Although there are several variances in biogas plants, the technical heart of each plant has to work according to the same method. This heart of the plant is solely for the purpose of gas production. The main differences appear on ground of the choice of substrates and the relevant treatment (input side). The further energetic utilization of the gas is also subject to variances and could be seen as an additional feature of the plant, depending on the main outcomes of gas, electricity or heat (output side).
Preparation & treatment sump:
Most substrates need a kind of pre-treatment such as mixing, removing of unsuitable matter, chopping or diluting.
After treatment, preparation and possible storage, the substrates enter the digester 1. This first container is for the fresh substrates and is needed to get the fermentation process going. A starter culture is needed for a discontinued process in a continuous process the bacteria cultures are already in place. The time the substrates remain in this first digester varies between 20 and 80 days. The amount of gas produces is not so high all generated gas flows into the gas storage. The digester temperature should be 40 - 60 �C. Thus, the digester must have a heating system, mostly it is in the digester basement.
Both digester containers must be absolutely gas- and waterproof and airtight and need to be heated. Usually they are built from steel or ferroconcrete.
Stirrer/mixer in the digesters:
Each digester has to contain a stirrer, which is crucial for keeping the substrate homogeneous and guaranteeing that the gas produced is evenly discharged.
The gas in the gasholder varies, so it should be flexible. However, the intrusion of air must be prevented. The first result of the progress is the production of biogas and the digester residues.
The digester residues are very high quality fertilizers. During the digester process carbon is degraded and the carbon-nitrate ratio of the manure get closer. So the nitrate is better to handle and the fertilizer-effect is easier to calculate. Also the volume is reduced and the manure is more fluent. Additional advantages are the decrease of malodour and the deadening of pest plant seeds.
Block heat and power plant:
Usually ,the biogas gets in the block heat and power plant but it also can be cleaned and used for tanking cars or fed into a natural gas pipeline.
But all biogas used normally needs to cleansed by removing hydrogen sulphide and ammonia.