Coal Quality Assessment-the Validity of Empirical Tests
AUTHOR: Anne M Carpenter
DATE: September 2002
In the current increasingly competitive environment, long established quality criteria for assessing coals for pulverised fuel-power plants are being re-examined. Reliable tests are needed for evaluating potential fuels. Supplies are concerned that their products should not be arbitrarily excluded by inappropriate tests and power plant operators need to be confident that they can adequately predict the consequences of using an unfamiliar coal. There is a growing consensus that the current standard tests are inadequate and inaccurate, and their ability to predict full-scale performance can be unreliable. Among the tests whose validity has been questioned are the ash fusion temperature, volatile matter, and Hardgrove Grindability Index.
This report reviews these and other tests currently in use, examines their validity, and assesses proposed alternatives. It includes tests for assessing a coal's handling and milling behavior, its combustion characteristics (ignition, flame stability, char reactivity and burnout), and its slagging and fouling propensities. Coal properties affecting the emission of air pollutants (sulphur dioxide, nitrogen oxides, particulates, trace elements and carbon dioxide), and methods for their determination are also covered. It is concluded that the tests will probably be used, for the foreseeable future, primarily to rank unfamiliar coals in comparison with known coals, rather than to give absolute performance parameters.