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.