Processes, systems, and associated control methodologies are disclosed that control the flow of biogas during the biogas cleanup process to create a more consistent flow of biogas through the digester, while also optimizing the output and efficiency of the overall renewable natural gas facility. In representative embodiments, a biogas buffer storage system may be used during the cleanup process to control the pressure and flow rate of biogas. The biogas buffer storage system may monitor and control the biogas flow rate to either bring down or increase the digester pressure, thereby maintaining a normalized biogas flow rate.

Proposed is a carbon dioxide conversion system and method. More particularly, proposed is an eco-friendly carbon dioxide conversion system and method, the system and the method returning, in the recycling of Fischer-Tropsch synthesis reaction off-gas, a part of the off-gas to a Fischer-Tropsch reactor and producing a synthetic natural gas through methanation of the remainder of the off-gas, thereby improving overall energy efficiency and carbon efficiency, and thus a useful hydrocarbon fuel is produced from carbon dioxide, thereby providing a carbon dioxide-reducing effect.

Proposed is a carbon dioxide conversion system and method. More particularly, proposed is an eco-friendly carbon dioxide conversion system and method, the system and the method returning, in the recycling of Fischer-Tropsch synthesis reaction off-gas, a part of the off-gas to a Fischer-Tropsch reactor and producing a synthetic natural gas through methanation of the remainder of the off-gas, thereby improving overall energy efficiency and carbon efficiency, and thus a useful hydrocarbon fuel is produced from carbon dioxide, thereby providing a carbon dioxide-reducing effect.

An energy conversion system includes a fuel synthesis device, an H.sub.2O supply unit, a CO.sub.2 supply unit, and a supply control unit. The fuel synthesis device includes an electrolyte, and a pair of electrodes provided on both sides of the electrolyte. The H.sub.2O supply unit supplies H.sub.2O to the fuel synthesis device. The CO.sub.2 supply unit supplies CO.sub.2 to the fuel synthesis device. The supply control unit controls a supply of H.sub.2O and a supply of CO.sub.2. The fuel synthesis device electrolyzes H.sub.2O and CO.sub.2 using external electric power, and synthesizes a hydrocarbon using H.sub.2 and CO generated by electrolysis. The supply control unit starts the supply of H.sub.2O to the fuel synthesis device by the H.sub.2O supply unit after the supply of CO.sub.2 to the fuel synthesis device by the CO.sub.2 supply unit is started.

An energy conversion system includes a fuel synthesis device, an H.sub.2O supply unit, a CO.sub.2 supply unit, and a supply control unit. The fuel synthesis device includes an electrolyte, and a pair of electrodes provided on both sides of the electrolyte. The H.sub.2O supply unit supplies H.sub.2O to the fuel synthesis device. The CO.sub.2 supply unit supplies CO.sub.2 to the fuel synthesis device. The supply control unit controls a supply of H.sub.2O and a supply of CO.sub.2. The fuel synthesis device electrolyzes H.sub.2O and CO.sub.2 using external electric power, and synthesizes a hydrocarbon using H.sub.2 and CO generated by electrolysis. The supply control unit starts the supply of H.sub.2O to the fuel synthesis device by the H.sub.2O supply unit after the supply of CO.sub.2 to the fuel synthesis device by the CO.sub.2 supply unit is started.

A process and/or system for producing fuel that includes providing biogas, removing carbon dioxide from the biogas, transporting the upgraded biogas to a hydrogen plant; providing the transported upgraded biogas and fossil-based natural gas as feedstock for hydrogen production. The carbon intensity of the fuel is less than 11 gCO.sub.2-eq/MJ, at least in part because carbon dioxide removed from the biogas and carbon dioxide from hydrogen production is captured and stored.

A power generation system comprises a fuel gas supply device 13 for controlling methane concentration or carbon dioxide concentration in a mixed gas MG containing methane and carbon dioxide within a setting range for the concentration in the fuel gas of a gas engine 11, and for supplying the mixed gas MG to the gas engine 11 as the fuel gas, and a gas concentration sensor 14 for measuring the carbon dioxide concentration or the methane concentration of the mixed gas MG. The fuel gas supply device 13 comprises a carbon dioxide removal device 16 for removing carbon dioxide in the mixed gas MG, and an operating condition control device 17 for controlling an operating condition that affects an increase or decrease of a carbon dioxide removal rate of the carbon dioxide removal device 16, and the operating condition control device 17 controls the operating condition of the carbon dioxide removal device 16 based on the measurement result of the gas concentration sensor 14, thereby controlling the concentration of methane and carbon dioxide in the mixed gas.

A method and system are provided to recover water and carbon dioxide from combustion emissions. The recovery includes, among other things, electrolysis and carbon dioxide capture in a suitable solvent. The recovered water and carbon dioxide are subject to reaction, such as a catalytic methanation reaction, to generate at least methane.

A vessel for control of aquatic plant species (100) in seas, rivers and lakes that is configured to extract from the surface of the water and hoist to a deck of the vessel (100) a plurality of plant remains of a given aquatic ecosystem by means of an elevator belt (101); and/or receive from a coastal installation a plurality of aquatic plant remains mixed with grey water from coastal human settlements; and that is characterized in that the remains of aquatic plant species extracted from the surface of the water and/or received from coastal human settlements are deposited in a cooking chamber (102) where they are subjected to controlled temperature conditions configured to modify, ferment and rot said remains preventing their reproduction.

The description describes the integration of a gas fermentation process with a gasification process whereby effluent from the gas fermentation process is recycled to the gasification process. The one or more effluents which can be recycled include a stream comprising microbial biomass, a product stream comprising at least a portion of the at least one fermentation product, a by-product stream comprising fusel oil, and a waste water stream comprising microbial biomass. The stream comprising biomass can be dried before it is passed to the gasification zone. At least a portion of the waste water stream can be passed to the gasification process where one use is to replace at least a portion of the process water. The waste water stream can be further processed to produce a clarified water stream and a biogas stream comprising methane either or both of which can be passed to the gasification process.