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Flexibility of Fossil Fuel Plant in a Renewable Scenario

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 24 th Jan 2006 . Presentation Aims.

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Flexibility of Fossil Fuel Plant in a Renewable Scenario

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  1. 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 SETRIS_24 Jan 2006, Slide 1

  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 design which will be capable of rapid response to electricity demand SETRIS_24 Jan 2006, Slide 2

  3. 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 SETRIS_24 Jan 2006, Slide 3

  4. 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 SETRIS_24 Jan 2006, Slide 4

  5. At Present Two - Shift Operation Implies Running for 10-15 hours a day Shut down at weekends Frequent load changes Extra Costs 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 5

  6. Big CHP PWR Nuclear Hydro Will grab the base load Wind Power Photovoltaic Will be the growing intermittent suppliers FOR THE FUTURE 2010-2025 PERIOD Fossil fuel plant will have to cycle much more SETRIS_24 Jan 2006, Slide 6

  7. 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 SETRIS_24 Jan 2006, Slide 7

  8. 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 SETRIS_24 Jan 2006, Slide 8

  9. Exhaust from Gas Turbine Typical Layout of a Horizontal HRSG Image source: www.bhpi.com.ph Man sized object Image source: www.bhpi.com.ph SETRIS_24 Jan 2006, Slide 9

  10. Outlet Header Steam Condensate 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 SETRIS_24 Jan 2006, Slide 10

  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 11

  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 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 SETRIS_24 Jan 2006, Slide 12

  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 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 SETRIS_24 Jan 2006, Slide 13

  14. 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 SETRIS_24 Jan 2006, Slide 14

  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 because HRSG can be kept hot and ready using steam supply from gasifier SETRIS_24 Jan 2006, Slide 15

  16. Flexible IGCC-Hypogen Plant Layout SETRIS_24 Jan 2006, Slide 16

  17. 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) 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 SETRIS_24 Jan 2006, Slide 17

  18. Thank You The views in this presentation are those of the authors 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 SETRIS_24 Jan 2006, Slide 18

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