Production Mechanism And Control Method Of Drying Induced Dust In Coking Coal

Coal moisture control is a process that the moist coking coal will be used to remove part of the water before its coking, until its moisture content is dried to about 6% and then is sent to the furnace for coking. Coal moisture control technology is benefitful to improve the production capacity of the coke, improve coal' s flowability and quality, reduce the energy consumption and pollution emission of coal coking. It's also helpful to extend the selection range of coking coal materials. However, low moisture content will reduce adhension between coal particles and increase the coal dust. Coal dust cause a bad working environment and sometime explosion danger. Thus,coal dust is a difficult technical problem in the coal moisture control process,and knowledge of the producing mechanism of dust is the foundation to solve the problem.This thesis focused on studying the producing mechanism of coal dust during the coal moisture control process,and then discussed the possible the method to control the coal dust.The main research contents and results in this thesis are as following:1) The drying property of coking coal:a series of experimental measurements were conducted to measure quantitatively the composition, particle size distribution, bulk density,flow characteristics and pyrolysis temperature of the coking coal. Experimental results showed that the flowability and particle size distribution of the coking coal changed greatly with the decrease of water. The fine, coal particles shedding contintiously from the initial largecoal particles cause the increasing mobility of coking coal; also, it is the main reason to form the coal dust.2) Dust phenomenon occuring in the drying of coking coal: This thesis carried out hot air drying and superheated steam drying of the coking coal in the static fixed bed, as well as dynamic fluidized bed and gravity fluidized bed.Experimental results showed that the water inside coking coal can beregarded as the surface water which is easy to be dried, and the dust mainly appeared in the final drying stage of coking coal. The wind speed had greatimpact on the drying rate and dusting of coking coal.3) The mechanism and control methods of coal dust:This thesis made some quantitative experimental studies about the relationship among the dust, water content and velocity of drying medium. According to the experimental results, the producing mechanism of coal dust can be explained as:Adhension between coal particles was reduced with the decrease of the coking coal's moisture content. The fine particles didn't aggregate anymore and shed continuously from the large particles' surface. These light fine coal particles easily produce coal dust under the drag force of the hot air. Possible control methods for coal dust can be: Maintaining a higher final moisture content of the coking coal;using multistage hot air jets, adjusting hot air velocity according to the water content of coking coal; the method of wet coal re-adsorption dust and so on.