Abstract: A furnace (10) includes a series of lower compartments (18) extending in a vertical arrangement, with at least one of the lower compartments (18) having one or more fuel nozzles (20) which tangentially fires fuel into the combustion chamber at an offset from a diagonal (DD) passing through opposed corners of the combustion chamber. At least one of the lower compartments (18) has one or more air nozzles (22) which tangentially introduces air into the combustion chamber along an offset direction which is offset from the diagonal (DD) to the same side as the fuel firing offset direction. The tangentially fired air and the offset fired fuel create a swirling fireball (RB) in the combustion chamber.

Abstract: A method of operating a solid fuel-fired furnace having a plurality of windboxes each having a plurality of compartments through which fuel and air are introduced into the furnace and a fuel and air arrangement operated in accordance with the method are provided. Solid fuel is fed into the furnace and primary air and fuel are fed through the same compartments into the furnace in a direction tangential to a first imaginary circle generally located in the center of the furnace so as to interact with the fuel fed into the furnace so as to create a rotating fireball. Overfire air and offset air are also supplied into the furnace, the offset air being that portion of the air supplied to the furnace so as to support a second imaginary circle concentric to, and having a larger diameter than, the first imaginary circle.