| The cyclonic-static micro-bubble flotation column is the representative ofcolumn flotation for its better separation selectivity and suitability of fine particlesseparation. However, with the development of industrialization process, problemsbecome more obvious in structure optimization, scale-up, processing control andseparation performance improvement. The main reason is the insufficiency ofsystematical research and realization to the separation processing, including its flowpatterns and processing intensification. The author studied this process in terms offluid dynamics.By CFD multi-phase flow numerical method and advanced flow filedmeasurement technique, this thesis studied the gas-liquid flow field of flotationcolumn in the aspects of macro-and micro-scale. First, a PIV test platform for thelab-scale flotation column was set up. Compared with the experimental data and andbased on multi-phase theoretical analysis, the proper numerical model for flotationcolumn was confirmed. Then, numerical simulation for an industrial-scale flotationcolumn with a diameter of1m was carried out. According to the simulation results,the flow structures in different separation unit of column and their correspondingmineralization way were analyzed. Subsequently, through the study of the effect ofmicro-fluid-mechanics on flotation kinetics, and combined with the process feature ofthe mineral floatability, the “process intensification mechanism” in this columnflotation was explored. The main content and conclusions are listed as follows.A PIV test platform for lab-scale flotation column was built-up. Bubble velocityin low-gas holdup flow field was measured. The bubble distribution features wereobserved qualitatively. The numerical model of flotation column was confirmed. Theresearch shows that, The numerical approaches, which employ the standard k-εturbulent model to calculate the turbulence, the Eulerian-Eulerian two fluid model tofigure out the gas and liquid phase, and the Universal drag model to compute thegas-liquid interforce, can be utilized to simulate our research object-flotation columnwhich involves turbulent flows of varying degrees and different flow patterns.The flow field of the industry-scale flotation column was numerically calculated.The flow path of gas and liquid, the velocity of per phase, and the gas holdupdistribution were achieved. The multi-flow characteristic can be presented as: alongwith column unit, cyclone unit and pipe unit, the flow patterns are: axially reverseflow, swirling flows and highly turbulent flow. The flow field of column unit and cyclone unit were investigated respectively.Based on their fluid flow feature, the mineralization methods were deduced. Thefollowing conclusions were obtained,①In column unit, both gas and liquid phasemoves slowly with the velocity of-0.1~0.35m/s in axial direction. The flow directionsof two phases are the same in near-axis region and opposite in near-wall region. Themineralization type appears as a “reverse and axial” style, and this unit plays theroughing and concentrating role in the whole flotation process. The gas-holdupdistribution has a feature of radially decreasing with the value range of1%~13%.②In cyclone unit，the tangential velocity （0~0.6m/s） of both gas and liquid phases ishigher than axial velocity and radial velocity. The two phases moves with the sametangential direction. The separation role of this unit reflected in the separation oftailings and the coarse-grained minerals. While the mineralization method bases moreon the "radially reversed" style in inner-cyclone region and weak "axially reversed"style in above-cyclone region. For the under-cyclone region, mineralization usuallycannot happen for no bubbles.③In pipe unit, the gas and liquid phase moves axiallyand the velocity is about1~2m/s in pipe region and greater than10m/s in jet region,gas hold-up is higher than25%.④To get a higher separation result, the thoughts of"non-uniform" packing style and "axis disturbance" were presented.The turbulent mineralization mechanism was explored by studying theturbulence and flotation kinetics theory. The results show that, the turbulent kineticenergy k and turbulent dissipation rate ε can be used to predict the mineralizationefficiency. The larger the k is, the stronger the large-scale low frequency vortexshows. While the larger value of ε indicates the strengthening of small-scale highfrequency vortex. The separation and selectivity of micro-fine particles requires thesmall-scale vortex. The turbulent energy in the ore sorting processing of flotationcolumn was investigated. The results show that, in column unit, no matter thevolume-weighted value or maximum value of k and ε, ranked the lowest amongthe three units. Therefore, the separation ability to micro-fine particles is the worst;For pipe unit, it has the highest k and ε value. Especially the maximum ε ismuch higher than the other two units. So the pipe unit has the highest mineralizationefficiency for micro-fine minerals, but the selectivity is not as good as mineralization;For cyclone unit, Both k and ε ranked the middle. The hydrophobic andmiddle-size particles are easy to be separated, but the fine particles are hard to berealized. Systematically and theoretically, the "column flotation process with stepwiseintensification mechanism and multi-flow patterns" conception based on the mineralprocessing method of cyclonic-static micro-bubble flotation column was deeplyanalyzed. Namely, In the whole process of flotation column, following the order ofcolumn unit, cyclone unit and pipe unit, the turbulent environment is enhancedgradually with regard to their respective feeding minerals. This certain featurehappened to be adapted to the processing feature of mineral floatability that behavedpoorer and poorer. Therefore, the cyclonic-static micro-bubble column integrates thedifferent flow structures into one column according to two destinations that aremineralization ability increasing and selectivity improving, what is called the “columnflotation with stepwise intensification process and multi-flow patterns. Furtherly, asthe main influencing factor, the effect of circulating pump pressure was studied. Thesimulation results of cases with different circulating pressure show that: within acertain range of pressure, the increasing of pumping pressure can intensify theswirling flow in cyclone unit, enlarge the gas-holdup in column and strengthen theturbulence, and improve the separation recovery rate finally. |
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