Simulation Of Flow Field And Particle Motion Inside Dual-cone Hydrocyclone And Its Industrial Application Research

Hydrocyclone which is a general efficient separator by means of centrifugal forcefield, has been widely used in many industrial fields, such as petroleum industry, chemicalindustry, mining industry, food industry, wastewater treatment, etc. The requests ofreducing energy consumption and cut size are raised by the modern industrialdevelopment, which also are the focus of the research orientations of solid-liquidhydrocyclone. The study of the flow behaviors of the multiphase inside the hydrocycloneand the investigation of the influence rules of hydrocyclone parameters on the separationperformance will provide theoretical basis for the optimization of the hydrocyclone, andpromote the development of separation engineering.In this dissertation, the dual-cone hydrocyclone was selected as the research object.On the basis of multiphase flow field in the dual-cone hydrocyclone numericallysimulated by the implement of computational fluid dynamics (CFD), the flow fieldcharacteristics and the flow behaviors of particles were analyzed. Association with theexperiment desigh, the influence of structural parameters of the dual-cone hydrocylone onits separation performance was investigated. The industrial applications of the designeddual-cone hydrocyclone in preparation of classified tailings and production of single highgrade sulphur concentrate in Fankou Lead-zinc Mine were achieved.Based on the time-averaged Navier-Stokes equations, the Reynolds Stressturbulence model (RSM), the Volume of Fluid multiphase flow model (VOF) and theMixture multiphase flow model (Mixture) were used to numerical compute the liquid-airflow field and the solid-liquid-air flow field in the30°(upper cone angle)-10°(Mixture)(lower cone angle) dual-cone hydrocyclone and10°(cone angle) single cone hydrocylonewith a diameter of100mm. The simulation results were compared with the laboratorialresults in terms of water split ratio and solid-liquid separation performance. It is shownthat the simulation results are in good agreement with the laboratorial results, and thechosen CFD models are reliable. The comparative study between flow field parameters of the dual-cone (30°-10°)hydrocyclone and single cone (10°) hydrocyclone were conducted. It is shown that thedistribution laws of flow field parameters are not influenced by the change of the conicalstructure of hydrocyclone. On the premise of same feed velocity, the tangential velocity ofthe dual-cone (30°-10°) hydrocyclone is significantly higher than that of single cone (10°)hydrocyclone. The frequent radial perturbance derived from the air core in single cone(10°) hydrocyclone gives rise to the little difference between the values of radial velocityin the studied two types of hydrocyclones. That flow field characteristics in the dual-cone(30°-10°) hydrocyclone possesses the ability to decrease the cut size.The size dependent flow behaviors were also discussed in this thesis based on theresults of multiphase simulation inside the dual-cone hydrocyclone. A process, where theparticles were introduced into the dual-cone hydrocyclone till the steady multiphase flowfield was achieved, was numerically simulated. The instantaneous mass flow rates ofdifferent particle sizes on the overflow and underflow and the volume distribution duringthis process were studied. It is found that the finer the particle size, the less time needed toenter the overflow pipe. Longer time is required for the particle size, close to the cut size,to reach the steady mass flow rate on the outlets of the hydrocyclone than particles withany other sizes. The volume distributions of particles at the steady multiphase flow fieldshow that the fine particles tend to distribute more evenly in the hydrocyclone; as theparticle size increases, the particles in the cylinder and upper cone region graduallydeviate from the cyclone center and form concentration segregation; the coarse particleskeep close to the inner wall of the hydrocyclone and flow in the state of aggregation ofspiral flow. The fine particles continually flow into the circulation flow, which lead to theparticle accumulation occurs in the circulation flow, and form a ring shape highconcentration area with a concentration gradient. Stop the injection of particles into thehydrocyclone, the process where the particles flow out of the hydrocyclone was studied. Itis shown that the trajectories of the particles flowing out of the hydrocyclone depend onthe particle size. The fine particles mainly escape to the overflow; as the particle size increases, the particles can either go into the overflow and underflow; the coarse particlesmainly enter the underflow. It seems that the short cut flow of particles is not along theouter wall of vortex finder and then flow into the vortex finder. It is likely caused by theentrainment of the water’s radial flow. The finer the particle size, the faster the formationof short cut flow. The coarse particles would not flow into the circulation flow and shortcut flowThe influence of cylinder height, upper cone angle, lower cone angle and thediameter of the cone joint of the dual-cone hydrocyclone on the cut size and pressure dropare discussed based on the Yates experiment design and CFD technique. The analysis ofvariance shows that the significance order of the four structural parameters to the cut sizeis: lower cone angle> diameter of the cone joint> upper cone angle> cylinder height. Asfor the pressure drop in the hydrocyclone, the significance order is: cylinder height>diameter of the cone joint> lower cone angle> upper cone angle. And the effects of coneangles on pressure drop and cut size are positive, while the diameter of the cone joint andthe cylinder height are negative. Regression equations between the cut size, pressure dropand the structural parameters in the test scope are obtained through regression fitting, andthe correlation coefficient is0.9918,0.9900respectively. In the scope of studied structuralparameters of dual-cone hydrocyclone, smaller cut size can be achieved at the lowerenergy consumption when the lower cone angle is10°, upper cone angle is30°, the ratiobetween joint diameter of cone and diameter of hydrocyclone is0.7, and the ratio betweencylinder height and diameter of hydrocyclone is2.Based on the numerical simulation results, the dual-cone hydrocyclone used forclassifying the beneficiation tailing in Fankou Lead-zinc Mine was designed. Theindustrial application shows that compared with the original single cone hydrocyclonepossessing equal diameter, the designed dual-cone hydrocyclone can effectively decreasethe cut size so that the yield of classified tailing increases. In the process design ofseparating single high grade pyrite concentrate (sulfur grade>46.5%) used gravityseparation and floatation in Fankou Lead-zinc Mine, the dual-cone hydrocyclone waschosen as the gravity separation facility based on laboratorial tests and numericalsimulation. It was used to preferentially separate about half of the pyrite concentration from the rough concentration. The economic benefit of the enterprise was significantlyimproved by the production of single high grade sulphur concentrate. The industrialoperation data show that the dual-cone hydrocyclone is reliable and the production indexis steady.