The first two plants to come into operation as part of a development project by Lazzari & Lucchini in northern Italy
Bio Verola is one of the first agricultural biomethane production plants in Italy and is one of the two plants already in production in the province of Brescia, as part of Lazzari&Lucchini SpA’s development project in the sector.
The strategy foresees the construction of biomethane production plants with a capacity of 1.3 MWel equiv. (about 550 Sm3 biogas per hour and 300 m3 biomethane per hour), based on the synergy with the territory and the farmers of the area, both for the supply of biomass and for the efficient management of digestate.
In the initial phase, in fact, the feed is based on a mix of zootechnical effluents (cattle manure, cattle slurry, pig slurry, poultry manure), triticale silage and sorghum silage. Subsequently, thanks to an amendment to the Simplification Decree, agro-industrial by-products will also be introduced.
Biomasses come mainly from owned or leased land and from local farms with which agreements are stipulated that provide for both the transfer of biomasses from second-harvest crops (sorghum and triticale) and the transfer of zootechnical waste.
After the process of anaerobic digestion, thanks to the abatement plants, the digestate is returned to the suppliers with a nitrogen content halved compared to the one initially present in the wastewater. In this way, a virtuous cycle is created thanks to which biomasses and agro-industrial by-products of the area can be enhanced. The wastewater is not only valorized but, at the same time, becomes a resource for farms that, with the digestate, will have the opportunity to improve their agronomic management and sustainability by optimizing the nitrogen loads on their land.
Coming to the technical aspect, the Bio Verola plant has two primary digesters of 28 meters in diameter and 6 meters high and two secondary digesters of equal capacity.
There are two covered tanks of thirty meters in diameter for the storage of digestate and a nitro-denitrogen plant for the abatement of nitrogen.
Another peculiarity is the composting system of digestate, which takes place in a shed of 120 meters in length thanks to the presence of a mobile screw for mixing and continuous oxygenation of the substrate.
The biogas produced undergoes desulfurization pre-treatment with scrubbers and activated carbon filters before being conveyed to a membrane upgrading plant. Finally, the biomethane is fed into the Snam network.
The second plant, Bio Industria, came into operation at the end of May 2021 and is characterized by the presence of a liquefier with a production capacity of 5 tons of bioGNL per day.
The process involves the presence of a biomass receiving tank with sand collector and sand classifier (requirement caused by the use of poultry), two primary digesters of 26 meters in diameter by 6 meters in height and two secondary digesters of equal volume.
The biogas coming out from the digesters undergoes a pre-treatment very similar to what we have seen before as far as desulfurization and subsequent membrane upgrading are concerned.
The digestate, also in this case, undergoes a solid-liquid separation process. The liquid phase is sent to a nitro-denitrogen plant for nitrogen removal and, subsequently, stored in 2 covered tanks. For the treatment of the solid phase, on the other hand, a composting plant is also about to be put into operation here.
Compared to the Bio Verola plant, in this second case the biomethane undergoes a further purification process, with physical adsorption on zeolites and regeneration of the same at high temperature. This is motivated by the need to reduce the carbon dioxide content of the biomethane to below 50 ppm in order to have suitable conditions for liquefaction.
The liquefaction plant, in particular, is based on the Linde cycle, which uses methane itself as the working fluid, so as to minimize energy consumption. The process consists of 3 phases: the incoming biomethane is compressed to reach the ideal pressure for liquefaction; the gas undergoes various stages of pre-cooling/cooling by exploiting the recirculation flows coming from the cryogenic zone; the gas is brought to a temperature of about -150°C and a pressure of about 3 Bar, thanks to pressure drops through Joule-Thomson valves.
With regard to the challenges of the near future and in the realization of the next planned plants, the intention is to continue to focus on liquefied biomethane. The choice is motivated above all by the prediction that the number of private cars fuelled by compressed (bio)methane is not likely to increase due to both political guidelines and the intention of the main manufacturers to cease production of internal combustion vehicles in the coming years. On the contrary, in the heavy transport sector and in the maritime naval sector a strong increase in the consumption of liquefied methane is expected, with growing interest in biofuel of renewable origin.
Other points considered strategic and of forthcoming development are the realization of relevant distribution plants (authorization has already been requested for some of them) and the possibility of valorising digestate by producing both high quality composted organic soil improver and organic fertilizers.