The plant is formed by one or more closed containers, heated and hermetically sealed (called “Reactors” or “Digesters”) where the biochemical reactions occur and from which gas is extracted (called “Biogas”), used to feed an engine capable to produce energy and warm water. The plant is also composed by possible dugouts for vegetable products storage, a mixing pool for manure and/or a dunghill and finally a pool to storage the digestate.
PAHSE 1 – Production and storage of the feeding material
If the plant operates with dedicated energetic cultivations, apart from zootechnical wastes, during this phase occurs the seeding, the harvesting and then the conservative storage and/or the silage of vegetable cultivation dedicated to the production of energy and/or the collection of waste residuals of food products (residuals from agro-industrial production) necessary to feed the plant.
Instead the zootechnical residuals are recycled form the livestock and brought to the plant through a pipe system or tanker. The storage must guarantee the availability of the raw material for the whole year, even in presence of seasonal agricultural productions.
PHASE 2 – Anaerobic digestion and biogas production
The fermenter is fed daily by a dedicated system that uploads the zootechnical residuals and possible vegetable substances (substrates). Inside the fermenter, the material is kept at a temperature between 35° and 38° and by appropriate shakers continuously agitated so to avoid deposits and to mix the different organic substances.
The final product of the reaction are biogasses (gas mixture) and the digestate (solid and liquid mix) with the latter at the end of the process being discharged in the residual tank; in here the product is stored to be used during the ideal period of the year based on the existing legislation.
PHASE 3 – Cogeneration and spreading of the digestate
The produced biogas is then stored inside domes that cover the fermenter and from here conducted into the cogeneration plant.
The cogenerator, installed in a container or dedicated technical room and equipped with all the necessary technical devices for its optimal functioning, transforms biogas into energy by means of a gas engine and alternator and recover of thermal energy, resulting from the cooling of the engine with the help of dedicated heat exchanger.
The energy produced is channelled into the distribution network of the area, while the heat is recovered and partially used to keep the temperature inside the fermenter.
The heat in excess, and the possibly recoverable thermal energy from exhaust fumes, will be used for heating the utilities of the firm (i.e. greenhouses, piggery, etc.) or for remote heating of buildings not far away from the firm (schools, offices, etc.).