| The proportion of fine grain particles has gradually increased in raw coal with mechanical coal mining.At present,the first selection technology for separating fine particle coal is flotation.The commonly used flotation devices are mechanical agitator flotation machine,air jet flotation machine and flotation column.However,because of the difference of flow field,the three types of flotation machines are difficult to achieve optimal separating results in concentration adaptability,flotation efficiency and processing capacity.According to the characteristics of fluid and working characteristics of flotation machines,the characteristics of the fluid that have great influence on flotation are jet,eddy current and stirring.The three-phase flow mechanics mechanism that has the three fluid characteristics has important significance on optimization flow field,formation of fine bubbles,and improving the efficiency of fine mineral separation.Therefore,a novel self-absorption-air flotation device drived by pulp is proposed.Then mechanism of energy conversion and microbubble formation was explored and tested,based on the structural design and fluid mechanic analysis.The main conclusions are as follows.1.The working principle and characteristics of flotation device are described,based on the model of flotation device.The impact force of jet flow impacted on the impeller and the relationship between stirring shaft power and impeller rotational speed were obtained by analyzing theoretically driving and stirring mechanism of jet flow impacted on the impeller based on the hydromechanics theory.And,the consequences of theoretical analysis and experimental investigation of inspiratory mechanism of flotation device show that,the liquid level descended to the stirring wheel with high impeller rotating speed,so as to inhale air from stirring inspiratory tube.The jet inspiratory capacity increased linearly with the increase of jet flow,and stirring inspiratory capacity increased as quadratic function with increasing impeller rotational speed.The stirring inspiratory capacity decreased rapidly with increasing liquid level,under the influence of internal pressure of the device and the viscous resistance of the slurry,and jet inspiratory capacity increased with the increase liquid level,and total inspiratory capacity decreased with increasing liquid level.Because of jet inspiration and stirring inspiration,both of two inspiratory methods influenced the inspiratory effect with shallow liquid level.However,with deep liquid level,the major inspiratory way was jet inspiration,and stirring inspiration was unconspicuous.Although,the impeller rotating speed of the flotation device was lower than mechanical agitator flotation machine,under the deepest liquid level and maximum impeller rotating speed,the flotation device could acquire hypothetical inspiratory capacity,the maximum inspiratory capacity was 4.31 L/min?2.The energy conversion mechanism of flotation device was studied.Based on establishing energy conversion experimental system,the relationship between stirring shaft power and impeller rotating speed was analyzed theoretically,and the relationship aimed to forecast the impeller rotating speed,between impeller rotating speed and flow rate of circulating pump or hydraulic head was established.The energy conversion efficiency of the flotation device was studied by testing.The results showed that:the larger the projected area on the incident flow face for different shape impellers were,the higher the energy conversion efficiency,that was,jet energy consumption of stirring wheel was lager.Impeller rotating speed increased linearly with increasing jet flow rate,and increased as power function relationship with increasing hydraulic head.Because of viscous resistance of pulp,the shaft power drived by jet was larger,and energy conversion efficiency was lower,that was,impeller could get higher impeller rotating speed by larger impact kinetic energy.And,the stirring mechanism of the flotation device was verified by studying the energy conversion mechanism.3.Bubble broken system stirred by impeller and bubble collection and size measurement system were established.It could be confirmed from analyzing theoretically superficial chemical characteristics of bubbles that bubble size was related to surface tension.The littler the surface tension of bubbles was,the easier the bubble to break up into small bubbles.Surfactant could change surface properties of bubbles and was critical factor for generating bubbles.Bubble break-up mechanisms stirred by impeller and bubble size distribution regularities were studied.The results showed that shearing action of turbulence eddies produced by impeller rotation and direct mechanical force of impeller blades were the major methods for bubble break-up stirred by impeller.The turbulence eddies could change the surface free energy of bubble surface,and caused seriously tensile deformation until broken,while bubbles broken up rapidly into small bubbles by mechanical force of impeller blades.Foaming agent changed bubble surface properties,and prevented the coalescence process between bubbles.Bubble diameter decreased with increasing foaming agent concentration,and the bubble size distribution was more balance.Bubble diameter remained unchanged with increasing foaming agent concentration surpassed Critical Coalescence Concentration(CCC).Bubble diameter increased with increasing inspiratory capacity,and first increased then decreased with impeller rotating speed.A critical intersection,n=610 r/min,q=4.08 L/min,between inspiratory capacity and impeller rotating speed existed while the bubble size influenced together by inspiratory capacity and impeller rotating speed.And the minimum bubble mean diameter was about 0.45 mm.Bubble size decreased with increasing liquid level.Bubble produced by self-absorption-air flotation device was collectively influenced by multi-factors.4.Mineral separating system was established.The preprocessing action of flotation device was verified by experimental investigation.The mineralization effect of the flotation device was illustrated by comparing the separating results between self-absorption-air flotation device and laboratory single groove flotation machine.The experimental results showed that preprocessing action was existed in the mixing chamber of the flotation device.After preprocessing in the mixing chamber for mineral particles,agent adsorbing capacity on the surface of mineral particles increased with increase of agent dosage,and remained unchanged with increasing agent dosage surpassed saturated adsorption capacity.Agent adsorbing capacity on the surface of mineral particles increased with increase of impeller rotating speed,which was,impeller rotation had dispersion effect on foaming agent and accelerated foaming agent adsorbed to the surface of mineral particles.Results of preprocessing separating test showed that productive rate of concentrate increased 2.66%by preprocessing pulp in the mixing chamber.The separating experimental results of flotation device showed that productive rate of concentrate,increased 8.66%,was higher and productive rate of tailings was lower and ash content of tailings was higher,compared to laboratory single groove flotation machine with the same flotation condition.Although,the ash content of concentrate was higher than laboratory single groove flotation machine,ash content is lower than 10%,that was,the flotation device could separating out low ash content concentrate.The combustible material recovery and flotation efficiency were increased 8.38%and 6.24%respectively with increasing impeller rotating speed,and both of them were high than separating result of laboratory single groove flotation machine.Figure[95]Table[25]References[194]... |
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