NOVELTY - Increasing biogas net calorific value, involves subjecting generated biogas to drying, purifying sulfur compounds, compressing, mixing biogas with hydrogen, subjecting mixed gases to hydrogenation, then cooling down the post-reaction gases and separating hydrogen, while the remaining gases mixture is combusted and energy is generated, and drying the resultant combustion gases, filtering dust, and then decomposing nitric oxides, after which carbon dioxide is separated from combustion gases, and the resultant gas, with nitrogen as the main gas, is let out to chimney.    USE - For increasing biogas net calorific value (claimed), which is used for gas engines.    ADVANTAGE - Use of the plasma reactor in the method generates unbalanced plasma for the qualitative change of the gas fuel generated in biogas plant by increasing its net calorific value. As a result of the chemical reaction in the plasma generator which generates unbalanced plasma, carbon dioxide contained in biogas is hydrogenated and simple aliphatic hydrocarbons are created, and thus carbon dioxide from biogas is transformed into components with high net calorific value. Use of plasma reactor controls the initial parameters of the process within the entire scope of changes of biogas composition in the course of its enriching which enables to use the device according to the invention independently from the type of the biomass used. The transformation of the carbon dioxide contained in biogas into simple aliphatic hydrocarbons causes enriching of gas due to increase of its net calorific value and improvement of gas adequacy for use in gas engines through the possibility to control its composition relating the content level of carbon dioxide (CO2). As a result, the processed biogas, in relation to the unprocessed gas, has much higher combustion heat, thus also net calorific value, which is shown in the examples below. Since the main component of chimney gas is nitrogen, the biogas enriching installation is environment friendly and the very process in practice produces no waste.    DETAILED DESCRIPTION - Increasing biogas net calorific value, involves subjecting generated biogas to drying, purifying sulfur compounds, compressing, mixing biogas with hydrogen, subjecting mixed gases to hydrogenation in unbalanced plasma with the electron energy of ca. 1 eV and inert gas temperature of 1500-2000K, as a result of which carbon dioxide is hydrogenated and aliphatic hydrocarbons 1-2C are created, then cooling down the post-reaction gases and separating hydrogen, while the remaining gases mixture is combusted and energy is generated, and drying the resultant combustion gases, filtering dust, and then decomposing nitric oxides, after which carbon dioxide is separated from combustion gases, and the resultant gas, with nitrogen as the main gas, is let out to chimney. An INDEPENDENT CLAIM is included for a device for increasing net calorific value of biogas, equipped with the following systems connected with biogas plant: drying system, biogas purification system of sulfur compounds, and purified gas compressing system, where the device has a plasma reactor with gas feeding system, the device is equipped with post-reaction gases cooler with condensed water tank, the device is connected with hydrogen separator, where the post-reaction gases cooler and hydrogen separator are connected with the post-reaction gases control system, and hydrogen separator is connected with hydrogen tank which is connected with the gases feeding system and post-reaction gases control system and co-generator, which in turn, is connected through the combustion gases drying system and dust filter with the reactor used for nitric oxide (NOx) decomposition connected with the carbon dioxide separation system from the combustion gases, where the hydrogen separator with the hydrogen tank and gas feeding system to plasma reactor is connected by hydrogen return line, and the carbon dioxide separation system from the combustion gases is connected with cogenerator by carbon dioxide return line.