Abstract: A boiler which is designed to be fired by oil and/or gas comprises a water cooled combustion tube closed at one end and located within a water space of the boiler, is connected to a solid fuel fired boiler by an auxiliary furnace having a combustion chamber with means to introduce solid fuel into the combustion chamber, and an opening in the wall of the combustion chamber, the opening having an extension nozzle extending therefrom whereby hot gases may pass from the extension nozzle of the furnace into the combustion tube of the boiler at a position intermediate the ends of the combustion tube.

Abstract: A grateless furnace has a combustion chamber, means to introduce solid fuel into the combustion chamber and to permit said fuel to form a fire bed in the bottom thereof, the combustion chamber being of such configuration that slag formed during combustion of the fuel accumulates under the influence of gravity, at a low part of the bottom of the combustion chamber, said low part having an opening through which said slag may pass for removal from the furnace. The bottom of the chamber may be V-shaped.