Productivity Improvement And Process Optimization Of Vertical Leaf Filters In Wenshan Alumina Refinery

In the production of alumina by the Bayer process,the main task of controlling filtration is to refine the green liquid resulting from settling operation into purified liquor through the vertical leaf filters.Because of the influence of external factors,such as the complex composition of ore and the unstable quality of lime,both the productive capacity of vertical leaf filters and the proportion of lime milk added have not reached the design values since the operation of Yunnan Wenshan Aluminum Co.,Ltd.Moreover,the filters cake generated by the filters has not been recycled efficiently.Considering the problems existing in the practice,four Vertical Leaf filters with each filtering area of 377m²were taken as the research object in this thesis.Based on the theory of liquid-solid separation,the principles of filtering equipment and the alumina production,the spare parts of Vertical Leaf filters,auxiliary equipment,lime milk system and filters cake of the leaf filter were respectively studied in detail.The optimum volume proportion and reaction time of the green liquor reacting with lime milk are determined,and a new type of component of Vertical Leaf filters and a filter for filter cake filtration have been developed.The capacity of the Vertical Leaf filters si increased remarkably and its index is optimized greatly.Some of the key technologies have reached the advanced level.The main research contents are as follows:（1）Through in-depth analyses of the body equipment andmachine accessories of the vertical leaf filters,a new type of filter is developed,the filter cloth adhesive strip is replaced,the blockage of filter cake and buffer green liquid tank was solved,and the mismatch between the green liquid pump and the vertical leaf filter is completely eliminated.Finally,the capacity of vertical leaf filter is increased from 380m³/h to610m³/h.（2）By studying the change of Gibbs free energy with temperature in the reaction of forming hydrated garnet with different silicon saturation coefficients,the optimum reaction temperature is optimized to be 88°C.Through the on-the-spot tests of the volume ratio of lime milk added to green liquor,the ratio is decreased from 32.4‰to 6.4‰.（3）A new type of plate-and-frame press filter,which can run stably for a long time at 92°C and 160g/L Na₂O_kconcentration,has been developed.Furthermore,the recovery rate of the filter cake has been increased from 43%to 100%.（4）An annual increased benefit of 33.72 million yuan has been achieved with the total investment of 3.89 million yuan for this project.