This subclass covers general aspects of, or methods for, steam generation. Methods of steam generation characterised by the form of heating method, constructional features of steam boilers, control systems for steam boilers and all component parts or details of steam boilers are covered. Thereby this subclass is limited in only methods of, or apparatus for, the generation of steam under pressure for heating or power purposes.

Steam engine plants where engine aspects predominate are classified in F01K, domestic central heating systems using steam are classified in F24D, heat exchange or heat transfer in general is classified in F28 and the generation of vapour in cores of nuclear reactors is classified in G21.

Attention is drawn to the definition of "steam" and "vapour". In cases where a specific entry for vapour is missing, documents related to special vapours are classified in groups where only "steam" is explicitly mentioned.

Methods of steam generation

Use of waste heat of combustion engines, in general, is classified in F02G, solar heat collectors per se in F24S, Heat pipes in F28D 15/02 . When steam is produced and explicitly mentioned as being superheated steam F22G should be consulted.

This covers all other methods of steam generation and steam boilers, which are not covered by the group F22B 1/00. These methods of steam generation and steam boilers include involving working media other than water, steam generation by drop in pressure of high-pressure hot water within pressure reducing chambers, by transformation of mechanical (kinetic) energy into heat energy and steam generation at critical or supercritical pressure values.

Methods for superheating steam are classified in F22G

Steam boilers containing a closed vessel designed to withstand internal pressure for generating steam. The drum is contacted externally by flue gases. The group also covers old documents (state of the art, which basis is not up to date, for example basic techniques used at the beginning of the 19th century) with big rotating drums, documents with auxiliary water tubes outside the boiler body and components and accessories of the drum.

Covers or similar closure members are classified in F16J 13/00

Boilers in which combustion of fuel is performed inside one or more furnace-tubes running through a sealed container of water. Combustion heat is transferred through the walls of the tubes by thermal conduction, thereby heating water and creating steam. The group also covers steam boilers of furnace-tube type with auxiliary water tubes inside the furnace tube and outside the boiler body, with auxiliary fire tubes and component parts of the boiler, like for example walling of flues. Components and accessories of the furnace-tubes itself are classified in F22B 37/06.

The following types if steam boilers are covered by the following classification schemes:

Steam boilers with drums having a furnace tube or a furnace box also in combination with drums contacted externally with flue gases should be classified in F22B 7/00 and F22B 13/005. This applies also to boilers with special shape of furnace tube and subsequent flue.

Boilers in which hot flue gases from a combustion chamber outside the boiler body said body being a sealed container, are channelled through tubes built-in the boiler body that are surrounded by the fluid to be heated. Heat of the gases is transferred through the walls of the tubes by thermal conduction, heating the water and creating steam. This group covers also arrangements of the fire-tubes and the boiler as well as components of the boiler itself.

The following types if steam boilers are covered by the following classification schemes:

In this group boilers which are mainly of fire-tube type are classified. If the boiler contains also water tubes, the boiler is considered of being a combined fire-tube and water-tube boiler. Concerned documents should be classified in F22B 11/00.

All combinations of the steam boilers of fire-tube type with steam boilers of water-tube type consisting of a fire-tube boiler with auxiliary water tubes or a water-tube boiler having auxiliary fire-tubes in a water or steam containing vessel. This group covers also boilers with fire-tubes being in upright and horizontal arrangement.

The following types if steam boilers are covered by the following classification schemes:

Boilers in which combustion of fuel is performed inside a chamber called fire box and fire tubes of flues being attached to the wall of the fire-box and carry the hot gaseous products of combustion through the boiler water, heating it, before they escape to the atmosphere. Both, the fire-box and fire-tubes are built-in in the boiler body. This group covers locomotive boilers, fire-box boiler with flues other than fire-tubes and component parts of said boilers.

The following types of steam boilers are covered by the following classification schemes:

Details and constructional features of water tube boiler in which water circulates in tubes heated externally and characterised by strictly horizontal arranged water tubes or water tube walls. If the water tube sets are inclined slightly with respect to the horizontal plane, than group F22B 17/00 should be considered.

The following other types of steam boilers are covered by the following classification schemes:

Details, constructional features and component parts of water tube boilers in which water circulates in tubes heated externally and characterised by horizontally-inclined water tubes or water tube walls.

If the water tube sets are inclined horizontally, then group F22B 15/00 should be considered.

The following other types of steam boilers are covered by the following classification schemes:

Details, constructional features and component parts of water tube boilers in which water circulates in tubes heated externally and characterised by horizontally inclined water tube sets being connected to or having also an auxiliary water tube set with vertical or substantially vertical water tubes.

The following other types of steam boilers are covered by the following classification schemes:

Details, constructional features and component parts of water tube boilers in which water circulates in tubes heated externally and characterised by vertically or substantially vertically water tubes or water tube walls. This group covers straight water tubes and serpentine, helical bent in U-loop or spirally formed water tubes disposed vertically.

The following other types of steam boilers are covered by the following classification schemes:

Details, constructional features and component parts of water tube boilers in which water circulates in tubes heated externally and characterised by sets of spaced double-walled water tubes of return type in unilateral abutting connection with a boiler drum or with a header box forming for example an annular flow.

The following other types of steam boilers are covered by the following classification schemes:

Details, constructional features and component parts of water tube boilers in which water circulates in tubes heated externally and characterised by sests of water tubes with internally arranged flue tubes or fire tubes forming thereby an annular flow of the water to be evaporated.

The following other types of steam boilers are covered by the following classification schemes:

Steam boilers of fire box type are classified in F22B 13/00.

All steam generators and steam generation methods with an instant steam generation process including flash steam boilers. The group covers instantaneous steam boilers built up from fire tubes, from water tubes, from rotary heat-exchange elements or from heat-exchange elements arranged within a confined chamber having heat retaining walls and steam boilers with spray nozzles for sprinkling or injecting water particles on to or into hot heat-exchange elements.

Steam boilers in which means are provided, such a pump in order to ensure the flow of the working medium. The group covers details, component parts and arrangements of steam boilers of forced circulation type, steam boilers of combination type in which natural flow (convection circulation) is promoted by additional measures and boilers of once through type in which flow is forced (forced ounce through boilers).

Water tube boilers of horizontal type (F22B 15/00) are normally steam boilers of forced flow type and Water tube boilers of vertical type (F22B 21/00) are normally boilers of natural convection type.

In subgroup F22B 29/06 steam boilers of once through type are classified. Even it is not explicitly mentioned said subgroup covers forced once through boilers.

Modifications of boiler construction or of tube systems dependent on the installation of combustion apparatus like

Chemical or physical processes in general, conducted in the presence of fluids and solid particles and apparatus for such processes are covered by B01J 8/00. Fluidized bed combustion apparatus per se are covered by group F23C 10/00 and fluidised bed furnaces by group F27B 15/00.

Steam generation plants in the meaning of devices for the generation of steam with other apparatus in mutual association with the steam boilers. Steam boilers of different types in mutual association having a single combustion apparatus in common, like combinations

self contained boilers comprising as a unit the steam boiler, the combustor and fuel storage accessory machines,

combinations of low and high pressure boilers and

combinations of steam boilers with other apparatus, like a condenser, a chemical reactor or other are also covered.

Steam engine plants related to the thermodynamic cycle and focussed in power generation are classified in F01K.

The following types if steam boilers are covered by the following classification schemes:

Documents which contain a boiler of combined water tube and fire tube type should be classified in F22B 11/00. Subgroup F22B 33/08 covers steam generation plants comprising several boilers having a single combustion apparatus in common where at least one boiler is a boiler of water tube type and at least an other is a boiler of fire tube type.

Control system of steam boilers in general like control by flue gas dampers, control by recirculating flue gases, control systems for steam generators of nuclear power plants, control systems for instantaneous steam boilers, control systems for waste heat boilers, control systems for two or more steam generators, control systems for steam boilers with natural convection circulation and control systems for steam boilers of forced flow type.

Documents related to control of nuclear power plants are classified in G21D 3/00, to control of nuclear reaction in G21C 7/00, control of steam engine plants in F01K 13/02, to control of feed water heaters in F22D 5/00 and control of superheat temperature in F22G 5/00.

Component parts or details of steam boilers categorised in three groups:

The group, which is applicable to more than one kind of steam boiler and which could be applied also to nuclear steam boilers, steam boilers of pre fabricated elements, instantaneous type boilers and forced flow type boilers, covers:

Working or processing of sheet metal or metal tubes are classified in B21D, pipes, joints and fittings for pipes in F16L and cleaning of internal or external surfaces of heat exchangers in F28D.