The effect of packing on a fluidized bed

Abstract

A study has been made of the effect of fixed packing on the properties of a gas-fluidized bed, including minimum fluidization velocity, pressure drop, and bed expansion. Experiments using a range of glass beads as fluidizing solid with smooth uniform spheres as packing indicate that both packing size and the ratio of particle to packing diameter are the main variables in correlating the results. Other solids of varying density and shape have also been used. In addition to smooth spherical packing, rough spheres and variously shaped packings such as Raschig rings, Bert saddles, and a cylindrical, open-ended screen packing have received preliminary study. With the screen packing, which occupies only 5% of the column volume, i t has been possible to operate a fluidized bed at a much higher gas throughput without slugging than is possible with a conventional bed.A preliminary study has also been made of heat transfer rates, and the results indicate that the same factors are significant. The fluidization of particulate material is a technique which has many industrial applications. Good mixing and high rates of heat and mass transfer are generally associated with its use. However, the nature of conventional gas-solid fluidization imposes certain restrictions on the design of fluid-bed reactors. For example, there is a limit to the length-to-diameter ratio which can be used without serious slugging. Also, if high gas flow rates are desired, the reactor depth must include a Iarge freeboard to allow for fluctuations in bed height. Although many proposals have been made for expanding the useful range of gas-solid fluidization, very little quantitative information about their effect on the behavior of fluidized beds has been published. The data which are available, including an extensive study by Massimilla into the use of screen baffles (9, 10, 11) and a paper by Gabor, et al. on heat transfer rates in fluidized beds containing fixed spherical packing ( 1 2 ) , indicate that the changes resulting from the insertion of these devices can be very marked. Reactor internals affect not only the overall quality of the fluidization but also the expansion and the flow pattens of both gas and solid. As a result, heat and mass transfer rates can deviate significantly from those occurring in conventional beds.The work described in this paper is an introductory investigation into the effect of fixed packing on the properties of gas-fluidized beds. Most of the experimental work was performed with beds of packed spheres, but a limited number of experiments were done using packings of different shapes, in particular a cylindrical screen packing which was felt to be particularly suitable for use in fluidized beds. Results are reported for unit pressure drop and gas velocity at incipient fluidization and for bed expansion. A limited number of results showing the effect of packing on heat transfer rates are also given. APPARATUS AND PROCEDUREThe equipment used was of conventional design. The column consisted of a 3-in. I.D. plastic tube mou...

Some aspects of liquid‐solid fluidized beds

“…G,,jfp was found to be independent of the initial bed height and $ ratio, but less than that of the same fluidized bed without packing. Similar observations had been made by Sutherland et al (1963) for gas-solid systems packed with solid spheres and Ravindrapandian et al (1980) for liquidsolid systems. This indicates that only a fraction of the total voidage is available for liquid flow.…”

Increasing Gas–Solids Mass Transfer in Fluidized Beds by Application of Confined Fluidization—A Feasibility Study

“…The challenge of limited mass transfer between the bubble and emulsion phases can be addressed by means of using confined fluidized beds, i.e., inserting inert spheres of a size size much larger than the bed material to break down the bubble-emulsion flow structure. It has been shown that doing so provides smooth fluidization and increases bed expansion [3,4]. This will also have other effects that can be beneficial to mass transfer, such as locally increased relative gas-particle velocity.…”

Confined fluidization of fines in fixed bed of coarse particles

“…4), which was also formulated in the paper.  As results from the experiments, the confined fluidized systems in spite of geometrical condition d f /D p < 0.096 (Sutherland et al, 1963) should also satisfy the formulated condition ε p /ε p rel < 2.5 (cf. Eq.…”

“…Values of  mf rel / ba are up to 10% higher than those obtained in direct measurements within the range of high  p / p rel values. In various papers, the value of d f /D p < 0.096-0.414 (Sutherland et al, 1963) is considered as a boundary condition fluidization of fine particles in a fixed bed. Difficulties related with fluidization of fines from A group Geldart's classification, where extensive development of external surface precludes obtaining uniform fluidization like in case of conventional fluidized bed (Donsi et al, 1990;Zabierowski, 2008), was also mentioned.…”