Simulation Research Of Reaction And Coking In Feed Injection Zone Of Industrial FCC Riser

Reactive and fixed coking in the riser reactor seriously affect long-term safty and low-consumption running of industrial fluid catalytic cracking(FCC)unit.Fixed coking exists the interaction between the physics and chemical process,and therefore the coking extent is difficult to be truly and quantitatively predicted.Here,based on the formation mechanism of coking,a novel prediction model for coking probability is developed considering coke residence,deposition and adhesion.A multi-phase Eulerian model coupling with the models of EMMS drag and mass transfer,oil droplet vaporization and twelve lumped reaction kinetics were used to simulate a 100 Mt/a industrial FCC riser for predicting complex three-phase flow,vaporization and reaction behaviors.Otherwise,through combining the coking model into the reactive simulation,the whole reaction coking process was disclosed accurately,then the suitable anti-coking measures were proposed.For traditional feed injection schem(30° upward along the axis of riser)in the feed injection zone of riser,the distributions of concentration and temperature,and coking extent at different vaporization and key operation parameters were compared and discussed.The results indicate that the diameter of atomized droplet and the initial vaporization temperature have a significant influence on the rate of oil droplet vaporization.The ratio between catalyst to oil,the feed velocity and the mass fraction of atomized steam affect the flow and mixing in a certain range.All these factors influence the reaction conversion rate and the coking extent of the feed injection zone by the interphase momentum transfer.Suitable droplet diameter(such as 60 μm)and initial vaporization temperature(such as 727 K)can reach a balance between vaporization and reaction.Suitable operating parameters,such as the 7 ratio between catalyst to oil,the3.75 momentum ratio between the feed jet to the pre-lifted flow from riser bottom and the 3.5 wt% atomized steam account at feed nozzle(i.e.5.1 wt% account for the whole reactor),can improve the mixing between catalyst and oil,and the reaction rate in the feed injection zone,also increase the yield of target product and reduce the probability of coking.For novel reverse scheme(35° downward along riser axis),the feactures and rules of flow and reaction at different vaporization and key operation parameters were investigated.The results show that suitable paramrters,including the diameter of atomization droplet of 60 μm,the range of initial vaporization temperature of 654 ～ 727 K,the catalyst-oil ratio of 6.5,the momentum ratio of 4.11 and atomizaed steam account of 4.0 wt%,can greatly improve the yield of target product and alleviate the coking extent in the feed injection zone.Compared with the traditional upward injection scheme,the novel scheme can obviously improve the contact of oil and catalyst,meanwhile,it could greatly increase the yield of target product(such as the yield of gasoline is increased by 7.2%),and reduce the coke amount,and the formation of fixed coking near wall in the feed injection zone.