MULTIPLE ORIFICE BUBBLE GENERATION IN GAS-SOLID FLUIDIZED BEDS: THE ACTIVATION REGION APPROACH

This work addresses the bubble generation mechanism at multi-orifice distributors in gas-solid fluidized beds (FB). Different measurements techniques such as high speed video camera and Kistler pressure transducers were applied to obtain information from both local, and global bed dynamics. Pressure fluctuation time series are used for dynamic diagnosis of the 2-D facility used during the study. The bed was operated with different distributor plates at several bubbling conditions leading to different bubble flow patterns characterized by digital image analysis of both the dense and the bubble phases. In order to explain the bubble pattern developed within the bed and the measured bubble dynamics, a phenomenological discrete bubble model is used. This model proposes an activation region (AR) mechanism for multi-orifice bubble generation. The underlying hypothesis is that the bubble formation can be placed in a region above the distributor plate where the initial bubble size is the result of the dynamical interaction of neighbour orifices. From the analysis of the experimental results, it is observed how for two different uniform gas distribution across the distributor plate, bubble dynamics interactions play the main role as the driver of the resulting bubble flow pattern developed within the bed. Moreover, when the activation region hypothesis is used as a bubble generation mechanism in a phenomenological discrete bubble model, it is seen that the proposed activation region mechanism, explains the observed bubble generation phenomena at multi-orifice distributors, and leads to a substantial decrease of the computational cost to simulate bubbling FB dynamics.