Transformation of coal mineral matter during pulverized coal combustion

Abstract

The theoretical development of a sequence of mathematical sub-models capable of calculating the fouling tendency of a coal based on microscopic analysis of the coal mineral matter is described. The sub-models interpret computer controlled-scanning electron microscope analysis data in terms of mineral size and chemical composition distributions; follow the transformation of these mineral property distributions during the combustion of the coal; determine the probability of the resultant fly ash particles impacting on boiler-tube surfaces and of their sticking upon impaction. The sub-models are probabilistic, and take account of the particle-to-particle variation of coal mineral matter and fly ash properties by providing mean values and variances for particle size, chemical composition and viscosity. The various sub- models are combined into a Coal Fouling Tendency (CFT) computer code. Comparison of CFT modeling results obtained for any coal or coal blend with those obtained for a coal whose behavior in a given boiler plant is known, can give useful information on their relative fouling tendencies. The report also includes data on the deposition characteristics of five coals or coal blends, obtained from combustion experiments in the 1-2 MW flame tunnel at MIT. The measurement data were used for validation of the CFT calculations, and for ranking the five fuels with respect to their fouling behavior. Similar ranking of other coals, without combustion testing, can be based solely on results from the CFT model, and examples are given in the report.