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A two-dimensional transient Eulerian model integrating the kinetic theory for emulsion phase is used to simulate the bubbling and slugging gas-solid fluidized beds, including the Geldart B and D particles, respectively. CFD results show that utilizing an algebraic granular temperature equation, instead of a full granular temperature, one leads to a significant reduction in computational time without loosing accuracy. Different drag models have been examined in the current study. CFD results show that the Syamlal–O’Brien and Di Felice adjusted drag models, based on minimum fluidization velocity, are not suitable for the bed, including coarse particles (Geldart group B). The Gidaspow drag model displays better results in comparison with the others. A good agreement with the available experimental data and the researcher’s findings has been reached quantitatively and qualitatively. The proposed model can reasonably be used for simulation of slugging fluidized beds. This study reduces the computational error compared with the previous works.

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A multi-fluid Eulerian model incorporating the kinetic theory of granular flow is used for the simulation of bubbling fluidized beds containing a binary mixture of Geldart B particles at low gas velocities. The cases of density, size and combined density/size segregation are investigated using computational fluid dynamic simulations. Various expressions for the drag force are evaluated for predicting different segregations. The simulation results show that summation of the particle-particle drag force, i.e., the "hindrance effect" term, and the Stokes drag of particles, which is modified based on the Wen-Yu drag model can be used for accurate simulation of a binary mixture of particles differing in size, density, or both. Bed expansion and dimensionless axial segregation profiles of CFD results are compared with the experimental data and good agreement is found. IntroductionMixtures of solid particles of different sizes and/or densities tend to separate during fluidization. The segregation behavior of a mixture of particles is important since particle distributions in the fluidized bed influence chemical reactions, bed expansion, and various mass and heat transfer properties in the fluidized beds. In fluidized bed reactors in the food, chemical, pharmaceutical and metallurgical industries, the processes of particle mixing and segregation change the distribution of the mixture components in the bed, and therefore, play a very important role in the overall processes [1]. Segregation, as a transient process, is strongly affected by gas velocity [1]. Bubbles, which are known to play an intricate and ambiguous role in fluidized bed reactors, can strongly influence the different mixing and segregation phenomena. Both the chemical reaction and mass/heat transfer depend on the local particle size distribution (PSD) in the bed. Therefore, a better understanding of the spatial distribution of different solid components for a given particle size distribution is required to improve the design, operation and scale-up of different gas-fluidized bed processes.While there are several experimental procedures for measuring particle size distribution and the physical properties of fluidized beds, the use of computational fluid dynamic (CFD) tools for providing valuable information for the design of the reactor, scale up and optimization has attracted considerable attention in recent years. Two methods have been typically used for CFD modeling of gas-solid flows, i.e., the EulerianLagrangian method and the Eulerian-Eulerian approach. In the Eulerian-Lagrangian approach, the computational demand rises sharply with the number of traced particles, which constrains its applicability to high concentration flows. In the Eulerian-Eulerian method, which is used in the current study, two phases are mathematically treated as interpenetrating continua. The success of a multi-fluid model (MFM) depends on the proper description of the interfacial forces and the solid stresses. The interfacial forces are used to describe the momentum transfer be...

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The algae biomass is one of the potential biomass resources for extracting lipid to produce fuel. The off grade or residuals of dehydrated algae particles can be used in pyrolysis reactions to produce fuel or useful chemicals. Due to higher ash contents of algae biomass, pyrolysis process needs an appropriate design of pyrolysis reactor. The heating rate of algae biomass is a key factor for increasing of bio-oil production rate. Instead of heat transfer from reactor walls to the biomass, heated inert particles are added to the conventional fluidized bed reactor to increase heat transfer rate and yield of the bio-oil as called flash pyrolysis. The introduced pyrolysis reaction in the novel heating method of fluidized bed reactor studied numerically. For this purpose, an Eulerian-Eulerian CFD model utilized for modeling of the dehydrated algae pyrolysis in the fluidized bed reactor. The appropriate reaction rate of the algae pyrolysis is based on the heating rate, temperature sensitive activation energy and the reaction selectivity utilized to the algae pyrolysis. In addition, the segregation and density change of the biomass particles investigated in the CFD modeling to analysis mixing of the particles and corresponding heat transfer between the mixed particles. The validation of the CFD model investigated using results of prepared experimental setup.

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