Kishan B. Mathur

Vapour phase chemical reaction in spouted beds: Verification of theory

Abstract The performance of a 0.15 m diameter spouted bed reactor has been studied for decomposition of ozone on iron oxide catalyst. The variables include bed depth, catalyst particle size and spouting gas velocity. The spouted bed conversion data are compared against predictions from theoretical models proposed previously by Mathur and Lim who assumed vertically upward flow of annular gas in their first, one-dimensional model, and flow along curved streamlines in a subsequent, more rigorous, streamtube model. Experimental results show good agreement with conversions predicted by both models, but the latter model is expected to be superior for design of larger reactors. Additional experiments to discriminate between the two models and to establish their range of validity are planned.

Vapour phase chemical reaction in spouted beds: A theoretical model

Abstract A theoretical model of a spouted bed chemical reactor, involving vapour phase reaction in the presence of catalyst or heat carrier particles, is proposed. The hydrodynamic features relevant to the model are described in as generalized a manner as permitted by the available information. The application of the model is then demonstrated by making certain predictions concerning the effect of the major variables on gas conversion for a first order reaction, as well as on the relative performance of spouted, fixed, and fluidized bed systems.

Prediction of spout diameter in a spouted bed—A theoretical model

Abstract A theoretical equation for spout diameter has been derived from a force balance analysis which, in addition to the hydrodynamic forces, also takes into account solid stresses based on hopper flow of solids. The functional form of the equation is supported by a wide range of experimental data, the value of the multiplying coefficient showing an order of magnitude agreement with the empirical value. The theoretical analysis, though less comprehensive than a previous one due to Lefroy and Davidson, leads to a spout diameter equation which shows a greater measure of agreement with experimental results than the earlier equation.

Dynamics of Spouted Beds

Publisher Summary The full benefits of fluidization, although with coarse and uniform-sized particles, are not always realized because of the growth of large bubbles in the bed causing a tendency toward slugging. This limitation of fluidized beds can be overcome if the gas enters the bed through a small opening at the center of a conical base instead of a uniform distributor. In the process of the bed becoming a composite of a central spout, a systematic cycle pattern of solids movement is established with effective contact between the gas and the solids, giving rise to a unique hydrodynamic system, which is more suitable for certain applications than more conventional fluid–solids configurations. This chapter signifies the growing acceptance of spouted beds lies primarily in the specific fluid and particle dynamics associated with them. Spouting action can be achieved with either a liquid or a gas as the jet fluid. The minimum particle diameter for which spouting is practical appears to be 1–2 mm. Fine materials tend to fluidize rather than spout. For a given solid material, column diameter and fluid inlet diameter, a “maximum spoutable bed depth” exists beyond which the spouting action degenerates into poor-quality fluidization. A typical spouted bed has a substantial depth, which in the case of a cylindrical vessel is usually at least of the order of two column diameters, measured from the inlet orifice to the surface of the annulus. The total pressure drop across a spouted bed is always lower than that required to support the weight of the bed. Spouting can be achieved only within certain limits of solids properties while whether or not a material having properties within these limits will spout depends upon the geometry of the column, including to some extent the design of the gas inlet.