OT-why are propane converted gas stoves cooler?

Well, you use less propane -- the orifice is MUCH smaller. But I always thought a gas stove with 12kbtu burners had 12kbtu burners whether it was hooked to NG or propane. Go figger.

Grant

Yes, Grant, the orfices are much smaller for CNG. I've been looking for a long time to find out those sizes as I want to convert a nice little BBQ to natural gas and nobody can give me a size for the new hole. I'd think there's a formula or chart to use to go from a given size propane orfice to go to natural gas....

can anybody help?

TIA.... bILL

Try going to your local stove repair shop and look at orfices for propane and NG for the same stove. Bring your own drill set to measure the holes and establish the ratio.

Just take out your set of #60 to #80 drills and start with the smallest until the flame looks right. I did this for a camp stove that was made to run on propane at the tank pressure. With a regulator between the tank and stove the flame was quite small. Just going up one drill at a time it took about 30 minutes to get the right flame. ERS

On Fri, 10 Dec 2004 21:46:40 -0700, "Bill P" calmly ranted:

Call your local gas company or a conversion supplier and ask one of their technicians. Or google for an answer:

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This is about the best packet of info for this type conversion I've seen after a hours' cramming from the Google link. It relates back to other sites and info as well as a link on how to make a simple water column pressure guage. There is also a link to a chart to cross reference for orifice sizes as compared to WC pressures. There is even reference to multiple orifices and hybrid burners. THIS is an EXCELLENT SITE.

Thx again, guys!.... Bill

I like this plan. Since the above question was how to go from propane to NG, it should work well. Going the other way, it is easy to reach a point where the amount of air you can get into the burner and mixed with the gas limits how much you can increase the orifice size.

Pure methane (the major component of NG) has a stoichiometric air-gas ratio of 9.53 to 1 on a volume basis (the weight ratio is 17.2 to 1). For air-propane, you need 23.82 to 1 by volume, or 15.25 to 1 by weight.

The BTU/cuft for NG is 1012, and for propane is 2516, so you need only

40% as much propane by volume for the same output. Taking 40% * 23.82 / 9.53 gives almost exactly 1 - theoretically the same amount of air through the burner, with 40% as much propane, should give the same output.

Somehow in real life I've never found that to be true. NG is lighter than air and mixes well with it, but propane is heavier than air and doesn't want to flow up and out of the burner. Even though propane is delivered at much higher pressure, it doesn't seem to encourage airflow as well. The sizes of the holes where the mixture actually emerges at the base of the flame are as critical as the orifice - too small and the flame lifts off the burner and goes out; too large and the flame pops back through the holes and burns at the orifice making enough black soot to clog the burner.

Not only have I never reached equal heat output converting from NG to propane, I've usually run into serious usability issues that forced me to back off to even lower than maximum possible output.

Anybody out there understand why?

Loren

Loren... Isn't NG a bit heavier than air (N+O2)? Why does it collect in missle silos (sp) rather than float up and out when the doors and vents are open? Just wondering... Bill

Bill There appears to be too many variables to give you an answer. From:

"To select correct orifice size for rated burner input. The selection of a fixed orifice size for any rated burner input is affected by many variables, including orifice coefficient, and it is recommended that the appliance manufacturer be consulted for that purpose. Where the correct orifice size cannot be readily determined, the orifice flow rates, as stated in the tables in this appendix, can be used to select a fixed orifice size with a flow rate to approximately equal the required rated burner input."

But I think that there is enough information in that PDF file that you could get pretty close by comparing your existing orifice size. There are 32 pages of information and table for your perusal.

Hope this helps.

Lane

On Sat, 11 Dec 2004 13:35:42 -0800, Loren Amelang vaguely proposed a theory ......and in reply I say!:

remove ns from my header address to reply via email

makes sense, and it saved me the trouble....

I wonder if it's because propane is _not_ delivered at much higher pressures. BBQs etc have that regulator that really throttles things down. You get a propane heating torh that comes straight off the bottle and it has no trouble with burnback or blowout, and really belts out the heat. Also I have a propane-based instant gas water system, and it roars with gas and produces enormous amounts of heat. Again at a higher pressure, largely letting the orifice do the work.

One reason for the non match is Propane is very often Not Propane.

Liquefied Petroleum gas or LPG - is a mixture of a number of gases to make a general heat content of real Propane.

In warm states Butane is the word and they switch to LPG / Propane in the winter as it won't liquefy like Butane will.

My bet is the mixture.

Mart>

Well, I hadn't _really_ checked the exact numbers, so...

Air 1.000 Butane - C4H10 2.067 Ethane - C2H6 1.049 Ethylene (Ethene) - C2H4 0.975 Methane - CH4 0.554 Natural Gas (typical) 0.660

I think the answer to your question is similar to one of the comments about propane - "natural gas" can include a lot of heavier components along with the methane. For sure, the methane will rise out of the silo, but just about any other flammable component will stay down.

Loren

...

Standard pressure around here for regulated and piped propane service is 11" WC. The natural gas service I'm familiar with was between 4" and 5" WC. Other parts of the world may be completely different...

With a burner designed for propane, it is no problem to get a roaring fire. And you're right, they tend to make more noise than NG.

Loren

Now that you mention it, I have noticed the usability of my converted gas range changing with the seasons. At my home here in California it rarely gets too cold even for pure butane, but I guess my gas company delivers on the other side of the mountain with the same trucks, so they proably are changing mixtures.

Loren

Appreciate the info! I guess for the sake of limited paper space in the article I read some time ago, the author was either ignorant him self or had to cut down on article size hence making the statement 'methane gas collected in copious quantities missle silos and detection devices were mandatory....'

thx again Loren!!

Bill

I first got wind of it in Texas - Dallas area - winter gas and summer gas. The company name changed from xxxx Propane to xxxx LPG and that started the questions. Someone called them on the Summer gas that was weaker than the winter gas - non house use.

Martin [ bought his first 20 gallon tank there and now have a 30 for furnace ]

On Sun, 12 Dec 2004 18:07:26 -0800, Loren Amelang vaguely proposed a theory ......and in reply I say!:

remove ns from my header address to reply via email

OK. But I have a torch that runs straight off the gas tank, no regulator. I can't see why BBQ burners cannot be allowed to run LPG at a pressure that allows them to be as good as NG.

hmmm....I wonder if the burner design is the problem, and that's why LPG will either suck back or blow otself out. I was really supposing (am still) from limited experience. I look at the "ring" and "strip" burners that run from the tank via a regfulator and they are every slow.