Article Cite This: Energy Fuels XXXX, XXX, XXX−XXX
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Novel Integrated Reactor-Regenerator Model for the Fluidized Catalytic Cracking Unit Based on an Equivalent Reactor Network Yupeng Du,*,†,∥ Lejing Sun,†,∥ Abdallah S. Berrouk,*,‡ Chengtao Zhang,§ Xiaoping Chen,† Deren Fang,† and Wanzhong Ren† †
College of Chemistry & Chemical Engineering, Yantai University, Yantai 264005, China Mechanical Engineering Department, Khalifa University of Science and Technology, Petroleum Institute, P.O. Box 2533, Abu Dhabi, United Arab Emirates § China Petroleum Engineering and Construction Corporation (Huadong Design Branch Company), Qingdao 266071, China Downloaded via IDAHO STATE UNIV on July 17, 2019 at 13:32:19 (UTC). See https://pubs.acs.org/sharingguidelines for options on how to legitimately share published articles.
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ABSTRACT: Fluidized catalytic cracking (FCC) is the most used process for converting heavy oil into more valuable fuels and chemical products such as gasoline and propylene. The conventional steady state and dynamic models that have commonly been used to study FCC units assume simple plug flow in the riser reactor and two-region (i.e., freeboard and dense bed)twophase (i.e., bubble phase and emulsion phase) in the catalyst regenerator. As a remedy to the limited accuracy yielded by such assumptions, an integrated model based on the equivalent reactor network (ERN) approach is built in order to accurately model a pilot-scale residue FCC (RFCC) unit. The model involves 8-reactor and 10-reactor networks to characterize complex hydrodynamics within the regenerator and the riser reactor, respectively. Also, a coke combustion kinetic model and a ten-lump kinetic model describing the cracking reactions, as well as the necessary thermodynamic models, are coupled with the ERN hydrodynamic models. The validation of the integrated models shows good agreement with available experimental data. The model is subsequently used to investigate the effects of operating conditions such as reaction temperature, residence time, and catalyst-to-oil ratio on the product yield distribution in the RFCC unit. Finally, the model is used to demonstrate the superiority of the RFCC-Maxing-Propylene process over the conventional RFCC process. It is believed that the developed model can help researchers and engineers carry out further RFCC process investigations such as dynamic analysis and real-time control and optimization.
1. INTRODUCTION Fluid catalytic cracking (FCC) is one of the core processes in petrochemical refineries. It plays a significant role in converting heavy oil (HO) to valuable products such as transport fuel and light olefins.1,2 The riser reactor and the catalyst regenerator are the most complex parts of any FCC unit because of intricate multiphase flow behavior coupled with complex chemical reactions.3,4 For monitoring, controlling, and optimizing purposes, fast and accurate description of riser reactors and catalyst regenerators is quite essential in the development of both steady-state and dynamic models for FCC units.5,6 This requires an integrated model that couples both the reactor and regenerator. A great many of the steady-state and/or dynamic models for FCC units are available in the open literature with various degrees of simplifications and assumptions.3,7,8 Kumar et al.9 developed a steady-state process simulator for an FCC reactorregenerator system. They integrated a 10-lump kinetic model10 coupled to a plug-flow type of hydrodynamics for the riser reactor with a grid model for the regenerator. Fernandes et al.11 presented a model for an industrial R2R-type FCC unit that simulated the performance of FCC units in both steady and dynamic modes for both control and real-time optimization purposes. However, riser hydrodynamics was modeled as a plug flow reactor with a 1-D model that only considered axial variations of the variables while diffusional and © XXXX American Chemical Society
turbulent transport of mass, momentum, and heat were neglected. Regarding the regenerator, the freeboard was neglected and the dense phase was modeled as a CSTR. Arbel et al.8 proposed a model for a typical side-by-side FCC unit that was used to predict both steady-state and dynamic operations of this type of units. In this model, a pseudo steady state, plug flow, no-slip velocity between the gas and catalysts, and adiabatic operation were assumed for the riser reactor. As for the regenerator, they described the solid phase in the dense bed as a stirred tank, the gas flowing through it as a series of three stirred tanks, and the dilute phase in an analogous way. Using this model, Arbel et al.8 studied state multiplicity and control problems of an industrial FCC unit. A dynamic model of an UOP stacked unit was presented by Ali et al.12,13 Regarding the regenerator, it was assumed that bubbles move in plug flow and the catalyst behaves as a continuous stirred tank reactor. However, the effects of the freeboard region on the overall performance of the regenerator were ignored. Later, Malay et al.14 modified this model to include the effects of gas volumetric expansion and the slip velocity between the gas and solid phases. The model was utilized for design, control, and optimization applications following a procedure developed by Received: May 21, 2019 Revised: July 2, 2019 Published: July 3, 2019 A
DOI: 10.1021/acs.energyfuels.9b01616 Energy Fuels XXXX, XXX, XXX−XXX
Article
Energy & Fuels
Figure 1. Schematic diagram the reaction-regeneration system of a pilot-scale FCC unit.
of the effects of different flow structures, including back mixing, on both interphase heat exchange and cracking reactions. The price for such an increase in accuracy was a relatively longer computation time (5 s for the CFD-based ERN model compared to
