Economic and Control Performance of a Fluid Catalytic Cracking Unit: Interactions between Combustion Air and CO Promoters

Abstract

The presence of CO combustion promoters significantly affects the heterogeneous CO combustion in the regenerator of a fluid catalytic cracking (FCC) unit. Neglecting the quantitative correlation between the heterogeneous CO combustion and the amount of added CO combustion promoters in the previous models makes it impossible to predict the steady-state and the dynamic behaviors of the system with respect to the CO combustion promoters. Therefore, an augmented dynamic model of an FCC unit with high-efficiency regenerator incorporating the quantitative correlation between heterogeneous CO combustion and the CO combustion promoters is developed, and the corresponding closed-loop dynamic responses are obtained. Since CO combustion in the regenerator is affected by both the combustion air flow rate and the CO combustion promoters, a sensitivity analysis of some important variables related to the combustion air flow rate and the amount of added CO combustion promoters is carried out and the overall operating map of the system is developed by selecting the conversion of the riser, the integrated absolute errors of the controllers, and the temperature rise between the dense bed and the outlet of the freeboard to represent the concerns of economics, control, and safety.

Dynamic Optimization of Continuous-Batch Processes: A Case Study of an FCCU with CO Promoter

“…The model adopted in this work is derived from the model of an industrial FCCU with a high-efficiency regenerator under complete combustion as proposed by Luo et al , A schematic diagram of the FCCU with a high-efficiency regenerator is given in Figure . Here, a short description of each part is given and the details of this base model are given in the paper …”

“…For the cracking kinetic model, we adopt a five-lump model as follows The high-efficiency regenerator is generally designed with excess air to guarantee fast fluidization in the combustor; with the presence of CO promoter, the reactions in the regenerator include the following where β denotes the intrinsic molar ratio of CO 2 /CO, which adopts the following correlation proposed by Xu et al The CO homogeneous and heterogeneous combustion kinetics are illustrated by eqs and , respectively where c Pt denotes the mass fraction of platinum in the CO promoters, which is 500 ppm on average; x pro denotes the concentration of CO promoters in the catalyst inventory; and η Pt denotes the activity of CO combustion promoters.…”

“…However, the effect of transition in a continuous process will be amplified by batch operations for their repeatability, which renders the continuous process to behave more like a batch process. As the case will be discussed in this paper, the CO promoter is put into the regenerator repeatedly and the dynamic of FCCU changes in every period. − The steady state can only be achieved at the end of every cycle. The batch operations are normally decided by the operators according to experience or heuristics, i.e., seeking to improve the performance from batch to batch.…”

“…Several papers have considered the correlation of heterogeneous CO combustion with CO promoter. They introduced a factor x pt to represent the relative combustion rate , and factors x pro and η pt to represent the concentration of CO promoter in the catalyst inventory and the activity of the CO promoter. − A detail FCCU model including quantitative correlation between the amount of added CO promoter and CO combustion dynamic is still lacking, which is the prerequisite for formulating hybrid dynamic optimization, which is developed in this paper as an extension of previous work by authors. , Then, the proposed integration optimization method implements optimal batch operations as the solution of the hybrid dynamic optimization and optimal continuous operations as extra PID controllers by tracking the necessary conditions of optimality (NCO-tracking scheme), , which maintains a near-optimal performance under uncertainty.…”

An Adaptive Soft Sensor Based on Nonlinear Differential-Algebraic Observer for Chemical Processes

“…The dynamic model of FCCU was given by Wang, Luo, and Xu [32]. A schematic diagram of the FCCU with high-efficiency regenerator is given in Fig.…”