For the knowledge about the mass transfer process or heat transfer process in the rotary kiln, the active layer is considered as the most important part. However, when the reaction rate and the heat transfer rate are low, the mass transfer and the heat transfer of the materials in the inactive layer are also very important. For the gross cut value, the simple inactive layer model is only applicable to the mass transfer situation of the deep bed and low coefficient. Otherwise, the model for the inactive layer must be combined with the model for the active layer.
Based on the study on the physical process of the particle movement in the active layer, the thickness and the shape of the active layer can be calculated to establish the model of the mass transfer in the active layer. Then you can use the model to estimate the concentration distribution of the gas and finally determine the effective mass transfer coefficient of the rotating speed of the given rotary, the particle size and the thickness of the material bed. At last, the comprehensive model for the mass transfer can be established.
The model of the inactive layer is mainly the convective mass transfer produced by the gas due to the movement of the particles of the material, while the model for the active layer regards the spreading effect between the particles of the materials as the main body. For the high cut value, the model of the active layer can not accurately describe the mass transfer process in the rotary kiln. You must also consider the impact of the gas into the inactive layer.
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