Advanced numerical simulation of fluidized catalytic cracking riser reactors
Abstract
Fluidized Catalytic Cracking (FCC) is the primary conversion process in modern oil refining. It uses a catalyst to convert heavy oil into lighter oil products in a riser. In order to meet increasing demands and succeed in a competitive market, it is desired to improve performance of current FCC units and to design new, advanced units. To achieve these goals, industry's focus is currently on the development of new catalysts that are able to crack heavier feed oil stocks more effectively and also on the design of a new low profile, multi-staged FCC riser. Recently, numerical simulation of the riser section has been recognized as a valuable tool with the means to facilitate and reduce the design time of new units, and also optimize existing units. However, the complex nature of the multiphase interactions and chemical reactions that occur in the riser reactor presents a huge challenge for analysis. In this study, new phenomenological models for feed oil droplet vaporization and catalytic cracking kinetics were developed for FCC riser simulation. These two models address the current trends in oil refining mentioned above. For the low profile riser design, residence times in the riser section are decreased dramatically and the numerical modeling of the feed oil droplet vaporization process becomes key. The new droplet vaporization model considers the effects of multicomponent vaporization. The new model is implemented by the definition of a new droplet transport property for each droplet size group that relates the boiling point of the size group to the amount of liquid mass remaining in each size group during the vaporization process. This new feature describes the actual physical characteristics of the feed oil as it undergoes vaporization and improves vaporization rate calculation accuracy. The new catalytic cracking model is based on the physical fundamentals of the cracking process. The model relates the kinetic constants of the cracking reactions to the physical properties of the catalyst. By using the properties to describe the cracking process, if the catalyst is redesigned with different properties, the model can still be used. This expands the application of the kinetic model for use with various catalysts. Using the new models, numerical simulations of FCC risers were conducted. Parametric studies of the design and operating conditions of FCC risers were conducted and found to have significant effects on product yields and profitability of the FCC unit. A new conceptual low profile FCC riser design was also evaluated and optimized for product yields.
Degree
Ph.D.
Advisors
Fleeter, Purdue University.
Subject Area
Mechanical engineering|Chemical engineering|Petroleum production
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