Experimental Study On Combustion And Grinding Characteristics Of Coal And Semi-coke

The environmental pollution caused by energy consumption has become serious with the rapid economic development of China in recent years.Based on the current situation of China’s energy reserves,the efficient and clean use of coal is becoming more and more important for building an environment-friendly and sustainable society.The combustion characteristics of coal and semi-coke directly affect the economic and environmental benefits of energy utilization.The grinding characteristics are an indispensable and important indicator in the pulverizing system.It affects the fineness and uniformity of coal particles after grinding,thus affecting its economic benefits and combustion characteristics.In this paper,four coal types of Ximeng lignite,Pingzhuang lignite,Shenhua sub-bituminous coal and Huainan bituminous coal were selected and pyrolyzed to produce semi-coke.The effects of different coal types and final pyrolysis temperature on proximate analysis,ultimate analysis,calorific value,semi-coke yield,surface morphology,pore characteristics and chemical structure were studied;The combustion characteristics and the release of gaseous products were studied based on TG-DTG-DSC coupled technology.The combustion characteristic index and reaction kinetics parameters were calculated;The grindability of coal samples and the effect of pyrolysis final temperature on the semi-coke grindabilitywas studied by Hardgrove apparatus;The particle size distribution characteristics of the pulverized whole particles and the less than 74μm fine powder were measured by a Malvern particle size analyzer.The Ronsin-Rammler distribution is used to calculate the uniformity parameter n and the thickness parameter b and the intrinsic relation between them and grindability is analyzed.The experimental results show that pyrolysis removes most of the water from the coal,resulting in higher calorific value,volatile fractionation,decomposition of oxygen-containing functional groups,breakage of bridging bonds,,loosening of the structure.The coal surface cracks and slits and pore structure developed.With the increasing pyrolysis temperature,the O/C atomic ratio decreases and the coal rank increases.When the temperature is higher than 600 ℃ thermal polycondensation occurs and the pore collapses.The TG-DTG-DSC curves shifted to the high temperature zone,and the CO and CO₂ rapid release temperature of the semi-coke was much later than that of the raw coal with the increasing pyrolysis temperature.The precipitation peak moves toward the high temperature region.The grinding process of coal and semi-coke is dominated by volumetric crushing,accompanied by surface crushing.The grindability of different coal coke is related to its coal quality.With the increasing pyrolysis temperature,the grindability of the semi-coke increases first and then decreases,which is in accordance with the variation law of porosity.The particle size distribution of the whole particles after grinding satisfies the Ronsin-Rammler particle size distribution.The median particle size and the characteristic parameters n and b have a good correspondence with the grindability.The particle size distribution of the fine powder less than 74μm is related to the inherent grinding characteristics of coal.