Experimental Study On Thermally Upgraded Low-Rank Coal Of Ximeng And Its Slurryability

Recently, as pattern of energy supply-demand in China is changing that the cost of high-rank coal such as anthracite and bituminous coal is rising and the reserves of it is declining, low-rank coal gradually highlights its advantages that having lower mining costs and lower market prices. It can be predicted that using lignite efficiently and cleanly would have a wide development prospect in China. However, the high moisture content and the greater tendency to combust spontaneously restrict the wide-range use of lignite. Therefore, the premise of its application is to study the drying of low-rank coal.This article described laboratory experiments conducted to characterize the status of the lignite of XiMeng from the Inner Mongolia before and after thermally upgraded process. The results on drying kinetics, re-absorption of coal samples, morphology change, and proximate analysis of coal samples before and after drying were discussed.The rapid moisture-determining instrument was used to simulate the process of constant temperature drying on the lignite of Ximeng. By the scanning electronmicroscope (SEM), it was observed that the surface morphology of dried coal is changed, such as breaking down and pulverization. By the Nitrogen adsorption instrument, it was observed that surface area and pore volume both have small amplitude. Different drying temperatures (70,100,120℃), particle sizes (0.5-0.6,0.6-1.6,1.6-4mm), and drying time (2,3.5,9,30min) were chosen to study the features of drying and reabsorption of the lignite. The results showed that the drying process was mostly affected by the particle size and temperature; the reabsorption amount of water mainly depended on the moisture of the dried coal, the damage of the void structure, the particle size and the variation of the environment humidity. Among common thin layer drying models, Modified Henderson and Pabis model showed the better predictions. At the same time, the effective diffusivity coefficient and the activated energy for the moisture diffusion were calculated by applying the Fick’s diffusion model and Arrhenius type relationship.The muffle furnace with nitrogen was used for the experiment of thermally upgraded at100-350℃. The experimental results showed that thermally upgraded process could effectively remove the moisture and oxygen-containing functional groups and improve the coal rank. As the temperature rised, the surface morphology of modified lignite gradually became smooth and hardened, the pore structure of the lignite had been changed that surface area and pore volume both increased first and then decreased, and it came to a head at100℃.The slurry experiment showed that lignite before and after thermally upgraded process CWS present pseudoplastic fluid characteristics with shear thinning. The solid concentration of CWS was effectively increased with improving thermally upgraded temperature. High thermally upgraded temperature is beneficial for the fluidity and stability of CWS.