Alternative Heat Source

Hi,

Has anyone considered using acetylene at low pressure generated from a system similar to old bicycle lamps?

Regards,

SFF

Calcium carbide up to £20/Kg, may be classed as hazardous for shipping purposes? Acetylene burns in air with a very smoky flame, or a very hot one if supplied with enough oxygen, which might melt the fitting! Decomposition is catalysed by copper and brass. When generated from carbide can include impurities of phosphine and arsine - nasty.

Camping gaz sounds more practical - cheap, easily available, relatively safe, use wide range of fittings.

Other than an old bicycle lamp, what did you have in mind to use it for?

Jim

Question being under "live steam locos" may be a clue.

Not a new or daft idea at all - the technology exists. Basically a giant acetylene lamp, except the gas can be used for brazing etc as well as lighting. Most used in places where cylinders and refills aren't readily available. The photo below is of an acetylene generator in Bali. I copied it from the Wikipedia Article on Acetylene.

Main downside is carbide generated gas is considerably more expensive than a cylinder. Generators used to be common in the UK before a safe way of storing acetylene was discovered. Once that happened generators disappeared quickly. Not only is cylinder acetylene cheaper, it's easier to use, which pretty much did for acetylene generators in most of the world. In their turn Acetylene cylinders have also become much less common due to the march of technology - a great deal of welding is now done with electricity.

Dave

Over the years including the first one (1898) there have been plans for acetylene generators in the ME magazine.

In the early days of NZ acetylene was quite popular for household lighting. At the small country school I spent my 4th Form year at we had an acetylene generator to supply gas for the Bunsen burners in the science lab.

Ian S C

It was once common for factories to have a central generator and a piped supply to work-places. It needed scrubbing to remove dust, and only provided low pressure. Old books on welding usually describe such setups.

Niall

I grew up in Malaya during the 50’s and remember the night time street markets where stall holders used acetylene lamps fuelled with carbide for illumination, had a very distinctive smell, once smelt never forgotten.

Dave W

The factory I worked in used to make their own acetylene until the plant blew up, they then switched to bottles on a manifold and piped it round the plant. As an apprentice we spent a week on gas welding and the first task of the day was to check the water trap used to prevent flashbacks. A contractor extending the distribution system forgot to fit a separator plate when they pressure tested the extension with compressed air and blew the system up again, one of the fires took out a 200 pair phone cable which cut the body shop off from the rest of the plant for a while. Acetylene is not stuff to play with in my book.

Mike

As mentioned above copper fittings and acetylene are a big no no, our welding instructor told the story of someone who joined an acetylene hose with copper pipe, to check that it does form explosive salts they put it on an anvil and hit it, it blew the head off the hammer.

Mike

Acetylene is indeed tricky stuff. If the pressure is too high it will spontaneously decompose, even if there is no oxygen present. This is why it has to be supplied dissolved in acetone.

Recently someone here in New Zealand decided that he could come up with a one bottle welding setup, and somehow managed to get oxygen into an acetylene bottle. The resulting explosion killed him.

I used to have both oxygen and acetylene in the shed, but gave it up because the prices were getting a bit high and I don't actually need it all that often. If I do find I need it for something, I will just hire the bottles short term and take the bottles back afterwards. It is not something you want to store near your house.

As has been mentioned, it can be generated on the spot as and when needed, but I would want a proper system, not just something lashed up. As mentioned above, the pressure on the acetylene must never get too high. The material safety data sheet makes for sobering reading, including such gems as "Never open the valve with no regulator attached. The gas may spontaneously ignite..."

A lot of what we need as model engineers can be achieved with oxy propane, a much less threatening combination, although still not to be taken lightly. .

John

I well remember a night about 65 years ago in Dunedin (NZ)One of the wharf sheds across the harbour from where we lived went on fire, there were about 200 acetylene cylinders, and some other types, from where we were watching, there were flaming trails arcing up over the water, then came the bang (of course the bang came first, but speed of sound and all that), it was much better than any fire works. The fire had to be left to burn its self out, and fortunately the cylinders were all projected away from the city.

Ian S C

If you are contemplating using Acetylene as a gas to heat your workshop, my advice is DON'T!

If you choose to ignore the safety considerations mentioned above, burning any hydrocarbon, (and Acetylene is one of the simplest), the products of combustion will be Water Vapour and either Carbon Dioxide (if you have sufficient air, or Carbon Monoxide if you haven't).

All are bad news; the Water Vapour will cause rusting, and the oxides of the Carbon will either smother you, or poison you.

Do not use any form of heating involving combustion in the shop. Hot water radiator(s) from the Central Heating system is the best alternative where electric heating is not feasible. But without electricity, powering your machines becomes an interesting, but not insoluble, problem.

Howard

Howard, you might want to read and reconsider what you just wrote. It isn't end of March/beginning of April yet, is it?

Mark, your posting puzzles me. I do not want to start a long running argument, but am really puzzled.

Admittedly, my knowledge of organic Chemistry stopped at Scholarship, or Inter BsC level.

As far as I know, Acetylene (CH2) is the simplest hydrocarbon.

Oxidising the Hydrogen will produce water, (Maybe a tiny amount of Deuterium - but of minimal interest, unless you wish to moderate a nuclear reaction)

Oxidising the Carbon with a full supply of Oxygen will produce Carbon Dioxide (CO2)which will not support mammalian life.

Restricted Oxygen supply results in Carbon Monoxide (CO) which is poisonous. the mechanism is that it combines with the haemoglobin in the blood to form Carboxyhaemoglobin, which is stable.

On the other hand, Oxygen combines to form Oxyhaemoglobin, which is unstable. This feature allows the blood to transport Oxygen to the lungs, and to other parts of the body which need Oxygen to function.

(The mammal body is basically an internal combustion system By oxidising the hydrocarbon food intake, energy is produced, with Water and Carbon Dioxide as waste products. Don't ask about the Sulphur content!)

So what did I get wrong?

As an aside, the Acetylene produced by dripping water onto commercially available Calcium Carbide is likely to be quite impure.

Machines can be powered by an external engine, via lineshafting, or locally produced electricity; or even by treadle power. A lot of early Drummonds were powered this way!

I am sure that many posters and readers on the Forum will advise against combustion heaters IN the workshop, for the reasons already set out. If you are a Health and Safety addict, leakage of flue gases could prove fatal.

Howard

Nothing wrong with what you are saying, Howard, although I suspect you lost him after the first sentence. Heating by burning hydrocarbons produces a lot of water and there is the risk of CO poisoning. Not clear why anyone would choose to use carbide of all things.

On another front, in many ways it's like lighting a fire - it takes ages for the carbide to stop producing acetylene and you can't store the gas safely. Hardly convenient or safe.

Murray

The point of the question is that no one, however rich, would consider heating their workshop with acetylene! The OP was not talking about that. I thought the hint was obvious...

As far as using acetylene as a source of heat for brazing, welding, heat treatment etc. It will produce less water vapour than any other gas you can obtain.

Oh, and it's C2H2

Edited By Mark Rand on 05/10/2018 22:43:41

Muzzer and Howard are victims of getting the wrong end of the stick over acetylene heating! I sympathise because I've just done exactly that over on the 3-flute drill thread. Somehow I missed the original posts very clear mention of DRILLS and went off on one with an answer about MILLs. Only spotted my blunder when it was too late to edit it.

We are all human.

Like Mark I thought Howard was pulling our legs by suggesting a workshop might be heated with acetylene. It would make a good April 1st joke for MEW! Even apart from the high cost, acetylene is perhaps the most inappropriate gas you could use for heating a workshop.

Although acetylene burns at a very high temperature making it ideal for cutting and welding steel, the gas has a low heat value. Compared with propane, butane, oil or coal it's a very poor choice for general purpose heating. Also, because acetylene has four different ways of causing accidental explosions, it's dangerous to handle and insurance companies will increase your premiums, or refuse to pay up after a disaster if you're not explicitly covered. Then there are the complexities of managing carbide generators or cylinders that must be stored up-right and which require particular fittings. Plus finding a heater that doesn't include brass parts that won't melt when you fire it up.

Finally if you do have a fire involving an acetylene cylinder, the fire brigade will enforce a 200 metre exclusion zone while they render it safe. Until recently, the 200 metre exclusion zone was maintained for a full 24 hours after cooling. In an example of Health and Safety going mad in reverse, today the brigade will cool the cylinder for an hour, and approach after leaving it alone for another hour. This still leaves plenty of time to explain yourself to the neighbours!

Some of what's unsafe with acetylene is counter-intuitive. For example, if a small fire heats a cylinder briefly before being put out, I'd have guessed venting the cylinder to reduce pressure was a good idea. Apparently not - in those conditions a sharp reduction in pressure can trigger polymerisation. Bang. Acetylene is safe when used as intended, and way dodgy if you take the piss!

If after all that you still persist in heating your workshop with acetylene, then Howard's advice is also correct, but by that stage a bit of rust is only heaping dust upon the bones.

Dave

In South Africa we had a a bottle catch fire, the foreman got one of the native labourers to put a sling around it and the crane driver dropped it in the boiler pond. As far as I know it's still there!

You only need acetylene in the workshop if you are gas welding steel or ali. Everything else can be done with propane.

Going by the section of the forum this thread is in I don't think Fred was asking about workshop heating, but heating for a steam boiler, in which case a bunsen burner could be used(no oxygen required) used, but I would say DON'T. Use LPG or similar bottled gas, it has more heat(BTUs) and is much safer, and easy to get.

Ian S C