Boiler using combustible fluid

A fluid fuel boiler comprising, a combustion chamber, a cover on said combustion chamber having an opening for introducing a combustion supporting gaseous fluid through said opening, means to impart rotation to the gaseous fluid about an axis of said combustion chamber, a burner for introducing a fluid fuel into the chamber mixed with said gaseous fluid for combustion thereof, said cover having a generally frustro-conical configuration diverging from said opening toward the interior of said chamber at an angle of between 15.degree. and 55.degree.;

• means defining said combustion chamber having means defining a plurality of axial hot gas flow paths from a downstream portion of said combustion chamber to flow hot gases into an upstream portion of said combustion chamber, and means for diverting some of said hot gas flow along paths in a direction circumferentially of said combustion chamber, said latter paths being immersed in the flow path of said water thereby to improve heat transfer and terminating in a gas outlet, said combustion chamber comprising at least one modular element, joined axially to said frustro-conical cover and coaxial therewith, said modular element comprising an inner ring and said means defining said plurality of axial hot gas flow paths defining a plurality of axial flow paths disposed circumferentially spaced from each other and radially of each ring thereby radially of said combustion chamber, said modular element comprises said means diverting hot gas flow circumferentially of said combustion chamber, and the last-mentioned means comprising means defining a spiral flow path about each said ring.