Acetylene Compressor 5

[JPan]

I need to compress a gas stream with 33% of Acetylene, 35% Methane, and 29% Hydrogen from atmospheric to 89 psia. Any suggestion on precautions to prevent Acetylene explosion?

 

[Montemayor]

JPan:

I've compressed all 3 gases under routine process plant conditions:

Pure Acetylene: from 3 psig to 350 psig; in 3 stage, submerged, reciprocating compressor - destined for Acetylene cylinders (under acetone absorption).
Methane and Hydrogen: from 10" WC to 5000 psig in multi-stage reciprocating machines with both gases in the pure stage or in a mixture. The Methane has also been compressed prior to liquefaction as LNG, in centrifugal compressors.

You need to tell us how, in what type of compressor you are going to compress the mixture, and in how many stages - if any more than one. This will give us a better picture of what you propose to do. An immediate concern is your stating that your suction stream will be at atmospheric pressure. I don't believe that you will be permitted to carry this operation out in a compressor that is capable of pulling a vacuum (however slight) in the suction. The common sense reason for this is that if that should EVER occur (& it can in most compressors) the operation would be in the very hazardous position of potentially sucking in atmospheric air (with 21% O2) into one of the most potentially explosive gas mixtures one could imagine and (and the following is the worst part!) compressing the subsequent mixture under increased pressure AND TEMPERATURE.

That is why potential flammable & explosive gases destined for further compression are always kept at a reasonable pressure above atmospheric, where they can be monitored and controlled to avoid such a bad scenario. If I were to try to compress this mixture I would not attempt it without a detailed report from Research & Development efforts and a detailed explanation of the mixture's properties and behavior at the final pressure as well as at the interstage pressure level (I assume you would not attempt to do this in one single stage because of the resultant high heat of compression.

I didn't have major problems with pure Acetylene because I was well aware of what I was limited to do via compression and fluid transport. In other words, we know that you are in a progressively more and more dangerous zone when you have free, pure Acetylene at pressures above 350 psig. And even then, I limited all piping to 3/4", sched 80. All separator vessels like interstage and final discharge pots were filled with chain in order to reduce the total free volume within the system. Only iron or steel was allowed as material of construction and potential reactants and catalysts such as silver, copper, etc. were kept out of the plant. How these procedures are reduced due to the dilution of the Acetylene content is something I am ignorant of but I would be very suspicious of any instructions or recommendations that lacked detail or research backup and experience.

I would be particularly cautious of any potential high activity or catalyst sites existing or created within the system that could precipitate an H2 + Acetylene saturation reaction. This is the type of studies that must be identified and verified prior to attempting a compression of such a mixture, in my opinion.

I realize I have not given you optimistic help but I hope I have identified some areas of potential concern that merit a high degree of precaution and planning. Some companies have already run into this sort of dilemma in the past. I seem to recall Union Carbide's attempt to dominate Reppe chemistry (synthesis starting with Acetylene) in the 1960's in a rather large Brazilian plant; I believe the results were a complete failure in trying to control the process of handling Acetylene. I have never heard of any other venture that has succeeded in conquering the Acetylene problem. I would welcome any news to the contrary from any other forum contributor, because this may be a sign of improved technology that has been developed with regards to safely handling Acetylene.

I believe this is a serious proposal that merits further attention and study and I concur with your concern about how to best handle this proposal. I wish you luck and success and I hope that you may awaken some experienced know-how and ideas from other contributors to this forum.

Art Montemayor
Spring, TX

 

[jsummerfield]

Absolutely PROHIBIT any COPPER or copper bearing alloys that could come in contact with acetylene, even in the event of seal failure, etc.


John

 

[JPan]

Thank you very much for your replies.

I am proposing an oil-flooded single stage screw compressor for the application. The discharge temperature is 200F maximum. However, I don't have control on the suction condition and it will be at 0 psig or even some vacuum. Should I submerge the compressor in water like the pure acetylene compressors?

 

[Torricelli]

JPan,

why not use a liquid ring compressor (isothermal compression using water as seal liquid) ?

potential suppliers are Nash-Elmo, Sterling-Sihi, NSB Gas Processing, GARO...

Torricelli

http://www.vacuum-guide.com

 

[Montemayor]

JPan:

As I stated before, I'm dead set against running any compressor in this type of application with the potential to suck a partial vacuum. At this point in my life, with 43 years (most of it in compressing industrial gases) in engineering, I refuse to design around this type of constraint and consider it ill-advised and dangerous to do so. That is my personal opinion as a professional, registered engineer and I will not advise anyone to try this in an industrial operating plant. True, you won't suck air through the compressor's flanged inlet when you have it submerged; you'll suck in water. But the remaining, above water, suction line will be subject to the same condition at every upstream joint and atmospheric air WILL migrate into the suction if a partial vacuum exists there. This I know from personal operating experience in the field. I wish you would reconsider and heed what I wrote before. However, I can't comment any further since I don't have any more basic data or job scope than what you've furnished - which is merely two sentences.

I wish you all the luck in the world and that this New Year be a safe one for you and all the personnel working with and under you.
¡Prospero Año Nuevo!


Art Montemayor
Spring, TX