Three Dimensional Simulation of Catalytic Cracking Reaction in an Industrial Scale Riser Using a 10-Lump Kinetic Model

Three Dimensional Simulation of Catalytic Cracking Reactions in an Industrial Scale Riser Using a 10-lump Kinetic Model

            Fluid Catalytic Cracking (FCC) is one of the most important processes in the oil refinery. It converts heavy hydrocarbon petroleum fractions into more usable products such as gasoline, middle distillates, and light olefins. A FCC unit is composed basically by a riser reactor, strippers, cyclones and a regenerator. As it is one of the most profitable operations in a petroleum refining industry, several researchers have been focused their works on developing mathematical models that can predict the behavior of this process.

            In this context, the application of the computational fluid dynamics (CFD) has assumed an important role in the study of the FCC process. Using appropriate mathematical models, the CFD tools allow the prediction of properties, such as velocity, temperature and concentration of the species. In addition it can also reduce enormously the time-consuming by computational resources and the cost spent for the improvement of the process and in the development of new projects.

             Many kinetic models have been proposed for the representation of the cracking reactions that occurs in the riser reactor. Due to the complexity of the reaction mechanisms and the large number of chemical species involved in the cracking process, these species are often grouped into lump, according to their boiling point and/or molecular characteristics (paraffins, olefins, naphthenic and aromatics). One of the most widely used lumping models is the ten-lump model proposed by JACOB et al., 1976 (BARAJAS et al., 2009). By dividing the feed in five volatile components, it can be used for different charge stocks. The important characteristic of this model relies on the fact that the feed composition affects the yield and quality of the gasoline formed during the process. As shown in the study carried out by CERQUEIRA et al. (1997), for example, paraffinic and naphthenic feedstock yields more gasoline. On the other hand, the aromatic feed is the main specie responsible for the formation of coke.

            The present study applies the ten-lump kinetic model proposed by JACOB et al. (1976) in the simulation of the catalytic cracking reactions in an industrial riser reactor.  A three-dimensional model was used to predict the dynamic behavior inside the riser reactor.

            The results were validated with a set of plant data and compared with the results obtained by LOPES et al. (2011), which applied a simplified four-lump kinetic model to simulate the process in a similar industrial reactor. The use of different feedstock compositions with ten-lump model showed a more accurate result for the gasoline yield. Furthermore, it was observed in this study that the influence of geometric configurations on the flow can drastically affect the reaction yields.