MULTIPHASE CFD MODEL OF GAS-LIQUID PACKED BED REACTOR

Abstract

Multiphase systems are commonly present in the process industries and are found in a number of diverse areas of commerce. Typical application areas include the manufacture of petroleum-based products and fuels, the production of commodity and specialty chemicals, pharmaceuticals, herbicides and pesticides, refining of ores, production of polymers and other materials, and pollution abatement. In most of these applications, a multiphase chemical reactor is the heart of the process. Trickle-bed reactors (TBR) (packed bed reactors with co-current downflow of gas and liquid) are widely used for heterogeneous catalyzed reactions between gas and liquid, such as hydro-treatments, oxidation or partial oxidation and detoxification of liquid effluents. The fundamental problem in modeling of TBR is due to the complex nature of the flow domain that is formed by channels around randomly packed particles. The structure of this interstitial space inside the packed bed is mainly determined by particle size, particle shape, ratio of column diameter and particle diameter and the packing method. Computational fluid dynamics (CFD) has emerged as an effective tool for investigation of gas —liquid packed bed hydrodynamics. In the literature, CFD has been used for modeling of multiphase flows to reduce the design time and cost. The Eulerian-Eulerian multiphase model treats both phases including the particulates as interpenetrating continua. To study the hydrodynamics of TBR operating at high pressure with turbulent flow condition, Eulerian multiphase model (k-epsilon —per phase model) is a best method to deals with these kind of problems. In this dissertation, to investigate hydrodynamics in trickle bed reactor, a 2D computational domain based on the different experimental operating conditions has been simulated using commercial computational. fluid dynamics (CFD) code Fluent. For simulation purpose, Attou drag model is used. The hydrodynamics of two-phase flow in trickle-bed reactors (TBRs) under high pressure conditions was predicted. The effect of time step, convergence criteria and discretization scheme of volume fraction equation on liquid holdup and two phase pressured drop were studied. Using Attou drag model, several simulations were performed based on the operating conditions in a trickle bed reactor and the results were validated against the extensive experimental database available in the open literature. The results showed that CFD simulation offers better agreement with the results of experimental investigations within maximum deviation of 15%. This work has proved that this CFD model can productively be implemented for high-pressure operation (most of the commercial TBRs operate) which is cumbersome to account for in case of three-phase Eulerian simulation.