Sorry for the delayed response. I am not really up on NOx beyond I know it is a problem. From what I did see, it is from ammonia. In coal plants, they can take care of it in a secondary burn, if they can get the airflow right.
I think what you end up with is essentially a forge for a gasifier. Your producer gas is going to burn as well. You may have too much O2 in your hearth if you are getting that much NOx emissions according to what I read.
If it is ammonia, and my lame liquids attempt had ammonia smelling fumes to it, then that is easily absorbed in water. A water filter might do the trick, which would also cool the gas. A simple design looks like a moonshiner thump keg.
The enriched oxygen machine might be good for welding/cutting torch o2, while I am thinking about it.
What you seemingly keep inching towards is a fluidized bed reactor.