I am building a forge that redirects the exhaust fumes back into the forge for a second burn following the wood gas generator principal.
Rocket mass heaters burn so hot that there is little smoke that comes out and the excess heat is trapped in the mass not wasting the heat. I've built one, they work. If your inner chamber is not firebrick, or well thought out, it can melt by burning just regular sticks.
Working on an electrolyzer to separate hydrogen and oxygen. HHO gas burns too hot (5100f max) to do most things with as it will make the metal brittle. But in the electrolysis phase, you can have the gas come out as just pure hydrogen and pure oxygen and I am going to channel in the pure hydrogen into the forge which burns at 1000f lower than the HHO gas. The FCHEA, fuel cell & hydrogen energy association has a list of some plants that moving away from coke to hydrogen to help fight carbon emissions.
