CFD modeling investigation of oxy-fuel combustion application in an industrial-scale FCC regenerator
Yuneng Tang, Cheng Liu, Shibo Kuang, Qianqian Liu, Zhenyu Chen, Haitao Song, Bin Su, Jianglong Yu, Lian Zhang, Baiqian Dai
Abstract
The increase in atmospheric CO 2 concentration and its consequential impact on climate change have elicited increased public concern. The refinery units including fluid catalytic cracking (FCC) generate substantial quantities of CO 2 . To mitigate the emission from the FCC process, oxy-fuel combustion has emerged as a prospective carbon capture and storage technology. This study presents the first trial for the modeling investigation of a 70 kt/a industrial FCC regenerator under the scenario of retrofitting it with oxy-fuel combustion technology. Employing the Eulerian-Eulerian model, a CFD model integrating heat transfer and coke combustion reactions has been established. The detailed hydrodynamics, temperature, and species concentration distribution inside the regenerator are obtained under both air-firing and oxy-firing conditions, which are further compared to exploit the possibility of oxy-fuel combustion retrofitting. As has been found, decreases in gas temperature and carbon conversion rate were observed for 21 % O 2 /79 % CO 2 atmosphere in comparison to the air reference case due to the differences in gas properties between N 2 and CO 2 . This discrepancy resulted in a drop of 17 K in dilute phase temperature and 2 K in dense phase temperature. The bed density also exhibited a large with the oxy-firing conditions, with notable observations revealing a lower bed density below a height of 4.2 m, transitioning to a higher density above said height. Sensitivity analysis was also conducted for three principal operating parameters, including superficial gas velocity, oxygen partial pressure, and catalyst circulation rate. An increase of oxygen partial pressure to 27 % or a decrease of the catalyst circulation rate to 20.7 kg/s proved effective in achieving the same temperature profile and even a slightly better carbon conversion in comparison to air-firing regeneration. • A CFD model is developed to investigate the air/oxy-firing regeneration in an industrial FCC unit. • Regeneration temperature, carbon conversion rate, and particle fluidity are impacted in oxy-firing atmosphere. • Increasing oxygen partial pressure to 27% in oxy-firing mode proved effective in achieving comparable performance. • The catalyst circulation rate reduction demonstrates the most significant impact on regeneration performance.