Energy & Fuels 2000, 14, 745-750
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The Effect of Pressure on Ash Formation during Pulverized Coal Combustion Hongwei Wu,* Gary Bryant, and Terry Wall Cooperative Research Centre for Black Coal Utilization, Department of Chemical Engineering, The University of Newcastle, Callaghan, NSW 2308, Australia Received May 4, 1999
A bituminous coal with a size faction of 63-90 µm was combusted under oxidizing atmosphere (air) in a drop tube furnace (DTF) and a pressurized drop tube furnace (PDTF) at a gas temperature of 1573 K and pressures of 0.1, 0.5, 1.0, and 1.5 MPa. Ash generated at high pressure was found to be much finer than ash generated at low pressure due to the differences in char structure. Pressure influcences ash formation by its effect on the structure of char particles after devolatilisation. Char samples produced at high pressure have higher proportions of porous char particles which fragment to form finer ash particles. This study confirms and elaborates upon previous studies relating the structure and morphologies of char to ash formation.
Introduction Inorganic impurities in coal are converted to ash during coal utilization processes. Reported ash formation mechanisms during pulverized coal combustion are shown in Figure 1. These mechanisms indicate that ash formed during coal combustion has a bimodal particle size distribution. Large ash particles (>2 µm) correspond to ash resulting from mechanisms which include coal or char fragmentation, structural disintegration of the char,1-7 coalescence of ash on the surface of a char particle or within the particle,4,7-9 fragmentation of minerals due to inorganic reaction,4,9,10 shedding of ash particles from the surface of chars during combustion,3,8,11 and ash cenosphere formation.9 Fine ash particles (
