NOVELTY - Reforming reactor (1) comprises reforming (4) and boiler (3) sections within a common volume and a combustion section (2). 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. The combustion section is provided with burner(s). The heat exchanging medium required for the reforming of process fluid in the catalyst tube(s) is a gas-liquid mixture. The gas mixture self-circulates and is encapsulated inside common volume containing the reforming and boiler sections.    USE - The reforming reactor is useful for the conversion of a process fluid into hydrogen used in industrial applications, e.g. metallurgical industry, chemical and pharmaceutical industry and fuel power plants.    ADVANTAGE - The invention has improved temperature distribution across all catalyst tubes. It is compact and free for mechanical mechanism 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 change in burner conditions or during 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 than in conventional reforming reactors. It provides fuel cell plants cable of producing less than or equal to 20-50 kW of power.    DETAILED DESCRIPTION - An INDEPENDENT CLAIM is also included for production of hydrogen from a feed process fluid in the reactor comprising passing a preheated process gas through reforming section, heating 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 reforming and boiler sections, retrieving reformed process gas from reforming section and optionally cooling reformed process gas by preheating of the feed process fluid, introducing a fuel into burner(s) in the combustion section together with combustion air, in which combustion air is preheated by indirect heat exchange with flue gas from the boiler section, retrieving flue gas from the burner and passing flue gas through a boiler section, and heating gas-liquid mixture that self-circulates and is encapsulated inside a common volume in the reactor containing the reforming section and boiler section by indirect heat exchange with the flue gas passing through boiler section.    DESCRIPTION OF DRAWING(S) - The figure shows schematic view of the reactor.    Reforming reactor (1)    Combustion section (2)    Boiler (3)    Reforming (4)    Reforming catalyst (5)    Conduct (6)    Process feed tube (7)