Study On The Positive Pressure Gradation Dewatering Mechanism Of Flotation Concentrate

In coal preparation, high moisture content of clean coal has a bad influence on transportation and subsequent production, the particle size of flotation concentrate is fine, so its dewatering is difficult and becomes the main factor of clean coal moisture. In the methods of flotation concentrate dewatering, adding coarse particle is economical and effective, but this technology just stays in the stage of production practice, related theoretical study is little.In order to find the influence mechanism of flotation concentrate, and provide theoretical supports to the technology of adding coarse particle, firstly, this research analyses the flowing state of liquid in filter cake and the process of positive pressure filtration based on the theory of filtration; secondly, based on the gradation theory, the research conducts filtration experiments of different particle size gradation through gradation type selection and optimization; at last, the research analyses the changes of filtration cake structure from particle size distribution, porosity and average resistance of filter cake, and then analyses the relationship between filtration rate, cake moisture and filtration cake structure combined with the change law of filtration rate and cake moisture. Research results and main conclusions are as follows:(1) Adding coarse particles to flotation concentrate can prove the dewatering effects, for single particle size concentrate, the finer it is, the longer cycle time is and the higher cake moisture content is.(2) Making use of the settlement characteristics of different particles, letting coarse particles reach the surface of filter media first, forming the cake structure that fine particles are in the upper layer and coarse particles are in the lower layer can reduce blockage of fine particles effectively and prove the dewatering process.(3) In the process of filtration, most of the filter cakes are unsaturated because of various factors. Through analysis, the filter cake moisture content equation is derived, it is: In different gradation type, porosity, thickness and pore size of filter cake are constantly changing. When the particle size of coarse particles is large and the content of coarse particles is high, compressed air penetrates the filter cake and moisture is remained in the cake, so the change law of moisture is different.(4) In any gradation, the filtration rate is reducing as the filtration process goes on, and it varies as power function, its change law can be described as bu a t-(28) ×, and a is positively correlated with the particle size. The change of filtration rate is related to various factors, such as filter cake average resistance, particle size distribution and pore structure. Generally, there exist inverse proportions between filtration rate and average resistance, but in some gradation, the filtration rate is greatly affected by drilling of fine particles, air penetration and leakage.In practical production, conducting some experiments to find the suitable particle size and content is a good way to reduce filter cake moisture and increase filtration rate.