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How to reduce sox emissions from FCC regenerator by changing which operating conditions..? Like Catalyst circulation reduction, combustor temperature reduction, ROT reduction etc.

Sep-2024

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Marcio Wagner da Silva, Petrobras, marciows@petrobras.com.br

This is an increasing concern for any refiner operating fluid catalytic cracking units (FCC) taking into account the necessity to reduce the environmental footprint of the refining processes in compliance with the current regulations. Unfortunately, act only in the process variables will get poor results and severely impact the performance and profitability of the FCC unit, the most widely and effectives ways to reduce the SOx and NOx emissions in FCC units are:

1: Managing the sulfur content in the feed stream - This can be achieved selecting low sulfur crudes or hydrotreating the FCC feed streams;
2: Applying catalyst additives capable of reducing the SOx and NOx emissions in the regenerator - There are several FCC catalyst licensors which developed commercial solutions of these additives like BASF and Grace Company. It's important to taking into account that the most part of the SOx reduction additives will convert the SOx into H2S which will be removed in the amine treating step, but it's possible to the high H2S concentration can raise the occurrence of Carbonyl Sulfide (COS) in the LPG and Propylene streams once this is produced by the hydrolysis reaction between H2S and CO2. Considering this fact, the refiner needs to manage this threat through and adequate management of the lifecycle of carbonyl sulfide adsorbing bed to avoid troubles in the chemical grade propylene specification;
3: In partial burning processing units, the use of low NOx burners can ensure significant reduction in the SOx and NOx emissions;
4: Applying a flue gas scrubbing system - There are some process technologies developed to this purpose in commercial stage;
5: Reduce the processing capacity from the FCC aiming to control the SOx and NOx emissions rate - This is a drastic alternative, but can be considered according to the severity of the local regulations faced by each refiner.

As described above, there is not an easy way to achieve an effective reduction in the SOx and NOx emissions from FCC units and the most part of the available solutions requires significant capital investment. Again, just acting on the operating variables is not an effective way to reduce the SOx emissions and will produce significant impact over the performance and profitability from the processing unit.

Sep-2024