| With the increase of the output in coal and the ration of coal preparation, the output of coal slime is greatly boosted. Due to its high content of moisture, the widely utilization of coal slime is limited. Thus the rotary drum dryer which can improve the quality and enhance the utilization of coal slime is used to dry the coal slime. And this method plays a significant role in environmental protection and recycling resources.Based on the motion mode of particles of coal slime in rotary dyer, the motion process is divided into two stages which are lifting and falling phase. First of all, the slime particles sliding angle and the maximum discharge angle can be calculated based on the physical parameters. Secondly, combining with discharging angle and the board characteristics and analysis on the effect of gravity on coal slime falling process, the average height and time of the drop of slime particles were calculated inside drum dryer. Lastly, the horizontal forward displacement of slime particles can be obtained based on analysis on the horizontal force of flue gas. A mathematical model that predicts the retention time of slime particles was established during lifting and falling period.According to the characteristics of coal slime, based on the theoretical analysis and experimental research, the function equation of moisture diffusion coefficient correlated with moisture content and temperature was obtained, which provides reference for calculating quality of moisture diffusion during drying process. The function of the heat loss on outside dryer wall was obtained by analyzing the thermal resistance of the drum and the heat preservation layer. The results of the heat transfer were analyzed to provide theoretical basis for the rotary dryer by using continuity equation, energy conservation equation, mass equation and heat transfer equation. Based on the above calculation, the parameters of quality of moisture diffusion, flue gas temperature, slime particles temperature and heat loss on outside wall which are in a stable operation process were obtained.Drying process of coal slime particles was divided into several circulation units. The simulation program have been developed according to the equation about relevant various programs and parameters in a particular unit. The change process of different parameters of coal slime in all circulation units can be simulated by inputting the initial physical parameters of coal slime, flue gas and roller. The heat loss on outside wall of roller and the moisture content in export can be obtained in the final calculation. And the influence on the heat loss and the moisture content in the production is analyzed.Comparing the simulation results and the actual parameters, it reaches that the model can fit well with the actual operation. So the simulation process can be used to replace the experiment to optimize the working parameters. Selected the flue gas temperature, velocity at entrance and rotary cylinder speed as dependent factor, and final moisture content of coal slime as response factor, the regression models were built using response curve method by Design-expert software. The optimal parameters were obtained as follow:the flue gas temperature at entrance is713.7℃, flue gas velocity at entrance is7.6m/s and rotary cylinder speed is4.7r/m. The interaction effects of factors on moisture content of coal slime were analyzed.In this research, a combination of simulation and analysis software was adopted to study the drum dryer based on interaction effect of the material motion, heat and mass transfer, and various factors. The comprehensive impact charts of various factors on the heat loss and moisture content were obtained, and the working parameters in operation were optimized. The results can provide a theoretical basis for actual design of the drum dryer which aims to improve efficiency and reduce costs. |
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