Nitrogen supply facilities for purging purposes 1

[genewarun]

Hello everyone;

I have been preparing an outline for a gas compressor station and have just found out that nitrogen supply for these facilites for inertization and purging purposes, and especially in isolated locations cryogenic tanks for liquid N2 storage and vaporization facilities (to obtain N2 gas) exist.

Is there a code/standard/guide regarding these, also capacities and pressures required in such facilities (for purging purposes)?

Thanks in advance.

 

[Montemayor]

genewarun:

I had to read the mile-long, first sentence of your query 3 times and I hope I understand correctly what you are trying to state: you are in need of purging a natural gas compressor station (presumably for pre-comission or start-ups) and have found existing supplies of liquid nitrogen (LIN) to use for this purpose. You want to know if there are codes, standards, or guidelines for using this type of cryogen equipment and what are typical capacities and pressures that you can expect from these facilities.

If my understanding is correct, then all you have to do is contact your closest supplier of the LIN - companies such as Air Liquide, Praxair, Air Products, BOC, etc, etc. The supplier will rent, lease, or sell you the facilities depending on your needs and requirements. The supplier will also install (& even operate the facilities) on your site or "across the fence". From my experience with natural gas compressor stations I don't believe you can justify a LIN consumption such that you would have a resident storage tank of the stuff. You would be venting most of the inventory while the compressor station operated. I've used Praxair and Air Products to supply start-up and purging requirements with their portable tank trucks - which they supply and operate on demand.

Under the above arrangement, you need not concern yourself with organizing and setting up safety and operational procedures for supplying and applying the inert atmosphere. The supplier will take care of that - but with your participation and preparation - such as in PSSRs and HazOPs. Regardless of what else you do, you will have to go to the LIN supplier for the product and industry has always resorted to the supplier as the cryogen expert in the applications. This is normal practice.

I hope this experience helps.

 

[sethoflagos]

Genewarun,

Montemayor's comments are very sound - fixed nitrogen storage is normally only justifiable where there is a sizable continuous demand such as a major petrochem tank farm. But you mention 'isolated locations' - are you somewhere that experiences supply difficulties?

If you are considering fixed liquid nitrogen storage, the plant is not complex.

The (well-insulated) storage tanks are generally designed for modest pressure (say 10-15 bar) at -190 deg C. Pressure is maintained via an external loop with control valve and air heated vaporiser drawing from the liquid phase and venting back into the vapour space. Outlet piping is often copper and heating to ambient can use a waterbath.

However, you can now obtain small skid mounted nitrogen generator sets based on membrane technology. These are widely used in O&G in remote locations, including offshore.

 

[unclesyd]

We use a lot of N2 for tank and process inerting and have used all manner of gas generation from old Kemp Generators (for Montemayor's benefit), Prism Separators, gas purification from process vents, bulk storage on site. The site presently has a Cryogenic Separation plant owned by Air Products and operated remotely. In the event of a plant outage the our demands are met by truck transfer. We have even worked with a vaporizer hooked directly to the truck for our low pressure requirements.

If you evaluate onsite cryogenic storage here is an excellent source of what's available and a lot of very good technical information.

http://www.taylor-wharton.com/

Here is one of the suppliers of membrane separation systems (Prism) and also onsite cryoplants if the quantity warrants.

Prism Systems

http://www.airproducts.com/Equipmen...ryId=1&intRegionalMarketSegment=215&intTab=57

 

[genewarun]

First of all thanks for your posts.

Indeed, this is going to be the first time that im gonna be involved in a gas compressor station, however i know all the utilites well from other projects except N2 plant. So, conceptually what is on my mind is how much capacity is needed, at what temperature and at what pressure. I think the capacity is going to be calculated from all the volumes of piping and enclosed systems for purge and inertization, but i dont know the basic tricks and know-hows regarding that. A code/standar/guideline shall be very useful, ofcourse otherwise i'll have to sit down with vendors without any data regarding conceptual data in my hands.

Thanks again.