(228d) A Novel Fcc Regeneration Process for Reduced CO2 Emission

The fluid catalytic cracking (FCC) unit is used to crack heavy oil, during which process coke deposits on the FCC catalyst. The regenerator of an FCC unit burns off the coke to recover the activity of spent catalyst. In a partial combustion process, the flue gas from the regeneration process includes a significant amount CO, as well as CO2. The flue gas passes into a CO burner, in which CO is totally converted into CO2. The production of from coke combustion in the FCC regenerator and CO burner is a dominant source of CO2 emissions from petroleum refineries.

The aim for this project is to develop a new process that significantly reduces CO2 emissions from FCC regeneration. In the chemical industry, CO is a valuable feedstock that can be used as a part of synthesis gas as raw material for producing methanol and other chemicals. It is worth to consider the possibility of CO recovery. However, for normal FCC regeneration, fresh air is used for coke combustion, which results in a large amount of N2 in the flue gas. The presence of N2 makes CO recovery very difficult and expensive. This work proposes an alternative process, in which instead of air, oxygen and recovered CO2 from the flue gas are used to regenerate the FCC catalyst. In this technology, O2 is no longer the only reactant for coke burning; coke also reacts with CO2 to produce CO, expressed as Boudouard reaction.

?Two-region and two-phase' theory (Kunii and Levenspiel, 1991) has been adopted to model the regenerator. The regenerator is represented as a dense region and a dilute region. The dense region model uses a CSTR reactor for the emulsion phase and a plug flow reactor for bubble phase. The dilute region is modeled as a two-phase tubular reactor. A kinetic model for the reaction of coke with air has been extended to account for CO2/O2 feed gas mixture. The kinetics of the Boudouard reaction accounts for the composition of the FCC catalyst.

The modified model has been validated by a conventional air feed regeneration process, and has been applied for a range of operating condition with CO2/O2 mixture. The CO yield from FCC regeneration can be increased by around 75%, equalized to a 12% reduction of CO2 emission. The model is to be applied for the development of novel process configuration that could further enhance these benefits.