(98b) Comparison of CFD Models in Predicting the Fluidization Behavior of Geldart B Particles

A particular flow regime occasionally observed when fluidizing Geldart B particles in small scale units is slugging. This flow regime, characterized by high pressure fluctuations and big bubbles that can cover the entire section of the fluidizing column (square-nosed slugs), may result in difficulty of extrapolation of the hydrodynamic results obtained for small units into larger scales.

CFD models represent a potential tool for the design of gas-fluidized beds. Despite the efforts of the scientific community, the ability of these models in predicting the hydrodynamic behavior of these multiphase systems is still limited. Robust and reliable CFD tools that can predict the hydrodynamics of group B particles slugging in lab or pilot scale units is extremely useful for beforehand definition of the operating conditions and geometry that can assure cold flow model experimentation reproducing the same hydrodynamics of large scale reactors.

In this work, two different commercial CFD tools have been compared in their ability of predicting hydrodynamic features of slugging gas-solid fluidized beds. The study is of special interest to chemical looping combustion process that employs Geldart B particles but also to fluidized bed combustion or gasification processes. Different parameters such as bed expansion, pressure fluctuations, voidage and solid velocity obtained experimentally have been compared with CFD results and the effects of simulation parameters on the predicted flow structures have been discussed.