Study On The Mechanism Model For FCC Simulation

Fluid catalytic cracking(FCC)is the main converting process of heavy petroleum hydrocarbons to liquefied petroleum gas(LPG),gasoline and diesel.Therefore,it is of great significance in the improvement of economic benefits for the refinery.The setup and use of FCC simulation platform has provided support for the optimization of process parameters and operating performance.However,as the current simulation platform has poor extrapolation ability and limited scope of application,researchers have developed a new kind of platform based on the reaction mechanism to simulate the Two-Stage Riser Fluid Catalytic Cracking(TSRFCC)particularly.As the developed model utilized too many empirical factors in the simulation of reaction process,it is not favorable for the case study of various operating parameters.Besides,the model is not conducive for the quantitative analysis of catalyst loss as attrition of catalyst was not considered in the modeling process.The stripping efficiency model and separation efficiency model of gas-solid separator are introduced to the existing models in our research group and the impact of each variable on the process are discussed respectively with the aim of the MATLAB software.What's more,the fluidization of catalyst is modeled separately taking the attrition rate and particle size distribution(PSD)model into consideration.Stripping efficiency was introduced into the current model as a structure function,and the results show that when the amount of stripping steam and inlet temperature increase while the circulation flow of catalyst decreases,all of the above are conducive to high stripping efficiency and will further reduce stripping carbon content on the catalysts,affecting the reaction temperature and the conversion of raw material oil,etc.It is proved to be in accordance with the experimental phenomena.For the separation efficiency model of the gas-solid separator,the separation efficiency increases with decreased quantitative loss of catalyst when the superficial gas velocity in the separator inlet increases.For the catalyst attrition,the entire reaction system was divided into six modules in total,including two riser reactors,one regenerator and three cyclones.Three attrition resources,namely,the jet region,the bubble region and the cyclone region were considered and studied separately according to different attrition mechanism.The results of the quantitative analysis show that the dominant source of the attrition is changed when different superficial gas velocities are investigated.The attrition rate of particles group is not only related to the particle size,but also to the particle mass distribution.After a period of attrition,the catalyst particles would have an increased average particle diameter,mainly because small particles produced by attrition are gradually separated out by the cyclone.But the increasing rate of the particle size would decline along with the increasing average diameter,and the amount of catalyst loss gradually run to equilibrium.An assumption is proposed that it is the balance between the added fresh agent and the lost catalyst as well as the discharged agent that make the system tend to the steady state.Meanwhile,as the fresh agent is added into the system,there will be a rapid attrition in the early stage,where the attrition rate is about three orders of magnitude higher than the steady attrition stage.