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What will happen with FCC products if visbreaking gasoline and HDS wild gasoline (H2S content up to 10%) are sent to FCC riser? Will these gasoline crack? Will the olefins be saturated? What will happen with sulphur content in FCC gasoline and could Merox of gasoline cope with that? It is important especially in the case of low sulphur feed at FCC.
 
Answers
12/05/2010 A: Saugata Palit, Intercat India Ltd, spalit@intercatinc.com
Yes, the gasoline will crack and will increase your LPG and gas make. The degree of cracking will depend on where you introduce the HS naphtha. If they are introduced in other recycle nozzles, other than the feed nozzles, then the effect is all the more better. If the recycle nozzle is below feed nozzle, then it can be used for LPG maximization.
Introducing wild naphtha in riser is a better option than introducing it in FCC HP separator. This will help you to reduce load on your stripper. Moreover, the total H2S will go to FG instead of in the naphtha cut. This will also help in reduction in H2S loading of LPG (when H2S escapes from stripper to debutanizer). Merox should not face any difficulty, moreover it will be benefited if naphtha is cracked.
Moreover this will help to raise you cat/oil ratio and increase conversion. This is especially beneficial for low sulfur feed because mostly the basic nitrogen content of low sulfur feeds are quite high. Basic nitrogen has negative impact on FCC catalyst. Introduction of H2S rich naphtha, helps in masking of the detrimental effect of the basic nitrogen. This will improve bottom cracking.
23/04/2010 A: Pawan Gupta, Essar Oil Limited, Pawan.Gupta@essaroil.co.in
Yes it will crack. I presume it is going from bottom with lift or riser steam. Probably 50% will convert Fuel Gas, Propylene and some Butylene. This is what some refiners do to maximise their propylene yield. it also help to increase the cat/oil ratio.
Sulphur content is gasoline probably not effected so much as gasoline will be mostly cracked back to RFG, propylene and butylene, I'd expect more likely that H2S content in FG & LPG will increase so it could be expected to put a heavier load on amine absorber treating FG and LPG plus also increased load on Sulphur plant downstream of that.
23/04/2010 A: Lindsay McRae, Pall Corporation, Lindsay_McRae@pall.com
Yes it will crack. I presume it is going back to riser via main feed nozzle? Probably will crack right back to Fuel Gas, Propylene and some Butylene. This is what some refiners do to maximise their propylene yield. Some of FCC designs even have a 2nd riser especially for that purpose.
No olefins will be largely unsaturated due to lack of H2 in FCC environment.
Sulphur content is gasoline probably not effected so much as gasoline will be mostly cracked back to RFG, propylene and butylene, I'd expect more likely that H2S content in FG & LPG will increase so it could be expected to put a heavier load on amine absorber treating FG and LPG plus also increased load on Sulphur plant downstream of that. Perhaps some marginal S increase in FCC gasoline might be seen. Merox could probably cope provided it is not already operating at its limit.