Study On The Macerals Enrichment Regularity Of Low-rank Bituminous Coal In Enhanced Gravity Field

Coal macerals are microscopic coal petrography with different chemical activities.The targeted enrichment of coal macerals can further develop the utilization efficiency of coal,which is an important direction of deep clean utilization of coal.There are many differences of coal macerals including physical and chemical properties,functional group distribution and surface polarity,etc.Among them,density differences of physical properties have been used as the most extensive method to separate and purify coal macerals in the laboratory.Due to the low-density gradient between vitrinite and inertinite,only centrifugal separator of mineral processing industry can provide enough centrifugal force to ensure that the coal maceral enrichment effect,but the centrifugal separation equipment was less used in the coal separation technology,the research of coal macerals separation theory,technology,application is relatively lack.This paper set the coal maceral separation as the core,using the enhanced gravity separator to explore the coordination movement mechanism of coal macerals and flow film.Study on the settlement and stratified rule of coal macerals in separation chamber,and combining with the physical,chemical properties of coal macerals to explore the enrichment process of coal macerals through the enhanced gravity separation with the dissociation characteristics of coal maceral as the foundation.The characteristics and differences of Shendong low-rank bituminous coal were studied in the chemical composition,microcrystalline structure,functional group distribution,surface properties and molecular structure with the assist of XRD,FTIR,XPS,13C-NMR,EDS,etc.spectral and microscopic observation equipment.Based on the different characteristics of coal macerals,the cause of the low gradient density difference between vitrinite and inertinite was studied.Based on different grinding equipments and grinding conditions,the dissociation characteristics of Shendong macerals was studied,and the crushing characteristics of different grinding methods and the selective crushing mechanism of coal macerals were studied by the observation of cracks distribution on the particle surface.Based on the motion of rotating flow film in compound force field,the space-time development of rotating flow film is studied.The process from forming to stabilizing of rotating flow film mainly goes through the following stages: fluid accumulation stage,flow film forming stage,flow film developing stage and flow film stabilizing stage.CFD numerical simulation and high-speed dynamic photography were used to explore the spatial distribution of rotating flow film in the separation chamber.The flow film was divided into three layers after stabilization.The bottom layer is mainly composed of turbulent flow film,and the stability of flow film is poor.The medium layer flow film is stable in shape and thin in thickness,which is suitable for rapid settling and sorting of particles.The upper layer flow film is convex in shape and is mainly generated by convection of fluid moving in opposite direction.The average thickness of rotating flow film in the separation chamber was measured based on the theoretical calculation,single fluid test and numerical simulation.By defining the concept of stability of the rotating flow film,an analysis method was established to satisfy the requirements of stability and thickness of the rotating flow film in the composite field.Through the enrichment rule of macerals from overflow with different test conditions,the migration rule of macerals in overflow was studied with the assist of CFD numerical simulation.Based on the narrow particle size macerals separation,the movement rule of the vitrinite-rich components is studied on the three dimensions:particle size,density level and separation time during the separation process.The effective separation time concept was defined in the enhanced gravity separation,and discovered the maceral migration-imbalances process with rotating flow film in the enhanced gravity field.Taking the settlment area in separation chamber as the observation object,the settling stratification rule of inertinite components in the compound field was studied.Based on the spatial distribution of settlment area,the low-density gradient layering and separation rule of macerals particles were studied through the distribution of density level.The dissociated Shendong coal macerals was set as the separation objects,and the process of enhanced gravity separation was explored.The appropriate sieving particle size of Shendong low-rank coal was determined based on the narrow fraction coal macerals separation test.The Krebs hydraulic classification cyclone was used to realize the 0.074μm particle size sieving of macerals,the classification effect was 84.72%,and classification sized reached 75.16μm.The orthogonal experiment of enhanced gravity separation of coal macerals was designed and analyzed from the underflow and overflow of hydrocyclone based on the adjustment of the four operating parameters:feeding speed,feeding concentration,rotational frequency and water pressure.The influence of test conditions and the interaction were analysized by the evaluation index:concentrates yield,concentrates vitrinite content,vitrinite recovery and vitrinite enrichment ratio,and the test conditions were optimized by response surface analysis method.The optimum test conditions of enhanced gravity separation was obtained based on the optimum solution of vitrinite recovery and vitrinite enrichment ratio respectively.The vitrinite content of concentrates achieved 71.94%,which 25.87%higher than that of grinding Shendong low-rank coal.The efficient enrichment of macerals in enhanced gravity field was realized.