| Under the general trend of global green,low-carbon and sustainable development and the call of peak carbon dioxide emissions and carbon neutral policies,the coal industry must speed up to solve the technical problems of low-carbon utilization and carbon removal of coal,and solid-liquid separation technology is the prerequisites and guarantees to achieving carbonization utilization.At present,the existing technologies,methods and equipment for mineral dewatering are used in production.However,the research on filter cake structure and seepage mechanism is still lacking,which seriously restricts the further improvement and development of solid-liquid separation theory and technology.This thesis focuses on the vacuum filtration test,cake structure characterization,numerical simulation,and permeability modelling to carry out research work to in-depth understand the three-dimensional structural characteristics of the filter cake and the flow law of the filtrate in the pores of filter cake.Based on this,establish a mathematical model suitable for describing the pore-permeability relationship of the slime filter cake,in order to improve the solid-liquid separation theory and optimize dewatering operation.The following research results have been obtained:Based on the vacuum filtration test,the thesis first investigated the filtration performance differences of five different minerals: kaolinite,montmorillonite,quartz,clean coal,and slime.The research showed that the filtration rate of montmorillonite and kaolinite was the slowest.The cake specific resistance and moisture are the highest,the filtration speed of coal slime is slower,and the filter cake specific resistance and moisture are higher,while the filtration speed of clean coal and quartz is the fastest,and the filter cake specific resistance and moisture are lower.Taking quartz particles with different physical properties as the research object,the effect of particle shape,particle size,and particle size grading system on the solid-liquid separation effect is studied.The results show that the filtering effect of spherical particles is significantly better than that of irregularly shaped particles.With the increase of particle size,especially after the average particle size of the feed material reaches 50?m,the filtering effect has been significantly improved.Adding a certain amount of coarse-grained materials to the fine-grained materials can improve the filtering effect.When the ratio of the coarse-grained to the fine-grained particles reaches 5 times,the filtering effect will be significantly improved.When the proportion of the particle fraction is reduced to 60%,the filtering effect will be significantly improved;when the four-grain gradation is used,when the fine particle content reaches 80%,the filtering effect has been significantly improved.The three-dimensional visualization and quantitative characterization analysis of the filter cake structure were realized by using the computer tomography(CT),and the influence mechanism of mineral types and particle physical parameters on the filter cake pore structure was further explored.The results showed that the clean coal The pore size distribution in the filter cake is dominated by large pores,but there are a certain amount of isolated small pores inside,the pore connectivity is general,but the tortuosity is the smallest;the quartz filter cake has the largest porosity,the best connectivity,and good pore homogeneity.However,the pore size is small and the tortuosity is large;the mineral composition of the coal slime filter cake is very complex,the pores of the filter cake are not uniformly developed,mainly in a narrow strip distribution,the pore size is small,the overall porosity is low,and there are a lot of blind holes.And the terminal pores have poor connectivity and high tortuosity,so the filter performance is poor;while the filter cake formed by montmorillonite and kaolinite clay minerals has very few pores and is mostly composed of pores below 10 ?m.The degree of tortuosity is large,and the connectivity is also poor,so its filtering effect will be seriously deteriorated.The porosity of the filter cake formed by the filtration of irregular particles is significantly greater than that of the filter cake with spherical particles.The larger the particle size,the higher the porosity of the formed filter cake.When the size distribution of the feed particles is similar,the particle shape hardly affects the pore size distribution of the filter cake.Increasing the particle size will increase the porosity of the filter cake porous media,and increasing the porosity will increase the average diameter of the pores.The filter cake formed by irregularly shaped particles has the lowest connected porosity and the highest tortuosity.As the particle size increases,the connectivity of the filter cake pores gradually increases,and the degree of tortuosity decreases significantly.In addition,the particle size and shape will also affect the pore coordination number and pore ratio of the filter cake.The filter cake formed by coarse-grained spherical particles has the highest average pore coordination number,and the number of high-coordination pores is relatively large.The pore-throat ratio is also the smallest,and the pore space is the most uniform.The filter cake with fine-grained irregular particles has the lowest average pore coordination number and contains a large number of blind pores and terminal pores.At the same time,the pore-to-throat ratio is the largest,and the pore space has strong non-uniformity.Numerical calculations of single-phase microflow in two-dimensional artificial pores and three-dimensional real filter cake pores are carried out based on the lattice Boltzmann method.The influence of mineral types and particle physical parameters on the seepage law is investigated.The results show that the lattice Boltzmann method is suitable for complex channels.The single-phase micro-flow calculation has feasibility and superiority,which can accurately reflect the flow law of single-phase fluid at the micro-scale and the characteristics of velocity distribution in the flow channel.When the particle size of the spherical particles forming the porous medium is fixed,the permeability increases with the increase of the porosity;when the porosity of the porous medium is fixed,the permeability of the porous medium increases exponentially with the increase of the particle size.Trend;when the particle size and porosity of the porous media are fixed,the permeability of irregularly shaped particles is significantly lower than that of porous media composed of spherical particles;the permeability results of different particle gradations show that changing the particle size composition of the porous media can be significant To increase its permeability,the more complex the particle size composition,the greater the impact of fine particle size on the flow rate and permeability of the entire system.The filter cake formed by the filtration of five different minerals has very different seepage speeds.The pores of the clean coal filter cake and the quartz filter cake are more evenly developed,and the connectivity is good.There is a certain amount of seepage main channel in the filter cake,and the seepage in the main channel The speed is higher and the permeability is the highest.The pore homogeneity of the coal slime filter cake is poor,mainly narrow and long pore channels,and the tortuosity is larger,the main seepage channel becomes smaller,and the seepage speed is also significantly lower than that of the clean coal filter cake and the quartz filter cake.However,montmorillonite and kaolinite filter cakes have extremely uneven pore development,poor connectivity,and almost no connected pore channels,so the permeability is extremely low.The classical KC equation and the dual permeability fractal model,the current mainstream permeability prediction models,have relatively large prediction errors for the filter cake permeability.The error comes from not considering the filter cake pore cross-sectional shape and the influence of the irreducible water saturation on the permeability.influences.After correcting the existing dual fractal permeability model by introducing the fractal dimension of the pore cross-section shape,the derived triple fractal permeability model controls the prediction errors of the permeability of the quartz and clean coal filter cake at2.55% and 2.05%.However,for Mongolia However,the prediction results of permeability of montmorillonite,kaolinite and slime filter cake are obviously higher.The irreducible water saturation of filter cakes of different minerals was detected by low-field nuclear magnetic resonance technology,and the existing three-fold fractal permeability model was revised again,and a predictive model of filter cake microscopic permeability was established.The results show that the model can not only perform well It is competent to predict the permeability of pure mineral filter cakes,and for the complex composition of coal slime filter cakes,the permeability prediction error can also be controlled within 5%.The applicability to the clean coal filter cake is the best,and the prediction error is only 0.96%,and the calculation error of montmorillonite permeability has also been reduced from 40.27% to 13.42%. |
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