基于二元加重质的分选流化床密度调控机制研究

发布时间：2018-03-06 21:21

  本文选题：空气重介质流化床　切入点：二元加重质　出处：《中国矿业大学》2017年硕士论文　论文类型：学位论文

【摘要】：空气重介质流化床能够实现对-50+6 mm粒级煤炭的有效分选,但传统的空气重介质流化床使用单一加重质(除自生介质外),只能形成单一且较高的分选密度。为降低床层分选密度,实现物料的有效分选,将低密度石英砂和高密度磁铁矿粉作为混合加重质给入到空气重介质流化床中,形成较低密度的床层,扩宽气固流化床分选密度、粒度下限,为实现低密度煤炭的有效分选提供理论基础。试验中石英砂物料粒度组成为0.25-0.35 mm,磁铁矿粉粒度组成为0.15-0.2mm。选择两类介质颗粒粒度组成为窄粒级,不仅考虑石英砂颗粒与磁铁矿粉颗粒存在较大的密度差异,还考虑使整个床层形成一个相对稳定的低密度分选介质层,这不仅有利于低密度煤炭颗粒的分选,更有利于阻止高密度煤炭颗粒的错配,加快各密度级煤炭颗粒的分层,改良气固流化床分选效果。对于床层介质流化质量的评价从两个方面考虑。首先是床层密度的分布规律性,包括床层密度沿床高轴向及床层水平面径向的空间分布。其次是床层密度的均匀稳定性,床层密度以各组测压点测量计算的密度值作为样本,用样本标准离差Δ表征床层密度的均匀稳定性。由试验结果可知,二元混合加重质床层密度分布受石英砂含量、流化数及静床高的影响而呈现不同的分布规律。当石英砂含量介于5%-20%之间时,当流化数1.0≤N≤1.3时,床层密度整体分布不均,波动较大。当石英砂含量大于25%时,床层密度沿竖直方向自下向上呈逐渐降低的变化趋势。不同组成加重质床层密度分布标准差变化规律也不尽相同。当加重质中石英砂含量较低(ω=5%-15%)时,床层密度标准差随流化数的增大而减小;当加重质中石英砂含量增大(ω=20%-30%)时,床层轴向或径向密度标准差均较大,床层受气速影响,床层密度波动较大,床层稳定性差,为了使床层密度均匀分布,需控制试验流化数N=1.4-1.6的范围。根据理论推导的计算床层密度的公式,测定相关试验参数,得出二元混合加重质流化床床层密度与石英砂含量、床层流化数的数学关联式,得出流化床床层密度模型,并与实测值比较,检验其适应性。试验中选择-13+6 mm粒级中等灰分等级的焦煤作为分选研究对象。分选结果显示,对试验原煤的分选可能偏差为0.085 g/cm~3。当使用单一加重质分选时,分选所得精煤灰分偏高;当使用二元混合加重质分选时,随石英砂含量的增加,床层分选所得精煤产物灰分呈逐渐降低的变化规律,精煤灰分最低可达8.76%。
[Abstract]:The air heavy medium fluidized bed can realize the effective separation of -506mm granular coal. However, the traditional air-heavy medium fluidized bed uses a single aggravation (except for the autogenous medium, which can only form a single and high separation density.) in order to reduce the separation density of bed and realize the effective separation of materials, The low density quartz sand and high density magnetite powder are used as mixed additives to be fed into the air heavy medium fluidized bed to form a lower density bed, and the separation density and the lower particle size of the gas-solid fluidized bed are widened. In order to realize the effective separation of low density coal, the particle size composition of quartz sand and magnetite powder is 0.25-0.35mm and 0.15-0.2mm. Not only the density difference between quartz sand particles and magnetite particles is considered, but also the formation of a relatively stable low density separation medium layer in the whole bed is considered, which is not only beneficial to the separation of coal particles with low density. It is more helpful to prevent the mismatch of high-density coal particles and accelerate the stratification of coal particles of different density levels. Improved separation effect of gas-solid fluidized bed. The evaluation of fluidization quality of bed media is considered from two aspects. First, the distribution regularity of bed density, It includes the spatial distribution of bed density along the axial direction of bed height and the radial direction of bed horizontal plane. Secondly, the uniform stability of bed density. The uniform stability of bed density is characterized by the standard deviation 螖 of samples. From the experimental results, it is known that the density distribution of binary mixed aggravation bed is affected by the content of quartz sand. When the content of quartz sand is between 5% and 20%, when the fluidization number is 1.0 鈮，

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