MissOP
At my house, we have biogas we burn. I was wondering if there was a biogas design to make a biogas forge or Foundry?

thank you for your time.
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Skarzs the Cave Troll
That's an interesting question. Unfortunately, I don't have an answer. . .
My guess would be that it's the same as a propane design, provided the pressure is the same, though maybe a forced air would be better. However, it looks like the BTUs produced by biogas is much less than propane.
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Hank Rearden
I wonder if there's a college that might have plans on something like this. I remember coming across something a few years back before starting this forum. old or ancient technology was the subject matter of the lessons. I'll try to see if I can remember or find a link.   
code[Maglio.gif]  Keep the fires burning hot!
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MissOP
the pressure would be less than propane. so the question would be can I get biogas up to the same pressure as propane. If that is safe. Or if there is another way for example using more streams.
 
I will also look into ancient designs. 
 
We don't have tons of trees at this point. I don't have a coal or charcoal supply. I figured if propane was my only option. Biogas might work better since we already use biogas.
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jmccustomknives
You would have to build a blown forge.  They require less pressure than a venturi style burner.  Getting the volume of gas/air mixture right will be important.  Will you be able to reach welding temps?  Idk. 

Rule #10;  "I can make that" translates to; "I'm to cheap to buy it new."

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MissOP
Thank you for the direction to look into for plans. 
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Skarzs the Cave Troll
Good luck. Keep us updated on what you can find!
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MethaneMan
So I can help a little with the biogas questions. In short, yes you can fire forges with biogas - we do it all the time. But getting the pressure and quantity you'll need will be the tough part.

We use biogas from a closed landfill to fire forges, a foundry, and glass furnaces - and that makes it a lot easier for us. Our smith can reliably make damascus with any of our forges, and they're ready for working (1700F) is under 10 minutes. We use forced air blowers from Kayne and Sons on our forges, along with ribbon burners from Essential Craftsman, which both do a bang-up job. We try to run the gas system at 32 iwc pressure, or just over 1 psi. By my best guess, our forges only use about 3 or 4 cubic feet of gas per minute. And our gas from the landfill runs at about 70% methane.

Biogas from a digester is usually only about 50% methane, and the rest is CO2. Pure methane is roughly 1,000 Btus per cubic feet. So 500 Btu for a cubic foot of biogas. If you've got an idea of how much heat you need for your forge (based on how much propane you burn), you can backtrack and figure out how many cubic feet of biogas per hour you'll need.

We have a little digester to make biogas as well, but it doesn't hold nearly enough gas to forge with - we use it to make tea. You can buy really big gas storage bags (like 500 or 1000 cubic feet), and place sandbags on top of them to create a pressure. Conversely, I've seen simple things like tarp-covered swine lagoons, and inverted floating tanks, being used to store gas at low pressures. You *may* be able to compress the raw biogas, but mixed gases don't compress well - plus the damp gas will rust out your storage tanks in no time, so I haven't tried that yet.

So getting the volume and pressure of the gas you need from a small digester will take some tinkering. But know that if you get it right, it will absolutely give you a hot enough fire to forge with. Good luck!
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