Research On Drying Process Of Lignite In Paddle Dryers

Lignite is becoming more and more significant and catching more and more attention because of its abundant resources and low cost, but its high moisture content affects its value in use. So developing lignite drying upgrading technology which has wide adaptability to improve the utilization of lignite has significant implications.The author mainly researched the drying process of lignite in paddle dryer, the main contents include:basic properties of lignite, experimental research on drying lignite in paddle dryer, heat and mass transfer researches on drying lignite in paddle dryer and design of pilot system of drying lignite in paddle dryer.Research on moisture distribution of lignite got the conclusion that lignite has high total moisture and external moisture accounts for74.25%of total moisture, therefore removing most of external moisture can improve the utilization value of lignite. Because removing lignite’s external moisture is easy, the evaporation drying process is more appropriate in removing lignite’s external moisture.Experimental research on drying characteristics of fine particle lignite discovered that improving the drying medium temperature and reducing particle size of lignite was in favor of the removal of moisture in lignite. The drying process of lignite is in the falling drying rate stage. By fitting the experimental data, discovering that water effective diffusion coefficient Deff increases with increasing the drying medium temperature and decreasing the particle size. The drying activation energy of Jalainur lignite, which is in the range of36.400～37.458kJ/mol during isothermal drying process, is not controlled by particle size.Designing and setting up the drying lignite system in the one-shaft paddle dryer to study the characteristics of drying lignite, the author got the conclusion that speeding up the spindle speed leads to reduce the retention time and increase the output of lignite. The relationship between output of lignite and spindle speed presents a linear relationship. Increasing the angle of paddle dryer results in decreasing of retention time and increasing of the output of lignite. The influencing factors of drying lignite in paddle dryer include the oil temperature, the spindle speed and the particle size of lignite. Higher oil temperature, faster spindle speed and smaller particle size have better effect on drying lignite in paddle dryer. The drying process of coarse particle lignite in paddle dryer not only has a poor fluidity which even results in stuck phenomenon, but also has a poor heat transfer performance.The author considered the effect of oil’s thermal-convection resistance and wall’s thermal-conduction resistance in the particle transfer model of moving heating-plate type. Through numerical test, the error of average heat transfer coefficient and wet basis moisture content of dried lignite compared to experimental test is4.80%and7.72%in a typical condition. The modified heat and mass transfer model can simulate the lignite drying process in paddle dryer accurately.The pilot system ran stably and has the feasibility of large-scale industrialization.