What scenes and objects can you find in this model?
Agitators inside the tank keep the mass agitated to let the biogas freely bubble out and so prevent the formation of layers.
A storage place for dry organic matter like municipal biowaste, silage, corn or grass. The storage tank for liquid manure could be also part of the biogas powerplant area.
By burning biogas, heat and electricity can be produced in a cogeneration unit, also called a combined heat and power unit (CHP). Before entering the engine, the biogas goes through a cleanup process in which water, hydrogen sulfide, and impurities are removed to produce clean biomethane. There are many types of technologies that could be used: stirling engines (mainly small, domestic applications), combustion turbines (turbines propelled by burning gas), steam turbines (large applications, the burning gas is used to heat water and produce steam that propels the turbine) or combined cycles (successive use of gas turbines and then steam turbines, with an alternator connected to each turbine). The produced heat is mostly used for in-site processes, like digester heating, pasteurization of manure or drying the digestate, but could be also used off-site for domestic heating or industrial processes.
Microorganisms in a digester cannot be made to stop their process, so during engine shutdowns (e.g., for maintenance) the excess biogas is safely burnt in the gas burner, called the flare. The flare is about 5 m high.
Biogas is gas, consisting mainly of methane (CH4) and carbon dioxide (CO2) and containing impurities like hydrogen sulfide (H2S), produced during the anaerobic digestion of organic materials.. The gas is stored in the upper part of the digester under the gas holder. It consists of two membranes made from polyester fabric with plastic coating on both sides. The outer one acts as a roof for the whole system; the biogas is stored under the inner membrane. Between those membranes air is permanently blown by a support air blower. The pressurized air has two functions: First, it keeps the outer membrane in shape to withstand external winds and snow loads. Second, it exerts a constant pressure on the inner membrane and thus pushes gas at a constant volume and pressure into the outlet pipe. A small window is usually incorporated on the outer membrane to provide easy inspection of the inner membrane. On the top of the digester tank is a horizontally stretched net connected to a central column, which serves as a membrane catcher and holds the inner membranes when deflated.
When the fermentation is ended, residues called digestate are pumped out of the digester and stored in a storage tank. They can be used as a high-quality fertilizer. Sometimes the heat generated by the cogeneration unit is used to dry the digestate to lighten it before transportation.
Every few hours a portion of organic matter is added to the first digester. Dry organic matter is first ground by rotating screws and then conveyed by a screw conveyor feeder into a digester.
After anaerobic digestion in the first digester, the central pump pumps the digestate into the second digester where it matures for about 25 days and produces more biogas. Its content has a lower dry to liquid matter ratio than in the first digester. After digestion the resulting digestate is pumped out of the second digester and stored in a storage tank.
All processes taking place in a biogas power plant are monitored and controlled from the control room.
A large cylindrical concrete tank, water-proof and air-tight, with insulated walls. Inside, the anaerobic digestion or fermentation is held. During this process, microorganism (bacteria and Archaea) in the absence of oxygen feed off carbohydrates, fats and proteins that form organic waste and in series of metabolical processes produce biogas consisting mainly of carbon dioxide and methane. Anaerobic digestion can occur at mesophilic (35-45˚C) or thermophilic temperatures (50-60˚C), both of which need supplementary sources of heat to reach their optimal temperature. The digestion takes about 20 days and during it the organic matter is shifted by agitators to prevent formation of layers at the top and bottom of the tank and to let biogas bubble out freely. The content of the digester consists of dry matter (silage, corn or grass, municipal biological waste) and liquid manure mixed into an optimal density.