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 (P AHs) and other trace organics from pulverized coal combustion. The beh aviour 7 of coals, having different characteristics and geographical o rigin, was tested in a small scale furnace (50kWt), under relatively g ood 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 Co mbustion (including unburnts, the total Organic Material Extractable b y methylenchloride (EOM), PAHs from naphthalene to coronene and n-alka nes (n-A) from C12 to C36) was performed on solid and gaseous emission s. The fluorescence emission spectra of the integral methylenchloride extracts, in the range from 270 to 600 nm, were also studied. The expe rimental data concerning stack emissions and light hopper ashes showed that, under relatively good combustion conditions, both absolute leve ls 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 g ets definitely worse, PAH levels in the emissions may increase by up t o 2 orders of magnitude more than other variables related to fuel carb on conversion, such as CO in flue gas, unburnts and other classes of o rganics, even though the variations of all these parameters seem to be related.