There are at least one misconception here that I can see (I work in gasification technology).
You only need the pure oxygen for producing enough heat to pyrolysize the fuel (wood/biomass), once it's broken down into tar gas, you can feed it through your charcoal layer to further reduce it into syngas. The syngas can then be burned at a separate space with air at a lower temperature where nitric oxides aren't created.
Utilizing the residual heat in the exhaust gas (flue gas) is another means of feeding the pyrolysis phase. As you mentioned its also a great source of CO2 and H2O as a feedstock for producing CO and H2 from the hot charcoal.
What I'd like to see happen is usage of the "waste" oxygen produced while producing hydrogen from electrolysis of water. The oxygen could be used to produce syngas, and the hydrogen could be fed into this fuel stream or used separately for off hour electricity production.
There is at least one misconception here that I can see. You don't need pure oxygen to initiate pyrolysis, combustion with atmospheric air is suitable to initiate pyrolsyis as well as gasification systems that pyrolyze biomass without any oxygen/combustion using electric resistive elements eg powered by solar pnaels if you want to learn more about gasificatoin theres soem great resources in the internet
You only need the pure oxygen for producing enough heat to pyrolysize the fuel (wood/biomass), once it's broken down into tar gas, you can feed it through your charcoal layer to further reduce it into syngas. The syngas can then be burned at a separate space with air at a lower temperature where nitric oxides aren't created.
Utilizing the residual heat in the exhaust gas (flue gas) is another means of feeding the pyrolysis phase. As you mentioned its also a great source of CO2 and H2O as a feedstock for producing CO and H2 from the hot charcoal.
What I'd like to see happen is usage of the "waste" oxygen produced while producing hydrogen from electrolysis of water. The oxygen could be used to produce syngas, and the hydrogen could be fed into this fuel stream or used separately for off hour electricity production.