Compressed CNG Gas Forge

[daniel17319]

Wondering if you can use compressed natural gas in a propane forge.

 

thanks

[timgunn1962]

There seems to be no technical reason why not.

It will get hot enough for anything you are realistically going to want to do with it: Wikipedia gives adiabatic flame temperature as 1960 degC/3562 degF for Natural Gas and 1963 cegC/3565 degF for Methane vs 1980 degC/3596 degF for Propane.

NG composition is actually pretty variable, depending on the source, and it might be worth getting hold of the specs from your suppliers to see what sort of range you might expect to see. Be warned though, the specs they'll provide are usually little more than a heat value per unit volume.

The biggest problem with using Natural Gas in a forge is usually down the low pressure available on the mains gas supply and that simply isn't a problem with CNG.

You'd need to see what sort of hoops you'd be expected to jump through to meet local safety codes though. I get the impression that, where a lot of stuff on LPG got grandfathered into safety legislation worldwide because it was already widespread, CNG seems to have been pretty unusual until quite recently and therefore got the latest gold-plated safety standards applied in many jurisdictions.

 

[Mikey98118]

So, "Wikipedia gives adiabatic flame temperature as 1960 degC/3562 degF for Natural Gas and 1963 cegC/3565 degF for Methane vs 1980 degC/3596 degF for Propane huh"?

With an oxygen fed flame maybe, but not with air. These figures are for an adiabatic  flame, which is a concept use to help scientistsand engineers to play with formulas; not for builders to deal with equipment in the real world; slash those figures in half and it will actually work there.

What is said to happen with methane combustion, is is a partial recombination of the combustion products, which cools down the flame quit a bit. Do i know that is the problem for sure? Nope; what I do no for sure is that methane is rated at about 1/2 the practical heat output of propane. I also know for sure that air methane burners are utterly puny. 

[Charles R. Stevens]

Good to see your bi-line Mike. 

[ianinsa]

 

1 minute ago, ianinsa said:

It's good to see you online again Mike.  Just a question on the air/Methane being puny? I have a venture/rocket charcoal retort that really gives it stick! With blue flames at in excess of 8ft. Isn't that predominantly Methane /air? I'm interested and not disputing your assessment.

Regards Ian

 

[timgunn1962]

On 02/05/2016 at 7:11 PM, Mikey98118 said:

 

So, "Wikipedia gives adiabatic flame temperature as 1960 degC/3562 degF for Natural Gas and 1963 cegC/3565 degF for Methane vs 1980 degC/3596 degF for Propane huh"?

 

I appreciate that Wikipedia is far from being an authoritative source of information. However, it does have the big advantage of being accessible by everyone and I'd much rather give anyone who might be interested the opportunity to check whether I'm spouting complete drivel or not, than take values from a more authoritative text. I did check that the Wikipedia values agreed pretty closely with the values in the books I've been using for the last 25 years or so before posting.

 

On 02/05/2016 at 7:11 PM, Mikey98118 said:

With an oxygen fed flame maybe, but not with air. These figures are for an adiabatic  flame, which is a concept use to help scientistsand engineers to play with formulas; not for builders to deal with equipment in the real world; slash those figures in half and it will actually work there.

Those values are for adiabatic combustion with air. With Oxygen, the values are obviously higher. Wikipedia gives an adiabatic flame temperature of  2526 degC/4579 degF for Propane/Oxygen, almost 1000 degF higher than Propane/Air at 1980 degC/3596 degF, but does not give values for Methane or NG with Oxygen. 

I am not sure what you mean by "slash those figures in half and it will actually work there". Can you provide any further information or references? 

Using a type S thermocouple and pyrometer, I have measured forge temperatures in a couple of forges with Propane burners built to the designs in "Gas Burners for Forges, Furnaces and Kilns". One had been running at a nice forge welding temperature (making Damascus for blades) of about 1300 degC/2372 degF while in use and reached 1470 degC/2678 degF when we wound it up to maximum. That certainly seems to be considerably more than half the adiabatic flame temperature by any criteria most of us might use. 

On 02/05/2016 at 7:11 PM, Mikey98118 said:

 

What is said to happen with methane combustion, is is a partial recombination of the combustion products, which cools down the flame quit a bit. Do i know that is the problem for sure? Nope; what I do no for sure is that methane is rated at about 1/2 the practical heat output of propane. I also know for sure that air methane burners are utterly puny. 

 

Do you have any references for the partial recombination phenomenon? I have been unable to find anything online and I'm very interested.

Methane is much less dense than Propane, so its energy per unit volume is indeed about half that of Propane (measured as BTU/cuft, MJ/m3, etc). However, when measured as energy per unit mass (BTU/lb, MJ/kg, etc), Methane has a slightly higher value than Propane. 

I've been unable to find anything useful by googling "practical heat output", so it does not seem to be a recognized technical term.

 

Pretty much every NG burner I've seen has, as you say, been utterly puny, at least in forge burner terms. However, they have all been fed with low-pressure NG, where pressure is measured in inches of water column.

If we are going to compare Methane/NG with Propane, we really should at least compare the 2 gases at broadly similar pressures. 

Here in the UK, regulators for use with Propane BBQs have an outlet pressure of 28 mbar, or about 11" WC. Mains NG supply pressure to domestic uses is nominally 8" WC, so I think it's fair to say that the pressures are broadly similar. I gather the pressures are also broadly similar in the US. A forge burner running on propane supplied by a BBQ regulator also seems pretty puny. 

The OP was specifically asking about running a burner on Compressed Natural Gas, not domestic NG supply, so there seemed a good chance that low pressure would not be an issue.

[Charles R. Stevens]

High pressure taps are a avalable from your gas company (not an issue with compressed gas)

to further complicate the issue "natural gas" is not pure methane. It is a mixture of gasses. I was talking to a guy that works at the local natural gas refinery (15 miles up the road) and he told me that after they cut off (distill) propaine and other marketable gasses (and CO2) what they have left is the "natural gas" the sell to you. 

Sorry I didn't take notes, as he rattled off 1/2 a dozen chemicals. I'll try to catch up the next time we are training together, I think he is out of the Alex fire station. 

[Mikey98118]

Ianinsa,

Thank you; it's good to be back. It's mostly through the magic of Spellcheck.

The answer to your question is no. Charcoal is a complex chunk of hydrocarbons, which gives off various fuel gases during burning: I believe that the main gases produced are are hydrogen and carbon monoxide. I'm not sure you cold even obtain a reliable list of what all the combustible ingredients in charcoal, as they would change according to source..but they probable wouldn't contain much methane.

 

[Mikey98118]

Timgunn,

You are quite right, and furthermore I use it all the time for quick references too. BUT when you see someone casually spewing out facts and figures in this source, don't trust them for a New York minute! I don't buy what I read in real Encyclopedias without reservation. And after years of reading whoppers passed off as 'facts' when it comes to fuel sources, it is the last subject I would listen to without a very large grain of salt.

On the other hand, I wasn't very nice to you, and I apologize for that. It was the guy who wrote that double talk I felt angry with; not even the guy who got suckered into parroting that con job in Wikipedia.

"Do you have any references for the partial recombination phenomenon? I have been unable to find anything online and I'm very interested."

No; I'm sorry but I did that research seventeen years ago, after discovering how poor the results were from an air/methane heating torch at school. You see, I was one of those guys myself who wanted a magic low cost fuel to use for my own business plans, and so I understand just how frustrating it is to told "nice idea kid, but it isn't going to fly."

Of course the data is still out there, somewhere in cyber space, but it could take a long time to find it again, and once you did it would only be the same bald statements that I gave you.

I was satisfied with the explanation because of having encountered the puny effects in actual experience; that is the better research method, unless you can corner a combustion engineer, or other expert in the field so that you can listen to the explanation from an expert authority, which still amounts to taking it on faith There is a chemical formula for the process, which shows the recombination of some of the combustion by products; perhaps you can get a chemistry  guru to show you that from a book?

 

Charles,,

Yes, but, supposedly, the other gases only amount to two percent or less of the content, and supposedly, the rest is methane. However, as stated previously, take such "facts" with a large grain of salt

[Mikey98118]

I suppose that after dropping such a load of disappointment on the whole subject, the leased that's owed is a substitute possibility. And there happens to be one; it's called propylene; this is the fuel gas that finally put MAPP gas out of business. Why? Because it didn't have MAPP gas's instability as was within fifty degrees of MAPP gas's rated flame temperature.

Polypropylene, in regular industrial cylinders only costs about one-third more than propane to buy, and I estimate will put out an additional 600 to 1000 degrees  flame temperature over propane, depending on how good your burner is. Anyone looking for a better deal from their fuel gas might find it it here. For look to see that its low price in my market also applies in yours. Also, turn your burner down, or you will burn up your forge!!!

[Mikey98118]

timgun wrote 

"Wikipedia...does not give values for Methane or NG with Oxygen."

This casts an eye on the heart of the problem. Various railroads use natural gas to do torch work, including oxy-fuel cutting. At one point it was popular enough that a whoe class of special torch were built to use the high pressure oxigen feed to induct the low pressure natural gas into the cutting head in suficient quantities to run cutting operations on rail track. Some of these torches are still around today, but you can't find any numbers on methane burning in oxygen; the reason why is that  today it has no commercial importance.   

[Mikey98118]

timgunn writes

"Using a type S thermocouple and pyrometer, I have measured forge temperatures in a couple of forges with Propane burners built to the designs in "Gas Burners for Forges, Furnaces and Kilns". One had been running at a nice forge welding temperature (making Damascus for blades) of about 1300 degC/2372 degF while in use and reached 1470 degC/2678 degF when we wound it up to maximum. That certainly seems to be considerably more than half the adiabatic flame temperature by any criteria most of us might use."

It is pleasing to run across one more dependable indication that my old burner design runs as high as I think, since I'm just to reach to pay out for a laboratory evaluation.

But the figure I was talking about   has to include a lot of simpler burner designs, which just won't hit the  figures that you're enjoying. I consider those other designs to be a very important part of our  world. Frosty has taught me to respect the importance of the burner equivalent of the family car; yours are hot rods. Look up the final paragraphs to page  two in the Burner Design 101 thread to see where I'm heading with this.