Experiment study on partical size affected to coal spontaneous combustion limit parameters in goaf

In order to study the paricle size affected to the limit parameters of coal spontaneous combustion in the goaf, a programmed temperature rising test devi ce of coal spontaneous combustion was applied to measure the spontaneous combustion feature parameters of the long flame coal, weak coking coal and lean coal sa mples under the condition of five different particle sizes. According to the spontaneous combustion feature parameters measured from the test, the spontaneous combu stion limit parameters of coal under the different particle sizes were calculated and obtained. The test results showed that the heat released strength of the coal sample s would be in a declined tendency with the coal metamorphic degree increased and the critical temperature of the coal samples would be increased with the coal metam orphic degree increased. A minimum thickness of the coal left and the lower limit oxygen concentration would be in a positive correlation to coal metamorphic degree, th e upper limit air leakage strength would be in a negative correlation to coal metamorphic degree. During the coal oxidization process, an extremum of the coal spontane ous combustion limit parameters would be occurred in the vicinity of the spontaneous combustion critical temperature. The coal particle size would have obvious influen ces to the spontaneous combustion limit parameters. Under the same condition, the upper air leakage strength would be decreased with the coal particle size increased and the minimum thickness of the coal left and the lower limit oxygen concentration would be increased with the coal particle size increased. The relationship between t he coal spontaneous combustion limit parameters and coal particle size could meet the twice polynomial relationship. The test results could provide the basic parameter s to judge the spontaneous combustion danger area in the goaf.