Radial Distribution Of Particle Concentration In Riser

Fluid catalytic cracking(FCC)is one of the most critical oil secondary processing units in the refinery and it undoubtedly plays a vital role in China petroleum processing industry.More than 70% gasoline as well as about 30% diesel oil is produced via the FCC process.In a modern FCC unit,the catalytic cracking reaction mainly occurs in the riser reactor.The high-value target products including gasoline,diesel oil,liquefied gas etc.,are all converted in the riser reactor.In riser reactor,the flow and distribution of oil & catalysts will influence the whole reaction directly.However,the actual condition is far from the ideal uniform contact of gas with solids phase.In fact,the local FCC particle concentration is relatively high in the vicinity of the riser wall;while the local density assumes low value in the core area of the riser.It is the so-called typical core-annular structure,which also means a high gas phase volume fraction in the core region and a low voidage in the annular region.This non-uniform radial concentration distribution of particle/gas may result in an uneven contact of two phases and lead to undesirable effects on the cracking reaction.In these years,the occurrence of the core-annular structure was usually simply contributed to the velocity gradient in the boundary layer.However,how can the boundary layer influence the distributions of the two phases? What is the relationship of the particle velocity gradient to that of the particle concentration? There is still no quantitative description of these two problems.In this paper,the aerodynamic theory and field theory is “transplanted” into the two-phase flow.A lateral force,namely the Kutta-Joukowski force,is used to explain and quantify the formation of the core-annular structure in a riser.Both the experimental research and the theoretical analysis were employed in this paper.The PV-6A optical fiber probe was applied to investgated the local particle concentration and local particle velocity distribution in a large-scale cold-model riser.Furthermore,the method to calculate local Kutta-Joukowski force is proposed via theoretical analysis.This force is the function of particle velocity curl(The particle velocity curl does not mean the actual rotation,but a function of velocity gradient),slip velocity and gas density.Based on the experimental data combining with that proposed in the published literatures,the distribution of Kutta-Joukowski lateral force in the riser is given.On the other hand,and effects of operating parameters on the Kutta-Joukowski lateral force distribution profile is analysed.The result shows Kutta-Joukowski lateral force is the main reason of the core annular structure occurence.The force is towards the riser wall;while its valus were mainly determined by the particle physical property,the particle flux,the superficial gas velocity,the radial/axial position.Finally,On the other hand,the particle concentration gradient force is introduced and quantified.This force balances the Kutta-Joukowski lateral force in the riser.The quantitave correlation of these two forces is established.