(569a) Entrainment into a Submerged Jet within a Fluidized Bed

Several processes employ multiple fluidized beds between which solid particles are continuously shuttled via long transfer lines, including catalytic cracking, coal gasification, oil shale retorting, fluid coking, and polymerization. The primary goal of such systems is to circulate the solids in a controlled manner while limiting the amount of gas transferred between beds. Typically, the fluidization gas applied to each bed is different and it is important to avoid cross contamination. Conventional mechanical valves are prone to problems with plugging, erosion, and corrosion and require insulation for high temperature applications. Furthermore, the use of long transfer lines with L, J, or V valves is cumbersome and energy intensive.

A single compartmented fluidized bed would be more compact and cost effective due to a lower initial capital cost and lower operating costs. The compartmented fluidized bed employed in this study utilizes a horizontal gas jet to entrain and transport solids from one compartment to the other through a connecting draft tube. The solids entrainment is measured using a novel technique to study entrainment into a submerged gas jet. The primary goal of this study was the optimization of the solids entrainment rate and quantification of the fluidization gas entrainment rate. Principal variables under consideration were the distance between the nozzle tip and the inlet of the cylindrical draft tube connecting both fluidized bed compartments, the motive gas flow rate, and the nozzle/draft tube geometry.

The nozzle/draft tube geometry was altered in order to affect how and where the fluidized solids first contact the jet and was studied using several different internals. Videos were recorded using a special transparent plate on the wall of the fluidized bed of the gas and solids flow patterns for a half-jet with and without internals. The amount of fluidization gas entrained was quantified using a CO₂ tracer. The solids entrainment measurements, CO₂ tracer tests, and half-jet videos were carried out in a fluidized bed having a rectangular cross section (1.2 m x 0.1 m) and 1.2 m tall. Fluid coke particles (135 μm Sauter mean diameter and density 1450 kg/m³) were used for bed material and air was used for both the motive and fluidization gas.

New types of internals substantially increase the entrainment rate of fine fluidized particles into a submerged horizontal gas jet by altering the configuration of the nozzle outlet. 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. CFD modeling has been undertaken to characterize the behaviour of the internal and further elucidate the mechanism behind the increase in solids entrainment. 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%. In total, 5 different nozzle configurations were studied.