Computational Analysis of the Hydrodynamic Behavior for Different Air Distributor Designs of Fluidized Bed Gasifier

Abstract

Fluidized bed gasification has proven to be an appropriate technique for converting various biomass feedstocks into helpful energy. Air distributor plate design is one of the critical factors affecting the thermochemical conversion performance of fluidized bed gasifiers. The present study is proposed to investigate the mixing pattern and pressure drop across different configurations of air distributors using a two-fluid model (TFM) of finite volume method-based solver ANSYS FLUENT. The pressure drop across the bed and mixing pattern have been investigated through qualitative and quantitative analysis of CFD results using three diverse distributor plate designs: perforated plate, 90° slotted plate, and 45° swirling slotted plate. The pressure drop by employing the perforated distributor plate reveals the highest pressure drop due to the smallest open area ratio. However, the pressure drop in the case of 90° slotted plate is found to be 7% and 4% lesser than perforated and 45° slotted plate respectively due to a smaller velocity head developed through the wider open area of the straight slotted plates. The distributor design configuration having a 45° slotted plate exhibits considerable pressure drop compared to the 90° slotted plate due to the longer path length of the slot. Numerical pressure drop results across the bed with different types of distributor plates prove reasonable agreement with the experimental results available in the literature. Mixing behavior in perforated distributor plates exhibits lower portion solid volume fraction of around 0.58. However, it falls rapidly as go up the riser (7.7% of column height); 90° slotted plate shows bottom region solid volume fraction of around 0.5. In addition, it exhibits an even broader range of sand volume fraction and column height (13.46% of column height). Finally, the 45° distributor plate reveals the highest range of volume fraction through the riser height (17.3% of column height), indicating the better mixing characteristics of the fluidized zone.