Preservation of Sulfur Storage Tanks

[refiner258]

Good day!

I am currently working in a petroleum refining company. Anyone who knows preservation procedure for molten sulfur storage tanks? I've read that the tanks need to be purged with nitrogen and sealed. However, I am not sure if this implies that the tank needs to be pressurized. Sulfur storage tanks are atmospheric tanks so I don't think it's a good idea to pressurize them.

Thank you.

 

[EdStainless]

There needs to be just enough positive pressure to keep moist air out. What happens in when the tank warms during the day it vents, and as it cools the nitrogen fills.

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P.E. Metallurgy, Plymouth Tube

 

[mk3223]

The tank blanketing with N2 purge is very typical method to avoid the oxygen to get into the tank. The purge control valve is used to control the pressure and flow to comply with the tank design pressure. API 650 and 2000 have more details for design requirements.

 

[refiner258]

Thank you very much EdStainless and mk3223. Our sulfur tank has no nitrogen purge control valve. It was designed without that. Our tank was just repaired due to severe corrosion of tank internals, which resulted from sufficient heating. To address the heating issue, source of steam will be upgraded but the project might take some time (probably a year). The tank will be commissioned once the project has been completed. This is why I want to preserve the tank. Is continuous nitrogen purging a viable option?

 

[mk3223]

I saw the sulfur storage tanks with a N2 blanketing system. IMO, the continuous N2 purge could be a workable option too with a proper N2 source. And, a proper control valve set up on either the N2 blanketing or purge systems can provide a better flexibility for operation with the proper N2 flow and pressure.

 

[EdStainless]

I have seen these on sites using locally generated nitrogen (swing absorption) rather than bulk. It depends on what is available.

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P.E. Metallurgy, Plymouth Tube

 

[georgeverghese]

Check with the mechanical engineers what was used as the vapor space upper design pressure by the tank fabricator. Then set up a forward sensing regulator set at say 50% of this design pressure to feed the tank. And another backpressure sensing regulator on the tank free vent line to maintain the max operating pressure at say 70% of design pressure. Add another safety breather valve / PSV set at 80% of design pressure in parallel with the backpressure valve. You'll have to include a vacuum safety valve ( or use a combination PVSV ) for safety also for obvious reasons.

 

[refiner258]

Thank you for your inputs. Actually, it says in the drawing that the design pressure is full liquid so I assume that it is unsafe to pressurize the tank. Are there any other ways we can preserve the tank?

 

[georgeverghese]

From what I read on previous discussions on this topic in this forum ( you can do a search on API650 design pressure), a rerate of the tank's test pressure may be required if it is not designed to API 650 Appendix F. Again, this is a topic for the mechanical engineers in your company. Once a higher test pressure is set and passed by the mechanical engineers, you can then proceed to set up the blanket pressure regulators as suggested earlier.