NOVELTY - Reforming reactor for conversion of a process fluid into hydrogen, comprises reforming section (4) contained within a closed volume; boiler section (3); and combustion section (2). The reforming section contains catalyst tube(s) filled with reforming catalyst. The boiler section has flow channel(s), and the combustion section is provided with burner(s). The heat exchanging medium required for reforming the process fluid in catalyst tube(s) is a gas-liquid mixture that self-circulates and is encapsulated inside the closed volume, and portion(s) of closed volume protrudes inside boiler section.    USE - For the conversion of a process fluid into hydrogen to be used in industrial applications, e.g. metallurgical industry, chemical and pharmaceutical industry and fuel cell power plants.    ADVANTAGE - The reforming reactor has improved temperature distribution across all catalyst tubes. It is compact and free of mechanical components for circulating a heat exchanging medium from the high temperature section of the reactor to the reforming section of the reactor. It is able to rapidly and simply achieve or maintain its operating temperature after a change in process conditions, such as a change in hydrocarbon feed flow or temperature or a change in burner conditions or during a start-up operation. It is less sensitive to divergent catalyst packing across the catalyst tubes. It is simple in its construction, inexpensive and with lower heat loss.    DETAILED DESCRIPTION - Reforming reactor for conversion of a process fluid into hydrogen, comprises reforming section which is contained within a closed volume (8); boiler section; and combustion section. The reforming section contains catalyst tube(s) filled with reforming catalyst (5). The boiler section is provided with flow channel(s) for the passage of flue gas from the combustion section, and the combustion section is provided with burner(s). The heat exchanging medium required for reforming the process fluid in the catalyst tube(s) is a gas-liquid mixture that self-circulates and is encapsulated inside the closed volume and portion(s) of the closed volume protrudes inside the boiler section.    DESCRIPTION OF DRAWING(S) - The figure shows a schematic of the reactor where the passage of flue gas in the boiler section is diverted by baffles.    Combustion section (2)    Boiler section (3)    Reforming section (4)    Reforming catalyst (5)    Closed volume (8)