最低点火温度条件下煤粉自燃特性试验研究

火电厂及煤化工行业中需要将原煤加工成煤粉,煤粉在制备及输送过程中具有粒度小、环境温度高和供氧条件充分等特点,易发生自燃现象。最低点火温度Tm指在一定条件下煤粉能够发生自燃的最低环境温度,是衡量煤粉自燃危险性的重要参数。因此,研究煤粉在最低点火温度下的自燃特性参数及热动力学行为,对了解在最低点火温度时煤粉自燃行为、建立相应的预警机制具有重要意义。以3种不同变质程度的煤粉(张家卯弱黏煤ZJM、兖州气煤YZ和长治贫瘦煤CZ)为研究对象,采用油浴程序控温试验装置对煤样自燃特性进行测试,确定了3种煤粉的Tm和延迟点火时间ti;得出最低点火温度下各煤样耗氧速率、CO及C2H4产生量的变化规律;采用热动力学分析方法计算了3种煤粉的表观活化能。试验结果表明:①ZJM、YZ和CZ煤粉的最低点火温度分别为120、130、164℃,随变质程度的增加而增加;煤的变质程度越高,内部活性基团数量越少,自燃需要热量更多,导致高变质程度煤的最低点火温度较高;3种煤粉在最低点火温度处的延迟点火时间均约为20 min。②耗氧速率呈现出先增加后缓慢减少的趋势,在试验后期由于氧气浓度较低,引起煤粉氧化反应强度降低,最终导致耗氧速率出现缓慢下降;最低点火温度处的CO产生量随时间呈现出先升高后降低趋势,当煤粉温度约120℃时,产生C2H4。③最低点火温度处ZJM、YZ和CZ煤粉的表观活化能分别为24.33、29.50和18.67 kJ/mol,其中变质程度最高的CZ煤粉的表观活化能低于另外2个煤样,这表明高变质程度煤样的最低点火温度高,初期氧化反应速率较高。

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 metamorphism 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.