The Chemical Engineering Journal~ 55 (1995) 19-26 19 A simplified model for gas flow in conical spouted beds M. Olazar*, M.J. San Jos~, F.J. Pefias, A.T. Aguayo, J.M. Arandes and J. Bilbao Departamento de lngenierfa Qutmica, Universidad del Pals Vasco, Apdo. 544, 48080 Bilbao (Spain) (Received October 12, 1992) Abstract A model for gas flow in spouted beds in totally conical contactors is described. The model is applied by establishing the streamtubes in the annular zone of the bed in direct relation to the geometry of the contactor and of the gas inlet. In each streamtube, the deviation from plug flow is described by means of a dispersion coefficient. The validity of the model is confirmed in an experimental system at pilot plant scale. The application requires knowledge of the bed height, of velocity profiles in the contactor and the use of a gaseous tracer. The value of dispersion coefficient (Dffi0.01 m 2 s -~ for the experimental system studied) is similar to that given in the literature for cylindrical spouted beds and is an intermediate value between dispersion coefficients for fixed and fluidized beds. 1. Introduction Spouted beds of conical geometry are suitable for use with particles that are difficult to treat in cylindrical contactors [1, 2]. This applies to sticky solids or to solids that have a wide particle size distribution. Other qualities of conical contactors include the following: the operation conditions are versatile; they do not have a maximum spoutable height; they have a low pressure drop [3]; their expansion capacity under stable conditions [4]. In view of these qualities, conical contactors have recently been used in an expanded or jet spouting regime in reactions such as coal gasification [5-7] and catalytic polymerization of gaseous benzyl al- cohol [8, 9]. The spouted beds of conical geometry are also suited for the treatment of wood residues (sawdust, industrial by-products, agroforest resi- dues) by combustion, gasification or pyrolysis [ 10]. They are also useful in the drying of vegetables of different degrees of humidity and of pharmaceutical products. The design problems for attaining stability of conical beds and the determination of hydrodynamic correlations have been discussed in previous papers [11-141. This study is concerned with the definition of a model for gas flow, which is necessary for the rigorous design of conical reactors in the spouting *Author to whom correspondence should be addressed. regime for the aforementioned applications. As the fluid-particle contact takes place mostly in the annular zone, it is important to have a flow model for this zone, from which the fluid residence time distribution can be calculated. At the present state of this subject, some models have been proposed for cylindrical spouted beds which axe not applicable to conical spouted beds, and application of the only model for conical contactors proposed by Hadzis- majlovic et al. [2] can be very laborious. 2. Flow models in the literature The use of the conventional cylindrical spouted bed as a chemical reactor is a recent development [15-18 ]. Two basic axisymmetric models have been proposed in the literature to determine the radial velocity profiles in these reactors. The first is due to Lefroy and Davidson [ 19 ], who solved a boundary condition problem for calculation of the pressure distribution. They assume that the gas flow in the annular zone follows Darcy's law, that the spout diameter is constant, that pressure at the top of the annular zone is constant, and that the pressure distribution at the interface between spout and annulus follows a cosine function. The model of Lefroy and Davidson [19] was modified by Littman et al. [20] with the aim of determining the maximum spoutable height. It was recognized that the fluid does not fulfil Darcy's law 0923-0467/95/$09.50 © 1995 Elsevier Science S~A. All fights reserved SSDI 0923-0467(94)02847-4