Experimental Study Of Gas-solid Flow In Catalyst-feed Countercurrent Contacting Injection Zone And The Structure Optimization

FCC plays a crucial role in China refinery;However,academic investigation and commercial application revealed considerable differences between the ideal and actual flow conditions in the traditional feed injection zone of FCC riser.A new type of feed scheme is proposed by China University of Petroleum(Beijing).The feed oil and catalysts contact counter-currently by changing the feed jet nozzles from upward-pointed to downward-pointed.The distributions of oil and catalyst show more uniform in the new structure;The mixing and matching of the two phases are more desirable as well.However,the type of feed injection zone needs further structure optimized.On the other hand,only one diameter of the new scheme has ever been studied in the present experimental research.Therefore,it is necessary to compare different figurations/sizes of the new feed injection scheme.And the oil-catalyst two-phase flow and match characteristics under different sizes of the proposed scheme are experimentally investigated.Three types of schemes are put forward by varying the diameters of the feed injection zone including nozzles above diameter-increased structure,nozzles below diameter-increased structure and the small uniform-diameter structure.By using a number of modern multiphase flow measuring techniques,the flow and match of the two phases in these schemes are detected in a large-scale cold model experimental setup.The experimental results are compared with those in the present injection schemes.By comparing the flow parameters including the radial distributions of the particle concentration,the particle velocity,the jet gas concentration and the solid radial nonuniformity index,as well as the axial distributions of cross-sectional average oil/catalyst match index in the proposed four type of feed injection zone,it is found that the two-phase distribution is comparatively uniform in the nozzle below diameter-increased structure.Moreover,the match of gas and solid is quite desirable in this structure as well.Based on the measured flow/mixing characteristics in the optimized schemes,the whole feed injection zone can be divided into three sub-zone,i.e.the upstream diameter-decreased zone,the oil-catalyst mixing zone and the downstream recovery zone.Furthermore,in order to obtain a good match of oil and catalyst,the prelift gas velocity and the jet gas velocity are controlled by U_r=2.4 m/s and U_j=78.5m/s,respectively.Considering all the influential parameters,the empirical formulas for evaluating the axial distributions of the cross-sectional average oil-catalyst matching index in the most optimal structure are established.The calculated data agree well with the experimental results.It can be used for industrial design purpose.