Assesment of Spontaneous Heating Susceptibility of Coals Differential Thermal Analysis

Abstract

The auto-oxidation of coal is a complex physico-chemical process which is accompanied by the absorption of oxygen, formation of coal oxygen complexes and their decomposition leading to the liberation of heat. This complexity of the process is enormous because of the great diversity in the coal substance with the associated mineral matter and the condition of the heterogeneous mass, concurrent and over lapping reactions takes place which are very difficult to separate out. The rate of oxidation of coal at ambient temperature gives a measure of the proneness of coal to auto oxidation. From the economics stand point, even a small incidence in auto oxidation causes loss of production when it becomes necessary to seal off a section or a district resulting in the possible loss of machinery and the deterioration of reserves is potentially great. Fires in coal mines are one of the serious problems of Indian coal mining industry. In India every year many incidence of the fire occur in the underground and surface due to spontaneous combustion. Mostly the fire occurring due to spontaneous combustion per year is a function of the quality of the coal and the circumstances which it is subjected. They endanger not only the valuable lives of men in mine but also cause considerable economic losses to the organization affected by them. History of coal mines fires can be traced back to the year 1865, when the first fire was reported in Raniganj coal fields. Over 140 years fires have been reported till the year1967 from both Jharia and Raniganj coal fields and superior quality non-cocking coal in Raniganj coal fields.
Various methods have been used in laboratory for the study of relative tendency of coals to heat spontaneously. Most of the methods are based on the measurement of the oxidation rate and ignition temperature. The propensity of different coal to self heating has been studied in the laboratory using crossing point temperature, different thermal analysis, oxygen absorption method etc. the result of the test analyzed according to readily recognizable characteristics temperature and rates of heating under non adiabatic condition. These simple indices have historically been considered to be prediction of self heating liability.