Dynamic Simulation Of Reactor And Regenerator Section In FCCU Based On Standard Pseudo-Component Kinetic Model

Fluid catalytic cracking (FCC) is a key unit in which heavy oils areconverted into lighter and more valuable products. It was reported that about75%gasoline,30%diesel and40%propylene in China were produced byFCC up to2007. It is of great significance to optimize the design andoperation of industrial FCC units for their huge throughputs. Therefore,modeling and simulation of FCC processes have been being an importanttopic ofresearch since about1940's.Riser-regenerator system is the most important part of FCC unit. One ofthe challenging problems in modeling a riser-regenerator system is to describethe chemical reactions of feed and product oils which are complicatedmixtures of numerous hydrocarbons and non-hydrocarbons. The traditionalapproach is based on lumping of compounds. However, one majordisadvantage of reaction schemes using a few lumps is that a change inproduct specifications or in the number of products requires reformulating themodel and refitting the data.To overcome this shortcoming, standard pseudo-components are proposed and defined in pairs of light and heavy narrow cuts of true boilingpoint (TBP) distillation. The standard pseudo-components have invariant anddefinite physicochemical properties, normal boiling temperatures anddensities at present. The stock and oil products are then expressed with asystem of standard pseudo-components. A steady state model is formulatedfor a commercial fluid catalytic riser, and the kinetic model of Gupta et al isadopted. The semi-empirical cracking model of in this paper includes morethan10,000detailed reaction equations, and the reaction rate constants arecorrelated with the normal boiling temperatures and molecular weights ofstandard pseudo-components. Therefore, parameters of a reaction scheme canbe independent of stock oils, product distributions and operational conditions.To further investigate the dynamic behavior of riser-regenerator systemin this paper, the dynamic models of disengaging-stripping section andregenerator were also developed. Then, the dynamic responses to changes oftype and flowrate of feedstock are performed. Finally, dynamic changes ofseveral major process variables were discussed.