Study On CFD-DEM Coupling Simulation Of Coal Slime Coagulation Process

Slime water treatment plays an important role in the production process of the whole coal preparation plant.In order to realize the recycling of coal mud water,many scholars have been devoted to the study of the factors affecting the settlement of coal slurry,but it is difficult to observe the process of coagulation and flocculation on mesoscale by experimental means.Therefore,there is no direct understanding of the influencing factors and mechanisms of flocculation and sedimentation of coal slurry.In this paper,the method of computational fluid dynamics?CFD?coupled discrete element method?DEM?is used to simulate the coagulation of slurry,and the effect of XDLVO force on the process of coal slurry coagulation is discussed from mesoscopic scale.The main work and results are as follows:At first,the particle size,contact angle with different liquid and Zeta potential at different concentration of coagulant(Ca²⁺)were obtained by laser particle size analyzer,contact angle measuring instrument and zeta potentiometer.The condensed state analysis of simulated slime composed of coal and illite was carried out by numerical calculation of XDLVO theory.The calculation results show that Vander Ed Ley,static electric power and polarization force?hydrophobic force?play a dominant role in the range of particle distance?>1 mu m?,medium range?2 nm¹ m?and short range?<2 nm?,respectively.When the kinetic energy of the particles is large enough,the polarization force determines whether the particles adhere or not,and the static electricity is determined.The effect of stopping the particles from approaching.Therefore,coal particles are easy to agglomerate,illite-coal and illite-illite are not easy to agglomerate,and the addition of coagulant can weaken static electricity in favor of coagulation by compressing the action of double layer.Using the open source software OpenFOAM,LIGGGHTS and CFDEM as the framework,the XDLVO force is integrated into the LIGGGHTS through programming,and the CFD-DEM coupling simulation of the single particle free settlement collision condensation process is carried out by comparison and verification with the numerical calculation results.The results show that the van Edward force accelerates the particle near the process,and the polarization force is the key factor to determine whether the particle adheres or not;the collision rebound force of the DEM soft ball model does not play a leading role in the condensation;the velocity of the particle's motion reaches the final velocity of settlement?i.e.the fluid and heavy forces are close to 0?.The grain will have periodic oscillating.The simulation results show that there is agglomerate between coal particles,but illite-coal and illite-illite do not coalesce.The accuracy of the simulation results is verified by microphotography.The focusing beam reflection meter?FBRM?was used to monitor the agglomeration process and particle size distribution of coal slurry in the beaker test from a statistical point of view.The experimental results show that the agglomeration of particles can be achieved at a lower rotational speed by increasing the amount of coagulant,which shows that the influence of concentration of coagulant on particle agglomeration is mainly reflected in the weakening of electrostatic repulsion,thus reducing the energy required for the particle collision process.And the mixing speed will be selective through the size of the micro vortex.Finally,the coagulation experiment was carried out,and the effect of the flocculation was evaluated by the macro evaluation index through the flocculation and settlement of the slime water,and the mechanism of the action of the XDLVO force was verified.The experimental results show that,due to hydrophobicity,the coal particles can effectively coagulate the settlement,the illite particles are difficult to agglomerate because of the hydrophilicity,and the turbidity of the supernatant is larger.However,the coal-illite is not like the theoretical calculation results,and its turbidity and settling velocity are superior to the pure illite particles,indicating that the two play the role.This may be the existence of nanoscale bubbles at the edge of illite particle crystals.The hydrophobicity of bubbles adsorbed them onto the hydrophobic surface of coal and adhered.