Acetylene plant

[wilmers]

Dear friends:
I would like to know if anyone knows anything about the necesary quality that water to produce acetylene should have, to improve the process eficiency.
Wilmer

 

[Montemayor]

wilmers:

You fail to give us any details or specific basic data on what you are doing, so I'll have to speculate as follows:

1) I assume you are using the Calcium Carbide process to produce Acetylene and not the Wulff or other processes;

2) I assume you are referring to the process water utilized to react with the Calcium Carbide thus:
CaC2 + 2H2O = Ca(OH)2 + C2H2

I've used essentially "potable" water sources without any problems in producing Acetylene in Jamaica, Trinidad, Belize, Peru, Chile, besides the USA and others. This implies that you have no solids, sludge, or dissolved gases in the feed process water - it virtually is "drinkable".

I detect a concern on your part about having to use de-ionized, distilled, or specially-treated water. I have never resorted to this extreme and never found a need to do so. However, in order to obtain really expert recommendations, I recommend you contact experienced people who design and build Acetylene generators – such as the Rexarc Company at:

http://www.rexarc.com/history.cfm

Talk or write to their people at

Phone: (937)839-4604 Fax: (937)839-5897
35 East 3rd Street, Ohio 45381, USA
P.O. Box 7 West Alexandria, Ohio 45381, USA

I’m sure they can provide you with even more information about any water quality you may have concerns about.

I would also recommend you obtain a copy of the CGA (Compressed Gas Association) booklet on Acetylene and its handling. Good Luck.


Art Montemayor
Spring, TX

 

[wilmers]

Thanks Montemayor, but do you know something about any experiencie using recycled water of the same process?
Wilmers

 

[Montemayor]

Wilmer:

You still haven't verified that you're using the Carbide process. I have to guess that you are.

I also have to guess that you are unfamiliar with the process and have no experience operating an Acetylene generator.

The process water fed as a reactant to the generator is done in excess of the stoichiometric requirements in order to drive the reaction to completion, absorb reaction heat, and secure all the C2H2 available. This is also done on a practical basis to obtain a slurry Lime product that can be stirred, handled, and expelled from the generator with ease. This slurry is drained or pumped to external ground pits or "lakes" where the slurry cools and is allowed to emit its dissolved residual C2H2 and solidify. All associated water with this slurry eventually evaporates into the atmosphere. I can see no practical value in trying to separate the slurry from its water content and re-using the latter. The amount of water and the cost and effort to do this is not practical. I know of no one who has even contemplated this possibility and I've never read or heard of such a venture.

Are you operating a Carbide plant or is this a study or feasibility study of some sort? What is your scope of work and goal in looking at the proposed water recovery from the slurry? It would help me help you if you furnished more detailed basic data and your scope of work.



Art Montemayor
Spring, TX

 

[EdStainless]

Art, I think that he means water that has been reclaimed from other uses.
Art's comments were to the point, it should be clear, neutral, de-gassed. It doesn't need to be drinkable, but it should look like it is.

= = = = = = = = = = = = = = = = = = = =
Corrosion never sleeps, but it can be managed.

http://www.trenttube.com/Trent/tech_form.htm

 

[sigmaeng]

There is no data as of yet regarding water quality and how it affects acetylene production or gas quality. There are other ways to improve gas quality and overall system performance.
we are currently consulting an acetylene site with an unusual contamination problem that may be related to the water quality. As it happens they use well water that is hard and is also next to their lime storage pit which is unlined. The issue is known to rexarc but they are at a loss. We are therefore investigating how this particular contamination occurs and what is the cause.
Therefore its our opinion at this time that water quality is not an issue for gas quality but may factor into unusual reactor and system issues, which could translate into saftey issues-- our primary concern.
we have also boosted the performance of their equipment considerably without comprimising saftey which is the first concern in this application

 

[25362]

When speaking of the carbide processes, as I understand, there are carbide-to-water (most common) and water-to-carbide plants in which the cooling effect is provided by total water vaporization (dry-generation with a mass ratio ~ 1:1).

Whether the water quality is important to reduce acetylene impurities is not known to me, but the gas four main contaminants are ammonia, phosphine, hydrogen sulfide, and organic sulfides mostly originating from the carbide itself. These are removed by oxidation and neutralization methods.

Industrial-grade calcium carbide used for the generation of acetylene gas may contain just above 80% calcium carbide, the remainder being CaO with 2-5% other impurities that probably originate in the coke and lime used for its preparation.

NB: Besides the mentioned important safety considerations, temperatures are kept below 150 deg C to minimize acetylene polymerization and other undesirable side reactions.

 

[Montemayor]

sigmaeng:

Since I invested time and effort into this thread, I am very interested in what anyone can contribute to it. I have the following questions/comments on your post:

1. What do you mean by “water quality”? Can you furnish a base water analysis as the basis for an acceptable feed to an Acetylene generator? There are so many components that are associated with process water that we could spend the rest of the month talking generalities. Do you consider dissolved solids as undesired contaminants? If so, which ones? How about dissolved gases? Before we can discuss water quality we must quantitatively identify what we label as acceptable or not acceptable.

2. The original issue and query involved improving “the process efficiency” but this was never defined by wilmers, so we are still in the dark as to what he specifically wants to improve. Again, specifics are lacking in the problem description. We know that there are ways to improve the Acetylene product purity – for example, Rexarc uses “Purifier” beds and dryers. What, specifically, do you mean by “overall system performance”?

3. What, specifically, do you mean by “an unusual contamination problem” in your operations and how is it related to the process water feed?

4. When you infer that there are safety issues involved in the water quality used in an Acetylene generator, you are making a very serious and important assertion. This can be of tremendous importance and safety value to current operating plants. Can you be specific and share with us exactly what you are referring to as “unsafe” process water.

Safety in all phases involved in an Acetylene generation plant is not only essential, it is a 100% requirement 100% of the time – even when the plant is shut down for whatever reason.

I would ask you to share with us what you mean by “unusual reactor and system issues” surrounding the use of well water as process feed water.

25362 brings up a good point. The type of Acetylene generator I’m familiar with is the Calcium Carbide-to-water type of generator – the type produced by the Rexarc company. I’ve heard about the possibility of having water-to-Calcium Carbide, but I wouldn’t try to operate this type of reaction because of the safety hazards involved in trying to achieve a “dry” residue product – it just isn’t practical from an operating perspective. A slurry product is considered much safer and easier to handle and process and a complete reaction is ensured.

I’d like to thank you for your comments and anxiously await your reply in order to perhaps learn something new that could avoid a potential hazardous situation in an Acetylene plant.


Art Montemayor
Spring, TX

 

[25362]

I fully agree with Art Montemayor's safety concerns.

Only for the records, as quoted from Chemical Process Industries by R. Norris Shreve (McGraw-Hill):

"For large-scale industrial applications "dry generation", a continuous process featuring automatic feed, is popular. Here 1 lb of water is used per pound of carbide and the heat of the reaction (166 Btu/cu.ft. of acetylene) is largely dissipated by water vaporization leaving the by-product lime in a dry, fairly easily handled state. Part of this can be recycled to the carbide furnaces. Continuous agitation is necessary to prevent overheating."

Kirk-Othmer's Concise Encyclopedia of Chemical Technology:

"Water-to-carbide generation is a method of limited use mainly employed is small acetylene generators, eg, portable lights or lamps where the generation rate is slow and the mass of carbide is small. A dry generator, water-to-carbide method is used in some large-scale operation and requires ca. one kilogram of water per kilogram of carbide and dissipates the heat of reaction through vaporization of the water. The dry lime by-product is considered to be favorable compared with the wet lime by-product."

 

[sigmaeng]

Response to questions.
we have been looking at the supply water as a source of unusual deposits in locations within the system that generally do not occur. In the locations noted this is producing adverse conditions within the distribution system and causing premature failure or fouling of hardware.
analysis at other sites suggest that the only item unique to this site is the water and general operation. When we perform more extensive analysis there will be more info to provide.

water analysis was just mentioned last week and site is currently working on that and will forward here for review.
Carbide supplied is same as others, ( there are only several sources still around) so we rule out so far the carbide.
It leaves water and op temp. as possible candidates

We consulted with OEM and they frankly didn't know what to say.

We have developed a number of saftey and performance upgrades for acetylene plants . Each site has unique requirements and upgrades are based on what a site operator is looking to do. Saftey upgrades and overall performance improvements in some systems are done together as a rule.

Saftey asside we can contribute these items--

OEM was advised about 1993 concerning compressor connecting rods on the model 9 and 18 that are being used that have copper clad bearings.
we continue to find them in the field on units rebuilt only a few years ago. Because of our familiarity with these systems we spec all rods here and insure this does not happen.

also recently on a site during a inspection of the flashback arrestors on the reactor, unions used had copper seats.

copper reacts directly with acetylene in a dangerous way.

we are replacing unions and seats with other hardware.
These were the origional factory hardware. Seats should have been replaced during production with brass or something less hazadarous. While it could be said that both seats and bearings pose little hazard, we are not inclined to take the chance.

Once we have a water analysis available we can provide more info on this particular issue. Hopefully it will help solve the question as to why our particular issue is occuring and if not the source lead the way to it.

note : another site uses recycled water, rain water, tap water urine, etc -- whatever is available without performance problems.
temperature of the process may hold the key.

K L.
Sigma Engineered Systems.

 

[Montemayor]

K L:

First and foremost, allow me to thank you for your generous and timely response to my request. I appreciate (as I’m sure all interested forum members do also) your time and effort in addressing the safety and operational issues on Acetylene generation.

For many years I led Acetylene production plants in what many here in the USA categorize as 3rd World or developing countries. My experience forces me to categorize all Acetylene operations as safety issues – even when shut down. Allow me to explain myself in order to qualify my subsequent points: In all my 44+ years of practicing as an engineer, I never had a safety fatality or injury under my command or responsibility. I was very lucky and fortunate for most of my operations personnel were illiterate and analphabetic. But they were hard-working, zealous, attentive, and dedicated to an honest work ethic. However, it was my tragic misfortune to return to two plants as a visitor to learn of two tragedies that occurred after I had departed. One of these tragic accidents happened to a favorite Acetylene operator that I had in Jamaica. Contrary to strict rules and instructions, he found himself in a situation where he was pressed for time and frustrated while de-scaling the interior of a Rexarc Acetylene generator down for maintenance and clean-out. The normal scraping tool (as you are well-aware) to be used was a wooden scraper while he was inside the generator, with the horizontal mixer removed. He was in an enclosed vessel whose walls were coated with residual, hard-caked calcium deposit. In order to proceed when his wooden tool broke, he resorted to employing a steel tool. Why he did this was never explained – the un-thinkable! He struck a caked-pocket of trapped Acetylene gas and it ignited into a fireball, with him enclosed inside the generator. He escaped with his life, but with terrible and painful 2nd and 3rd degree burns throughout his body. I returned to Jamaica 5 months after the incident and he was still in the hospital. This experience explains my unrelenting insistence on safety at all times when within the environs of any Acetylene plant. I have never allowed any maintenance around an Acetylene plant without strict supervision and safety procedures. This type of process doesn’t allow for any mistakes or oversights. It is unforgiving. Now lets discuss more safety items.

I agree whole-heartedly with your concern over unexpected solid deposits within your generator. I fail to understand how you can distinguish between the usual, expected “sludge” deposits and those contributed by the suspected water, but I assume you have identified them as such. I would particularly be wary of any copper compounds or deposits and would have a qualitative analysis of the suspected deposits made in order to make sure that every compound found in the generator is identified qualitatively. I wish you success in doing so.

I thoroughly agree with your rejection of copper-based connecting rod bearings in your Acetylene compressor. I’m assuming you’re using the usual Rexarc-type, 3-stage reciprocating compressor and not an old Norwalk, horizontal, 3-stage unit. For those readers not familiar with Acetylene compressors, the Rexarc-type has a crankcase pressurized with suction gas. Consequently, your concern for the potential of forming extremely hazardous copper acetylides is a valid one – in my opinion. I never allowed the use of copper or copper-clad bearings in the compressors because of the potential for acetylide formation. I always used babbit bearings. That is a major reason why I have always favored the use of a slow (50-75 rpm), rugged Norwalk machine that had the crankcase totally separated from the process and was open to atmospheric pressure. Unfortunately, like all good things, the Norwalk company ceases to exist anymore – a victim of modern mass-production and downsizing. However, I have seen used Norwalk Acetylene compressors for sale in compressor yards and on the Internet and if I found one now, I would grab it up.

You are absolutely correct with your observation that Rexarc uses cheap, common, “plumber”-oriented pipe unions on the LP gas exiting the generator. You are to be congratulated on being detailed and observant in spotting the copper seats in the cheap pipe unions. This is yet another point for concern in dealing with acetylene and is totally un-called for. However, the reality of the case is that Rexarc, like all suppliers and contractors, will employ the cheapest materials that they can “justify” when they are asked by users to bid or quote competitively on industrial equipment. By using cheap pipe unions instead of sturdy and dependable flanges, they are taking the steps to ensure that they offer the lowest price to be evaluated for purchase. What I always do is that I scrutinize their proposed supply prior to asking them for a competitive bid and then I specifically detail out those items that I insist (or demand) that they supply under my specifications – like the compressor bearings, the flanges, the welded piping instead of screwed, the required temperature and pressure alarms on the generator as well as the compressor, etc., etc.. I have found that when I take an active part in the specifications, the supplier is freed up to deliver a safer and more efficient piece of equipment.

I hope this experience and exchange of information is of use or interest to you in your operations and that you have ultimate success in identifying the present solids deposits within your generator.



Art Montemayor
Spring, TX

 

[sigmaeng]

A. Montemayor

Further discussion on water issue--
we as said before are working with a site we have done a number of upgrades that have helped them nearly double production with a nominal cost-- to their delight.
Anyway the water issue is something that is peaking my interest here because its causing headaches for them there. further I am personally beginning to correlate this particular issue with other problems , high pressure drop at the reactor outlet, failure of downstream components or problems. This is how we discovered the union issue.
the flashback check valves become fouled and do not seal effectively. eventually they are jammed open and become totally fouled.
Our do list on the next visit is to visually inspect the outlet inside the reactor for clogging.
On those check valves, we had some custom ones made that have teflon seats, stainless bodies and hard plastic poppets. of real interest is that we had socket heads welded onto the top retainers that allow for a snap- on locking extension to be used to install and remove. Makes for easier inspection.

rexarc quality--- no comment--

client had a new amonia scrubber installed and it arrived with broken internals. Either they were installed badly or the thing fell from a plane.-- I don't think the facory coughed up new parts. it also arrived with faulty wiring and pneumatics-- I know , I had to fix it.

compressor tank piping-- sent unthreaded, 50 years later you would think they know where to put the threads and bends.

item

on all our projects and rebuilds we install 4.5inch gauges at the critical points. the small gauges commonly used are not accurate enough for this individual.

In this particular case the lime buildup on the check valves is affecting operation and possibly reactor functions.
as said the water is the current suspect, only that in some way its components are reacting or combining with slury in a way that promotes buildup in places not normal.

When we return to the site I probably will personally have to climb into the reactor and see what is going on.
My personal rule is that when you have such a situation that defys analysis you take things apart until you find what you want.-- completely apart.

Note-
client had drive shafts locally made by a machine shop that could not tell the difference between stainless steel and stock steel. made for some short life parts.

last
we note that there is a trend to forgo maintenance on equipment and personell are less and less competent.
All makes for a bad combination, in any country.

Want a norwalk we got one and a NA7 reactor-- complete plant.

we currently have a couple of type M compressors in shop for rebuild -- going south.-- way south.
anyway far as we know we got the only parts available for these units. Have been told that there are more in SA

only seen a few.

if we get any data on water that is relevant will pass it on

question to you-- I heard from soneone that there is a stray molecule in the gas that occasionally causes explosions.

any data on this, never heard it before, know of a couple of incidents but mechanical or maint. related.

for your acetylene operators-- if the r19 is bled down incorrectly and check valves are not working correctly it will overpressure the crancase and blow the seal out of the front of the compressor. If the operator is not wary this could have some serious consequences

we also had an operator advise that he had 3 inch sparks eminating from his R19 oil canister and arcing to the belt guard. apparently somehow the oil pump and belt drive were acting as an electrostatic generator. --incorrect grounding or none. I figure that was about 500,000 volts


kl