SETRIS_24 Jan 2006, Slide 1

Flexibility of Fossil Fuel Plant in a Renewable Scenario

F. Starr, E. Tzimas, & S. PetevesEuropean Commission - DG JRC

Institute for EnergyPetten, The Netherlands

Coping With Variability: UK Open University Conference 24th Jan 2006

SETRIS_24 Jan 2006, Slide 2

Presentation Aims

Highlight the fact that plant cycling tends to be overlooked in future plant design concepts

Indicate some of the problems which currently constrain rapid start ups in CCGT and coal fired steam plant

Highlight the issues which cycling can create in advanced fossil fuel electricity-only plants in a renewables scenario

Introduce an IGCC based hydrogen/electricity plant designwhich will be capable of rapid response to electricity demand

SETRIS_24 Jan 2006, Slide 3

Commonly agreed priorities for future fossil fuel plants:

High efficiencyAbility to capture CO2 is a preferred optionCapital costs similar to today

Priorities that tend to be overlooked:

Need for increased load following, two shifting and stop/start operation resulting from any or all of the following:

Wind and solar renewable electricity Nuclear base load plants Large scale cogeneration

SETRIS_24 Jan 2006, Slide 4

Today There Are Four Ages of Fossil Fuel Today There Are Four Ages of Fossil Fuel Plant OperationPlant Operation

Years 1-2Years 1-2:: Post Commissioning with frequent plant trips Post Commissioning with frequent plant trips

Years 3-9Years 3-9:: Base Load Operation with biannual shutdowns Base Load Operation with biannual shutdowns

Years 10-14Years 10-14:: Load Following down to 80% output (gas) 40% Load Following down to 80% output (gas) 40% (coal)(coal)Years 14-30Years 14-30:: Two Shifting (stop-start operation) with shutdown at Two Shifting (stop-start operation) with shutdown at night and weekendsnight and weekends

By year 9 plants will need to cycle By year 9 plants will need to cycle although many although many components have aged and corrodedcomponents have aged and corroded

SETRIS_24 Jan 2006, Slide 5

Running for 10-15 hours a day

Shut down at weekends

Frequent load changes

Thermal and pressure cycling

Over temperature running

Bad water conditions in boiler

Poor furnace conditions

Stop-start operation will be worse in renewables scenario

SETRIS_24 Jan 2006, Slide 6

Will grab the base load

Big CHPPWR Nuclear

Hydro

FOR THE FUTURE 2010-2025 PERIOD

Will be the growing intermittent suppliers

Wind PowerPhotovoltaic

Fossil fuel plant will have to cycle much more

SETRIS_24 Jan 2006, Slide 7

Estimated German Power Output and Demand in October 2020

0

20

40

60

80

100

0 1 2 3Number of Weeks

Elec

trica

l Dem

and

or O

utpu

t (G

W)

Total Demand

Fossil

Renewables

In the future peak to trough ratiofor fossil plants increases to 3/1

For original data see refs at end

SETRIS_24 Jan 2006, Slide 8

The HRSG Section of CCGT

•Most current designs intended for base load operation

• Thermal stress and fatigue is a problem due condensation of steam during start up and shutdown

• HRSGs are difficult to repair- avoid thermal stress by careful operation

Combined Cycle Gas Turbine Plant

•Gas turbines and steam turbines produce the power

•Steam is produced for steam turbines in a HRSG (Heat Recovery Steam Generator )

SETRIS_24 Jan 2006, Slide 9

Image source: www.bhpi.com.ph

Exhaust

from Gas

Turbine

Typical Layout of a Horizontal HRSG

Image source: www.bhpi.com.ph

Man sized object

SETRIS_24 Jan 2006, Slide 10

Combination of cold air from gas turbine needed to flush

potentially explosive gases out of duct from gas turbine,

plus poor drainage of condensed steam, causes tubes to cool down unevenly

Front Viewof

HRSG Superheaterduring

Shutdown

Steam condensation in HRSGs tends to limit quick start up afterCCGT plant shutdowns and poor drainage of condensate

can result in uneven temperature distribution and thermal stress

Steam

Condensate

Outlet Header

SETRIS_24 Jan 2006, Slide 11

CCGT Cycling Issues of Today

• Hot section of gas turbines and HRSGs suffer from thermal stress because of temperature changes and condensation effects

• Boiler water conditions can be poor

• CCGTs can give relatively fast start ups and shutdowns at the cost of increased maintenance

• Big changes in output, when load following can be difficult with current units

• Drop in grid frequency will result in reduced power output will require some over- temperature running by the GT to restore frequency

• Acting as spinning reserve is probably not practical with most current CCGTs

SETRIS_24 Jan 2006, Slide 12

Future CCGTs

Gas turbines will be more complex

Blade cooling using steam, reheat or interstage combustion but Controls and water treatment should be better than today

HRSGs can be made to drain better, reducing build up of condensate and reducing thermal stress

Higher inlet temperatures from GT to the HRSG may permit better load following

Conventional CCGTs have the disadvantage that high amount of excess air increases difficulty in capturing CO2

CCGTs may still be difficult to run in a spinning reserve mode

SETRIS_24 Jan 2006, Slide 13

Advanced Coal Fired Steam Plant

• Superheater Metal Temperatures 675-780°C

• Pressures 300-400 bar

• Inlet HP and IP Turbine Rotor 650-720°C

Heavier walled pipe work, need for stainless steels, and

increased temperatures implies start up

times of several hours

High carbon level in fuel make it more essential to capture CO2

Spinning reserve capability may be compromised in advanced plants

Image source www.ocp.tudelft.ph

SETRIS_24 Jan 2006, Slide 14

IGCC- Hypogen Carbon Capture Concepts

Coal-Oxygen-Water Into Gasifier

( for purification and conversion to

hydrogen for use in CCGT)

Raw Gas Out

Slag and

Water

Production of hydrogen for CCGT

•Removes sulphur and chlorine

•Removes CO2

•Similar electrical efficiency to steam plants with CO2 capture

•More efficient at producing hydrogen from fossil fuel than steam plant plus electrolysis

Note : IGCC based concepts are not easy to start up or

to use for load following

SETRIS_24 Jan 2006, Slide 15

Main Characteristics of Flexible IGCC-Hypogen Plant

Plant works as a base load energy producer all the time

Gasifier and gas purification systems in constant operation Able to change energy output from 100% electricity to 100% hydrogen

Does not require external source of electricity for ancillaries

Electricity from CCGT section of plant can be produced

extremely rapidly- can be used as spinning reserve

becauseHRSG can be kept hot and ready using steam supply from gasifier

SETRIS_24 Jan 2006, Slide 16

Flexible IGCC-Hypogen Plant Layout

SETRIS_24 Jan 2006, Slide 17

Flexible IGCC - Hypogen Plants will be extremely good at responding to changes in the demand for electricity

and capturing CO2

Conclusions for 2010-2025

CCGT plant can be made more efficient, and at some additional cost, can be made to be more flexible than today’s units (1-2 hour start ups)

With steam plant, at some point, efforts to improve efficiency will greatly compromise the ability to change to two – shift operation

The preferred option for future fossil plants is to have the facility to capture carbon

This could be a problem for CCGT and Steam Plantas CO2 capture systems probably need to be run continuously

CCGTs may still have problems when used for spinning reserve

SETRIS_24 Jan 2006, Slide 18

Thank You

The views in this presentation are those of theauthors and not necessarily those of the European Commission

References:

Quaschning, V.: Simulationserebnisse fűr die regenerative Erzeugung im Jahr 2020 c/o V. Quaschning (2001)

Starr F, Tzimas E, Steen M , Peteves SD : Flexibility in the production of hydrogen and electricity from fossil fuel plants c/o EU Institute for Energy

Starr F : Background to the Design of HRSGs and Implications for CCGT Plant Cycling in OMMI Power Plant Internet Journal Vol 2/1 2002