Experimental study on spontaneous combustion characteristics of pulverized coal under minimum ignition temperature

In thermal power plant and coal chemical industry，raw coal needs to be processed into pulverized coal.Pulverized coal has the characteristics of small particle size，high ambient temperature and sufficient oxygen supply conditions during the preparation and transportation process，and is prone to spontaneous combustion.Minimum Ignition Temperature (Tm) refers to the minimum ambient temperature at which pulverized coal can spontaneously ignite under certain conditions，and it is an important parameter to measure the natural danger of pulverized coal.Therefore，it is of great significance to study the spontaneous combustion characteristics and thermodynamic behavior of pulverized coal at the lowest ignition temperature，to understand the spontaneous combustion behavior of pulverized coal at the lowest ignition temperature，and to establish a corresponding warning mechanism.In this paper，three kinds of coal powder with different metamor-phism degrees (Zhang Jiamao weak sticky coal ZJM，Yanzhou gas coal YZ and Changzhi lean coal CZ) were used as research objects.The spontaneous combustion characteristics of coal samples were tested with an oil bath program temperature control experimental device，and three kinds of coal powder Tm and delayed ignition time ti were determined.The variation rule of oxygen consumption rate and gas production of CO and C2H4 were obtained at the lowest ignition temperature.The apparent activation energy of three kinds of pulverized coal is calculated by means of thermodynamic analysis.The experimental results show that:①the minimum ignition temperatures of ZJM，YZ and CZ pulverized coal are 120 ℃，130 ℃ and 164 ℃ respectively，which increase with the degree of deterioration.The higher the degree of coal deterioration，the less the number of internal active groups，and the more heat required for spontaneous combustion，resulting in a higher minimum ignition temperature for high-degradation coal.The delayed ignition time of the three kinds of pulverized coal at the lowest ignition temperature is about 20 min；②the oxygen consumption rate showed a trend of first increasing and then slowly decreasing.At the later stage of the test，the low oxygen concentration caused the reduction of the oxidation reaction intensity of pulverized coal，and eventually the oxygen consumption rate showed a slow decline.The CO production at the lowest ignition temperature showed a first trend over time.After increasing，it will decrease，and C2H4 will be produced when the temperature of coal powder is about 120 ℃；③The apparent activation energies of ZJM，YZ and CZ pulverized coal at the lowest ignition temperature are 24.33，29.50 and 18.67 kJ/mol，respectively.Among them，the apparent activation energy of the most modified CZ pulverized coal is lower than that of the other two coal samples.High-deterioration coal samples have a high minimum ignition temperature and a high initial oxidation reaction rate.