Experimental Study on Crushing Characteristics of Lignite under Different Load Conditions

Abstract

Coal particle size and the degree of compaction significantly affect the goaf heritage ventilated environment and the process of spontaneous combustion of coal, the distribution of particle size and compaction degree are also affected by the load size and the application process, and the distribution of stress in goaf is not uniform, resulting in the distribution of particle size and compaction degree of mined-out coal. It is necessary to carry out experimental studies on coal crushing granularity and compaction degree under different loads and loading processes to clarify its distribution law. Therefore, experiments on the coal crushing were conducted, to analyze the compression behaviors and the distributions of the particle size with different loading speeds and loads. The results show that, in the process of slow pressure application, the lump coal was constantly compressed, compacted, and broken. With the increase in the axial load, the coal compressibility increased, and the coefficient of fragmentation and porosity decreased. When the stress was greater than the compressive strength, the variation trend slowed. When the stress was greater than two times the strength, as the load continued to increase, compression basically did not occur. The thickness and porosity of coal will be reduced to 0.5 times that of loose coal when a significant change of the compression ratio occurs. After the coal body was under pressure, the degree of crushing intensified. The fractal dimension of the particle sizes of broken coal particles followed a logarithmic relationship with the increase in the stress. With the increase of stress, the degree of crushing increased, and in the process of pressure crushing, the particle size of 2.5 mm was an important boundary. When the stress was more than two times the strength value, the degree of crushing under the increased load did not increase significantly. When the residual coal in a goaf is affected by pressure, if there is no impact, the influence of the initial pressure and periodic pressure variations on the residual coal in the goaf will not be significant, and the accumulation and crushing degree of residual coal will only be affected by the peak stress.