Effect of a shroud on entrainment into a submerged jet within a fluidized bed

Abstract

Following the discussions of Bohnet and Teifke [M. Bohnet, J. Teifke, New results on the efficiency transformation in gas solids-injectors, in: Proceedings—Reliable Flow of Particulate Solids: EFCE Publication Series, 1985, pp. 383–400] and Idelchek [I.E. Idelchek, Handbook of Hydraulic Resistance, CRC Press, Boca Raton, 1994] it was decided to investigate the effects of altering the region surrounding the jet in order to affect the method of contact between the jet and the fluidized bed. This was accomplished using several different configurations of “shrouds” that formed physical barriers either around the nozzle tip or draft tube inlet, or both. These new types of internals substantially increased the entrainment rate of fine fluidized particles into a submerged horizontal gas jet. The internals have been observed to affect both the solids flow pattern surrounding the jet and flux of entrained solids into the jet and the amount of fluidization gas entrained into the jet. Under the best conditions studied experimentally, the solids entrainment rate was increased by over 100% while the amount of fluidization gas entrained was reduced by approximately 50% as measured using a CO 2 tracer. In total, 5 different nozzle configurations were studied. Fluid coke particles (135 μm Sauter mean diameter and density 1450 kg/m 3) were used for bed material and air was used for both the motive and fluidization gas. CFD modeling has also been undertaken to characterize the behaviour of the internal and further elucidate the mechanism behind the increase in solids entrainment. Analysis of the simulation results reveals the presence of strong gas recirculation zones close to the nozzle tip and at the shroud inlet.