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Nitrogen Piping

Nitrogen Piping

Nitrogen Piping

(OP)
Is it possibe to design a low cost Nitrogen Application System for applying nitrogen at the base of a silo (60 feet diameter x 70 feet tall)through strategically placed diffusersin a large stockpile of wood pellets as a fire suppression system to minimize oxygen levels if internal temperatured are approaching dangerous levels?

My thoughts are to have the piping in place and call local Air Products to deliver nitrogen by truck tanker to connect.

Any commets would be apprecated.
 

RE: Nitrogen Piping

I'd suggest contacting Air Products first and see what kind of stipulations they may have on this system. If you are concerned about fire, I think Air Products would be concerned about pulling a tanker up near it to use like a fire truck.

The concept sounds good - it would be easy enough to hook up a truck and offload liquid nitrogen (LIN) directly without even running the pump on the truck, just using pressure in the tanker. Note that the tankers don't have any way of vaporizing the LIN so either you need to provide a vaporizer or you will have to dump cryogenic LIN into the fire; which might not be a bad solution actually. If you put in a permanent system, and need a truck to make the delivery, and knowing you want to dump cryogenic LIN on the fire, you will also need to consider materials of construction along with thermal contraction of the pipe. Generally, copper pipe is used and the joints silver soldered. Depending on the temperature the fire might get, it may be too hot for these copper joints. Another option is stainless steel welded pipe or even stainless tubing with compression fittings. Steel pipe can't be used if it will be exposed to cryogenic temperature.

Another concern you may have is how quickly they could get a truck on site. Generally, LIN deliveries are made to regular customer tanks and scheduled a few days in advance so an oddball like this may not get scheduled right away, so you would need to discuss this with them.

You might consider having a small amount of LIN on site depending on how much you need. One or more 200 to 500 liter dewars of LIN isn't very expensive, and could be hooked up and swapped out every month or two. These are transportable cylinders that can be fork lifted and rolled around on castors. Boil off is about 1 to 2 % per day. If you need much more than that, the smallest cryogenic tanks start at around 500 gallons and go up from there.
 

RE: Nitrogen Piping

CO2 is a far more common extinguishing agent because it is more practical to store it on site and cheaper.

RE: Nitrogen Piping

CO2 is also somewhat less of a hazard to personnel in the instance of a slow undiscovered leak, because it produces a physiological response, whereas nitrogen does not.

 

Mike Halloran
Pembroke Pines, FL, USA

RE: Nitrogen Piping

Ande CO2 is heavier than air/oxygen, and will displace oxygen from inside a pile of pellets.  Nitrogen is the main constituent of air, and hss to be pushed through your pellets to inert the atmosphere in the silo.  And CO2 is also available by the semi-trailerload.

RE: Nitrogen Piping

(OP)
Thank you all your comments as they have been very helpful.  I will have infloor diffusers in place for aeration of the wood pellets.  I planned on adding internal piping with nozzles located in the diffusers for dispersing the Nitrogen into my stockpile.  Can I apply CO2 in the same manner or since it is heavier than air should it be applied at top of the pile?  

RE: Nitrogen Piping

While quite expensive and I think you can still get it - Halon has always been my favorite.  At a 5 or 6% it will extinguish any fire and you can still breathe it.  Can cause heart fibrillation in some people after long exposure - but quickly goes away when removed from the area.

Check it out.  You don't need much - even if expensive.

RE: Nitrogen Piping

I think, if in the U.S. - halon is only allowed to be used for replenishment of existing systems - not new construction.

RE: Nitrogen Piping

CO2 can be applied from the top or bottom.  Your under-the-pile diffuser header would work very well -- until the pellets and dust clogged the nozzles.  Just shoot it in from the top, using downward-pointing pipes.  I'd keep the open end at least 3-ft below the top of the silo.

And hold safety training, a purged silo is DANGEROUS.  Some knucklehead will drop a wrench or his wallet into a full bin, and want to climb down in to retrieve it.  Then one or 2 more guys will try to help out with the downed guys.  Truple fatality in less than a minute.  Teach them that you feel distressed in moderate consentrations, and fall over unconsious during your second breath in high concentrations -- no time to decide to leave.

RE: Nitrogen Piping

I agree with other posters concerning the hazards to personnel. Confined space came to mind. When we do confined space entries, we:

Use only personnel that have had confined space physicals and  training
Set up a hoist over the opening
Tie the person to the line
Have someone standing by at the hoist
Take oxygen measurements at different heights within the space using a portable oxygen meter-before allowing entry
Provide each person inside with a portable oxygen meter
Person on top constantly talks to personnel inside
Provide fresh air with a fan and collapsible ductwork

I have probably left out a few steps. I have not done an entry myself.

Sounds extreme? Would you rather call the person's wife and tell her that her husband came to work, but won't be coming home?

I wonder if oxygen levels would deplete naturally. Reminds me of the advice to keep oily rags in an airtight container to prevent spontaneous combustion.   

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