Fragmentation characteristics of Xianfeng lignite during thermal upgrading

LI Songze; QIN Xizhuang; HAO Meilu; LIANG Peng

Abstract：China's lignite resources are abundant,it is difficult to utilize for the high oxygen content and water content.Thermal upgrading is one of the effective means to achieve clean and efficient utilization of lignite.However,the lignite in the process of thermal upgrading faces the problem of easy fragmentation and pulverization,resulting in high dust content in tar,difficulty in dust removal,and pipeline blockage,which has become a bottleneck hindering the de-velopment of lignite upgrading technology.This article takes Xianfeng lignite(XF)as the raw coal,the particle size change,cumulative distribution curve,overall particle size distribution,relative fragmentation rate and fractal di-mension of XF at different temperatures were investigated on the rotary furnace thermal upgrading experimental device,and the distribution of XF thermal fragmentation product at different temperatures was studied,and the differ-ences in ash content and mineral composition of thermal upgrading products were analyzed by X-ray fluorescence(XRF)and X-ray diffraction(XRD).The results show that XF undergoes significant fragmentation dur-ing the thermal upgrading process,with a particle size of 1-6 mm being the main generation range of fragmented parti-cles.The pulverization particle size increases with increasing temperature,with the largest increase observed at 0-0.1 mm.At 450-500℃,the relative fragmentation rate of XF increase the most,and the increase of temperature pro-motes the fragmentation,leading to an increase in fractal dimension and a more complex degree of coal particle frag-mentation.The variation of ash content with fragmentation particle size is not significant,and minerals in coal are more likely to exist in the pulverization particle size.The ash content gradually increases with the decrease of particle size of thermal fragmentation products.The ash content of the thermal fragmentation product at 550℃is higher than that at 450℃and 350℃,the Ca element content decreases with decreasing particle size,the Si and Fe element content in-creases with decreasing particle size,and the change of Al element content is not obvious.The XRD results show that quartz and calcite belong to passive distribution,while pyrite is more easily distributed to pulverization particle size due to thermal decomposition,which belongs to active distribution,and pyrite thermal decomposition leads to the formation of cracks and cavities inside the coal particles,which is one of the causes of lignite fragmentation.