NOVELTY - A catalytic reactor to catalytically react a feed stream and thus produce a product stream comprises at least one reaction zone located within a housing and having a set of reaction tubes to provide parallel flow paths for subsidiary feed streams. The reaction tubes contain a catalyst to promote a chemical reaction, and are of helical configuration and positioned in the coaxial arrangement to form a coil-like structure.    USE - The reactor is used to catalytically react a feed stream and thus produce a product stream (claimed). It is used for steam methane reforming followed by a water-gas shift reaction to produce a hydrogen rich synthesis gas product stream.    ADVANTAGE - The reactor is compact and the pressure drop through components is minimized. It has improved heat transfer characteristics and is far easier to thermally insulate than prior art compact reactor designs.    DETAILED DESCRIPTION - A catalytic reactor (1) to catalytically react a feed stream and thus produce a product stream, comprises a housing (2); at least one reaction zone located within the housing and having a set of reaction tubes (26, 34) to provide parallel flow paths for subsidiary feed streams composed of the feed stream; at least one reaction feed inlet in communication with the reaction zone to introduce the feed stream to the reaction zone; and at least one product outlet in communication with the reaction zone to discharge the product stream. The reaction tubes contain a catalyst to promote a chemical reaction within the subsidiary feed streams to produce the product stream. The reaction tubes are of helical configuration and positioned, at least substantially, in the coaxial arrangement to form a coil-like structure.    DESCRIPTION OF DRAWING(S) - The figure is a schematic, sectional view of a catalytic reactor.    Catalytic reactor (1)    Housing (2)    Sulfur treatment canister (14)    Reaction tubes (26, 34)    Reforming catalyst (27)    Heat exchange tubes (30, 86, 89)    Water-gas shift catalyst (35)    Cooler (42)    Burners (84)    Annular chambers (90, 92, 94)    Header chambers (112, 124)