Understanding HCN in FCC:Formation,effects and mitigating options

摘要

In these challenging times,fluidized catalytic cracking units(FCCUs) aim to improve margins by processing poorer-or different-quality feeds,while maintaining good yield performance.These feeds may produce more coke and have elevated nitrogen levels,which can then increase the potential for higher cyanides and associated equipment damage in wet hydrogen sulfide(H2S) service.A general overview of cyanide formation and associated corrosion problems in the catalytic fractionator and gas plant is provided to help explain the nature of the problem and what mitigating actions can be taken.Many FCCUs have no history of cyanide-related problems,as potential cyanide effects are adequately controlled by water washing and by using chemical additives.In addition,unit operating parameters can be adjusted to help control cyanide production.Application of this approach is discussed for a unit that observed higher cyanides in the catalytic fractionator overhead water following increased processing of heavier feeds enabled by a catalyst change.An in-depth investigation showed that the amount of cyanides was increasing with the heaviness of the feed.This unit subsequently found no cyanide-related problems during a unit turnaround inspection.