The main components of the biogas plant
А digester is a metal, reinforced concrete or plastic structure in which biochemical reactions occur with biomass fermentation. It can be underground, elevated or half-submerged. The purpose of fermentation is to create ideal conditions for biomass fermentation (biomethane bacteria eats biomass) and collection of bacteria-allocated biogas in the gasholder. For the fermentation process, the temperature in the fermenter is maintained by the heating system. Raw materials are fed into the fermenter using various equipment: loaders or pumps (depending on the technology). The substrate in the fermenter is mixed with mechanical agitators. The fermenter also includes pipelines for supplying nutrient medium, water, steam, air, defoamers and other substances.
Post digester is a substrate anaerobic digestion tank, similar to a fermenter, and at the post digester, the main raw material is the biomass from the fermenter, it can also be fed directly from the receiving tank. Post digester allows better fermentation of raw materials due to the presence of biomethane bacteria that eat biomass while increasing overall gas production. The purpose of the post digester is the maximum well-being of biomass after the fermenter and the production of biogas.
Receiving tank is a system where raw materials are pre-treated to ensure their optimal fermentation in the digester. Also, this tank is designed to store the substrate for its direct supply to the digester and post digester. Its volume and design depend on the size, type and timing of the supply of raw materials.
A loader is a system of automated mechanical equipment designed to transport and feed raw materials into the tank through a system of screws. By adjusting the system, the device provides accurate automatic dosing of the substrate into the fermenter, which occurs proportionally around the clock during the entire time of the station.
Dome is a protective membrane located above the gasholder and protects it from the effects of the atmosphere. The dome has high UV resistance, it is stretchable and elastic.
Gasholders in fermenters and post-digestors are special membranes designed for the accumulation and storage of biogas. Gasholders can be low, medium or high pressure. To guarantee the safe operation of the station, the gas holder must be leak-proof and resistant to pressure and temperature. The gas holder is constantly selecting biogas for a cogeneration plant to generate electricity and heat.
Substrate, raw material is biomass that is used as source material for biogas production, in the process of which the substrate eats a methane bacterium that emits biogas. The main substrates for the operation of agricultural biogas plants are renewable energy crops (corn, beet) and animal excrement (manure, droppings). Substrate categories: livestock and poultry waste, agro-industrial waste, energy crops (corn, cereals, grass and beets), compost, etc.
The filtrate is a substance (liquid) formed after squeezing out the spent substrate by a separator. It is necessary for dilution of raw materials (silage), i.e. its dilution and better mixing with mixers in digesters, as well as to improve biochemical reactions for the release of biogas.
Sulfur absorption system – this is a system (wooden trussed beams, PE belts and mesh, etc.) designed to collect hydrogen sulfide on its surface, it also serves to facilitate the installation of a dome and a gasholder.
Desulfation –is the process of reducing the hydrogen sulphide in biogas, which is due to the supply of oxygen by blowers in a certain amount to the gas space of the fermenter.
Mixers are used to mix the substrate. They are divided into inclined and submersible, vertical and horizontal mixers. The choice of type of mixers depends on the technology, so there are mechanical, hydraulic or pneumatic.
Separator is a device intended for separation after being in the fermenter of a digestate full of organic inclusions (pork pus and beer-driven wood, etc.). Once the digestate has been separated, a filtrate and a compressed substrate are produced through the separator.
Biogas sulfur H2S removal system is a special equipment for biogas purification from sulfur H2S and ammonia NH₃ containing raw biogas. Granular activated carbons are used as a cleaning filter. This system is very efficient and is widely used as the last stage of biogas purification before being supplied to the consumer (cogeneration plant) and before biogas purification into biomethane.
The biogas cooling system is a system for drying biogas from H2O. Water is removed from the biogas by condensation drying. The drying process is accompanied by gas cooling in the heat exchanger with the help of a cooling liquid, i.e. during the passage of the gas flow, moisture condenses, which is discharged into the condensate collector and removed to the industrial sewer.
Cogeneration module is equipment that is used to burn biogas (with methane content CH₄ 50 – 70%) at the appropriate biogas temperature and get rid of moisture to generate heat and electricity. One of the most important structures in a biogas plant and in order to obtain energy, there must be a responsible attitude towards the maintenance of this machine (oil change, temperature maintenance, etc.).
Additional components of the cogeneration module, expanding the scope of its use, can be:
– Flue gas waste heat boiler is a shell-and-tube heat exchanger equipped with control valves and an overheat safety group. A flue gas waste heat boiler is used to extract heat from the flue gases from the cogeneration module and to transfer the heat supply system of the biogas system to the main water with a temperature schedule of 90/70 °C. This measure involves increasing the release of thermal energy;
– ORC-module – is a container-modular installation that makes it possible to transform the excessive high-potential thermal energy of flue gases (temperature +360…400 °C) or the low-potential thermal energy (heat carrier with a temperature +80…90 °C) into mechanical energy using steam along the Renkin cycle. A liquid with a low evaporation temperature is transformed by heat into a gas state and fed to the turbine. After the turbine, the gas condenses and returns to a liquid state. The turbine sets in motion a generator generating additional electrical energy.
– The steam generator is equipment that makes it possible to convert the high-potential heat of flue gases (temperature +360…400 °C) from a cogeneration module for heating chemically purified water and to convert it into saturated steam with a pressure of P=3 Bar, P=6 Bar, etc.
– The three-generation module is equipment enabling the cogeneration plant to release three types of energy (electric energy, heat and cold). The cold output carried out by the absorption cooling system makes it possible to maintain the temperature of the cooled water equal to +6/+12 °C, and ammonia or freon is used for producing a low-temperature cold up to minus 60 oC. The whole system works with a maximum efficiency of 73%.
A gas burner (gas candle for biogas) is required for the combustion of low-quality biogas at the start of biogas plant operation and for the combustion of excess biogas.
Gas blowers and blowers are a type of air injection device that is located between compressors and fans in terms of pressure level. They are used to create transport flows for biogas.
The Biomix pump is special equipment for feeding the substrate used in biogas plants or anaerobic digestion plants. The main operations in which pumps are used are the supply of solid material: the solid substrate is crushed and fed into the pump through a screw feeder, mixed with the liquid component of the fermenter; separator power supply; loading devices for separating solid and liquid fractions of materials.