NOVELTY - The method involves performing gasification process of combustible materials in multiple gasification chambers (1). Synchronous gas from the gasification chambers is transferred to a combustion unit and combusted in the combustion unit. Mixture of external air and recirculated flue-gas from the combustion unit is blown under combustible material in separated nozzle areas of a bottom part of each gasification chamber at different times of a gasification cycle, where the nozzle areas correspond to plenum sections of the bottom part.    USE - Method for realizing thermal oxidation of combustible materials such as waste material, fuel and biomass (all claimed) to produce useful energy i.e. electricity, that is utilized to preheat air, water, thermal oil used as working media for a Rankin cycle system and for industrial and space heating applications.    ADVANTAGE - The method enables controlling the flow of the air and the recirculated flue-gas due to the separated plenum sections and the nozzle areas in the gasification chambers and provides even flow distribution in all plenum areas at the end of the process of each chamber to ensure full burnout of all carbon in the waste, thus producing high heat value synchronous gas and high quality ash with less amount of carbon content batch, and hence decreasing excess air combustion producing fully combusted flue-gas rather than gasification producing energy rich synchronous gas. The method enables providing small sized gasification chambers, so that waste load is filled uniformly in all corners and center part of the chambers, thus avoiding complications of loading material into the chamber. The method enables promoting production of nitrogen oxides by high oxygen concentration and high temperature and increasing flue-gas recirculation efficiency using recirculation of the flue-gas.    DETAILED DESCRIPTION - The combustion unit is selected from a group comprising a synchronous gas combustion chamber, a reciprocating engine, a boiler, a gas turbine or an internal combustion device. An INDEPENDENT CLAIM is also included for an apparatus for realizing thermal oxidation of combustible materials.    DESCRIPTION OF DRAWING(S) - The drawing shows a schematic view of a thermal oxidation apparatus in which synchronous gas is combusted in a reciprocating engine or a gas turbine after passing through a synchronous gas conditioning chamber and a synchronous gas cleaning system.    Gasification chambers (1)    Cooling fluid fan (10)    Ignition burner (11)    Synchronous gas conditioning chamber (13)    Synchronous gas cleaning system (14)