EMMS-based Simulation For Bubble Column Reactors By CFD-PBM Model

In view of geometrically simple,high production,easy operation and excellent mass and heat transfer,bubble column reactors are widely employed in traditional chemical engineering,petrochemical engineering and biochemical engineering,such as oxidation process,Fischer-Tropsch synthesis,biological fermentation,waste water treatment and so on.A deep understanding of multiscale phenomenon in bubble column reactors would be significant and meaningful to the scale-up of reactors,design of structure and optimization of operation.Due to the development of computer technology and maturity of the computational fluid dynamics(CFD)modelling,the numerical simulation method has become an important research tool for the study of gas-liquid two phase flow in the bubble column.Bubble diameter,as one of the input parameters in the two-fluid model(TFM)model,has a great significance on the accuracy of the simulation results.The main objective of this paper is to study the influence of bubble diameter on CFD simulation for bubble column reactors under high superficial gas velocity and the application in modelling bubble size distribution using an EMMS based population balance model(PBM)model.Chapter 1 outlines the experimental and theoretical studies of bubble column reactors and the recent progress of CFD simulation and PBM application in bubble columns.In the end of multiphase reactors in literature.Finally,the Energy Minimization Multi-Scale(EMMS)model and the EMMS-PBM coupling method is introduced.Chapter 2 briefly introduces the basic setting of the CFD-PBM model.Grids of bubble column have been carried out by the Gambit software,the phase force model and the turbulence model are chosen for the system to model the bubble column reactor.In Chapter 3,the effect of PBM model modified by EMMS model to the simulation results is studied,which is compared with the uncorrected PBM model and the uniform bubble diameter model.The results show that the EMMS-PBM model considering the mesoscale energy dissipation has an improvement prediction on the simulation results of the bubble size distribution,and the improved bubble size information has an obvious optimization on the gas-liquid flow simulation.The study of Chapter 4 and Chapter 5 provides a corresponding supplement for the influence of bubble diameter on the study of bubble column and discusses the effect of the initial bubble diameter setting and the drag model on the gas holdup and the axial liquid velocity.The inhomogeneity of bubble size distribution on different axial and radial position in bubble column are investigated and the effects of different correctors for coalescence kernel model in PBMon bubble size distribution,gas holdup and axial liquid velocity are compared.Finally,chapter 5 summarizes the main results in this thesis and prospects the future work.