Parts of Biogas Plants
- Influent collecting tank
- Inlet and outlet
- Digester
- Gasholders
- Gas pipe, valves and accessories
- Stirring facilities
- Heating systems
- Pumps
- Weak Rin
Influent collecting tank
Fresh substrate is usually gathered in an influent collecting tank prior to being fed into the digester. Depending on the type of system, the tank should hold one to two days’ substrate. An influent collecting tank can also be used to homogenize the various substrates and to set up the required consistency, e.g. by adding water to dilute the mixture of vegetable solids (straw, grass, etc.), or by adding more solids in order to increase the bio-mass.
Location
A sunny location can help to warm the contents before they are fed into the digester in order to avoid thermal shock due to the cold mixing water. In the case of a biogas plant that is directly connected to the stable, it is advisable to install the mixing pit deep enough to allow installation of a floating gutter leading directly into the pit. Care must also be taken to ensure that the low position of the mixing pit does not result in premature digestion. For reasons of hygiene, toilets should have a direct connection to the inlet pipe.
Inlet and outlet
The inlet (feed) and outlet (discharge) pipes lead straight into the digester at a steep angle. For liquid substrate, the pipe diameter should be 10-15 cm, while fibrous substrate requires a diameter of 20-30 cm. The inlet and the outlet pipe mostly consist of plastic or concrete. Both the inlet and the outlet pipe must be freely accessible and straight, so that a rod can be pushed through to eliminate obstructions and agitate the digester contents. The pipes should penetrate the digester wall at a point below the lowest slurry level (i.e. not through the gas storage). The points of penetration should be sealed and reinforced with mortar. The inlet pipe ends higher in the digester than the outlet pipe in order to promote more uniform flow of the substrate. In a fixed-dome plant, the inlet pipe defines the bottom line of the gas-holder, acting like a security valve to release over-pressure. In a floating-drum plant, the end of the outlet pipe determines the digester’s (constant) slurry level. Inlet and outlet pipe must be placed in connection with brick-laying. It is not advisable to break holes into the spherical shell afterwards, this would weaken the masonry structure.
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Digester
The slurry is fermented inside the digester and biogas is produced through bacterial action.
Gas holder or gas storage dome
The biogas gets collected in the gas holder, which holds the gas until the time of consumption.
Basically, there are different designs of construction for gasholders used in simple biogas plants:
- floating-drum gasholders
- fixed-domes gasholders
- plastic gasholders
- separate gasholders
Gas pipeline
The gas pipeline carries the gas to the point of utilization, such as a stove or lamp
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