant as basisNordjyllandsvaerket coal fired power plant as basis– The steady-state performance of the dynamic power plant model is

reasonable, compared with plant data• Data for dynamic validation is scarce dynamic behavior• Data for dynamic validation is scarce, dynamic behavior

reasonable?– PCC system does not have a large influence on the power plant

load ramp rate• The coupling between the power plant steam cycle and the

post-combustion system needs to be carefully designedp y y g– Flow conditions in LP turbine might prove problematic at low loads

Dynamic modelling of a supercritical coal fired power plant integrated with coal fired power plant integrated with

post-combustion CO2 capture

3rd Post Comb stion Capt re Conference (PCCC3)3rd Post Combustion Capture Conference (PCCC3)8-11th September 2015

Stefanía Ósk GarðarsdóttirChalmers University of Technologyy gy

Division of Energy TechnologyE-mail: skst@chalmers.se