The Transfer Model Of Lignite Drying In The Impulse Pneumatic Dryer And Process Design

Coal resources have an irreplaceable position in the energy field because of the rich reserves in the world. Shortage of oil and natural gas resources determines the strategic target in China-developing the coal chemical industry. Faced with the over-exploitation of high quality coal, people have focused on the development of lignite resources. China has vast indigenous reserves of Lignite. However, as the low rank coal, lignite have the disadvantages, like high volatile, high humidity content and low calorific value. Direct combustion of lignite not only has a low utilization rate, but also doesn't accords with utilization of clean energy resources. Its gasification, liquefaction, pyrolysis and drying is the main way to take advantage of the clean use of lignite.In this paper, momentum-heat transfer model of lignite drying was established for the purpose of improving quality. The performance of lignite drying in the impulse pneumatic dryer was studied in the laboratory, and was used to prove the reliability of the mathematical model. A large-scale impulse pneumatic dryer was designed based on the mathematical model, to achieve lignite drying in a small investment. The gas-solid flow in the pneumatic dryer was simulated by FLUENT.The model was one-dimensional including particle acceleration and particle deceleration, according to air drying technology. Experimental data were compared with simulation data to prove the accuracy of the mathematical model. The numerical relationship among tube height, heat quantity and gas-solid velocity difference was analyzed, as also the relationship of diameter and height of the impulse pneumatic dryer. It provided the basis for the equipment design.The main device was the impulse air tube. The subsidiary structure including screw conveyor, cyclone and bag filter was designed. System resistance model was made, and it provide the basis for selection of fan. A traditional pneumatic dryer, which was equal in height with the impulse pneumatic dryer, was designed. Efficiency of the impulse pneumatic dryer is verified by comparing the data, including gas temperature, moisture contents of particles, volumetric heat transfer coefficient, collected from the impulse pneumatic dryer and the traditional pneumatic dryer.The designed impulse tube was appropriately simplified. Two different structural model was established. One of them was arranged in parallel with intake-pipe and feeding-pipe, the other was arranged vertically. The two-fluid multiphase flow model in the two structural model was simulated with CFD software FLUENT. Velocity distribution, pressure distribution in gas phase and particle trajectory in solid phase was analyzed. It confirmed that, stable two-fluid multiphase flow was formed easily in the structural model that was arranged vertically.