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Fluid Catalytic Cracking (FCC), Flue Gas Scrubber SO3 break through. We are facing with Wet Gas Scrubber (FGSU) outlet stack dense plume issue. It is taking longer to disperse and getting landed in nearby area causing eye irritations. As per licensor, this dense plume is due to SO3 breakthrough. Stack outlet analyzer only measures SO2 and and values are within limit. These phenomena happening during Heavy Sulphur feed processing and issue gets aggravated during winter season. We tried to limit the excess Oxygen in flue gas. Also maximized the circulating water. But no noticeable changes occurred Is any refinery facing the same issue and what are the troubleshooting activities have been carried out to resolve this issue? Will SO2 breakthrough occurs first before SO3, which not happening in this case? Flue gas composition: SO2, SO3, CO2, O2, N2.

Dec-2024

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David Inward, Sick spol., david.inward@sick.cz

I wonder whether the SO2 analyser is measuring correctly. Since normally, there is a well established relationship between SO2 & SO3. So when the SO3 goes high, it is hard to imagine that the SO2 does not do likewise. However, measuring SO2 behind a wet scrubber is tricky, since SO2 is a water soluble gas. So if the SO2 analyser has a sample system to remove the (very high) water content to ensure a dry sample gas is measured, it is quite possible that a significant portion of the SO2 is washed out in the cooler which removes the water & therefore is not measured. There are alternative stack analyser techniques which are better suited to measuring behind a wet scrubber (no need to remove water prior to analysis)

Feb-2025
Marcio Wagner da Silva, Petrobras, marciows@petrobras.com.br

This is a very important topic nowadays, considering the growing relevance of the FCC units for refiners due to the increasing demand by petrochemicals and the necessity to reduce the atmospheric emissions from the processing unit. The condition is aggravated under lower atmospheric temperatures due to thermal inversion effect where the cold air with high density is trapped near the ground, hampering pollutants dispersion. By the question description it seems that the gas scrubbing is operating under low SOx/NOx efficiency removal once the plume is causing eye irritation. According to some references it's possible to avoid plume formation in flue gas scrubbers using a re-heater which also avoids acidic gas condensation. Considering the available operating variables, it's possible to try to reduce the sulfur content of the FCC feed through blending with low sulfur streams or hydrotreating the feed, despite the relatively high capital cost of this alternative. Another strategy is to use SOx reduction additives in the FCC catalyst in synergy with the flue gas scrubber, reducing the SOx concentration in the flue gas which will be treated. It's not clear in the question if is used only water as scrubbing media, so a good strategy to reduce the SOx concentration in the scrubbed gas is to use fresh water treated with sodium hydroxide aiming to maximize the performance of the SOx removal.

Dec-2024