Dry Gas Seal versus Oil Seals

[Imran.Idris]

When is it recommended to use dry gas seal in place of oil seals?
Can we use dry gas seals on all rotary machines or some selected ones?
What is the economical justification of dry seal?

[fraz]

Dry gas seals are recommended on hazardous / high cost gases, oil seals can also be used on hazardous gases, but following are the disadvantages of oil seals in comparison to dry gas seals.
1. Contamination of oil with hazardous gases.
2. Very high initial cost due to a seal oil tank, seal oil pumps and pipings.
3. High running cost ( pumps and oil circuit running)
4. Relatively high leakage.

We dont need to use dry gas seals on all machines. Dry gas seals are used only on hazardous gases or very high cost gases ( For example dry gas seals are not used on LP stage of CO2 compressor while these are used on HP stage of CO2 compressor ( due to high cost of leakage), while no dry gas seal is used in any stage of air ompressors). On fluids we use mechanical seals or gland packings.
I think this answers all your questions

[Imran.Idris]

Thanks fraz, but in case of dry sealing we need to maintain flow of some inert gas like Nitrogen etc which is a big running expanse, I mean we have to ensure the availability of such inert gas, and maybe we need to install a small inert gas generation plant for this. Or there are other means to fulfill the requirement?

[fraz]

Normally nitrogen plants are normally required in Ammonia Urea complex for purging etc, and as an added advantage this nitrogen can also be used as an inert gas in dry gas seal

[Imran.Idris]

Thanks Faraz

[Muhammad Ahmed]

Faraz is right, since at the new plant dry gas seals are installed on synthesis and refrigeration compressors and not on the air compressors. Both syn and refrig gases have the toxic as well as fire potential.....