This is something similar, but too bulky for transportation. N2 free wood gas - #9 by MikeR
From other point - lets go wild and design an gasifier to work on charcoal-water slurry.
On low-tech side - plain charcoal gasifier + instead of recycled gas or steam for cooling, lets spray small amount of slurry + preheat air to help vaporizing water. It will spray and will give better distance than plain gasifier. How to calculate this - i do not know for sure.