Prediction of the Optimal Reaction Temperature of the Riser of an Industrial Fluid Catalytic Cracking (FCC) Unit

Abstract

A pseudo homogeneous two-dimensional (2D) model of an industrial Fluid Catalytic Cracking (FCC) riser is here presented. The FCC riser models of previous researchers were mostly based on the assumption of negligible mass transfer resistance and 1D plug flow. These assumptions undermine the accuracy of the models by over-predicting the optimum residence time of the riser. In this work the coke content of FCC catalyst was modeled as a function of the reactor temperature with the aim of predicting the operating conditions that will reduce coke on catalyst without undermining the yield of the key product (gasoline). Mass transfer resistance was incorporated in the reactor model to enhance the accuracy of the results. Catalyst deactivation was modeled based on the exponential decay function. The mass transfer coefficient and the catalyst effectiveness factor were estimated from empirical correlations obtained from literature. Data used for the simulation were sourced from an existing plant (KRPC) as well as from open literature. Finite difference numerical scheme was used to discretise the model governing equation. At the end of the investigation, three different operating temperature regimes were identified from the simulated results for the coking of FCC catalyst (low temperature, optimal temperature and high temperature regimes). An optimum operating temperature range of 786K-788K and an optimum catalyst-to-oil ratio (COR) range of 4.60-4.71 were predicted for the riser.

Keywords: FCC; Finite difference, Mass transfer resistance, Catalyst deactivation, Riser models.