The Study On Distribution Of Feed Jet Gas Concentration In The Injection Zone Of A Novel Riser

Catalytic cracking process is one of the most important processes in the oil refining industry while the riser reactor is one of the most key units in the FCC process.In the feed injection zone of a riser reactor,the contact and flow between oil and catalysts will directly affect the FCC reactions.In the traditional feed injection scheme,some disadvantages such as the uneven distribution of catalysts and the serious particle back mixing have been found,which is believed to be harmful for the contact and reaction of oil with catalysts.Therefore,it is necessary to improve the contact between feed oil and catalyst particles by optimizing the feed injection scheme.China Petroleum University(Beijing)has proposed a downward-pointed feed injection scheme in which the feed oil and catalyst particles contact countercurrently.The particle flow behavior in that feed injection scheme has been investigated.In order to investigate the gas-solid two-phase flow in proposed feed injection scheme in detail,the distribution of feed jet gas and the match between feed oil and catalyst particles were investigated in a large-scale cold mold in this research.The jet gas characteristic concentration,the local oil/catalyst matching index and the average oil/catalyst matching index were proposed to describe the experimental results.The effects of pre-lift gas velocity and jet gas velocity were also analyzed.Moreover,comparisons between the new and traditional feed injection scheme were made and the advantages of the new type of feed injection scheme were obtained.According to the characteristics of gas-solid two-phase flow and the match between oil and catalysts,the new type of feed injection scheme can be divided into three zones,i.e.the upstream transition zone,the jet controlling zone and the downstream transition zone.Results show that the jet gas can reach the center of riser more easily in the proposed downward pointed feed injection scheme.Then the jet gas moves towards the riser wall together with some catalyst particles.Compared with the traditional structure,the new riser has more advantages in the velocity of oil mixture,the concentration distribution of oil gas and catalyst particle in the initial measurement section,the average catalyst-oil matching index,etc.With increasing of the setting angle of nozzles,the influence region of jet gas below the feed nozzles becomes smaller,the mixing speed becomes higher and the distributions of jet gas in each section are more uniform.Higher jet gas velocity(Uj =78.5 m/s)and higher pre-lift gas velocity(Ur =4.1 m/s)should be taken in order to obtain a better mixing of feed oil with catalyst particles in the proposed feed injection scheme.Compared with the traditional one,the feed oil can mix with the catalyst particles in a shorter axial distance(H <0.7 m)in the new feed injection structure,which is a great improvement in the promotion of oil mixing.Besides,the distribution of feed jets in the initial contact area of the oil with catalysts is more uniform.Furthermore,the empirical formulas for estimating the distributions of jet gas concentration and local catalyst-oil matching index in different zones were established based on the experimental results.The proposed computed results are in good agreement with the experimental data,which can provide reference for engineering design purpose.