A general methodology and the correlation for the prediction of the solids flow rates through the L-valves

Abstract

L-valves are used as a non-mechanical valve for the solids flow rate control in circulating fluidized beds (CFB). To quantify the solids flow rate through the L-valve, a number of correlations have been proposed in the last few decades. These correlations are mainly empirical and are developed based on the given information of either the gas aeration rate or the pressure drop across the L-valve with known values of such parameters as particle and aeration gas properties and L-valve geometry. The range of the applicability of these correlations are limited and their accuracy remains to be further validated. In accounting for the solids flow rate through the L-valve, a mechanistic correlation based model is developed in this study on a generic framework that describes the relative velocity between solids and aeration gas at the L-valve from the information including the pressure drop across the L-valve, the total aeration rate, and the properties of aeration gas and solids. With the L-valve voidage further estimated, the solids flow rate through the L-valve can be calculated. The proposed predictive scheme yields a much wider range of applicability and a more accurate solids flow rate prediction. Specifically, the literature data for Geldart Group B particles are used to determine the coefficients of established dimensionless correlation that accounts for the intrinsic flow property associated with the momentum transfer between the gas and solid flows. The correlation is applicable also to Geldart Group D particles verified using the new experimental data obtained in this study that include experiments conducted under the ambient and high temperature (up to 1000°C) conditions. This dimensionless correlation that considers operating conditions with various L-valve sizes and lengths is demonstrated to provide a much versatile predictive scheme on the solids flow rate through the L-valve, compared to the work reported in the literature.