Experimental Study on the Variation of Surface Widths of Lignite Desiccation Cracks during Low-Temperature Drying

Abstract

Significant volume shrinkage and drying cracking of high-water-content lignite will occur during low-temperature drying. To determine the variation behaviors of the drying shrinkage rate and desiccation crack surface width in the process of lowtemperature drying, low-temperature and low-humidity drying experiments were conducted, and the variations of the surface widths of the desiccation crack with time and water content of old lignite were examined. The results showed that the slow drying of lignite at low temperatures caused significant volume shrinkage and desiccation crack formation, and the occurrence and development of desiccation cracks were highly nonuniform. Three stages of the variation of surface widths of the desiccation cracks were observed with the water content decrease: an initial rapid increase stage, a second slow decrease stage, and a final stable stage, and the average width of the desiccation cracks increased in a Gaussian function. The higher the evaporation rate and volume drying shrinkage rate, the lower the surface width of the desiccation cracks under low-temperature drying conditions. To achieve safe and green mining, storage, transportation, processing, and utilization of lignite, the moisture content of old lignite should be controlled to be above 13− 15%.

Experimental Study on Spontaneous Combustion Characteristics of Large Coal Particles after Soaking

“…When coal was immersed in water for a certain period, the water content increased from the outside in, accompanied by significant swelling. 16 When coal was under evaporation conditions, moisture loss via evaporation occurred gradually. As the moisture loss occurred, the coal began to exhibit different degrees of drying shrinkage and volume shrinkage, the surface exhibited many cracks, and the crack width, crack length, and humidity in the sample chamber gradually increased.…”

“…The samples of lignite in this experiment were obtained from the Fengshuigou Coal Mine of the Pingzhuang Coal Company in Inner Mongolia, China. The process of coal sample crushing preparation is the same as refs ( 7 ) and ( 16 ), and crushing and soaking are shown in Figure 10 , the water used for soaking is distilled water.…”

Low-Field NMR Experimental Study on the Effect of Confining Pressure on the Porous Structure and Connectivity of High-Rank Coal

“…The pore and fissure structure characteristics of coal determine the physical and chemical properties of coal seams to a certain extent. 1 − 3 Coalbed methane (CBM) is mainly stored in coal reservoirs in an adsorbed form or a free state, which is high-quality clean energy. 4 − 6 China is rich in CBM resources, ranking third in the world.…”

Rapid Contrastive Experimental Study on the Adiabatic Spontaneous Combustion Period of Loose Lignite

“… 2 − 4 Moreover, it significantly affects other coal-related activities, such as the storage, transportation, processing, and utilization of coal. 5 After coal contacts oxygen, oxidation reactions occur. Under the comprehensive influence of internal and external factors, when heat accumulates, the temperature of the coal increases continuously, and spontaneous combustion occurs.…”

“…The spontaneous combustion of coal is a well-known phenomenon worldwide . It significantly affects and restricts the safe production of coal mines, threatens the lives and health of miners, and causes greenhouse gas emissions and environmental pollution. − Moreover, it significantly affects other coal-related activities, such as the storage, transportation, processing, and utilization of coal . After coal contacts oxygen, oxidation reactions occur.…”