Biomass-fueled furnace

A biomass-fueled furnace for burning dry, green, or wet biomass fuels, such as logs, wood and brush chips, sawdust, nut shells, peat, and biomass waste products of agriculture and industry, at high temperatures and high combustion efficiency, comprising:

• a gravity feed hopper into which the fuel is charged;
• a grate system below said hopper upon and between which the fuel rests, said grate system comprising several hollow grate rungs and interconnecting channels through which combustion air travels, thereby preheating said air to aid drying and igniting of said fuel and cooling said grate system to retard the formation of ash slag and the deteriorating of said grate system;
• a fully insulated ignition/pyrolysis zone into which the preheated air enters through holes in said grate system and passes in a generally horizontal path through said fuel resting on said grate rungs, thereby drying and igniting said fuel and liberating combustible gases;
• a ceramically insulated secondary combustion chamber, laterally connected to the ignition/pyrolysis zone and capable of withstanding operating temperatures of at least 1500.degree. F., the secondary combustion chamber insulation enabling secondary combustion of the evolved gases at temperatures above 1200.degree. F., said secondary combustion chamber being partitioned by at least two substantially horizontally disposed baffles which effectively mix the preheated air with said combustible gases while allowing them to alternately travel horizontally and upwardly as they mix and burn;
• and
• a secondary combustion chamber air inlet including damper means for controlled delivery of additional preheated combustion air directly into the secondary combustion chamber without passing through the fuel charge.