| Froth flotation is an effective method to separate fine coal slime,and flotation machine is an important carrier in froth flotation process,the research and development of flotation equipment has always been a key subject in the mineral processing industry.A jet-stirring coupling flotation is proposed based on the working principle advantages and structural characteristics of traditional flotation machines in this paper.The research on the suction mechanism and gas dispersion characteristics of the coupled flotation provides theoretical support for the development of new flotation equipment.The working principle and gas dispersion mechanism of the jet suction-stirring coupled flotation device(JS)are systematically studied in this thesis,and the structural design and optimization of the flotation equipment system are completed based on the principle of fluid mechanics.The multi-stage refinement of bubble size,multi-stage mineralization mechanism and flow field working mode in JS flotation machine were discussed.It shows that the JS flotation machine can obtain a larger suction volume,a uniform bubble particle size,and a gas-liquid-solid three-phase flow field distribution at a lower energy consumption and lower speed.The double cosine self-aspirated nozzle is designed based on the principle of ejection suction,the nozzle structure is arranged in a non-submerged manner based on the principle of high energy conversion rate.The test results of the suction performance of the double cosine self-aspirated nozzle structure show that the nozzles can be arranged in a non-submerged manner to meet the requirements of the suction capacity;the working parameters(feeding pressure,gas-liquid ratio,etc.)and structural parameters(cross-section ratio,etc.)of the nozzle are the key factors affecting the suction volume,the negative pressure in the nozzle,the energy conversion of the jet,and the flotation effect.The jet mechanism was used to analyze the suction mechanism of the JS flotation device,and a mathematical model for the structure selection of the double cosine self-aspirated nozzle was established.The jet suction capacity is affected by the mathematical relationship between the jet boundary layer thickness 2e and the nozzle outlet diameter D parameter.The results show that the suction volume,the negative pressure the the double cosine self-aspirated nozzle and the impeller speed of gradually increased with the increase of the feeding pressure under the same nozzle distance condition;there is a positive linear relationship between inspiratory capacity and negative pressure.Under the condition of low feeding pressure and small nozzle distance,2e<D.and the suction capacity of the nozzle is weak;with the increase of feeding pressure and nozzle distance,2e?D,the suction capacity gradually increased,the negative pressure environment of the nozzle is improved;under the condition of high feeding pressure and large nozzle distance,2e>>D,the negative pressure zone is occupied by water medium,the gas phase space volume of suction zone is compressed,the suction capacity of the double cosine self-aspirated nozzle drops sharply.When the nozzle?distance is 20 mm and the cross section ratio d/D is 0.857?1,the increase range of inspirations is larger,the linear slope is the largest.The function relationship between the feeding pressure and the nozzle distance is established,L=56.10-17091.36P3.92,which guides the structure selection and model enlargement of the nozzle and has theoretical and practical significance.Based on the optimized structural parameters,a high-speed camera bubble acquisition and analysis system for JS flotation machine was established.The effects of frother concentration,feeding pressure,suction volume and sampling height on the bubble size distribution in the three coupling structures were studied.The results show that the triple reinforced coupling structure has obvious advantages for bubble size distribution and bubble miniaturization.With the increase of the MIBC concentration,the Sauter mean diameter decreases until the critical coalescence concentration,above which the Sauter mean diameter is constant.the bubble size is stable at about 0.31 mm,which is smaller than the bubble size produced by the traditional flotation machine,indicating that JS has generated bubbles of a suitable size.For example,when the MIBC concentration is 13.01 mmol/L,the intermediate bubble diameter is 0.32mm and the content is 33.73%.The Sauter mean diameter linearly decreased with increasing of feeding pressures and conversely increased with increasing suction capacities and sampling location heights,independent of the frother concentration.The differential pressure method was used to study the distribution of gas holdup in the three coupled structures.The differences in the air holdup distribution and the influence of working parameters in the three coupling structures were investigated,a multi-factor test was designed to examine the significant differences in working parameters and the mechanism of gas dispersion and gas dispersion state transition was revealed,the gas dispersion performance of JS flotation equipment was evaluated.The gas holdup increased with the increase in the MIBC concentration,feeding pressure,gas flow rate,and water depth,regardless of the stirring impeller.The increase in the gas holdup was particularly significant with the increase in the MIBC concentration in the absence of the stirring impeller until the critical coalescence concentration,above which the gas holdup remained largely constant at each feeding pressure.The maximum gas holdup in the single-nozzle and double-coupling structures is less than 24%,while the maximum air holdup is about 65%in the triple reinforced coupling structure,the air holdup has increased by 40%due to the action of the stirring impeller,indicating that the triple reinforced coupling structure has a significant effect on improving the gas holdup distribution.The significant test results of the influencing factors of gas holdup show that:the feeding pressure>the frother concentration>the suction volume.The increase of the rotation speed will gradually improve the gas dispersion state,and promote the miniaturization and dispersion of the bubbles.The fluid numerical simulation results also show that the distribution of the flow field in JS flotation machine is more conducive to the dispersion,collision and mineralization of agents,revealing that the structure of the upper feed tank achieves the design purpose of pre-mixing slurry.The numerical simulation method was used to study the hydrodynamic parameters and flow field distribution in the three coupling structures,the analysis results of the dynamic parameters of the near impeller region show that the near impeller region is accompanied by intense energy exchange and loss,which is beneficial to the improvement of gas dispersion,which verified the scientificity and structural validity of the JS flotation equipment design.The actual flotation efficiency of JS flotation equipment for different concentrations of pulp and the capture capacity of coal slurry of different particle sizes were compared through the slime flotation test,the flotation rate test was compared with the laboratory XFD-1.5 equipment to verify actual flotation effect of the JS flotation equipment.The coal slime flotation test results of the JS flotation machine show that it has a good separation ability for fine coal slime smaller than 0.25 mm,and the recovery rate of each size of fine coal reaches 70%to 80%;it can adapt to high concentration of coal slime flotation test,the flotation improvement index is higher than 50%,and the combustible gas recovery rate reaches 76%to 87%.The flotation rate test results verify that the actual sorting effect of the JS flotation machine is better than the laboratory XFD-1.5 flotation machine.It can realize the purpose of energy saving,improving efficiency and simplifying technological process flow.Figures[69];Tables[25];References[210]... |
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