The future of biomethane/biogas will be defined by increasingly efficient technologies. Our research & development activities have enabled us to obtain a patent on an efficient use of mechanically stabilized earth for the construction of biomethane/biogas plants. At present we are focusing our R&D efforts on advanced stover harvesting techniques and on a foil platform.
We are not biomethane/biogas plant builders, but technology providers. The construction of the plant is carried out by a local construction company.
Generally, biogas/biomethane plants consist of at least one anaerobic digester, basically a hermetically sealed and insulated tank, in which organic matter is fermented by anaerobic microorganisms. The vast majority of today’s biomethane/biogas plants have digesters made of concrete or steel.
Our concept provides for digesters made of mechanically stabilized earth (also known as reinforced soil), with lower overall costs, less visual impact, a longer plant life and greater flexibility in configuration.
We intend to introduce a new method for the recovery of corn stover in order to exploit them in a biomethane/biogas plant. We are studying a double bar to be mounted on the threshing machines: the first one, the upper bar, is a traditional threshing bar; the second (lower) one cuts the plant stalks as low as possible expelling them to the left or right of the machine. The swath produced will be recovered as soon as possible and shredded by the harvester. Thus the food parts (destined for animal or human consumption) are separated from the non-food parts (destined for the biomethane/biogas plant).
The foil platform is a standardized support that is integrated between the rigid structure, i.e. the embankment and the gas holder sheet. Its stability is ensured by the weight and friction of the gravel and it is sufficiently rigid and stable, so that all active components can be installed without negative effects on the gas holder sheet fixed to the foil platform.
We believe in simplicity. Clear and sound concepts are successful, especially when it comes to anaerobic fermentation or biomethane/biogas plants in general. The simplicity of the technology determines the effectiveness of its application and allows for significant reductions in operating expenses (OPEX) and capital expenditure (CAPEX).
Our technology differs from that of traditional suppliers in three main aspects. First of all, our process innovation relies on biomass stratification instead of homogenization. Our structural innovation sees digester walls made of mechanically stabilized earth (or lagoons, if the water table is low enough) instead of steel or concrete. Our third innovation is an assembly kit, which we are developing at present: Blueprints, pumps, tubes, valves, P&I, etc., as well as a foil platform and system control software.
A biomethane/biogas plant is fed continuously. Therefore, biomasses at different stages of digestion are present within the digesters. There is a widespread belief that substrate homogeneity should be maintained in digesters, as well as a homogeneous distribution of biomass and organic load. For this reason, mixing systems have been developed, but they consume significant amounts of energy. In addition, the mixers themselves are very expensive.
A negative effect of homogenization is the so-called “short circuit”: Fresh biomass (even newly inserted one) is taken out of the digester before it is fully exploited. This results in a significant waste of energy. This waste is traditionally reduced by implementing multi-phase systems.
To avoid a short circuit, we forego forced mixing and replace it with intentional stratification. Undigested (fresh) biomass has a lower specific weight than digested (spent) biomass. The substrate containing undigested biomass therefore tends to float on top of the substrate containing spent biomass. Due to the lower specific weight, fresh biomass remains in the upper part of the digester, thus increasing the residence time of fresh and semi-digested biomass in the digester.
Alvus takes advantage of this effect by extracting at the lowest point of the digester and reintroducing fresh substrate from above. This recirculation prevents the formation of crusts and foams.
Mechnically stabilized earth (also known as reinforced soil) makes the construction of tanks with large volumes. They are particularly suitable when the water table is too high to build lagoons.
Mechanically stabilized earth offers many advantages: