The fluid biomasses are loaded directly into the predigester, which operates at around 8% DM.
Dry, woody or undesirable biomass is loaded unprepared into the central system's peripheral tanks, where it is then showered with digestate from the predigester.
The liquid from the peripheral tanks circulates with the central digester. Residual digestate is removed from the peripheral tanks by grapple.
A 1500 m3 infinitely stirred central digester
It contains liquid inoculum heated to around 45°C
Ten 250m3 tanks around the central digester
These tanks are used to digest woody, solid or undesirable biomass.
A 2,000m3 predigester for processing fluid and liquid biomass
The contents of this predigester are used to shower the biomasses in the peripheral tanks
A material discharge system
Direct loading of woody, dry or undesirable materials eliminates the need for shredders, augers, belts or other preparation systems.
These biomasses are kept in peripheral tanks. Only the liquid moves, which is very gentle on the pumps and agitators.
Discharge by grapple or shovel also eliminates the need for phase separation equipment.
In the liquid digester, the level of dry matter remains low (around 8%) so as never to put the agitation and feed equipment at risk. Showering in the central digestion system eliminates the need for separation equipment.
Laboratory tests were carried out by INSA Toulouse to validate the efficiency of the degradation of unprepared materials and to simulate the biological operation of the full-scale process by percolation. These studies highlighted the efficiency and biological robustness of the proposed operating mode.
A full-scale tank mock-up was built and tested at a partner supplier's site, to test liquid circulation in the biomass. This mock-up was also used to refine the tank design and identify sensitive aspects.
The third phase of the program saw the construction of the Prémery site, from earthworks to the construction of the tanks and assembly of the purifier. This construction was an opportunity to improve the process, particularly in terms of the structure of the tanks.
The last phase of the program enabled us to test several operating modes, modify certain elements such as drainage systems and biomass immersion methods, and refine the operating mode. At the end of 2021, the site produced its first cubic meters of biogas, until the first volumes of biomethane were injected in March 2022. The ramp-up provided an opportunity to make further changes to the process, until a stabilized production mode was reached in September 2023.
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