NOVELTY - The method for operating a hydrothermal carbonization (HTC) plant for the production of carbon or humus through hydrothermal carbonization of biomass (2) in a reactor (4), comprises discharging heat of reaction from the reactor in the form of steam (7) and then controlling the reactor inside temperature. The discharged steam is brought into a preheater (1) and/or a preprocessor (9). The pressure in the preheater and/or in the preprocessor is lower than in the reactor. The HTC plant has a continuous or discontinuous operation and continuous or discontinuous process sections.    USE - Method for operating a hydrothermal carbonization plant for the production of carbon or humus through hydrothermal carbonization of biomass in a reactor.    ADVANTAGE - The method ensures economical production of carbon or humus through hydrothermal carbonization of biomass with less effort, high quality and less energy consumption.    DETAILED DESCRIPTION - The method for operating a hydrothermal carbonization (HTC) plant for the production of carbon or humus through hydrothermal carbonization of biomass (2) in a reactor (4), comprises discharging heat of reaction from the reactor in the form of steam (7) and then controlling the reactor inside temperature. The discharged steam is brought into a preheater (1) and/or a preprocessor (9). The pressure in the preheater and/or in the preprocessor is lower than in the reactor. The HTC plant has a continuous or discontinuous operation and continuous or discontinuous process sections. The HTC plants are parallely operated and the heat is deduced and/or led in the form of different aggregate condition of the process water between two or more parallely operated plants through tubes with the aim of further improvement of the energy balance. The separation of the carbon and water is carried out before the relaxation of the water and carbon mixture at ambient pressure. The water of the biomass separated in the HTC plant by the reaction of the carbon is added during the reaction. The heat capacity of the reactor content is increased to reach the point in time controlling the utilization of the reaction heat. During the operation of the HTC plant, the reaction heat is temporarily stored in the reactor as long as by warming the reactor contents until it can be used other or it is exceeded through a further warming of the maximum allowable reactor temperature. The biomass is added to water before starting the reaction so that it is surrounded by the water. The biomass subjected at reaction temperature is brought through a circulation again and again with water. The heat freed-up in the plant is used for the evaporation process of the reaction water. The point of the withdrawal of inert gases is carried out between the point of the condensation of the steam brought into the preheater and the point of the withdrawal of the steam from the reactor. An INDEPENDENT CLAIM is included for a device for hydrothermal carbonization (HTC) of biomass in a HTC plant.    DESCRIPTION OF DRAWING(S) - The figure shows a device variant for the implementation of the vapor extraction procedure and its recovery for a continuous process.    Preheater (1)    Biomass (2)    Reactor (4)    Steam (7)    Preprocessor. (9)