NOVELTY - Reforming reactor for the conversion of a process fluid into hydrogen, comprises reforming section (4) and boiler section (3) which are both contained within a common volume and a combustion section (2). The reforming section contains catalyst tube(s) filled with reforming catalyst. The boiler section has tube(s) carrying 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 common volume.    USE - For the conversion of a process fluid into hydrogen to be used in industrial applications, e.g. metallurgical industry, chemical and pharmaceutical industry or 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, e.g. 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 construction, inexpensive and with lower heat loss.    DETAILED DESCRIPTION - Reforming reactor for the conversion of a process fluid into hydrogen, comprises reforming section and boiler section which are both contained within a common volume (8) and a combustion section. The reforming section contains catalyst tube(s) filled with reforming catalyst (5). The boiler section is provided with tube(s) carrying 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 common volume containing the reforming and boiler sections. An INDEPENDENT CLAIM is also included for process for the production of hydrogen from a feed process fluid in a reactor containing combustion section, boiler section and reforming section, comprising passing a preheated process gas through the reforming section; heating the catalyst tube(s) in the reforming section by indirect heat exchange with a gas-liquid mixture that self-circulates and is encapsulated inside a common volume containing the reforming section and the boiler section; retrieving reformed process gas from the reforming section and optionally cooling the reformed process gas by preheating the feed process fluid; introducing a fuel into the burner(s) in the combustion section together with combustion air, in which the combustion air is preheated by indirect heat exchange with flue gas from the boiler section; retrieving flue gas from the burner and passing the flue gas through a boiler section, and heating the gas-liquid mixture that self-circulates and is encapsulated inside a common volume in the reactor containing the reforming section and the boiler section by indirect heat exchange with the flue gas passing through the boiler section.    DESCRIPTION OF DRAWING(S) - The figure shows a schematic of the reactor for production of 25-1000 Nm3/hour of hydrogen for use with a pressure swing adsorption (PSA) unit.    Combustion section (2)    Boiler section (3)    Reforming section (4)    Reforming catalyst (5)    Common volume (8)