The Waste to Fuel (W2F) process is an innovative solution developed by Eni to manage and transform urban organic waste into high-value products. In fact, the technology allows to enhance the value of waste biomass producing renewable and sustainable energy products as well as recover its water content. Such usages allow to reduce greenhouse gas emissions and represent a perfect fit within the framework of commitment towards the regeneration of resources and circular economy. W2F mimics, in just two to three hours, the natural process by which nature took hundreds of millions of years to generate hydrocarbons from prehistoric biomass. Core of the technology is a hydrothermal liquefaction, a thermochemical process in aqueous solution that transforms the initial biomass into a low sulphur bio-oil that can be used to replace traditional fossil fuels in the formulation of marine bunker fuel or as semifinished product to obtain advanced biofuels for automotive industry through refinery processes. The process also produces a biogenic CO2 rich gas and an aqueous stream whose organic content can generate biomethane, once purified.
This paper describes the main features of Waste to Fuel technology developed and patented by Eni. This innovative solution allows to recover waste, the main impacting fraction of municipal sorted waste collection, as reported data demonstrates.
The technology consists in a hydrothermal liquefaction, a thermochemical process in aqueous solution that transforms the initial biomass into a low sulphur bio-oil with high calorific value, with a yield of up to 16% (depending on the composition of the original feedstock), whose characteristics are similar to those of fossil fuels with low API degree, as in the dedicated paragraph is described. This can be used directly in blending as low sulphur fuel for shipping or refined to advanced biofuels. More in detail, in hydrothermal liquefaction, biomass is converted to liquefied products by heating in presence of a solvent, generally the constituent water of the raw biomass. This approach is especially designed for wet materials, saving the energy costs of drying feedstock before transformation. For this last reason, the liquefaction approach is good for valorising wet waste biomass such as OFMSW (Organic Fraction of Municipal Solid Waste). The process is optimized in order to concentrate the starting carbon content of OFMSW into bio-oil, while other by-products are co-produced. Among them, a water phase, a residue and a gas phase. Indeed, the process produces a biogenic CO2 rich gas (the gas phase which may be captured and reused according to a BECCU scheme) and an aqueous stream whose dissolved organic content can generate biomethane, once purified. Treated water can be reused within production cycles. Other than OFMSW, Waste to Fuel can treat sewage sludge, waste from the agri-food industry and from large-scale distribution. Furthermore, worthy of note is that the whole process involves lower temperatures with respect to its analogues: 250-310°C rather than 400-500°C for pyrolysis and 800-1000°C for gasification. The energy yield is high: 80% for hydrothermal liquefaction, compared to 50-60% for biogas and 10-30% for incineration1.
