Physical nature of the indexes for ranking self-heating tendency of coalbased on the conventional crossing-point temperature technique

The physical nature of the parameters defined by the conventional crossing-point temperature technique was investigated for the purposes of identifying their reliability in assessing the tendency of coal towards self-heating and spontaneous combustion.By theoretically simulating the thermal response of a coal sample in a linearly heating environment,the effects of sample moisture content on the crossing-point temperature(CPT)measured and the derived indexes such as HR and FCC were studied.Typical pattern was observed for the temperature variation at the sample center,which can be classified into three stages,initially linear temperature increase,progressive temperature increase,and the subsequent stage of drastic temperature increase.The simulated results were compared with those available in the literature.With the increase of sample moisture content,the CPT value increases,indicating the moderation of the sample’s self-heating tendency;however,the assessment results of the indexes HR and FCC show the reverse.It was confirmed that the CPT of a sample corresponds to the critical temperature for the sample to undertake significant oxidation,signifying the hardness of the sample to undergo self-heating.It can be used as a major index for ranking the self-heating tendency of coal.The indexes HR and FCC are the indicators of a sample to release heat at the CPT,which have no direct link to the oxidation capacity of a sample at the ambient temperature.Therefore,these two indexes are only suitable for the further assessment of the samples having an identical CPT.