Gas forge comparisons

[brian robertson]

Has there been any studies comparing venturi and blower propane forges in regards to btu and fuel consumption?

[Tom Oldsmith]

I did recently test. I built a new burner and tested the new furnace. For me, the results are obvious. Venturi and other atmospheric burners are worthless. The only advantage is the simplicity  construction, every kid will build burner  of tube 3/4 inches  :D

 

http://youtu.be/P0RrOrhSQZQ

[Frosty]

All such are nonsense. Propane has exactly x BTUs per cu/ft or 139,000 BTUs/liquid gl. . The stoichiometric (neutral) ratio is about 17.5 air to 1 propane. (17.5:1 air fuel)

 

It makes exactly zero difference in BTU output how you do the mixing, none at all. Where you do find the differences between naturally aspirated (NA) vs. gun burners lay in entirely different areas.

 

First is cost and ease of construction. Guns are EASY, cost more and are tied to electricity, NA burners are less expensive,  much harder to build and tune and will work as a stand alone.

 

Next, NA burners are a lot more sensitive to external conditions, breezes and back pressure most commonly. Guns don't much care so long as there's an exhaust port of some kind.

 

Absolute temp isn't an issue, either can reach temps to melt iron let alone steel so welding is no trouble once you learn to use them.

 

Interestingly enough, BTU/hr output is largely determined by the nozzle diameter, a gun can force a little more down the barrel than a NA can but not much.

 

So, here's how I usually put the difference. I can make a 3/4" NA burner that'll easily bring 700-750 cu/in to welding temp for about $9-$10. Regulator, hoses and tank fittings cost the lion's share regardless. A gun is really easy to build, virtually no precision required but will cost you the price of the right kind of blowe and you'll HAVE to have electricity on site to run it.

 

That help?

 

Frosty The Lucky.

[Frozenforge]

I also like the independent operation of the NA burner. You can also plumb in an idle circuit very easily with a NA burner and by turning 1valve can cut the fuel consumption drastically. Im not sure how easy that can be done with a gun type.

[BANAN]

 

Use both hands to subscribe to the opinion of Tom. Venturi burners are not suitable for professional use. Too little power and too capricious. The professional should forge furnace, which should work with a professional torch. As for the economy, the burners blow, either with the fan or the compressor render lower gas consumption and the ability to connect natural gas, which has a huge advantage over propane is cheaper, does not freeze and never missing during operation.

[ThomasPowers]

I don't quite understand why a NA burning 1 gallon of propane an hour is less efficient than a blown burner burning one gallon of propane per hour.  To get efficiency having a number of forges of different sizes will allow you to only be heating what you need to be heating.

 

As for natural gas---closest source is 10km from my shop and I don't even live in a remote area!

 

Very hard to compare forges/burners as the variables are almost never fully controlled.  Taking a propane forge to camping events with NO electricity for a km or two has meant that my NA forges get a lot more use than my blown forge; but when I need to heat a LOT of metal the larger blown forge/gas hog does the job like my NA ones can't.

[SJS]

Most BUGs (broad unsubstantiated generalizations) are wrong... a well built NA burner, in a well built forge will leave steel in a puddle if thats what you want to do... you can SIZE a NA burner and forge to do 3"breaker points, or melt cast iron or crucible steel... You just have to size the components and provide enough fuel. Most problems are operator error, ignorance, and a profound lack of patience;-) if a blown burner works fine for you, thats fine. But its not fine to say only an amatuerish idiot uses NA burners. There are lots of perfectly good answers if you ask the right questions. Most of the time there is not one right and true and Holy way proscribed by GOD!!! Most of the time there are several good answers that will get the job done safely. My way isnt the right way, its just my way. Your way most likely was not given to you by divine revelation, so lets not be dogmstic. It works for you, you understand it, and you can teach others, that good. But Forsty and others understand NA burners, have an easy time building and tuning, and helping others build them. They work. There is no accounting for taste, and everyone is entitled to their own opinion...

[BANAN]

But the question was about the difference in gas consumption. 11 pound cylinder of gas at the burner ejctor enough for me 8-9 hours. The burner air blower for 11-12 hours.

[Jack Evers]

Frosty is on the money. There is so much energy to be obtained from a unit of fuel with a proper air mix. That energy heats the combustion products to a given temp and it makes no difference how the mixing is accomplished..

[timgunn1962]

The OPs question was whether there have been any studies comparing Venturi and blown forges.

 

But the question was about the difference in gas consumption. 11 pound cylinder of gas at the burner ejctor enough for me 8-9 hours. The burner air blower for 11-12 hours.

 

In this case, you simply seem to be saying that your atmospheric burner uses more gas to achieve the same result as your blown burner.

 

This may be helpful information. I can't tell though, because you've not given any other information at all; a study would be expected to eliminate, or at least take account of, all the other possible variables.

 

One thing worth pointing out is that both Banan and Tom Oldsmith are apparently running on Natural Gas, presumably at a very low pressure. The low pressure is somewhat challenging for a Venturi design and is perhaps the only constraint under which I would tend to build a blown design in preference to a Venturi.

[basher]

I do not know of any studies.

 A good Venturi burner should be around the same gas consumption as a good blown burner in the same forge at the same temp IF the forge has the rite internal dimensions and enough exhaust to allow a Venturi burner to work optimally.

 most of the other advantages and disadvantages have been outlined above.

 I will add that you can but very good Venturi burners but pretty much have to make blown ones yourself.

[SJS]

Hopefully dodge will be willing to do some comparison with his T-burner and blown burner and see which one burns longer? You would think that they should use fuel at the same rate. But I supose that a blown burner could use less, but I would think you might have to run it lean...interesting???

[Bruno C.]

Not hijacking, just think it might be relevant?

 

I plan on lining my forges' tomorrow.    Building a Don Fogg style Vertical Forge that will use a 3/4" venturi, and a Smaller Horizontal that will run off a (home depot) 1/2" propane torch.     Flame me if I'm wrong, but I would think that all this talk of fuel consumption is relative to the design of the Forge.   I'm currently debating as to whether use 1" insulation in the Vertical forge, or 2" insulation.  The forge shell is built to be within the 350 Cubic Inch" Threshold of the 3/4" burner using 1" insulation, but I wonder if I'd get better results using 2".  

 

What are better results ?  

 

Providing I've made the forge correctly, then I would think that if I use 2" of insulation, that would lead to less gas consumption using a Venturi Burner, since I'd retain more heat in the Shell, and could run on a lower amount of gas vs. time at temperature (of forge).  If you lose much heat, then you need more heat to compensate, right ?  

I would think the same is true with a Blown burner.   Have not used one myself, as I appreciate the Lack of Electricity needed to run a venturi burner.   Got a full tank ,you good to go.    But even with a blown burner,  if you have a forge that is lined to 1" of insulation vs. 2" on insulation. Then the Forge using 2" of insulation would work better I think.  If you had 2 identical forges, one using a Blown burner, and one using a Venturi burner, then , from what I've read, the blown burner would beat it hand's down.  But again it's all relative.  If you had a forge that had say 3" of insulation running a venturi, and a blown burner running in a forge with 2" insulation, then maybe it evens out ?    Test's would have to be done.

 

Just think, a few cents on the dollar may help over 5 years, or if you deal in millions of money dollars it adds up.  Overall though, Maybe the cost in Extra fuel for a Venturi Design may Equal the Cost of Electricity needed to power the blower for a blown burner design.   Use what works for you because the science will always be different depending on you.

 

0.02 Cents.

[divermike]

By golly I sure love this site, seeing as how I have a couple of each, and really don't know that much about em, this sure is helpful.

[ThomasPowers]

2".  I had an amusing incident when I religned my blown forge with two inches of kaowool.  As the original 1" insulation had degraded I had been turning up the gas to compensate.  The regulator was thus set for the old insulation and I accidentally melted the stock into a puddle with the 2" insulation the firse time I used it.  I ended up turning the regulator way down to get the same heats as I was used to.

 

I also remember this when folks tell me that a propane forge doesn't get as hot as a coal forge---a puddle of steel sitting on a fire brick is quite indicative that it gets hot enough for me!

[Dodge]

Hopefully dodge will be willing to do some comparison with his T-burner and blown burner and see which one burns longer? You would think that they should use fuel at the same rate. But I supose that a blown burner could use less, but I would think you might have to run it lean...interesting???

 

I'm afraid I am at a loss here. I seem to remember posting to this thread, and I apparently must have based on your post, SJS. Unfortunately that post seems to have vanished and I don't remember what I said (I sometimes post late at night when I should be sleeping. :D )

 

That being said, after some though on a comparison study on my particular forges I could safely say they would not be the same consumption as the burner tubes are not equal in size. The blown, or gun, burner is 1.25" while the "T" burner is only 1". Furthermore, when I use the gun burner, while it uses the same gas supply tube as the "T", I generally change the mig tip orifice to a larger size for the larger burner tube; about .05" for the gun and .035" for the "T". Another factor is the size of the forge chambers themselves. They both have 2" of ceramic blanket (I used Inswool) covered by a refractory mortar for a rigidisizer. That is where the similarities end. The forge the gun burner was made for has an inside dimension of just under 15" long by 6" diameter. The forge chamber the "T" goes in is about 9" long by 5.5". In the end, it wouldn't be an equal test, however, I believe the gun burner, for the factors just mentioned must use more gas than the "T" burner.

[BANAN]

I conducted the comparison on the same overall dimensions burner at the same hearth. The differences are noticeable when hot stove when the mixture has to overcome a stream of hot gas pressure. In the burner venturi have little to increase gas pressure. In the burner of the ventilator simply add more air without changing the gas pressure.

[ThomasPowers]

The size of the tube should not matter that much you need to compare two burners with the same BTU output.

 

I could build a blown burner half the size of an aspirated one that used twice as much gas and produced twice as much heat!

 

This is what makes comparisons so difficult.  You really need to test how much fuel is used to raise a standard size test piece to a standard temperature in a standard time in the same forge.  *That* would be a measure of efficiency.