CFD modeling of multiphase fluidized Bed

Abstract

CFD is predicting what will happen, quantitatively, when fluids flow, often with the complications of, simultaneous flow of heat, mass transfer (eg perspiration, dissolution), phase change (eg melting, freezing, boiling), chemical reaction (eg combustion, rusting), mechanical movement (eg of pistons, fans, rudders), stresses in and displacement of immersed or surrounding solids. Knowing how fluids will flow, and what will be their quantitative effects on the solids with which they are in contact, assists chemical engineers to maximize the yields from their reactors and processing equipment at least cost; risk. CFD uses a computer to solve the relevant science-based mathematical equations, using information about the circumstances in question. Its components are therefore: the human being who states the problem, scientific knowledge expressed mathematically, the computer code (ie software) which embodies this knowledge and expresses the stated problem in scientific terms, the computer hardware which performs the calculations dictated by the software. Our project involves determining the validity of predictions made by CFD software (FLUENT) on three phase fluidization in a cylindrical bed by comparing with the practical results from the experiment conducted in lab. By this we were successfully able to predict the relationship of pressure drop and bed height vs. superficial velocity for different bed materials and liquid of different viscosities. For chemical processes where mass transfer is the rate limiting step, it is important to be able to estimate the gas holdup as this relates directly to the mass transfer. Although gas hold up in three-phase fluidized bed has received significant attention, most previous work has utilized air, water and small beads as gas, liquid and solid respectively. The gas hold up in such systems is often considerably lower than for pilotplant or industrial-scale units. In our project we have used glycerol of different concentrations to be able to maximize the usefulness of the result.