Emission of volatile organic compounds from coal combustion

The combustion of coal leads to the formation of small but significant amounts of volatile organic compounds (VOCs), toxic organic micropollutants as polynuclear aromatic hydrocarbons (PAHs), as well as CH4. The measurements of such trace emissions is difficult and expensive, consequently it is useful to examine these from a kinetic modelling and thermodynamic point of view in order to make design predictions, and derive a full analytical specification from incomplete experimental data. In this study, the thermodynamic properties combined with the kinetic pathways have been used to examine the likely routes of formation of PAHs. These compounds are formed in the combustion and post-combustion environment, although some pollutants are found in the cooled flue gases. These processes were modelled in detail for cooling using a sequence of perfectly stirred reactors. The affect of coal volatiles composition, air/fuel ratio, and temperature-time history on pollutant formation was examined. Results were compared against a combustion plant. It is shown that the pollutants undergo changes in concentration during the cooling process, and these changes are mapped out for the major pollutants arising from coal combustion in both pulverised coal flames and fluidised bed combustion. (C) 1999 Elsevier Science Ltd. All rights reserved.