A CFD study on the start-up hydrodynamics of fluid catalytic cracking regenerator integrated with chemical looping combustion

ABSTRACT

The integration of chemical looping combustion with fluid catalytic cracking (CLC-FCC) is an innovative concept that serves as a cost-effective method for CO₂ capture in refineries. This approach has the potential to reduce refinery CO₂ emissions by 25–35%, offering a promising solution. As in the conventional FCC unit, it is common for CLC-FCC regenerators to be exposed to an on-off process while they are being maintained and cleaned. The novelty of this research lies in its specific focus on a less-explored phase (start-up) of CLC-FCC regenerators, the application of advanced CFD modeling, and the comprehensive analysis of operational parameters that influence the system’s performance. To validate the CFD simulations of the different drag models for solid-gas granular, bed density profiles under steady-state conditions, collected from industrial processes, were used. For the flow period based on the start-up process of the drag models, the fluidization gas inlet geometry of the regenerator, flow regime (laminar and turbulent), and superficial gas velocity were comprehensively investigated to reveal their effects on hydrodynamic characteristics. The results show that Gidaspow and Syamlal-O’Brien drag models of the solid-gas multiphase granular flow exhibited a better fit with industrial data. The Syamlal-O’Brien and Gidaspow models closely align with industrial data under steady-state conditions, displaying similar bed densities in the dense phase region (230–310 kg/m³ for Syamlal-O’Brien and 235–300 kg/m³ for Gidaspow). During the initial stage (less than 0.2 seconds), both laminar and turbulent models yield comparable bed density profiles, approximately 510 kg/m³ in the dense phase. However, as the process progresses, the dense phase density decreases to about 250–350 kg/m³ at around 0.5 seconds, with laminar flow models showing a slightly better fit with industrial data. Notably, at 0.5 seconds of fluidization time, inlet geometries having better gas distribution achieve a highly diluted phase with bed densities of 10–20 kg/m³. Reaching a steady state, the bed density decreases from around 400 kg/m³ to 260–300 kg/m³, expanding into a higher section of the regenerator where it aligns well with industrial data. The increase in superficial gas velocity would result in the clarification of the difference and well mixing of the solid-gas multiphase flow.

KEYWORDS:

• CO₂ capture
• chemical looping combustion
• computational fluid dynamics
• hydrodynamics
• CLC-FCC

Acknowledgements

This work was supported by the Engineering and Physical Sciences Research Council (EPSRC) [EP/S036113/1], Connected Everything II: Accelerating Digital Manufacturing Research Collaboration and Innovation. The authors also gratefully acknowledge the financial support provided by the University of Nottingham, Faculty Pro-Vice-Chancellor Research Acceleration Fund (Fatih Güleç).

Disclosure statement

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Authorship contribution

Ahmet Erdoğan: Conceptualization, Formal analysis, Methodology, Investigation, Validation, Visualization, Project administration, Writing – original draft, Writing – review & editing. Fatih Güleç: Conceptualization, Methodology, Formal analysis, Funding acquisition, Project administration, Writing – review & editing.

Additional information

Funding

This work was supported by the University of Nottingham, Faculty Pro-Vice-Chancellor Research Acceleration Fund [NA]; Engineering and Physical Sciences Research Council [EP/S036113/1].

Notes on contributors

Ahmet Erdoğan

Dr Ahmet Erdoğan is a visiting academic at the University of Nottingham and an Assistant Professor in the Department of Mechanical Engineering at İnönü University. He obtained his Ph.D. in Mechanical Engineering from İnönü University in 2017. His areas of interest include Computational Fluid Dynamics, Refrigeration and Air Conditioning, and CO2 capture.

Fatih Güleç

Dr Fatih Gulec is an Assistant Professor in the Department of Chemical and Environmental Engineering at the University of Nottingham with expertise in energy and industrial decarbonisation. Dr gulec’s research encompasses (i) the synthesis and characterisation of advanced nanocomposites and their applications in chemical/calcium looping technologies, CO2 capture, negative emissions, energy storage and catalytic reactions and (ii) process integration/intensification based on waste/biomass-to-energy via thermal conversion.