NOVELTY - The exchanger reactor for implementing strong endothermic reactions such as steam reforming reaction of natural gas or naphtha to produce hydrogen, comprises a cylindrical grille (1) of which an upper part is closed by a ellipsoidal cap (2) and a lower part is closed by a ellipsoidal bottom (3), a reactant inlet and an effluent outlet arranged in an upper part of the reactor, a heating zone, and a fume circulating zone. The cylindrical grille is enclosed by vertical bayonet-shaped tubes with a length (Lt) extending along the grille.    USE - The exchanger reactor is useful for implementing strong endothermic reactions such as steam reforming reaction of natural gas or naphtha to produce hydrogen.    ADVANTAGE - The exchanger reactor is compact, and has a high capacity for producing hydrogen in a range of 500-10000 Nm2/hour.    DETAILED DESCRIPTION - The exchanger reactor for implementing strong endothermic reactions such as steam reforming reaction of natural gas or naphtha to produce hydrogen, comprises a cylindrical grille (1) of which an upper part is closed by a ellipsoidal cap (2) and a lower part is closed by a ellipsoidal bottom (3), a reactant inlet and an effluent outlet arranged in an upper part of the reactor, a heating zone, and a fume circulating zone. The cylindrical grille is enclosed by a vertical bayonet-shaped tubes with a length (Lt) extending along the grille, where the tubes have an end connected with an exterior of the reactor and are heated by a porous burners without premixer. The burners have a length (Lb) vertically extends between the tubes to be heated. Reactants circulate in an interior of the tubes. A ratio of Lb/Lt is 0.2-0.7. A distance between the porous burners and the tubes is 100-500 mm. A ratio of height (H) of the reactor and its diameter (D) is 2-8. A fuel distributor in the porous burner is present in a lower part of the reactor. The heating zone is equipped with a baffle so that a circulation speed of fuel fumes along the tube to be heated is 20-50 m/s. A number of tubes to be heated per m2 of an effective section of the reactor is 5-13. The tubes form a triangular pace with a distance of 2-4 times an internal diameter of an external envelope of the tubes. A deflector plate (14) is located in an upper part of the fume circulating zone at a distance of 5 cm with respect to a protected tubular plate. The fuel used in the porous burners contains hydrogen in a molar proportion of 5-100%. A porous element of the burners has a porosity of lower than 30%. A central distributor of the burners is divided in two sections of which each section has a diameter opening increasing with an axial distance along the distributor in a direction of fuel flow. An INDEPENDENT CLAIM is included for a steam reforming process.    DESCRIPTION OF DRAWING(S) - The diagram shows an exchanger reactor.    Cylindrical grille (1)    Cap (2)    Bottom (3)    Vertical tubes (4)    Deflector plate. (14)