+2 votes
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How to prevent pyrophoric scale formation in the cargo tank?

asked Jul 22, 2014 in Hull by aodai (1,960 points)
Fuel Gas Blanketing issue:

If the fuel gas contains a Hydrogen Sulphide (H2S) above oxygen concentrations, then there is a potential for the formation of pyrophoric iron sulphide within cargo tank.

For example: Considering the project has 24 ppm H2S concentration in the inlet gas which results in 29 ppmv H2S in the fuel gas. In absence of Oxygen, this will results in pyrophoric iron sulphide scale formation which is significant issue for tank entry.

2 Answers

+3 votes
answered Jul 22, 2014 by belmoreno (2,190 points) | selected Apr 16, 2015 by ChemKB
 
Best answer
The possible ways to mitigate this risk is to maintain an Oxygen concentration above the H2S concentration by injecting a small amount of Oxygen (via Nitrogen) with the fuel gas.  To comply with zero emission, the proposed process scheme is to recover cargo vent gases and recompress them using VRU which will feed this to Booster gas compressor and then ultimately routed to the main gas compression system. This will results in additional oxygen introduction in to the export / lift gas.

Considering mixing efficiencies, it is proposed to inject 5 to 6 times Oxygen than H2S concentration (i.e. approx. 100-130 ppm).
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