液固分选流化床数学模型与结构优化研究

发布时间：2018-04-14 21:24

本文选题：液固分选流化床 + 干扰沉降　；参考：《中国矿业大学(北京)》2017年博士论文

【摘要】：目前工业应用的主要粗煤泥分选设备有螺旋分选机、煤泥重介旋流器、水介分选旋流器和液固分选流化床(Liquid-Solid Fluidized Bed Separator,LSFBS)等。由于LSFBS在高固体颗粒体积分数和低流化速度下实现颗粒按密度分层,粒度效应受到一定程度弱化,与其它粗煤泥分选设备相比,LSFBS具有分选效果好,有效分选密度范围宽等优点。本文以LSFBS为研究对象,采用试验、理论分析和数值模拟相结合的方法分析了LSFBS内颗粒沉降、流化行为,探索了自生密相液固流化床内周围颗粒对目标颗粒运动影响的有效近似处理方法,建立了基于颗粒动力学方程的LSFBS数学模型以及基于CFD的LSFBS数学模型;利用建立的CFD模型对LSFBS结构进行了优化,并通过颗粒动力学分析探究了倾斜板抑制粒度效应机理,设计开发出新型LSFBS(内置倾斜板的变径LSFBS),最后试验研究了新型LSFBS分选特性。本文主要内容和结论如下:(1)探究了自生介质粒度对分选效果影响,发现对于同一粒度自生介质,上升水流越大浮物与自生介质床层界面越模糊,颗粒按密度差异的分离效率越低;自生介质粒度越小,能达到的最佳分离效率越好,对应的分离密度越低;提出了将自生密相液固流化床层类比为准流体,以准流体有效密度和表观粘度概念来体现颗粒间相互作用的处理方法;利用准流体法,并结合颗粒边界层理论,在ConchaAlmendra自由沉降速度公式基础上提出了新的干扰沉降末速模型,与已有干扰沉降末速模型相比,本文模型预测准确度明显更高,与试验值相比,相对误差基本可控制在10%以内;利用Euler-Euler法模拟了单组分颗粒流化过程,比较了不同液固两相动量交换系数的适应性,发现Hui-Gidaspow模型最适于固体颗粒在水介质中流化过程的模拟;探究了双组份颗粒流化过程反分层现象,提出了用于判定能否发生反分层的分界线模型,与Rual模型相比,本文模型对已有试验数据能给出更准确预测结果。(2)根据LSFBS主分选区流场特性,对颗粒受力进行了分析和量级比较,发现Magnus力、Saffman力和Basset力对颗粒沿竖直方向的干扰沉降运动影响很小,可将其从颗粒动力学方程中省略;采用准流体法处理自生密相液固流化床层内颗粒间相互作用,进一步简化了LSFBS颗粒动力学方程。基于简化的颗粒动力学方程,建立了新的LSFBS数学模型,检验了该LSFBS数学模型的准确性,溢流产率模型预测值与试验值的相对误差为2.84%。(3)探索了适于LSFBS分选过程数值模拟的有效方法,提出了EulerianEulerian-Lagrangian/RNG k-ε的LSFBS CFD模型,其中依然采用准流体法来简化自生密相液固流化床层内颗粒间相互作用,模拟分选结果能很好的符合试验结果,准确度优于基于颗粒动力学方程的模型预测结果;利用本文提出的CFD模型,探究了脉动上升水流对分选结果的影响,得出最佳脉动周期为1.25 s,最佳脉动波形为矩形,但无论改变脉动周期,还是脉动波形,都不能使其分选精度优于相应均匀上升水流的分选结果;提出了定量分析入料粒度分布特性对入料按密度差异分离过程影响的CFD方法,其中入料粒度分布特性采用R-R模型来描述,通过设定RR模型两参数来精确控制入料粗细程度和入料粒度分布集中程度。设计了两因素、五水平的CCD响应面数值试验,对数值试验结果进行方差分析可知,在区间Dx=(0.51,0.79)和n=(1.96,9.04),入料粗细对分选密度的影响大于入料粒度分布集中程度;而入料粒度分布集中程度对可能偏差的影响大于入料粗细;入料粗细程度和入料粒度分布集中程度间交互作用对可能偏差有显著影响,而对分选密度影响很小。(4)利用本文提出的LSFBS CFD模型,对LSFBS结构进行了优化设计,提出了两段外扩变径的LSFBS;根据液固两相流和平板边界层理论,对不同间距倾斜板间颗粒进行了动力学分析,揭示了滑移剪切升力是倾斜板抑制粒度效应的根本原因,进而提出了内置倾斜板的变径LSFBS;进行了内置倾斜板的变径LSFBS和传统LSFBS对比试验研究,相同分选密度下内置倾斜板的变径LSFBS可能偏差较传统LSFBS得到明显降低,在分选密度1.35-1.6 g/cm3区间上,可能偏差平均降低约0.027 g/cm3;提出了一个评价不同试验条件、不同设备分选效果的综合指标,即脱灰效率,该指标可同时兼顾溢流产率和溢流灰分,且与可能偏差密切相关,分配曲线越陡峭,该指标越大;进行了倾斜板数量单因素试验,发现随着板间距从27.56 mm减小到4.83 mm,脱灰效率一直增大;建立了Saffman力与板间距和板间水流速度间关联式,该关联式可为上升水流速率和倾斜板数量优化提供理论依据,对比了雷诺数小于100时,关联式和Mei公式计算结果,发现二者能很好的吻合;设计了二因素三水平正交实验(A:上升水流速率;B:板间距),对内置倾斜板的变径LSFBS上升水流速率和板间距进行了协同优化,得到两因素最优组合为上升水流速率3.11 m3/h,板间距4.83 mm。通过方差分析发现各因素对脱灰效率影响显著性由高到低依次为:BA×BA,其中上升水流速率对脱灰效率仅有一定影响,两因素间交互作用对脱灰效率影响高度显著。
[Abstract]:At present the main Coarse Slime Separator for industrial applications with spiral separator, slime heavy medium cyclone, water medium separation hydrocyclone and liquid-solid fluidized bed for separation (Liquid-Solid Fluidized Bed Separator, LSFBS). The LSFBS in high solids fraction and low fluidization velocity of particles by density stratification, the effect of particle size is the degree of weakening, compared with other coarse slime separation equipment, LSFBS has a good separation effect, wide range of effective separation density. This paper takes LSFBS as the research object, using tests, theoretical analysis and numerical simulation method of combining analysis of the settlement of LSFBS particles, fluidization behavior, explore effective approximate treatment method of authigenic effect dense liquid solid fluidized bed of particles around the target particle movement, is established based on LSFBS mathematical model of particle dynamics equation and a mathematical model based on LSFBS CFD; use of construction The CFD model established to optimize the structure of LSFBS, and to explore the inhibitory effect of particle size by inclined plate mechanism of particle dynamics analysis, design and develop a new type of LSFBS (diameter LSFBS built-in inclined plate), finally studied the separation characteristics of the novel LSFBS. And the main content is as follows: (1) the node explores the effect of self generated media the size of the separation effect, found that for the same size of autogenous medium, the greater the rising water float and autogenous medium bed interface is fuzzy, the separation efficiency of particles according to the density difference is lower; the smaller the particle size of autogenous medium, the best separation efficiency can achieve better separation, the density is lower; the self. Liquid solid fluidized bed analogy for quasi fluid, the quasi fluid density and apparent viscosity of the concept of effective processing method to reflect the interaction between particles; using the quasi fluid method, combined with the particle boundary layer theory in Concha Almendra free settling velocity formula is proposed based on the new interference settling velocity model, compared with the existing interference settling velocity model, the prediction accuracy is significantly higher, compared with the experimental values, the relative error can be controlled within 10%; using Euler-Euler method to simulate the single particle flow process, comparison the different liquid-solid two-phase momentum exchange coefficient adaptive Hui-Gidaspow model to find the most suitable for the simulation of solid particles in the fluidized processes of water medium; explore the two-component particle flow process of anti stratification, used to determine whether anti hierarchical boundaries model is proposed, compared with the Rual model, the model of existing test data can give a more accurate prediction results. (2) according to the LSFBS main flow characteristics of constituencies, particle force were analyzed and found that magnitude, Magnus force, Saffman force and Basset force on the particles along The vertical direction of the settlement movement interference effect is small and can be omitted from the particle dynamics equation; quasi fluid treatment of autogenous dense liquid-solid fluidized bed layer interaction, further simplifying the LSFBS particle dynamics equation. Kinetic equation of particles based on the simplified LSFBS, established a new mathematical model and test accuracy the mathematical model of LSFBS, overflow rate model, the relative error of the predictive value and the experimental value was 2.84%. (3) to explore the effective method suitable for numerical simulation of LSFBS separation process, proposed the LSFBS CFD model EulerianEulerian-Lagrangian/RNG k- e, which is still using the quasi fluid method to simplify the autogenous dense liquid-solid fluidized bed layer in between effect of simulated sorting results are in a good agreement with the test results, the accuracy is better than the particle kinetic equation model based on the forecast results; using the CFD model To explore the impact of rising, fluctuating flow on the separation results, the optimum pulse period is 1.25 s, the optimum pulse waveform is rectangular, but whether to change the pulse period, or pulse waveform, can make the sorting accuracy better than the corresponding uniform rising flow separation results; the quantitative analysis of the feed size distribution characteristics of CFD methods and materials according to the difference of density separation process, wherein the feed size distribution characteristics are described by the R-R model, by setting the two parameters of RR model to precisely control the feeding thickness and feed size distribution concentration. The design of the two factors, five levels of CCD response surface numerical test, analysis of variance the results of numerical experiments, in the interval Dx= (0.51,0.79) and n= (1.96,9.04), the influence of feeding size on separation density is greater than the feed size distribution and concentration degree; particle size distribution in the degree of possible bias The impact of the difference is greater than the thickness of the feed; feed thickness and feed size distribution concentration degree of interaction may be significant deviation, but has little influence on the separation density. (4) using LSFBS CFD model proposed in this paper, the structure of LSFBS optimized design, put forward two external variable LSFBS; according to the liquid-solid two-phase flow and boundary layer theory, the different spacing between the inclined plate particle dynamics analysis, reveals the slip shear lift force is the root cause of the inclined plate inhibition effect of particle size, and then put forward the adjustable LSFBS built-in inclined plate; the diameter of LSFBS built-in inclined plate and traditional LSFBS comparative study LSFBS, built in the same diameter inclined plate separation density possible deviation compared with the traditional LSFBS has been significantly reduced, in the separation density of 1.35-1.6 g/cm3 interval, the average deviation may be reduced by about 0.027 g/ cm3 is put forward; Evaluation of different test conditions, the comprehensive index separation effect of different devices, namely the ash removal efficiency, the index can be simultaneously taking the overflow rate and overflow ash, and the possible deviation is closely related to the distribution curve is steep, the index is higher; the single factor test found that the inclined plate number, plate spacing decreases with the from 27.56 mm to 4.83 mm, ash removal efficiency has been increased; Saffman was established and the plate spacing and inter plate flow velocity between correlation, the correlation for upward flow rate and provide a theoretical basis for the inclined plate number optimization, compared to the Reynolds number is less than 100, the calculation results formula and Mei formula, found the two can be in good agreement; design of two factors and three levels orthogonal experiment (A: upward flow rate; B:, reducing LSFBS of plate spacing) built-in inclined plate upward flow rate and plate spacing of collaborative optimization, the optimal combination of the two factors The rising flow rate of 3.11 m3/h, plate distance of 4.83 mm. through the variance analysis found that the influence of various factors on the ash removal efficiency was from high to low: BA * BA, the upward flow rate on the ash removal efficiency of only two factors influence the interaction between highly significant influence on ash removal efficiency.

【学位授予单位】：中国矿业大学(北京)
【学位级别】：博士
【学位授予年份】：2017
【分类号】：TD45

【参考文献】