Flexibility of Fossil Fuel Plant in a Renewable Scenario

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Flexibility of Fossil Fuel Plant in a Renewable
Scenario

• F. Starr, E. Tzimas, S. Peteves
• European Commission - DG JRC
• Institute for Energy
• Petten, The Netherlands

Coping With Variability UK Open University
Conference 24th Jan 2006
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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 design which will be capable of rapid
response to electricity demand
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Commonly agreed priorities for future fossil fuel
plants
High efficiency Ability to capture CO2 is a
preferred option Capital 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
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Today There Are Four Ages of Fossil Fuel Plant
Operation
Years 1-2 Post Commissioning with frequent plant
trips
Years 3-9 Base Load Operation with biannual
shutdowns
By year 9 plants will need to cycle although
many components have aged and corroded
Years 10-14 Load Following down to 80 output
(gas) 40 (coal)
Years 14-30 Two Shifting (stop-start operation)
with shutdown at night and weekends
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Stop-start operation will be worse in renewables
scenario
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FOR THE FUTURE 2010-2025 PERIOD
Fossil fuel plant will have to cycle much more
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Total Demand
Fossil
Renewables
In the future peak to trough ratio for fossil
plants increases to 3/1
For original data see refs at end
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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 )

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

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Typical Layout of a Horizontal HRSG
Image source www.bhpi.com.ph
Man sized object
Image source www.bhpi.com.ph
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Steam condensation in HRSGs tends to limit quick
start up after CCGT plant shutdowns and poor
drainage of condensate can result in uneven
temperature distribution and thermal stress
Front View of HRSG Superheater during Shutdown
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
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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

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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
CCGTs may still be difficult to run in a spinning
reserve mode
Conventional CCGTs have the disadvantage that
high amount of excess air increases difficulty in
capturing CO2
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Advanced Coal Fired Steam Plant

• Superheater Metal Temperatures 675-780C
• Pressures 300-400 bar
• Inlet HP and IP Turbine Rotor 650-720C

Heavier walled pipe work, need for stainless
steels, and increased temperatures implies start
up times of several hours
Image source www.ocp.tudelft.ph
Spinning reserve capability may be compromised in
advanced plants
High carbon level in fuel make it more essential
to capture CO2
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IGCC- Hypogen Carbon Capture Concepts
Coal-Oxygen-Water Into Gasifier
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

Raw Gas Out
( for purification and conversion to hydrogen
for use in CCGT)
Note IGCC based concepts are not easy to start
up or to use for load following
Slag and Water
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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 because HRSG can be kept hot
and ready using steam supply from gasifier
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Flexible IGCC-Hypogen Plant Layout
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Conclusions for 2010-2025
CCGT plant can be made more efficient, and at
some additional cost, can be made to be more
flexible than todays units (1-2 hour start ups)
CCGTs may still have problems when used for
spinning reserve
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 Plant as
CO2 capture systems probably need to be run
continuously
Flexible IGCC - Hypogen Plants will be extremely
good at responding to changes in the demand for
electricity and capturing CO2
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Thank You
The views in this presentation are those of
the authors and not necessarily those of the
European Commission
References Quaschning, V. Simulationserebnisse
fur 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