NOVELTY - The method involves feeding a gaseous mixture into a metal reforming tube (12) located inside a furnace burning area (24). Synthesis gas is obtained, directed into a burner (11) to be lit and burned as alternative gaseous fuel at exit of reforming process for ensuring rest of heat necessary for self-maintenance of synthesis gas production process in continuous flow by continuous combustion and operating a user boiler (18) to produce through cogeneration thermal agent and/or of electrical energy through an assembly composed out of the boiler, a steam turbine and an electrical power generator.    USE - Multi-phase technological method for obtaining synthesis gas i.e. natural gas, in continuous flow through sequence of operations of cold micro-cracking, pyrogenic reactions and non-catalytic reforming with steam at high temperatures of liquid fuels among complex hydrocarbons such as heavy fuel oil, light liquid fuels, diesel, tar, naphtha, mineral oils, shale oils, vegetable oils and biodiesel (all claimed), and wastes, where the synthesis gas is utilized as an alternative gaseous fuel to produce thermal, electrical and/or mechanical energy in thermo energetic industry.    ADVANTAGE - The method enables obtaining the alternative gaseous fuel so as to permit significant reduction in production costs of thermal energy and overall reduction of carbon dioxide emissions into an environment. The method enables achieving drastic reduction of costs of generating thermal energy, replacing classical fossil fuels with hydrogen obtained from water by using the synthesis gas as the alternative fuel while energy efficiency from burning synthesis is higher, and utilizing a technological equipment in an installation that produces synthesis gas to be small in size and with reduced technical complexity to reduce manufacturing costs and investments. The method enables simplifying technological process and facilitating exclusion of need to store synthesis gas since the synthesis gas is fully lit and burnt, for presenting lower risks of damage or accidents during plant operation. The method enables avoiding lime scale forming in a rotating cavitation/vaporization device since classic heating elements necessary to vaporize water are not used and avoiding chemical pretreatment of water used as raw material in production of synthesis gas. The method enables providing thermal energy generated from combustion of the synthesis gas obtained from water mixed with biodiesel or vegetable oils, representing a renewable energy source as biodiesel or vegetable oils and regenerating renewable energy sources and water used in process by oxidation of hydrogen from synthesis gas and found in exhaust emissions in form of water vapors, which are condensed to restore amount of water initially used to form the mixture. The method enables achieving significant reduction of carbon dioxide emissions into the environment, when synthesis gas is used as the alternative fuel while generating same amount of thermal energy.    DETAILED DESCRIPTION - An INDEPENDENT CLAIM is also included for a cylindrical horizontal furnace for overheating a gaseous mixture.    DESCRIPTION OF DRAWING(S) - The drawing shows a schematic view of an installation for obtaining synthesis gas and production of thermal power through cogeneration.    Burner (11)    Metal reforming tube (12)    Frontal panel access opening (17)    User boiler (18)    Furnace burning area (24)