Analysis of chlorine forms in hard coal and the impact of leaching conditions on chlorine removal

Abstract

This paper describes our current research into the removal of chlorine from commercial coals using leaching techniques in the Polish power industry. Chlorine removal studies were carried out for two samples from Polish power coals with the highest chlorine content. For the samples of output coals coming directly from mining plants, physicochemical property tests and technical and elemental analyses were performed along with a determination of the trace elemental content; furthermore, the physicochemical properties of ash obtained from the coals was tested, i.e., the chemical composition and fusion temperature of the ash. In addition, an analysis of the porous structure was carried out using physical sorption. Leaching tests for the removal of chlorine from coal were conducted to determine the impact of the following parameters on the degree of chlorine removal: temperatures in a range of 20–90 °C, times in a range of 30–240 min and coal fragmentation values in a range of 0.05–0.2 mm. For the purpose of this study, a Box-Behnken approach was used, and an analysis of variance (ANOVA) was used to determine the statistical significance of the variables studied. During each measurement, the dependence of the chlorine content of coal was determined after the leaching process on the tested Cld parameters (T, t, p); the tested parameters were then converted into values representing the dependency of each parameter on the degree of chlorine leaching β (T, t, p). The results of the studies, combined with the results of the X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) analyses, established economically optimal conditions for the removal of chlorine forms found in the tested coals, i.e., room temperature for HC2 coal samples and a temperature of 50 °C for HC1 coal samples, along with a leaching time of 120 min for both. Such conditions mostly ensure the removal of inorganic chlorine forms present in the coal material. Chlorine-free coal can be successfully used in combustion processes in the energy industry, thereby minimizing the adverse impact of chlorine on boiler components.