Abstract
The upwards flow of particles in an Upflow Bubbling Fluidized Bed (UBFB) is studied experimentally and modelled from pressure drop considerations and energy loss equations. For Geldart group A powders tested, the upward solid flux, Gs, in the tube can be expressed in terms of the applied superficial gas velocity, the free fall (terminal) velocity of the particles during their hindered settling, KUt, the pressure exerted at the base of the conveyor tube, and the tube length. The model expression {{boldsymbol{G}}}_{{boldsymbol{s}}}=frac{{boldsymbol{Delta }}{boldsymbol{P}}}{({U}_{{boldsymbol{g}}}-{boldsymbol{K}}{{boldsymbol{U}}}_{{boldsymbol{t}}}){boldsymbol{+}}frac{{{boldsymbol{K}}}^{{boldsymbol{2}}}{boldsymbol{g}}{boldsymbol{L}}}{({{boldsymbol{U}}}_{{boldsymbol{g}}}-{boldsymbol{K}}{{boldsymbol{U}}}_{{boldsymbol{t}}})}} can be used for design purposes, with K, the correction factor for hindered settling of the particles, approximately equal to 0.1 at high Gs-values, but a function of the solids fraction in the upward conveying. The energy efficiency of the system increases with increasing U and Gs. The model equation was tentatively applied to predict the effects of particle size, tube length and operation in Circulating Fluidized Bed mode. It is demonstrated that the UBFB is an efficient and flexible way of transporting particles upwards, with limited particle attrition or tube erosion due to the low gas velocity applied.
Highlights
The model equation was tentatively applied to predict the effects of particle size, tube length and operation in Circulating Fluidized Bed mode
Conveying in a dense regime at low gas velocities is recommended to limit the flow rate of carrier gas and to reduce particle attrition and conveying line erosion
The solid flux was determined per unit time and unit cross sectional area of the respective tubes
Summary
The research aims to develop a reliable method for the design and scale-up of the UBFB conveying systems, based on experiments in the CNRS concept. The development of a more generalized method is required to combine the relevant characteristics of particle, gas, conveying pipe and pressure drop (ΔP). This is further developed in the present paper from initial experimental results and theoretical considerations. The terminal (free falling) velocity of particle (Ut) was calculated according to the method described by Geldart[31]. Particles within the fluidized bed dispenser move upward in the conveying tube by (i) both the pressure difference imposed between the particle suspension at the tube bottom and the atmospheric disengagement chamber at the tube top, and (ii) by the drag force on the particles from the total of primary and secondary air flows. Pressure and differential pressure probes were installed at several positions
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