Turbulence enhancement mechanism of coal slime pulp conditioning and new type vortex enhancing pulp conditioning process

It has been acknowledged that a conditioning process can provide favorable interfacial conditions for fine coal flotation,thereby being a required premise of its efficient separation. Essentially,a fine coal conditioning is a process involving multiphase flow,throughout which the role of fluid exists.This paper focused on the turbulence effect in the coal pulp conditioning process,and designed a laboratory stirring device.Numerical simulation was used to acquire the turbulent characteristic parameters of the stirring device. Additionally,the properties of particle dispersion and surface hydrophobicity were analyzed under different conditions of flow field to characterize the influence of flow field characteristics on fine coal conditioning process,which was further verified by flotation tests. Based on the studied above,a new type vortex enhancing pulp conditioning process with adapted turbulence energy density was constructed for fine coal conditioning,and the flow field characteristics were analyzed. The results indicated that there was a circulation area with opposite flow in the stirred tank to promote particle dispersion,and the fluid velocity,together with the turbulent kinetic energy in the vicinity of impeller,was higher than that of other region. Trailing vortexes were formed behind the blade,which exhibited similar development trends to the distribution of the turbulent kinetic energy. The Kolmogorov scale was the lowest in the impeller region to enhance particle collector interaction. With the raising impeller speed,the fluid velocity and turbulent kinetic energy increased,while the Kolmogorov scale and variance of particle dispersion concentration decreased. At low impeller speeds,the particle concentration of the cell bottom was high,corresponding to poor dispersion performance.The wrap angle increased with rising impeller speed,and under the same condition,the maximum wrap angle of particles collected near the impeller was measured. In this experiment,the lager impeller speed corresponded to higher flotation recovery. According to the above mentioned laws,the different conditions of flow field,including pipe flow,opposite rotational flow and impact flow,were integrated in the fine coal conditioning process,and an MRM 800×3 600 mm coal slime mixing conditioner was designed. The results of numerical simulation showed that the turbulence energy density was properly distributed,with a tangential fluid motion in the area of rotational flow,and a strong shearing fluid motion in the vicinity of impact flow corresponding to lager turbulence energy density and smaller Kolmogorov scale.It has been manifested in industrial practice that the slurry capacity of the equipment is about 300-500 m3/h,and under the original process technology,the flotation recovery of clean coal increases over 4%.