Improved Evaluation Method of Coal Spontaneous Combustion/Oxidation Characteristics

Abstract

Coal spontaneous combustion often occurs in storage processes, especially for low-rank coal with high volatile materials, which may lead coal yard caught fire and coal thermal energy losses. Therefore, it is important to accurately predict the spontaneous combustion tendency under coal storage status in real time. In order to determine the ignition point, the existing methods are all using pulverized coal samples, adding special oxidant artificially and then heating to accelerate the oxidation process. The particle size and the test conditions of those methods were quite different from the real coal storage condition. This research developed a new test method to evaluate the spontaneous combustion tendency. The method used granular coal samples, which the particle size is similar to its storage process, to test its temperature increasing under the humidity, pressure and air flow which are similar to its storage conditions. The spontaneous combustion tendency was judged by the temperature rise rate V70 of the sample at 69°C–71°C in adiabatic heating condition. 10 samples of different rank of Chinese coals were used to study. The results show that lignite had the largest low-temperature oxidation heating rate, and anthracite has the minimum. The lower coal moisture, the greater low-temperature oxidation heating rate. When the environment temperature is 70°C, with the increase of air flow rate, the rate of temperature rise increases firstly and then decreases. As environment temperatures rise, the temperature rise rate increases firstly and then decrease for the three types of coal samples, lignite has the maximum temperature rise rate, while anthracite has minimal temperature rising rate. Six kinds of coal samples were selected in order to verify the method precision. It was found that the temperature rise rate and repeatability limit of coal samples have linear correlation, and the basis for judgment and repeatability limit of the method are also provided. The method has high sensitivity and resolution of different coal ranks. According to the research, coal could be divided into three categories: strong spontaneous combustion tendency, medium spontaneous combustion tendency and weak spontaneous combustion tendency according to their temperature rise rate V70. The method could give great practical significant guidance for the scientific storage, blending, safety and efficient utilization of coal.