The mode of occurrence and combustion characteristics of chlorine in British coal

Abstract

Both classical and instrumental methods of analysis have been used to establish the most likely mode of occurrence of chlorine in coal. Thermal and solubility characteristics of the chlorine to coal bond have been studied extensively. A method for the determination of ‘organic’ chlorine has been shown to be unsuitable for coal. X-ray radiographic studies for the measurement of porosity of coal seams have shown the need to take into consideration the variation in proportions of lithotypes present. Impregnation of coal with sodium chloride solution with and without a radiotracer has shown that a reaction occurs within the coal's microstructure. Various chemicals and heat have been tried to convert the chlorine present in coal to inorganic chlorides. Some success was achieved using calcium oxide. The likelihood is that chlorine is present in one form uniformly distributed and linked ionically to the coal substance but sufficiently labile to be evolved mainly as hydrogen chloride at temperatures above about 170°C. It has no particular relationship with nitrogen, sodium or other alkali/alkaline earth metals. It is further suggested that chlorine has been deposited in coal after the rank has been established (epigenesis) via hypersaline strata waters.