Experiments support an improved model for particle transport in fluidized beds

Abstract

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, G s , 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, KU t , the pressure exerted at the base of the conveyor tube, and the tube length. The model expression $${{\boldsymbol{G}}}_{{\boldsymbol{s}}}=\frac{{\boldsymbol{\Delta }}{\boldsymbol{P}}}{({U}_{{\boldsymbol{g}}}-{\boldsymbol{K}}{{\boldsymbol{U}}}_{{\boldsymbol{t}}}){\boldsymbol{+}}\frac{{{\boldsymbol{K}}}^{{\boldsymbol{2}}}{\boldsymbol{g}}{\boldsymbol{L}}}{({{\boldsymbol{U}}}_{{\boldsymbol{g}}}-{\boldsymbol{K}}{{\boldsymbol{U}}}_{{\boldsymbol{t}}})}}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msub> <mml:mrow> <mml:mi>G</mml:mi> </mml:mrow> <mml:mrow> <mml:mi>s</mml:mi> </mml:mrow> </mml:msub> <mml:mo>=</mml:mo> <mml:mfrac> <mml:mrow> <mml:mi>Δ</mml:mi> <mml:mi>P</mml:mi> </mml:mrow> <mml:mrow> <mml:mrow> <mml:mo>(</mml:mo> <mml:mrow> <mml:msub> <mml:mrow> <mml:mi>U</mml:mi> </mml:mrow> <mml:mrow> <mml:mi>g</mml:mi> </mml:mrow> </mml:msub> <mml:mo>−</mml:mo> <mml:mi>K</mml:mi> <mml:msub> <mml:mrow> <mml:mi>U</mml:mi> </mml:mrow> <mml:mrow> <mml:mi>t</mml:mi> </mml:mrow> </mml:msub> </mml:mrow> <mml:mo>)</mml:mo> </mml:mrow> <mml:mo>+</mml:mo> <mml:mfrac> <mml:mrow> <mml:msup> <mml:mrow> <mml:mi>K</mml:mi> </mml:mrow> <mml:mn>2</mml:mn> </mml:msup> <mml:mi>g</mml:mi> <mml:mi>L</mml:mi> </mml:mrow> <mml:mrow> <mml:mo>(</mml:mo> <mml:msub> <mml:mrow> <mml:mi>U</mml:mi> </mml:mrow> <mml:mrow> <mml:mi>g</mml:mi> </mml:mrow> </mml:msub> <mml:mo>−</mml:mo> <mml:mi>K</mml:mi> <mml:msub> <mml:mrow> <mml:mi>U</mml:mi> </mml:mrow> <mml:mrow> <mml:mi>t</mml:mi> </mml:mrow> </mml:msub> <mml:mo>)</mml:mo> </mml:mrow> </mml:mfrac> </mml:mrow> </mml:mfrac> </mml:math> can be used for design purposes, with K , the correction factor for hindered settling of the particles, approximately equal to 0.1 at high G s -values, but a function of the solids fraction in the upward conveying. The energy efficiency of the system increases with increasing U and G s . 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.