入料颗粒对分选流态化的影响及其分离行为
发布时间：2018-11-15 17:21
【摘要】：空气重介质分选流化床能够实现-50+6 mm级煤炭的有效分选,但气流与加重质密度的显著差异使形成密度均匀稳定的流化床层难度很大,这是由流化介质的性质决定的。另外,入料颗粒干扰也是影响分选流化床稳定性的重要因素,鉴于此,研究入料颗粒对床层特性的影响很有必要。大颗粒的动力学特性直接决定颗粒的分离行为,进而影响物料的分选分层效果。在不同因素条件下,重点考察了不同性质颗粒的运动行为及分布情况。对不同高径比条件下窄粒级磁铁矿粉的压降进行测量,通过绘制压降特性曲线,发现临界流态化速度随床层高度的变化而基本恒定,而床层的膨胀度有所变化;根据宽粒级加重质中各窄粒级的质量比,分析得到其临界流态化速度与各比重成函数关系;采用密度球构造物料层,得到了物料层对上部床层流化特性的影响规律。借助于标准的13 mm中间密度球(确保完全浸没在床层中)研究入料对床层活性的影响,通过对比浸没的密度球体积和床层的膨胀体积,确定了入料对乳化相的“挤压”特性;采集测量球流化状态与对应的静置状态下所处的床层高度数据,建立了颗粒在两种状态下的位置关系;采用分层分级效果不明显的窄粒级磁铁矿粉做为加重质,将床层控制在临界流化状态,不同静床高时床层的加重质颗粒浓度也不相同,低密度颗粒群的平均上浮速度随着加重质颗粒浓度的增大而减小,间接反映出床层流动活性的变化规律。采用测量过程中受气泡影响较小的高密度钢球做为试验球,借助SF-3测力计对试验球在流化床中的受力进行理论分析,推导出不同直径球所承受的附加合力及其变化情况;采用高速动态图像分析系统对不同条件下的气泡特性进行分析,得到合适的气泡尺寸计算模型;在附加合力F=0时确立与气泡相关的无量纲λ和试验球直径的关联式。采用入料颗粒轴向分布系数公式来评价颗粒在床层中按密度分层的效果,通过分割试验设计法研究高密度颗粒的沉降行为。结果表明,细粒级加重质相对粗粒级要在较大的流化数条件下才能取得最佳的沉降效果,而加重质颗粒对入料颗粒碰撞的影响小于床层粘度的影响。在低流化数状态下,床高的影响不明显,但当流化数大于1.2时,轴向分布系数值随着静床高的增加而减小。随着入料颗粒粒度的增大,达到最佳沉降效果的时间会缩短。低密度颗粒的返混程度随着流化数的增加而逐渐增强,同时加重质粒度的增大也有利于返混程度的削弱。密度低于床层0.3 g/cm~3以上的各示踪球之间很难分离开来,对低于床层密度0.3 g/cm~3以内的各示踪球来说,λ值随着流化数的增加基本不变。
[Abstract]:Fluidized bed separation with air heavy medium can realize the effective separation of -506 mm coal, but the obvious difference between air flow and aggravation density makes it very difficult to form a fluidized bed with uniform density and stable density, which is determined by the properties of fluidized medium. In addition, the interference of feed particles is also an important factor affecting the stability of separation fluidized bed. In view of this, it is necessary to study the influence of feed particles on bed characteristics. The dynamic characteristics of large particles directly determine the separation behavior of particles, and then affect the separation and stratification effect of materials. Under different conditions, the movement behavior and distribution of particles with different properties were investigated. The pressure drop of narrow grained magnetite powder was measured under different ratio of height to diameter. By drawing the characteristic curve of pressure drop, it was found that the critical fluidization velocity was basically constant with the change of bed height, and the expansion degree of bed changed somewhat. According to the mass ratio of each narrow grain in the wide-grained aggradation, the relationship between the critical fluidization velocity and the specific gravity is obtained, and the influence of the material layer on the fluidization characteristics of the upper bed is obtained by using the density sphere to construct the material layer. With the aid of the standard 13 mm intermediate density sphere (ensuring complete immersion in the bed), the influence of the feed on the bed activity was studied. The extrusion characteristics of the emulsified phase were determined by comparing the volume of the submerged density sphere and the expansion volume of the bed. Collecting and measuring the bed height data of the fluidized sphere and the corresponding static state, and establishing the position relationship of the particles in the two states. The narrow grained magnetite powder, which has not obvious effect of stratification and classification, is used as the aggravation, the bed is controlled in critical fluidization state, and the aggravation particle concentration of the bed is different with different static bed height. The average floating velocity of low density particle group decreases with the increase of aggravation particle concentration, which indirectly reflects the changing law of bed flow activity. The high density steel ball which is less affected by bubble in the measurement process is used as the test ball. The force of the test ball in the fluidized bed is theoretically analyzed by SF-3 dynamometer, and the additional force and the variation of the ball with different diameter are deduced. The bubble characteristics under different conditions are analyzed by using a high-speed dynamic image analysis system, and a suitable bubble size calculation model is obtained, and the correlation formula of the bubble dependent infinitesimal 位 and the diameter of the test sphere is established when the additional force is F = 0. The axial distribution coefficient formula is used to evaluate the effect of density stratification of particles in the bed. The settlement behavior of high density particles is studied by the method of split test design. The results show that the best settlement effect can be obtained only when the fine grained aggradation is relative to the coarse grain under the condition of larger fluidization number, and the effect of the aggravation on the impact of the feed particles is less than that of the bed viscosity. Under the condition of low fluidization number, the influence of bed height is not obvious, but when fluidization number is larger than 1.2, the axial distribution coefficient decreases with the increase of static bed height. With the increase of particle size, the time to achieve the best settlement effect will be shortened. The degree of backmixing of low density particles increases with the increase of fluidization number, and the increase of plasmid size is also beneficial to the weakening of the degree of backmixing. It is difficult to separate the tracer spheres with a density lower than 0. 3 g/cm~3 of the bed. For the tracer spheres less than 0. 3 g/cm~3 of bed density, the 位 value is basically unchanged with the increase of fluidization number.
【学位授予单位】：中国矿业大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TD94;TD922
本文编号：2333949
[Abstract]:Fluidized bed separation with air heavy medium can realize the effective separation of -506 mm coal, but the obvious difference between air flow and aggravation density makes it very difficult to form a fluidized bed with uniform density and stable density, which is determined by the properties of fluidized medium. In addition, the interference of feed particles is also an important factor affecting the stability of separation fluidized bed. In view of this, it is necessary to study the influence of feed particles on bed characteristics. The dynamic characteristics of large particles directly determine the separation behavior of particles, and then affect the separation and stratification effect of materials. Under different conditions, the movement behavior and distribution of particles with different properties were investigated. The pressure drop of narrow grained magnetite powder was measured under different ratio of height to diameter. By drawing the characteristic curve of pressure drop, it was found that the critical fluidization velocity was basically constant with the change of bed height, and the expansion degree of bed changed somewhat. According to the mass ratio of each narrow grain in the wide-grained aggradation, the relationship between the critical fluidization velocity and the specific gravity is obtained, and the influence of the material layer on the fluidization characteristics of the upper bed is obtained by using the density sphere to construct the material layer. With the aid of the standard 13 mm intermediate density sphere (ensuring complete immersion in the bed), the influence of the feed on the bed activity was studied. The extrusion characteristics of the emulsified phase were determined by comparing the volume of the submerged density sphere and the expansion volume of the bed. Collecting and measuring the bed height data of the fluidized sphere and the corresponding static state, and establishing the position relationship of the particles in the two states. The narrow grained magnetite powder, which has not obvious effect of stratification and classification, is used as the aggravation, the bed is controlled in critical fluidization state, and the aggravation particle concentration of the bed is different with different static bed height. The average floating velocity of low density particle group decreases with the increase of aggravation particle concentration, which indirectly reflects the changing law of bed flow activity. The high density steel ball which is less affected by bubble in the measurement process is used as the test ball. The force of the test ball in the fluidized bed is theoretically analyzed by SF-3 dynamometer, and the additional force and the variation of the ball with different diameter are deduced. The bubble characteristics under different conditions are analyzed by using a high-speed dynamic image analysis system, and a suitable bubble size calculation model is obtained, and the correlation formula of the bubble dependent infinitesimal 位 and the diameter of the test sphere is established when the additional force is F = 0. The axial distribution coefficient formula is used to evaluate the effect of density stratification of particles in the bed. The settlement behavior of high density particles is studied by the method of split test design. The results show that the best settlement effect can be obtained only when the fine grained aggradation is relative to the coarse grain under the condition of larger fluidization number, and the effect of the aggravation on the impact of the feed particles is less than that of the bed viscosity. Under the condition of low fluidization number, the influence of bed height is not obvious, but when fluidization number is larger than 1.2, the axial distribution coefficient decreases with the increase of static bed height. With the increase of particle size, the time to achieve the best settlement effect will be shortened. The degree of backmixing of low density particles increases with the increase of fluidization number, and the increase of plasmid size is also beneficial to the weakening of the degree of backmixing. It is difficult to separate the tracer spheres with a density lower than 0. 3 g/cm~3 of the bed. For the tracer spheres less than 0. 3 g/cm~3 of bed density, the 位 value is basically unchanged with the increase of fluidization number.
【学位授予单位】：中国矿业大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TD94;TD922
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