Switching to Cheaper Coals for Power Generation
AUTHOR: Anne M. Carpenter
DATE: April 1998
Since the fuel represents 60-80% of a power plant's operating costs, significant savings might be made by firing cheaper coals. These coals are usually outside the fuel specification that would normally be used. Problems may therefoe occur when they are substituted for the normal feedstock. The cheapest coal does not necessarily produce the cheapest electricity. Lower priced coals may be more successfully utilised when blended with the usual feedstock to dilute any undesirable characteristic. This report examines the utilisation of lower cost coals in power plants designed for bituminous coals. It begins with an overview of the effects of coal properties on the performance of power plants. Coal quality affects virtually every component in the power plant. Thus the compatibility of the alternative coal with respect to handling, storage, pulverising, combustion, boiler furnace and heat transfer performance, emission levels, and residues handling and utilisation has to be properly evaluated. Each of these aspects is examined. After briefly reviewing methods for predicting this behaviour of a coal or its blend, the experience of power plants when firing out-of-design coals is examined. Operating perameters which can be modifiied to accmodate the new coal/blend are covered. Since the behaviour of coals is strongly influenced by the design of the unit and the operating conditions, as well as the coal properties, the behaviour of the fuels will be plant specific. The report concludes that with better prediction and knowledge of how operating conditions can be optimised, and with the willingness and flexibility of plant operators to make the necessary plant adjustments, significant fuel savings can be achieved.