Influencing the solid fraction distribution in a circulating fluidized bed system using differently shaped internals

Abstract

Solids distribution and gas–solid contact gain in importance for new and alternative energy conversion processes realized with fluidized bed systems. The so-called dual circulating fluidized bed (DCFB) system represents a reactor concept proposed for these novel processes. This concept is based on the interconnection of two circulating fluidized beds via two loop seals. In this work, a cold flow model, designed according to the DCFB system, is used to investigate the influence of constrictions placed along the height of the secondary reactor. Experiments were performed with differently shaped constrictions, aperture ratios, varying distance between the constrictions and different length of the horizontal section at the smallest cross section in the constriction. In general, the mean solid fraction in the upper part of the secondary reactor benefits from the constrictions (mean solid fraction up to +1800% compared to a straight reactor without any constriction). The mean solid fraction in the reactor increased with the solid circulation rate between the reactors and the superficial gas velocity in the secondary reactor. Further, investigations showed substantial deviations for the solid fraction in the upper part of the reactor for the investigated geometries of the constrictions. Fluid dynamic limitations restricting the operating range of the cold flow model could be observed. These limitations depend on combinations of solid circulation rate and superficial gas velocity in the secondary reactor and differ for the investigated geometries. Solid fraction distribution in the secondary reactor showed high solid fractions in the constricted sections (up to 60%) while it remained low between the constrictions.