A mathematical model of ash formation during pulverized coal combustion

• Published in: Fuel (Guildford) Vol. 81; no. 3; pp. 337 - 344
• Main Authors: Yan, L., Gupta, R.P., Wall, T.F.
• Format: Journal Article
• Language: English
• Published: Oxford Elsevier Ltd 01.02.2002; Elsevier
• Subjects: Applied sciences; Ash formation; Combustion; Combustion of solid fuels; Combustion. Flame; Computer-controlled scanning electron microscope; Energy; Energy. Thermal use of fuels; Exact sciences and technology; Pulverised high-rank coal; Theoretical studies. Data and constants. Metering; Combustion; Ash formation; Computer-controlled scanning electron microscope; Pulverised high-rank coal; Scanning electron microscopy; Particle size distribution; Ash; Pulverized coal; Mathematical model; Bituminous coal; Mineral matter
• ISSN: 0016-2361; 1873-7153
• DOI: 10.1016/S0016-2361(01)00166-1

A mathematical model of ash formation during high-rank pulverized coal combustion is reported in this paper. The model is based on the computer-controlled scanning electron microscope (CCSEM) characterization of minerals in pulverized coals. From the viewpoint of the association with coal carbon matrix, individual mineral grains present in coal particles can be classified as included or excluded minerals. Included minerals refer to those discrete mineral grains that are intimately surrounded by the carbon matrix. Excluded minerals are those liberated minerals not or at least associated with coal carbon matter. Included minerals and excluded minerals are treated separately in the model. Included minerals are assumed to randomly disperse between individual coal particles based on coal and mineral particle size distributions. A mechanism of partial-coalescence of included minerals within single coal particles is related to char particulate structures formed during devolatilization. Fragmentation of excluded minerals, which is important particularly for a coal with a significant fraction of excluded minerals, is simulated using a stochastic approach of Poisson distribution. A narrow-sized sample of an Australian bituminous coal was combusted in a drop-tube furnace under operating conditions similar to that in boilers. The particle size distribution and chemical composition of experimental ash were compared to those predicted with the model. The comparisons indicated that the model generally reflected the combined effect of coalescence of included minerals and fragmentation of excluded minerals, the two important mechanisms governing ash formation for high-rank coals.