Fluorine distribution characteristics in coal and behavior of fluorine during coal combustion

The concentrations of fluorine in typical Chinese coals are determined by the pyrohydrolysis/FISE method. The distribution characteristics of fluorine in coal are obtained. The correlation between fluorine and ash, the probable mode of occurrence of fluorine in coal are discussed. Fluorine concentration ranges between 17-3145 μg &middot g-1 and the mean value is close to 200 μg &middot g-1. Good correlation between fluorine and ash content suggested that fluorine is present in these coals in inorganic mineral species. Fluorine emission characteristics during coal combustion are studied systemically in tube furnaces for the first time. The influence factors on fluorine emission and the relationship of fluorine emission with coal type, combustion temperature, retention period and combustion atmosphere are obtained and the production mechanism of gaseous fluorine during coal combustion are proposed. Experimental results indicate that fluorine emission appears to begin at 573-673 K and emission rates reaches about 96% at above 1473 K. Gaseous fluorine is probably originated from fluorine occurring as organic forms or adsorbed inorganic form in coals at low temperatures, and appears to come mainly from fluorine occurring as inorganic salt forms in coal at high temperatures.