Modeling of Circulating Flow of Solids between a Fluidized Bed and a Fast Fluidized Bed/Pneumatic Transport Tube Reactor Connected by Orifices

Interconnected and dual fluidized bed (FB) systems with various regimes of gas-solids flow are commonly studied with the aim to find and ensure suitable circulation of solids and control of flow between two chambers/reactors with different reacting gases. Dual separated fluidized beds or fluidized and transporting bed systems are convenient for cleaning of gases with regeneration of a solid sorbent or for gasification of solid fuels and production of rich fuel gas with practically no content of nitrogen. We concentrated in our theoretical study on development, comparison and checking of three simplified models for solid particle velocity, mass flux and pressure drop in a pneumatic transport reactor. The simplified models have been used in a more general model for flow of solids via orifice(s) between a FB near the incipient fluidization and a tube with pneumatic transport (PT) of solids and circulation back to the FB. The model solution we used for estimation of effects of particle size, gas velocity in pneumatic transport column, height of FB, orifice(s) cross sectional area and PT-column parameters (diameter and height) on mass flux of solids. We tried to estimate by the models theoretical influence of temperature on solids flow and circulation. Considering simplified equations for estimation of pressure drop in the cyclone/impactor and for gas penetration from FB to the PT-column we tentatively evaluated their possible effects on circulation of solids. Comparison of a theoretical forecast for saturation carrying capacity of gas in pneumatic transport (“choking”), computed by selected Yang correlation, with the model-computed mass fluxes of solids has indicated possible problems and instabilities of solids flow in some regimes and arrangements, especially with larger orifices, higher height of FB and/or lower gas velocities in PT-column and bigger particles. For control of circulation rate of a given particulate material in the dual FB/PT systems three practically important parameters should be considered: gas velocity in PT-column, cross sectional area of orifice(s) and height of FB.

WIECZOREK Kamila;  SVOBODA Karel;  MICCIO Francesco;  BAXTER David;  KALISZ Sylwester; 

2007-06-13

Slovak Society of Chemical Engineering

JRC37181