The combustion of coal leads to the formation of small but significant amou
nts 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 usef
ul to examine these from a kinetic modelling and thermodynamic point of vie
w in order to make design predictions, and derive a full analytical specifi
cation 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 comb
ustion and post-combustion environment, although some pollutants are found
in the cooled flue gases. These processes were modelled in detail for cooli
ng using a sequence of perfectly stirred reactors. The affect of coal volat
iles 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.