Projected Costs of Generating Electricity - OECD Nuclear Energy ...

Appendix 4
Generation Technology
This appendix briefly describes the power generation technologies which are the basis of cost estimates
presented in this report. These technologies are available currently or could be available by 2010-2015.
The basic base-load technologies and options are described for coal-fired, gas-fired, and nuclear power
plants. Several other plant types not falling under the most common technological choices are also
described.
App.
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Other sources describe these technologies in greater detail. Several useful references are “General
power plant design” (Sorenson, 1983); “Combined cycle gas turbines” (Kelhofer, 1991); “Steam boiler
electric generation” (Schultz, 1992); “Nuclear plants” (Glasstone, 1994); “Coal-fired plants” (Couch,
1997), “Renewable energy power plants” (IEA, 2003a) and “Research and Development Concept for
Zero-emission Fossil-fuelled Power Plants, Summary of COORETEC” (BMWA, 2003).
Coal-fired power plants
Most cost estimates for coal-fired power plants presented in this study are based upon combustion
of pulverised coal (hard coal and lignite) in conventional subcritical boilers. Several were based upon
supercritical boilers, fluidised bed boilers, or integrated gasification combined cycles (IGCC).
Pulverised coal plants
Conventional pulverised coal combustion burns finely ground coal particles in a boiler with watercooled
walls. Steam is raised in these walls and a series of heat exchangers which cool the hot combustion
gases. In the case of an electricity-only power plant, the steam is passed through a condensing steam
turbine which drives a generator. In the case of a cogenerating power plant, a back-pressure or extraction
steam turbine is used. Many variations on the steam cycle are possible in either electricity-only or
cogenerating power plants. For example, in a reheat steam cycle the steam, after partially expanding
through the steam turbine, is brought back to the boiler and reheated to peak temperature again in order
to improve overall power generation efficiency. The basic configuration of steam generation followed by
expansion in a steam turbine is used in all boiler steam-electric power plants.
The pressure and temperature at which steam is generated is a key design feature. The majority of coalfired
boilers built in the OECD to date have been subcritical. This means steam pressure is below the
critical pressure of water, or approximately 22 MPa (218 atmospheres). Supercritical boilers raise steam
above this pressure. By doing so, the efficiency of power generation is improved, but the cost of the boiler,
steam turbine and control valves is increased. The materials of construction of these components must be
resistant to the high-pressure steam and so are more expensive alloys. The choice of sub- or supercritical
design depends on the local balance of fuel costs, which are reduced by higher efficiency, and capital
costs, which are increased due to more expensive materials.
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