ABSTRACT
Coal is a heterogeneous material comprised of organic, or combustible matter, and mineral matter. The mineral matter in coal contains noncombustible impurities which are broadly divided into ash-forming and sulfur-forming products. Physical coal cleaning, which includes beneficiation, is used only in the second category of impurities. The first step in physical cleaning is crushing the coal to allow mechanical removal of impurities. The amount of crushing, screening and washing needed is described in P. S. Jacobsen's 1978 model. Besides cleaning coal prior to burning, other options are being explored. Cleaning during burning is a technology under research and development. Post-combustion devices used to clean coal are called flue gas desulfurizers (FGDs), Combinations of coal cleaning and stack gas scrubbers, or FGDs, are amenable to technological and economic trade-offs. Cost savings from using less expensive FGD systems must be balanced against the additional costs for the cleaning operation.
