Abstract: A combustion method in which heat is generated from particulate laden combustible gas containing mineral matter created from gasifying waste wood, coke or other combustible material in which the waste is fed into a pile, under-fire combustion air dries and gasifies the waste, oxidizing the fixed carbon in a first chamber to generate heat at a temperature less than the melting temperature of the non-combustible material so as not to form slag, adding air in the first chamber in an amount less than stoichiometric with the air introduced in a swirling fashion to move the particulate laterally away from the discharge of the primary chamber, impeding the movement of this particulate also by adding secondary combustion air in a downward swirling direction in the secondary chamber so that very little non-combustible material reaches the second chamber where melting can occur.

Abstract: A combustion apparatus having primary and secondary combustion chambers burns waste wood with an optional third chamber. The third chamber is used to blend the combustion products down to the desired process temperature. High pressure swirl air is admitted tangentially to the primary chamber above a burning fuel pile. The swirl air reacts with a small proportion of the pyrolized gases to maintain a steady temperature at the exit from the primary chamber. The swirl air also centrifugally separates particulate matter from the gas stream leaving the primary chamber. The total quantity of underfire and swirl air is closely controlled to maintain substoichiometric conditions in the primary chamber. Secondary air complete combustion of the pyrolized volatiles in the secondary chamber. The secondary air is admitted tangentially to establish a rotating mass of relatively cool combustion air adjacent to the walls of the secondary combustion chamber.