Estimate of solids circulation rate through an L-valve in a CFB operating at elevated temperature

An experimental study was carried out on a circulating fluidized bed (0.15 m diameter × 5.4 m high) equipped with an L-valve (0.10 m diameter × 0.23 m long) operating at ambient and elevated temperature (30–250 °C), for a variation in gas superficial velocity (Ug), secondary air fraction (SA), total solids inventory (Is), and external aeration flow rate (QA). Eight mathematical models are evaluated for their capability to estimate the solids discharge rate (Gs) of the L-valve, by using pressure measurements. Only the methods that consider the following features are found to qualitatively predict Gs: treating solid and fluid properties as variables, including gas–solid mass balance and the pressure difference (ΔP) on the two direction coordinates, and applying realistic assumptions for the gas–solid flow hydrodynamics. Validation results confirms that previous empirical correlations that were derived from experimental investigations at ambient conditions do not provide a reliable prediction of Gs at elevated temperature. A new correlation suitable for L-valve operation at higher temperature is given from which solids flow rate can be conveniently predicted using pressure measurements across the L-valve.