Study On Dewatering Mechanism And Regulation Of Coal Slurry Filtration Based On Filter Cake Pore Structure

In this paper,the coal slurry filtration device and coal slime filter cake solidification device were designed and set up,and the method of coal slime filter cake solidification and pore structure measurement were determined.The characteristics of filter cake pore structure and the change rule of filter cake pore structure with time or in space were studied.The microscopic model for permeability containing pore cross-sectional shape was derived,and the permeability of filter cake during coal slurry filtration was studied.The influence and significance of particle size composition,filtration pressure and filter chamber thickness on coal slurry filtration effects were studied,and the mechanism of coal slurry filtration is revealed from microcosmic angle.Finally,based on the regulation of filter cake pore structure,the processes of subsection filtration and secondary flocculation filtration for coal slurry were proposed.The main conclusions are as follows:I.Study on pore structure characteristics of coal slime filter cake(1)The influence of particle size composition on pore structure for filter cake shows that an increased amount of-0.074 mm particles content results in smaller pore diameter,pore area,pore perimeter and porosity,and slower decreasing trend of pore diameter,pore area,pore perimeter and porosity.With the increase of-0.074 mm particles content,the proportion of small pores increases,the uniformity of pore size distribution first decreases and then increases,and the skewness and kurtosis of pore size distribution gradually decrease.It also leads to more irregular pore shape,more zigzag seepage channel and more complicated pore structure.(2)The influence of filtration pressure on pore structure for filter cake shows that as the filtration pressure rises,filter cake pore compresses,pore area and porosity descend,but pore diameter and pore perimeter a ascends.The increased filtration pressure also enhances the penetration of high-pressure air,decreases the proportion of small pores,and increases the uniformity,skewness and kurtosis of pore size distribution.In addition,it complicates the pore structure with more irregular pore shape and more zigzag seepage channel of filter cake.(3)The influence of filter chamber thickness on pore structure for filter cake shows that an increase of filter chamber thickness results in smaller pore diameter,pore area,pore perimeter and porosity,and slower decreasing trend of pore diameter,pore area and pore perimeter.With the increase of filter chamber thickness,the proportion of small pores increases,and the uniformity,skewness and kurtosis of pore size distribution gradually decrease.It also leads to more irregular pore shape and more zigzag seepage channel of filter cake.(4)The change rule of filter cake pore structure with time shows that an increase in filtration time results in pores seriously filled with fine particles,smaller pore diameter,pore area,pore perimeter and porosity,and slower decreasing trend of pore diameter,pore area,pore perimeter and porosity.With an increase in filtration time,the uniformity,skewness and kurtosis of pore size distribution gradually decrease.It also leads to more irregular pore shape,more zigzag seepage channel and more complicated pore structure of filter ckae.(5)The change rule of filter cake pore structure in space shows that coal particles will appear sedimentation stratification duing filtration,resulting in uneven particle size distribution of filter cake in space.Under the uneven particle size distribution in space and pores filled with fine particles,the distribution of filter cake pore structure in space does not show a monotonous change,but fluctuates around a value.II.Study on the dynamics of filtration dehydration for coal slurry(1)The research on permeability of filter cake during coal slurry filtration shows that with the filtration process going on,the pore formed will be filled with fine particles,resulting that the permeability of filter cake decreases rapidly at the beginning,and then decreases gradually.The thickness of filter cake controlled not more than the critical thickness can achieve high-efficiency filtration of coal slurry.(2)The research on permeability microscopic model shows that the effects of the pore cross-sectional shape on permeability are found to be significant.It is also found that the more irregular the pore cross-section,the greater is the influence of the pore cross-sectional shape on permeability.Compared to other permeability models,the proposed permeability model containing pore size distribution,pore tortuosity,and pore cross-sectional shape is more closely related to the microstructure of filter cake,and it is more suitable for predicting the permeability of coal slime filter cake.(3)The research on filter cake permeability shows that an increase of-0.074 mm particles content or filter chamber thickness result in lower porosity,more complicated pore structure,smaller permeability of filter cake,and slower decreasing trend of filter cake permeability,which is in accord with the changing rule of dehydration rate for coal slurry filtration.The higher the filtration pressure,the smaller the permeability of filter cake is.This is in accordance with the change law of filter cake pore structure.III.Study on dewatering mechanism of coal slurry filtration(1)The influence mechanism of particle size composition on coal slurry filtration effects shows that with the increase of-0.074 mm particles content,the porosity of filter cake descend,the proportion of small pores increases,resulting that the moisture of filter cake rises gradually,the solid content of filtrate increases,the formation time for filter cake becomes longer,the dehydration rate of coal slurry filtration decreases,and the decreasing trend of dehydration rate for coal slurry filtration gradually slows down.This is consistent with the influence of particle size composition on filter cake pore structure and permeability.(2)The influence mechanism of filtration pressure on coal slurry filtration effects shows that Filtration pressure is the power for coal slurry filtration,and the higher the filtration pressure is,the smaller the pore replaced by high pressure is.As the filtration pressure rises,the moisture and formation time of filter cake decrease,and the solid content of filtrate and dehydration rate increase.The higher the filtration pressure,the slower the moisture and formation time of filter cake decrease.(3)The influence mechanism of filter chamber thickness on coal slurry filtration effects shows that with an increase of filter chamber thickness,the handling capacity of coal slurry increases,the porosity of filter cake descend,the proportion of small pores increases,and the pore structure is more complicated.Resulting that the moisture of filter cake rises,the formation time of filter cake increases,and the solid content of filtrate and dehydration rate decrease.This is consistent with the influence of filter chamber thickness on filter cake pore structure and permeability.IV.Study on the filtration method for coal slurry based on regulation of pore structure of filter cake(1)The research of coal slurry subsection filtration shows that subsection filtration can improve the effect of coal slurry filtration,and the effect is remarkable.Coal slurry subsection filtration avoids the fine arbitrary filling of pores formed by coarse particles,the pore diameter,pore area,pore perimeter and porosity of subsection filtration are larger than that of hybrid filtration,the pore size distribution is more uniform,and the pore structure is more uncomplicated.Resulting that the filter cake permeability of subsection filtration are larger than that of hybrid filtration,the moisture of filter cake,formation time of filter cake,and solid content of filtrate is smaller,but the dehydration rate of coal slurry filtration is larger.(2)The research of secondary flocculation filtration that secondary flocculation filtration of coal slurry has a significant effect on filtration effect.PAM of secondary flocculation filtration can connect with a number of coal particles forming flocs,resulting in a sharp decrease in the number of individual coal particles in coal slurry.That will increase the pore diameter,pore area,pore perimeter and porosity of filter cake,and reduce the complexity of pores which improve the permeability of filter cake.Finally,the dehydration rate of secondary flocculation filtration is increased,the formation time of filter cake and solid content of filtrate is reduced,but the moisture of filter cake is improved.