Predicting the pressure drop across the solids flow rate control device of a circulating fluidized bed

The control of the solids circulation rate in circulating fluidized beds (CFB) can be obtained by means of a mechanical valve located at the bottom of the return leg. The valve acts by provoking a pressure drop that depends on the degree of the opening. The aim of this work is to develop a predictive model for the pressure drop in a butterfly valve used as a control device for the solids circulation rate. A model has been developed and validated against experimental data obtained from a 0.1 m id, 6 m high CFB using a group B powder. The equations proposed by, Jones and Davidson [D.R.M. Jones, J.F. Davidson, The flow of particles from a fluidised bed through orifices, Rheologica Acta 4 (1965) 180] and Cheng et. al. [L. Cheng, P. Basu, Solids circulation rate prediction in a pressurized loop seal, in: K. Chen (Ed.), Chemical Engineering Research and Design, vol. 76, 1998, p. 761] to predict the discharge rate of granular solid through orifices have been modified to account for the shape of the openings in the valve. A corrective parameter, which is based on the dimensionless hydraulic diameter of the valve opening, has been introduced. Very good agreement with the experimental data was obtained.