气固下行床能量最小多尺度（EMMS）模型

发布时间：2018-10-18 06:43

【摘要】：气固下行床是典型的非线性、非平衡系统,呈现出时空多尺度结构。与快速流化床类似,气固下行床中也存在颗粒团聚现象。由于能量最小多尺度(EMMS)理论考虑了系统中的多尺度非均匀结构,能较好地描述气固两相流中非均匀流动结构特征,因而在循环流化床中得到了广泛的应用和发展。本文拟将EMMS理论进一步扩展应用于气固下行床中,以建立并流和逆流下行床的轴向一维模型来探究其流体力学参数的轴向分布特征。将气固并流下行床多尺度分解为稀相、密相和相互作用相,并用稀密两相及相间的10个流动结构参数来描述,并进一步建立多尺度质量和动量守恒方程。根据气固两相流竞争性协调原理,建立了气固并流任意轴向不同发展阶段的截面稳定性条件,并用统一的数学形式进行了表达。通过用局部稳定性条件来优化团聚物数密度的方法确定聚团尺寸,不需要引入团聚物经验关联式就可对并流下行床轴向一维模型进行数值求解。对模型计算结果的定性分析以及和实验数据的定量比较均表明该模型能成功的描述并流下行床轴向宏观流体动力学特征,并可望适用于从细颗粒到粗颗粒的不同气固系统。考虑气固逆流与并流下行床中气固两相流动机制以及颗粒团聚机理的异同,采用与建立并流下行床轴向一维模型相同的方法,依次对气固逆流下行床系统进行多尺度分解,建立相应的本构方程,分析截面稳定性条件,并利用团聚物数密度优化的方法进行数值求解。但逆流下行床一维模型的计算结果受经验性参数壁面摩擦力的影响较大,因此在模型使用过程中需要对此参数进行合理估计,以保证模型预测的准确性。气固并流和逆流下行床EMMS模型由于考虑了气固两相流中的多尺度相互作用,因而具有一定的普适性。该研究丰富了基于EMMS的复杂气固系统全循环稳态建模理论,从而为实现以工业过程的实时模拟为特征的化工虚拟过程奠定基础。
[Abstract]:Gas-solid downcomer is a typical nonlinear, non-equilibrium system with a multi-scale structure in time and space. Similar to the fast fluidized bed, particle agglomeration also exists in the gas-solid downflow bed. Because the energy minimization multi-scale (EMMS) theory considers the multi-scale non-uniform structure in the system and can describe the non-uniform flow structure of gas-solid two-phase flow, it has been widely used and developed in circulating fluidized bed (CFB). In this paper, the EMMS theory is further extended to the gas-solid downflow bed, in order to establish the axial one-dimensional model of the parallel flow and countercurrent downflow to study the axial distribution characteristics of its hydrodynamic parameters. In this paper, the gas / solid flow downstream bed is decomposed into rarefied phase, dense phase and interaction phase, and the multi-scale mass and momentum conservation equations are further established by using 10 flow structure parameters of dilute dense two-phase and interphase flow. According to the principle of competitive coordination of gas-solid two-phase flow, the cross-section stability conditions of gas-solid flow in different development stages in arbitrary axial direction are established and expressed in a unified mathematical form. By using the local stability condition to optimize the number density of agglomerates to determine the size of the agglomerates, the axial one-dimensional model of the shunt downlink bed can be solved numerically without introducing an empirical correlation of the aggregates. The qualitative analysis of the model results and the quantitative comparison with the experimental data show that the model can successfully describe the axial macrohydrodynamic characteristics of parallel flow downflow beds and is expected to be suitable for different gas-solid systems from fine particles to coarse particles. Considering the similarities and differences of gas-solid two-phase flow mechanism and particle agglomeration mechanism between gas-solid countercurrent and co-current downflow, the multi-scale decomposition of gas-solid countercurrent downflow system is carried out by using the same method as establishing one dimensional axial model of co-current downflow. The corresponding constitutive equation was established and the stability condition of the section was analyzed. The numerical solution was carried out by using the method of optimization of aggregate number density. However, the results of one-dimensional countercurrent downflow model are greatly affected by the empirical parameter wall friction, so it is necessary to estimate this parameter reasonably in order to ensure the accuracy of the model prediction. The EMMS model of gas-solid parallel flow and countercurrent downflow has a certain universality because of the consideration of the multi-scale interaction in gas-solid two-phase flow. The research enriches the modeling theory of complete cycle steady state of complex gas-solid system based on EMMS, thus laying a foundation for realizing the chemical virtual process characterized by real-time simulation of industrial process.
【学位授予单位】：中国石油大学(华东)
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：TQ051.1

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