Concentration profile of jet gas in the feed injection zone of a FCC riser

Abstract

The concentration profiles of jet gas are investigated in the feed injection zone of a cold-model FCC riser by using a hydrogen trace technique. Experimental results demonstrate that four types of jet gas concentration profiles can be used to describe the mixing between the jet gas and pre-lift gas in the feed injection zone. The four types are a distinct M-shaped profile for weak mixing, an indistinct M-shaped profile for medium mixing, a sharp profile for strong mixing, and a parabolic profile for full mixing. The heights for regions of initial and full mixing reduce when decreasing the jet gas velocity or increasing the pre-lift gas velocity. Furthermore, the momentum ratio, M j/ M r, (where M j is the momentum of jet gas, M r is the mixture momentum of pre-lift gas and solid particles) is introduced to describe the effects of gas–solid physical properties, operating conditions, and equipment configuration on the jet gas concentration distribution. The heights for regions of initial and full mixing between jet gas and pre-lift gas are found to be 0–0.375 and 0.375–0.675 m when M j/ M r < 0.29, 0.375–0.675 and 1.075–1.375 m when M j/ M r > 0.54, and 0–0.375 and 0.675–1.075 m when M j/ M r between 0.29 and 0.54, respectively.