New Type of Draft Tube Spout-Fluid Bed. Part 1: Hydraulic Transport of 1.94 mm Glass Particles in Water

Abstract

A new type of draft tube spout-fluid bed (DTSFB) is described in which the draft tube physically separates the particle feeder section from the particle separator section as seen in Figure 2, creating an extremely versatile fluid/solids processing apparatus. This arrangement, denoted a type 2 DTSFB, allows the fluid mass flow rate in the draft tube and the dynamic pressure drop across it to be independently specified. As a result, the solids mass flow rate in the draft tube can be set and/or varied by changing the solids fraction, the particle velocity, or both. An additional property of this new DTSFB is that the effluents from the draft tube and annulus do not mix. Either stream can be collected or recycled as needed. In addition, the unit is easily controlled and scaled, and fluid—particle processing can be conducted in the draft tube, annulus, fluid—particle separator, or a combination of all of these. Equations are presented and sample calculations made to show how this new DTSFB works and how the solids fraction and particle velocity in the draft tube are set and varied. The data of Grbavcic et al. (Can. J. Chem. Eng. 1992, 71, 895-905) form the basis for the sample design calculations presented for a water-driven type 2 DTSFB. It is also shown that three independent variables capable of specifying the total mass fluid flow rate entering the inlet section, the split in that flow between the draft tube and annulus surrounding the draft tube and the dynamic pressure drop across the draft tube completely specifies the fluid and particle flows. Basic control schemes are outlined. A general equation is derived for calculating the maximum superficial fluid velocity allowable in the annulus (U a.max ). That velocity must be less than (U mF - ∈ a υ a ). Calculations demonstrate the effects of varying the total fluid mass flow rate supplied to the inlet section, the split of that fluid flow rate between the draft tube and the annulus, and the effect of the solids fraction and the dynamic pressure drop across the draft tube. Other calculations showing the effect of feeding all the inlet fluid flow to the draft tube provides a means for calculating the bounding limits that the annulus flow has on the operation of a type 2 DTSFB. Finally, we show the maximum particle circulation rate in the draft tube for a given fluid velocity in the annulus that will result in incipient fluidization of the annulus solids.