Modeling a Biomass Fluidizing Bed With Side Port Air Injection

Abstract

Fluidized beds are used to gasify materials such as coal or biomass in the production of producer gas. Modeling these reactors using computational fluid dynamics is advantageous when performing parametric studies for design and scale-up. While two-dimensional simulations are easier to perform than threedimensional simulations, they may not capture the proper physics. This paper compares two-and threedimensional simulations with experiments for a reactor geometry with side port air injection. The side port is located within the bed region so that the injected air can help promote mixing. Of interest in this study is validating the hydrodynamics of fluidizing biomass. Two operating conditions of the fluidized bed are studied for superficial gas velocities of 1.5Umf and 3.0Umf , where Umf is the minimum fluidization velocity. The material used to represent biomass is ground walnut shell because it tends to fluidize uniformly and falls within the Geldart type B classification. The simulations are compared to experimental data of time-averaged local gas holdup values using X-ray computed tomography. Results indicate that for the conditions of this study, two-dimensional simulations overpredict the gas holdup trends when compared to the experiments. However, the three-dimensional simulations compare exceptionally well with the experiments, thus predicting the fluidization hydrodynamics, irrespective of flowrate or complexity due to the side air port. Furthermore, the study demonstrates the importance of using a three-dimensional model for bubbling fluidized beds with complex physics.

A Review of X-Ray Flow Visualization With Applications to Multiphase Flows

“…They have extended this work to fluidized beds, including a 9.5 cm ID [166][167][168], a 10.2 cm ID [56,169], and a 15.2 cm ID [169,170] cold-flow fluidized bed. The fluidized bed data have been used to validate computational fluid dynamics (CFD) models of this complex gas-solid flow [168,[171][172][173][174]. CT imaging was also completed of an impinging water jet to measure the hydraulic jump at any angular location [175], as well as the cavitation field from a butterfly control valve [150].…”