Experimental Studies for Assessing Spontaneous Combustion Risk of Some Indian Coals

Abstract

The self-heating or the spontaneous combustion of coal is processed by which the freshly exposed coal at ordinary atmospheric temperature when is exposed to oxygen undergo self-heating i.e. increase in its temperature and ultimately leading to auto ignition and mine fire. This spontaneous combustion leads to mine fires and are prime concern in the mining industry and let to huge coal loss and mine disaster. For safe coal mining, transportation, storage and uses, understanding the coal liability towards spontaneous combustion is important. Spontaneous heating liability depends upon the intrinsic as well as the extrinsic properties of the coal. In the present work, the spontaneous combustion susceptibility of a number of coal samples belonging to two different coalfields e.g.Bharat Coking Coal Limited (BCCL) and Central Coalfields Limited (CCL) of Coal India Limited, have been studied and its correlation with different intrinsic properties have been made. The objectives of this study is to assess the spontaneous heating liability of coal samples using differential thermal analysis and crossing point temperature and to establish a relationship between the spontaneous heating liability risk and intrinsic properties of coal samples. For this study, seven coal samples were collected from BCCL and CCL. Proximate analysis, bomb calorimetry, crossing point temperature (CPT) and differential thermal analysis (DTA), experiments were conducted to find the intrinsic properties of coals and assess their liability towards spontaneous heating. The paper summarizes the liability of different coal samples to spontaneous heating based on experiments conducted as well as broadly classifies the coal samples into poorly, moderately and highly susceptible to spontaneous heating risk. The transition temperature (T_c) indicated a very accurate measure of liability to spontaneous heating as they show high correlation coefficients with volatile matter, moisture and fixed carbon. These were 0.88% with moisture, 0.84% with volatile matter and 0.74 for fixed carbon contents. Lower the transition temperature of coal is higher will be the liability of coals to spontaneous heating. It was also observed that DTA study was found to give better correlation and hence, it may be used for assessment of spontaneous heating susceptibility of coal. It was observed that the coal samples containing high moisture are in general more liable to spontaneous heating. Spontaneous heating also shows a direct relationship with volatile matter hence higher the volatile matter in the coal samples is more will be the liability towards spontaneous heating. Ash percentage also has negative slope [-1.87] with transition temperature but the correlation coefficient is very low [0.15]. It has also lowest correlation coefficient (0.10) values with CPT. Gross calorific value is also directly dependent on the fixed carbon. Coal samples having higher fixed carbon are less liable for spontaneous heating. Ash has very low correlation coefficients with CPT and transition temperature and hence is not helpful in the assessment of liability towards spontaneous heating and it is of least importance.