Experiments support an improved model for particle transport in fluidized beds

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 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 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.

Experiments support simulations by the NEPTUNE_CFD code in an Upflow Bubbling Fluidized Bed reactor

“…The current development of particle suspension solar heat receivers use such small I.D. beds with Geldart-A powders as heat carriers [8,9]. Fig.…”

“…For cristobalite sand, used in the present research (~2640 kg m s 3 ), C powders will be smaller than 33 µm; the aeratable group A will cover the range of 33 to 86 μm; group B powders will range from 86 to 446 μm; and group D powders will have a particle size in excess of 446 µm. Although aeratable group A powders are widely used in commercial fluidized bed catalytic reactors [5], their recent application in Upflow Bubbling Fluidized Bed (UBFB) or Cross-flow Bubbling Fluidized Bed (CfBFB) indirect solar receivers opens new application perspectives [6][7][8][9][10][11] due to their high mobility [12], high wall-to-bed heat transfer rates [13], and their easy circulation around the concentrated solar energy loops. Gas bubbles in group A powders moreover split and recoalesce frequently, resulting in a maximum stable bubble size [1,14], as further discussed in the paper.…”

Gas-Solid Flow in a Fluidized-Particle Tubular Solar Receiver: Off-Sun Experimental Flow Regimes Characterization

“…This point is discussed in Section 4. The pressure drop over a height H can be decomposed into a sum of three contributions, as explained in [30]:…”

Flue Gas Desulphurization in Circulating Fluidized Beds

“…The continuous circulating fluidized bed (CFB) is demonstrated to be the most appropriate processing unit due to both the high gas velocity (U) and solid circulation flux (G) being used, thus reducing the plant size, and providing very good mixing and contact between SO 2 and reactant for the desired removal [39][40][41]. A cyclone will collect solids and recycle them to the riser of CFB.…”