Study On The Crushing Characteristics Of Lignite With A Laboratory-scale Medium-speed Mill

In China, most of the coal is for direct combustion, in which the consumption in power plants accounts for the largest proportion and has the fastest growth. In recent years, liginite, which was regarded as inferior coal, receives growing attention, and has been used in more and more power plants. At present, more than 90 percent of China’s coal-fired power plants applying pulverized coal combustion and grinding is an essential part in this coal pulverizing system. Energy consumption during grinding process and size distribution of grinding product are two important indicators of the whole system. The best condition is to get the optimum fineness of pulverized at the lowest energy consumption. Consequently, studies of lignite on its grindability index changes and grinding process are of great significance to reduce energy consumption, improve efficiency and control size distribution of pulverized coal.The mineralogy characteristics of typical lignite from Inner Mongolia were studied. The ash content of coal is 23.69% and its net caloric value, Qnet.ar, is 20.05MJ?kg-1. The lignite has medium ash content and medium calorie. Besides, the main mineral compositions of the coal are quartz(Si O2), pyrite(Fe S2) and kaolinite(Al2Si2O5(OH)4), which interlocked with coal tightly and disseminated finely.The influences of density and particle size on VTI grindability index were researched. The results show that at a same size fraction, the VTI grindability index of lignite increases with increasing of the density. While at the same density fraction, The VTI grindability index increases slightly with increasing of initial particle size.In this paper, a model machine of medium-speed mill was applied to study the grinding process. The results indicate that the grinding of lignite matches primary crushing kinetics. That is the breakage rate rises with increasing of initial particle size. As the initial particle size becomes larger, the production rate of-0.09 mm fraction changes from diminishing to increasing, and followed by a decrease during the grinding process. As for the mill power, it gradually decreases to reach a relatively stable state ultimately. With grinding time passing by, the fineness of grinding products diminishes with decreasing of initial particle size, and at different grinding stage, the size fraction presents approximately normal distribution. Besides, the grinded particle size characteristics can be reflected by R. Rosin—E. Rammler equation. When the feed size is 11.2 ~ 8.0mm and grinding for 1min, the corresponding equation shows as follows: = 100-0.58321.183What is more, effect of adding carbon black as grinding aid on grinding characteristics of lignite was preliminary analyzed. With the carbon black dosage rising, the increment yield of-0.09 mm rapidly increases first and then decreases slowly, and maximizes at the dosage is about one percent of coal. The VTI grindability index test results show that adding grinding aid can increase VTI grindability index of each density, and its increment increases with the increase of density. After adding grinding aid, production rate of-0.09 mm fraction keeps the same change rule as before, but has a higher production rate. Besides, the effect of grinding aid improves with a longer grinding time. To summarize, at an approximately same mill power, adding grinding aid can minish the fineness of grinding products, which indicates that adding grinding aid can reduce the power consumption of grinding.