入料顆粒對分選流態(tài)化的影響及其分離行為
發(fā)布時間：2018-11-15 17:21
【摘要】：空氣重介質分選流化床能夠實現(xiàn)-50+6 mm級煤炭的有效分選,但氣流與加重質密度的顯著差異使形成密度均勻穩(wěn)定的流化床層難度很大,這是由流化介質的性質決定的。另外,入料顆粒干擾也是影響分選流化床穩(wěn)定性的重要因素,鑒于此,研究入料顆粒對床層特性的影響很有必要。大顆粒的動力學特性直接決定顆粒的分離行為,進而影響物料的分選分層效果。在不同因素條件下,重點考察了不同性質顆粒的運動行為及分布情況。對不同高徑比條件下窄粒級磁鐵礦粉的壓降進行測量,通過繪制壓降特性曲線,發(fā)現(xiàn)臨界流態(tài)化速度隨床層高度的變化而基本恒定,而床層的膨脹度有所變化;根據(jù)寬粒級加重質中各窄粒級的質量比,分析得到其臨界流態(tài)化速度與各比重成函數(shù)關系;采用密度球構造物料層,得到了物料層對上部床層流化特性的影響規(guī)律。借助于標準的13 mm中間密度球(確保完全浸沒在床層中)研究入料對床層活性的影響,通過對比浸沒的密度球體積和床層的膨脹體積,確定了入料對乳化相的“擠壓”特性;采集測量球流化狀態(tài)與對應的靜置狀態(tài)下所處的床層高度數(shù)據(jù),建立了顆粒在兩種狀態(tài)下的位置關系;采用分層分級效果不明顯的窄粒級磁鐵礦粉做為加重質,將床層控制在臨界流化狀態(tài),不同靜床高時床層的加重質顆粒濃度也不相同,低密度顆粒群的平均上浮速度隨著加重質顆粒濃度的增大而減小,間接反映出床層流動活性的變化規(guī)律。采用測量過程中受氣泡影響較小的高密度鋼球做為試驗球,借助SF-3測力計對試驗球在流化床中的受力進行理論分析,推導出不同直徑球所承受的附加合力及其變化情況;采用高速動態(tài)圖像分析系統(tǒng)對不同條件下的氣泡特性進行分析,得到合適的氣泡尺寸計算模型;在附加合力F=0時確立與氣泡相關的無量綱λ和試驗球直徑的關聯(lián)式。采用入料顆粒軸向分布系數(shù)公式來評價顆粒在床層中按密度分層的效果,通過分割試驗設計法研究高密度顆粒的沉降行為。結果表明,細粒級加重質相對粗粒級要在較大的流化數(shù)條件下才能取得最佳的沉降效果,而加重質顆粒對入料顆粒碰撞的影響小于床層粘度的影響。在低流化數(shù)狀態(tài)下,床高的影響不明顯,但當流化數(shù)大于1.2時,軸向分布系數(shù)值隨著靜床高的增加而減小。隨著入料顆粒粒度的增大,達到最佳沉降效果的時間會縮短。低密度顆粒的返混程度隨著流化數(shù)的增加而逐漸增強,同時加重質粒度的增大也有利于返混程度的削弱。密度低于床層0.3 g/cm~3以上的各示蹤球之間很難分離開來,對低于床層密度0.3 g/cm~3以內(nèi)的各示蹤球來說,λ值隨著流化數(shù)的增加基本不變。
[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.
【學位授予單位】：中國礦業(yè)大學
【學位級別】：碩士
【學位授予年份】：2017
【分類號】：TD94;TD922
本文編號：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.
【學位授予單位】：中國礦業(yè)大學
【學位級別】：碩士
【學位授予年份】：2017
【分類號】：TD94;TD922
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