4 replies to this topic

[Art Montemayor]

MTS:

Your query brings up a specific question: What is the fire system proposed to do? What is the scope of work for the fire system?

I ask this question because:

1) We don’t know if a hydrocarbon-fueled Pool Fire is the subject here.
2) Ammonia – while it is classified as flammable – has never (at least to my knowledge) been successfully ignited and maintained as a fuel for a continuous fire. I know that many people have tried to ignite ammonia vapors and sustain a continuous fire with them; however, everything I have studied shows failure (& Thank God).
3) Fire water is sometimes used to fight the propagation of toxic and hazardous ammonia fumes by converting the vapors to an aqueous solution of ammonium hydroxide. This doesn’t eliminate the vapors, but it reduces the free quantity.
4) Why would you expect a fire at the top of the ammonia storage tank, if ammonia vapors are, indeed, not possible to keep aflame?

Exactly how high is your ammonia storage tank? From a practical point, it should be expected that a proper and conventional fire pump have the capacity to pump water to a height of approximately 50 feet. Does it make for a significant economic difference if the fire pump is specified to pump less head than that? Please be specific in your detailed explanations.

PS: While our forums may not be considered as some of the most erudite and intellectual engineering forums on the Internet, any visitor to your member profile page will instantly recognize that the pictures of your Friends certainly puts our Forums on the top of the list of beautiful chemical engineers. I congratulate you for the beauty of your chemical engineering colleagues. Clearly, the beauty of chemical engineering has increased tremendously since I graduated – and what’s more important is the fact that women engineers are academically obtaining better grades and results than their male counterparts. I hope my beautiful granddaughters follow me in the profession. Viva women engineers!!

[astro]

MTS:

Your query brings up a specific question: What is the fire system proposed to do? What is the scope of work for the fire system?

I ask this question because:

...

2) Ammonia – while it is classified as flammable – has never (at least to my knowledge) been successfully ignited and maintained as a fuel for a continuous fire. I know that many people have tried to ignite ammonia vapors and sustain a continuous fire with them; however, everything I have studied shows failure (& Thank God).

...

From my reading the ammonia tank disaster at Jonova, Lithuania circa 1989 resulted in an liquid ammonia pool fire. Excerpt from Lees, Loss Prevention in the Process Industries, 2nd Ed:
Another refrigerated atmospheric ammonia tank failure occurred on 20 March 1989 at Jonova, Lithuania (Case History A124). Some warm ammonia had been charged to the tank and in due course it erupted, causing a sudden increase in pressure. A massive failure occurred between the wall and the bottom of the tank and liquid ammonia rushed out. At the same time the tank was dislodged from its foundations and smashed violently through the containing wall on the far side from the escape, ending up 40 m away. A pool of liquid ammonia formed which in places was 70 cm deep. The ammonia suddenly ignited and the whole plant area was engulfed in flames. A burning conveyor belt transmitted the fire to a store of NPK fertilizer. Seven people were killed.

According to this:
Tank Failures
The 10,000t tank was 70% full.

Surprising that there was not more loss of life.

However, the above is an extreme case and would generally be regarded as the exception not the rule because with a lower flammability limit of 15% (or so), the high priority fatality risk for NH3 is its toxic effect. Knock down of gaseous ammonia using water sprays from a fire water monitor is a sensible prospect to plan for.

One credible fire risk for me is combustion of insulation. PUF, polyurethane foam, is a common form of cold insulation from my travels and produces nasty toxins of its own if it happens to catch fire (PUF is generally cheaper than other non-flammable forms of insulation). Again for an ammonia plant environment, I'd rate the risk low but it is possible. For a start, ignition is required and if the insulation is sitting under cladding (for a well maintained plant) then probabilities are low. Shutdowns &/or maintenance are exposures when cladding could be removed and hot work is in progress. A fire watch as part of a permit to work would be appropriate but ultimately not a guarantee that the worst will never happen.

[astro]

This report provides more detail on the Jonova tank failure:
Jonova ammonia tank failure

[djack77494]

Ammonia storage bullets that I've seen have been well covered with a water deluge system that can provide large quantities of water above and around the vessel. The purpose was to absorb any escaping ammonia vapors. Notwithstanding the possibility that ammonia pool fires are possible, I think they are so unlikely that I've never heard of anyone being concerned about them.