＞ About biogas power generation
Biogas plant structure
The overall flow of a typical biogas plant is shown in the flow chart below.
There are also facilities that are required depending on the type of raw material, fermentation method, digestive juice processing method and application.
① Acceptance of raw materials
Organic waste, which is the raw material for biogas plants, is received at the plant and put into the raw material receiving tank.
② Pretreatment
When using food waste as a raw material, a crusher that crushes it into small pieces is required.
In addition, when performing wet fermentation, it is necessary to adjust the amount of water.
③ Fermentation
Methane fermentation is basically divided into multiple fermenters.
This is to promote fermentation and for maintenance required at regular intervals. An absolutely anaerobic environment is indispensable for methane fermentation, and since the fermenter has a closed structure, the generated gas and odor do not leak to the outside.
④ Gas refining
Biogas is generally composed of about 60% methane and about 40% carbon dioxide, but it also contains trace amounts of hydrogen sulfide. Hydrogen sulfide has the property of corroding metals and corrodes the internal combustion engine and piping of generators, so it must be removed from biogas using a scrubber. There are two desulfurization methods, dry desulfurization and biological desulfurization.
⑤ Gas storage
It is necessary to balance the amount of generated biogas with the amount of consumption, and it is stored to some extent and supplied to the generator as needed.
⑥ Storage of digestive juice
Store a certain amount of residue (digestive juice) after generating biogas.
It is necessary to install storage equipment such as a secondary fermenter and a digestive juice tank.
⑦ Power generation
Power is generated using a generator with a gas engine.
Since it is not a thermal turbine generator, it can save space and obtain high power generation efficiency. It is also a device with high maintenance costs in the entire plant.
The generated power can be sold to the power company using the feed-in tariff (FIT).
Currently, the electricity from the biogas plant is purchased for 39 yen (excluding tax), and it is also possible to consume it in-house without selling it.
⑧ Heat recovery
The heat (hot water) recovered from the generator is used for heating the fermenter.
However, most plants have excess heat that can be used for other purposes. In domestic cases, it is used for cultivation and heating and heat retention of vinyl greenhouses such as vegetables, and overseas, it is also used for district heating such as floor heating in general houses and can be sold.
⑨ Utilization and processing of digestive juice
Digestive juice has a great effect as a fertilizer, and in the biogas business, whether or not the digestive juice can be used as liquid fertilizer is also a major point in establishing the business.
In some cases, the digestive juice is divided into solid and liquid by a machine (dehydrator), and the solid content is used for compost and the liquid content is used for liquid fertilizer. If it is not used as liquid fertilizer, it is necessary to install water treatment equipment to discharge.
