NOVELTY - The method comprises feeding biomass (3) in a reactor (1') and stimulating a chemical reaction, and removing reaction products from the reactor, where the supply of the biomass and/or removal of the reaction products takes place during an ongoing reaction operation in the reactor. The biomass is supplied in a pre-reactor (17), in which an initial reaction is carried out. The prereactor is separated during the supply in a main reactor, in which an exothermic chemical reaction is performed. The biomass is brought to a target pH-value by supplying reaction support agents (7).    USE - The method is useful for hydrothermal carbonization of biomass for producing brown coal, synthesis gas, liquid petroleum and humus and/or peat under release of energy.    ADVANTAGE - The method ensures simple, rapid and energy efficient hydrothermal carbonization of the biomass with high yield of the reaction products.    DETAILED DESCRIPTION - The method comprises feeding biomass (3) in a reactor (1') and stimulating a chemical reaction, and removing reaction products from the reactor, where the supply of the biomass and/or removal of the reaction products takes place during an ongoing reaction operation in the reactor. The biomass is supplied in a pre-reactor (17), in which an initial reaction is carried out. The prereactor is separated during the supply in a main reactor, in which an exothermic chemical reaction is performed. The biomass is brought to a target pH-value by supplying reaction support agents (7). The main reactor is divided into a first sub-reactor and an end-part reactor, which are temporarily separated from each other. The biomass and/or intermediate reaction products are forwarded from the pre-reactor to the main reactor and/or from the end-part reactor to the sub-reactor via locks and/or valves, where prior to removal of final reaction products from the end-part reactor, intermediate reaction products are removed from the sub-reactor that is arranged in the main reactor before the end-part reactor. A response to the presence of aqueous oil precursors is carried out in the first sub-reactor and/or a reaction to the presence of humus is carried out in the second sub-reactor and/or a reaction to the presence of reaction products is carried out in the third sub-reactor, where the reaction products comprise material properties of brown coal. The coal-like reaction products are passed for fueling a solar thermal power plant for producing electric current. INDEPENDENT CLAIMS are included for:    (1) a method of operating a power plant;    (2) a reactor;    (3) a power plant; and    (4) a power plant-reactor-complex.    DESCRIPTION OF DRAWING(S) - The figure shows a schematic view of a reactor for carrying out hydrothermal carbonization.    Reactor (1')    Biomass (3)    Reaction water (5)    Reaction support agents (7)    Pre-reactor. (17)