Subclass : METHODS OF STEAM GENERATION; STEAM BOILERS (steam engine plants where engine aspects predominate F01K ; removal of combustion products or residues, e.g. cleaning of the combustion contaminated surfaces of tubes of boilers, F23J 3/00 ; domestic central-heating systems using steam F24D ; heat exchange or heat transfer in general F28 ; generation of vapour in the cores of nuclear reactors G21 )