Theoretical and experimental study on low temperaturestage of coal self-heating

Understanding of coal spontaneous combustion could help reduce fire disaster in coal mines.This paper proposes a new view that temperature of coal-oxygen reaction in the low temperature phase of coal spontaneous combustion is not always accelerated increasing, even if external environment allows, but has the “self-limiting” feature in a certain period of time.The paper analyzes the reaction steps and coal oxidation model under low temperature adiabatic conditions and develop a theoretical model.The model is then validated by conducting adiabatic oxidation experimental on four different coal samples.The results show that at the beginning of adiabatic reaction between coal particles and oxygen, coal temperature accelerated increases with time, showing an exponential correlation.Then, the heating rate of low metamorphic coal samples decreases with time, showing a semi-parabolic correlation.With the increase of coal metamorphic degree, restricted temperature of low temperature adiabatic oxidation has the trend of shifting to high temperature and extreme heating rate decreases gradually.Adiabatic oxidation of coal at low temperature includes four stages, namely physical oxygen adsorption heating stage, free acceleration heating stage, restricted decelerated heating stage, and full reaction heating stage.The restricted decelerated heating stage is mainly resulted from interface effect of thin oxide layer.This effect should be paid attention to in the actual analysis of coal self-ignition.