Structure Optimization And Cooling Model Analysis Of Feed Counterflow Cooler

Cooling process is the last step in the pellet feed granulation process,which directly affects the quality of the finished products.Counterflow cooler is widely used in feed cooling due to its small footprint,low energy consumption,easy operation and the other advantages.Nevertheless,there are some general problems with the counterflow cooler,such as serious leakage of material,large wind resistance,poor uniformity of the wind speed field in the cooler and the scarcity of theoretical research on the cooling mechanism.Based on the above problems,the improved discharge mechanism is designed to improve the working performance of the cooler.The uniformity indexes of the wind speed field under different discharging schemes are analyzed to provide reference for the further structural optimization of the discharge mechanism.The effect of the low level caused by feeding process on the wind speed uniformity is studied and corresponding measures are put forward.The mathematical model of the cooling process is established and the effects of process parameters on the cooling process are studied to provide effective theoretical guidance for the actual process optimization.The main research work in this thesis is as follows:(1)Improved flap type discharge mechanism is designed in SolidWorks.The overall structure of the cooler is completed,and all the drive systems in the cooler are designed and calculated.(2)The stress,strain and maximum deformation of the dangerous parts under the working condition are obtained by ANSYS,including the cabinet,flap assembly,support and the spreader.The results show that all the stress values are within the allowable stress range of the material,and the maximum deformations are within the scope of the permit.(3)Six types of CFD models of coolers are established.The uniformity coefficients of the wind velocity field in three coordinate directions in 6 coolers are respectively obtained by simulating the wind velocity field in Fluent and processing the data later in Matlab.The results show that,in the horizontaldirection parallel to the inlet wind direction(X direction),the velocity uniformity in each type would rise along when airflow rises.In the horizontal direction perpendicular to the inlet wind direction(Y direction),the uniformity coefficient in 5 types is basically constant as airflow rises.The initial value of the uniformity coefficient in Y direction within the improved type is lower than others,but the value would increase gradually with airflow rising,thusly having little effect on the final moisture content of the feed.In the vertical direction(Z direction),the uniformity coefficient will increase in four types,however fluctuates greatly in the left two types.It is concluded that the multi-layer discharge structure limits the uniformity of wind velocity field in Z direction.The wind speed field at low level is studied and the results show that setting the installation height of the low level meter above 0.3m helps to reduce the influence of the low level on the uniformity of wind speed field during feeding process.(4)The deep-bed cooling of feed is simplified into several thin layers,and the partial differential equations of feed cooling is deduced according to the basic theory of heat and mass transfer.The model of drying performance parameters,for example,specific heat and equilibrium moisture content,and the model of drying media air are established.The thin layer drying equation of feed is established.The partial differential equations are discretized by the forward differential method and then the numerical calculations is carried out in the Matlab software.The moisture content,temperature of the feed and the humidity,temperature of air at any time or any height are obtained.The effects of initial temperature,initial humidity,airflow rate of air,initial moisture content,initial temperature of feed,height and residence time on feed cooling process are analyzed.