The Impacts of Cyanide on Fluid Catalytic Cracker (FCC) Overheads / Gas Plant Corrosion
The Impacts of Cyanide on Fluid Catalytic Cracker (FCC) Overheads / Gas Plant Corrosion. Once formed it can cause considerable corrosion, hydrogen blistering and waste water treatment issues.
Once formed it can cause considerable corrosion, hydrogen blistering and waste water treatment issues.
The resulting sour water is separated from the hydrocarbon products at various stages in the system.
At this point any free cyanide can contribute in a number of ways:
- Free cyanide may be deposited in the wet gas stream as corrosion products. Cyanide, in contact with Iron Sulphide (FeS) destabilises this FeS layer causing this free iron sulphide to be swept away in the process stream. This exposes the carbon steel surface, which corrodes again in contact with H2S to form a fresh layer of FeS. From there, the whole process is repeated causing corrosion thinning of the piping and equipment.
- Some free cyanide gets removed from the wet gas stream with the condensing water or water wash. Once in the water phase, the cyanide is transported with the water stream causing further corrosion downstream.
- If the free cyanide is not removed, it will be collected by the amine system and form heat stable salts. These heat stable salts will affect the efficiency of the amine system and cause corrosion and other amine system issues such as fouling.
Selection of crude feedstock is driven, in part, by cost and opportunity.
Many crude oils processed today can be increasingly sour and contain higher amounts of nitrogen.
As previously mentioned, increasing amounts of basic nitrogen forms more cyanise in the riser leading to cyanide accelerated corrosion, hydrogen blistering and cracking.
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