INFLUENCE OF COAL TYPE AND OPERATING-CONDITIONS ON THE FORMATION OF INCOMPLETE COMBUSTION PRODUCTS - PILOT-PLANT EXPERIMENTS

This experimental study was mainly aimed to evaluate the influence of the coal type on the production of Polycyclic Aromatic Hydrocarbons (PAHs) and other trace organics from pulverized coal combustion. The behaviour 7 of coals, having different characteristics and geographical origin, was tested in a small scale furnace (50kWt), under relatively good practical combustion conditions. As regards fuel carbon conversion, some observations were also made when the combustion conditions got worse, slightly differing from those set, or becoming definitely poor. A detailed chemical characterization of the Products of Incomplete Combustion (including unburnts, the total Organic Material Extractable by methylenchloride (EOM), PAHs from naphthalene to coronene and n-alkanes (n-A) from C12 to C36) was performed on solid and gaseous emissions. The fluorescence emission spectra of the integral methylenchloride extracts, in the range from 270 to 600 nm, were also studied. The experimental data concerning stack emissions and light hopper ashes showed that, under relatively good combustion conditions, both absolute levels and composition profiles of PAHs undergo not much marked variations with respect to the fired coal, whereas they can be strongly affected even by weak alterations of the process conditions. When combustion gets definitely worse, PAH levels in the emissions may increase by up to 2 orders of magnitude more than other variables related to fuel carbon conversion, such as CO in flue gas, unburnts and other classes of organics, even though the variations of all these parameters seem to be related.