Study On The Stirred Pulp-mixing Process Intensification And Multi-stage Compulsory Mixing Mechanism

The technique conception of process intensification which rises gradually these years raises a higher claim to the mineral separation technology. Its tenet is to insist the important significance of process controllability to the mineral separation on the basis of the cognizance that mineral separation belongs to process industry . At present, most researchers have put more attention to the main unit control factors of separation, such as high-efficient complex reagents, strengthened mineralization condition and compounded separation environment. There has no further research on the source of pulp mixing which is the whole separation process. Especially according to the mineral characteristics of poor, miscellaneous, difficult , the minerals always enter into the flotation unit in the form of fine or micro-fine particles for effective dissociation. In the chemical condition created by reagents dispersant, the mechanical characteristics should go together. As the starting point of the whole mineral separation, the intensification of pulp-mixing has become the focus of further research.According to the condition that there are few reports on basic theory on the research of stirred pulp-mixing, this doctoral dissertation starts with universality research. By means of investigating the power dissipation amount PV and mixing time ? m, the power dimensionless number N P, mixing time number N? and characteristic parameters which characterize cycle and shear characteristic have been used as the evaluation standard. So the influence law of vane type of impeller, pitched-blade angle, vane number and accessory type to mixing property has been summarized. And the evaluation standard of mixing efficiency has been put forward.By solid-liquid two-phase experiments the practical pulp-mixing process has been simulated. Basing on the materiel distribution regularity in tank under the effects of different stirred mechanism, the parameters and concepts of cumulative concentration variance, interval concentration variance, just-suspended capacity, poor mixing zone and effective range have been summarized to characterize the suspending characteristics of materiel. Axial effect of flow field is the key to determine the materiel suspension state. To realize effective suspension of materiel, not only the basic state of just suspension should be broken through, but also the flow field should have enough axial effect to realize materiel cycle in the range of main body. Only the constant renewal and transfer of materiel between different zones can realize a high efficiency of stirred system.By using the software of fluid dynamics named FLUENT, the flow fields of different stirred mechanism have been numerical simulated. It has been shown that no matter axial-flow flow field or radial-flow flow field, tangential velocity of circulation plays the most important role in the flow field while without baffles, and without exception weak mixing extents occur on the top of tank, which is corresponding to the effective range of the mixing system. Axial flow impeller mainly produces axial jet with tangential velocity and axial velocity mainly, so the whole cycle ability is much stronger. Radial flow impeller produces radial jet chiefly, which can realize a significant shear effect with baffles. Because of the lack of axial velocity in the outlet flow of radial flow impeller, the velocity energy shortage occurs in the cyclic zone.From the deduction of stirred tank flow field characteristic parameters, the secondary flow cyclic characteristic number and the secondary flow cyclic coefficient has been concluded. From the perspective of mixing time, further analysis about mixing process has been made, and it's pointed out that the mixing process mainly includes macro-mixing and micro-mixtures. Starting with the force analysis of mineral particles in stirred tank, the materiel dispersion probability equation has been deduced. From the perspective of turbulent diffusion, the reagents diffusion processes and their effect with mineral in stirred tank has been analyzed, and it's pointed out that the fluid shear effect can provide a certain amount of energy for the collision of reagents and particle as well as reagents and mineral particles themselves to improve the pulp-mixing effect. With the impeller force and torque balance equation as a starting point, the efficiency parameters ? characterizing the energy consumption allocation in stirred tank has been deduced. On the basis of further derivation of power dimensionless number and flux dimensionless number theory calculation formula, the cycle/shear quantitative ratio in stirred tank has been concluded.According to the secondary flow cycle characteristics to make optimization design on flow field, the double-impeller system has been constructed basing on the axial flow impeller and radial flow impeller interaction. With the successful fusion of strong circulation and strong shear mechanism in the double-impeller configurations, the stirred mechanism characterized as double-stage which means the double-stage combination mode with high-efficiency and mightiness mixing and high-shearing impeller stirring, has been formed initially, and it provides a practical basis for developing a new and effective pulp-mixing device. With the mean of numerical simulation, the flow field of the best double-impeller basic configuration has been analyzed. It's shown that the advantage characteristics on cycle and shear of two types of impellers have got coupling. The further optimization configuration of Basic Mode + Draft-tube makes the characteristics of two-stage more clear.To realize a further improvement of shear performance cache under the effect of double-impeller stirred mechanism, the optimization design taking the addition of static-guide-blade as main has been carried out basing on the model of Basic Model + Draft-tube using the static mixer function principle of chemical process for reference. By the phase-resolved analysis of velocity field, the development course of eddy in static-guide-blade zone has been achieved. Thus the new types of mixing devices with the characteristics of multi-stage and compulsory have been formed. Multi-stage means the multi-stage combination mode with high-efficiency and mightiness mixing, static-guide-blade shear mixing and high-shearing impeller stirring. Compulsory means the local compulsory convective mixing effect of static-guide-blade mixing unit and that the in-material is guide to the cyclic route of flow field compellingly with the addition of material-guiding-cone.The high-efficiency of multi-stage and compulsory mixing devices has been verified basing on the mixing characteristics and materiel-suspending characteristics. Mineral separation experiments have been carried out with high-magnesium collophanite ore from Kun Yang mine area of Yun Nan. Comparing with the effect of common stirred tank, it has been proved that multi-stage and compulsory mixing devices are superior to common stirred tank in the respect of pulp-mixing effect. Especially the effect of maleic-cutting configuration is more obvious: under the condition that MgO grade of concentrates has decreased under 0.80% effectively, the recovery rate of P2O5 has increased 4.84 percentage point. Then the maleic-cutting configuration has been used as the application delegate of multi-stage and compulsory mixing devices. Comparing with the common stirred tank, while using maleic-cutting configuration for pulp-mixing, reducing the pulp-mixing time of reagents has less influence on separation index. Basing on the recovery of particle analysis of concentrates separated with common stirred tank and maleic-cutting configuration pulp-mixing, it has shown that using maleic-cutting configuration for pulp-mixing, the P2O5 recovery rate and MgO removal rate has increased in every particle fraction. Multi-stage and compulsory mixing devices can construct high-shear mechanism on the basis of realizing high-efficient cycle in flow field, and it's the basic reason why multi-stage and compulsory mixing devices have intensified the pulp-mixing process of micro-fine particles.Comprehensive analysis basing on mixing characteristic parameters and suspending capacity parameters, comparing with common stirred tank, the optimization design configurations with the characteristics of multi-stage and compulsory have obvious advantages on rapid-mixing, effect suspending of materiel and pulp-mixing effect. The multi-stage and compulsory mixing devices designed in this doctoral dissertation research realize the intensification of pulp-mixing effect successfully.