Modeling, simulation, structural analysis and feed characterization of a fluid catalytic cracking process

Abstract

This thesis presents a mathematical approach on modeling the fluid catalytic cracking(FCC) process and its application including systematic analysis and feed characterization. Fluid catalytic cracking (FCC) is one of the most important re_x000C_nery processes. It is used for cracking high molecular weight hydrocarbon feedstocks to smaller, valuable molecules. The existing FCC plant in the re_x000C_nery consists of a reaction unit which is followed by the fractionation unit that separates the reactor e_x000F_uent into the final products. The reaction unit is composed of the riser and the regenerator therefore are modeled separately and interconnected. Meanwhile, The process disturbance or faults have a serious impact on process operation, product quality, safety, productivity and process economy if undetected. However, measuring all state variables of a complex FCC process is usually impossible or impractical. What is more realistic is to estimate the state variables based on a _x000C_nite set of measurements. Furthermore, we nave less accessibility on physical properties of the feed in the FCC process. Since direct measurement on the operating plant is not realistic because of both cost and time, alternative methods that provides complete description of FCC process feeds from measured process data is highly demanded.<br/> At _x000C_rst, reaction kinetics were developed to describe the reactor effluents and thermodynamic phenomena in the reactor. Empirical correlations that describe the reaction kinetics with model parameters were built. Also, an approach to apply the yield function for the kinetic model of the riser was made. Lastly, hydrodynamics, mass balance and energy balance equations of the riser reactor and the regenerator were considered to complete the modeling. Steady-state simulation results and dynamic responses to the change of process variables were simulated by the process model and compared to the plant data. The results showed good agreement with the measured data from the plant. After the modeling, a systematic analysis was performed to identify the structural<br/> observability of the system using the model and process design data. The reactor and regenerator unit in this system were divided into six nodes based on their functions and modeling relationships were built based on nodes and edges of the directed graph. Output-set assignment algorithm was demonstrated on the occurrence matrix. It was found that only a part of the system was fully observable and the states in the regenerator was not observable with current measurement sets. Optimal locations for additional measurement were suggested by completing the whole output-set assignment algorithm of the system. Finally, to estimate unmeasured properties of feed mixture, a correlation method relating properties of mixture were investigated. Various correlation methods between complex petroleum properties were found from literature and interconnected to find the distribution function. The correlation model was validated by comparing the reaction results from model with another results from the chemical process simulator. The comparison showed slightly disagreed expectation result for LPG and LCO. It is assumed that uncertainties about catalyst in the reactor and process model in the<br/> simulator have caused this di_x000B_erence. Considering that point, we conclude that the correlation model exhibits an acceptable agreement with the results of Aspen HYSYS V8.4. The proposed approach provided insights into the FCC process and was found to be a suitable technique for process design, operation and even more applications such as optimization.