Stripping in recirculating bubbling fluidized bed of Geldart group A catalyst.

摘要

Strippers are used as a seal in processes such as Fluid Catalytic Cracking (FCC) where solid is circulating in two beds (the reactor and the regenerator) to prevent gas losses from one bed to the other. If stripping efficiency is low, valuable products are lost by passage to the other bed. Therefore, an improvement in stripping efficiency could save the refinery industry millions of dollars per year. Therefore, the goal of this research was to understand stripping behavior in a bubbling fluidized bed. The effect of operating parameters such as gas superficial velocities and solid circulation rates on stripping efficiency was also studied. An improvement in efficiency was expected by putting baffles in the bed.; To achieve this goal, a pilot-plant scale cold flow model of a stripper was constructed from a 4 m tall and 0.33 m diameter semi-circular steel column. The semi-circular configuration is good for visual observation in the fluidized bed. FCC catalysts (Geldart group A) were circulated downward with entrained air and a helium tracer. Air was fluidized counter-currently in the form of bubbles. The catalysts left the column via a standpipe, were picked up by the riser gas, and were recycled back into the fluidized bed through the cyclone dipleg. Helium gas was injected into the leg of the primary cyclone in order to trace entrained air downward to be stripped. Gas was sampled from three locations (the top of the bed, the cyclone dipleg exit, and the bottom of the bed) and was analyzed by the thermal conductivity detectors. Some stripping was obtained using bubbling bed, particularly at lower fluidized gas velocity. To convert the bed into a baffled fluidized bed, three pairs of baffles and the dummy cell were inserted in the bed.; It was found that the presence of baffles enhances significantly the stripping efficiency by redistributing air and maintaining the small size of bubbles. The efficiency increased with increasing stripping air and decreasing solids mass flux. The results were in good agreement with those earlier reported by Rivault (1995). It is expected that optimum baffle design and higher solids mass flux will further enhance stripping efficiency.