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Waste to fuel

Technology

The Waste to Fuel system produces biofuels from the Organic Fraction of Municipal Solid Waste (OFMSW), made up of leftover kitchen waste. The first of its type in the world, it was designed, developed and patented at Eni's Renewable Energy and Environmental R&D Centre in Novara. A pilot plant is already operational at our bio-refinery in Gela: it can process about 700 kg of OFMSW per day, obtaining 70 litres of bio-oil, which can be used directly as a fuel or refined to obtain high-performance biofuels. Besides waste, Waste to Fuel can process sewage sludge and waste from pruning, agri-food and large-scale retail. The process also extracts 70% of the water, which, once purified, is reused in irrigation and other production cycles.

Context

Italy collects about 33 million tonnes of waste every year, of which 14 million tonnes is correctly separated. Of this, about 6 million tonnes is OFMSW. By promoting the increased and more accurate separation of kitchen waste, this figure could reach 10 million tonnes of OFMSW. Currently, it's mainly used to produce compost for agriculture and, to a lesser extent, biogas. An increasingly important sector, but with a rising cost for the community. By combining a well-managed separated waste collection and more Waste to Fuel plants across Italy, we could in theory obtain about a billion litres of bio-oil annually, equivalent to about 6 million barrels of crude oil per year. It would be like discovering a small oil deposit without having to drill a well, and, above all, without emitting any new CO2. With a single operation, we could make a major contribution to Italy's energy security and, at the same time, reduce the quantity of waste and greenhouse gas emissions. 

Technological challenge

With Waste to Fuel, in two or three hours, we imitate the natural process by which nature took hundreds of millions of years to generate hydrocarbons from prehistoric organisms. At the core of this technology is hydrothermal liquefaction, a thermal-chemical process in aqueous solution that transforms the initial biomass into a sort of “biological petrol”, or bio-oil. At this stage, nearly all the energy contained in the initial organic material is recovered and concentrated, retaining the precious hydrogen-carbon component and separating out the water. Each step is studied to reduce losses and obtain a product with a high calorific value (35 MJ/Kg) and low sulphur content. The main advantage of hydrothermal liquefaction over other waste treatment processes is that the water doesn't have to be eliminated. Indeed, all other processes evaporate off the water by heating the biomass, with an obvious energy cost. In this case, however, the water is used in the reaction itself, harnessing its acidic properties at high temperatures. Furthermore, lower temperatures are used: 250-310°C rather than 400-500°C for pyrolysis and 800-1000°C for gasification. The energy yield is also good: 80% for hydrothermal liquefaction, compared to 50-60% for biogas and 10-30% for incineration. But Waste to Fuel's most persuasive advantage is the transformation of waste into bio-oil – waste that would have a disposal cost – thus making it a useful raw material as per circular economy principles.

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Municipal waste becomes a resource - OFMSW | Eni Video Channel

Industrial integration

Following the first pilot plant, small-scale and discontinued, realised at Eni's Renewable Energy and Environmental R&D Centre in Novara, the first continuous Waste to Fuel pilot plant was established at the bio-refinery in Gela, fed each day by the OFMSW collected by a waste management company in Ragusa. The pilot plant now handles about 700 kg of OFMSW every day. OFMSW hydrothermal liquefaction technology also produces an aqueous stage, which can undergo biomethane separation for energy, and water separation for industrial use or irrigation. The bio-oil produced can be treated to obtain biodiesel. In the meantime, we're developing partnerships with waste collection companies in Italy's main cities to increase implementation of the technology. Through integration into our refineries and distribution plants, Waste to Fuel is contributing to the relaunch of the downstream sector. The whole project is managed by Eni Rewind, our environmental company.

Environmental impact

Waste to fuel energy recovery is virtually carbon neutral, since, by using the bio-oil obtained to power heat engines, the same amount of carbon dioxide is generated that was present in the initial biomass, in turn captured from the atmosphere by plants and fixed in organic matter during photosynthesis. There is thus no need to add additional carbon derived from fossil fuels to this virtuous cycle. In other words, instead of being released into the atmosphere, the carbon is stored in the bio-oil and biofuel, so helping to reach the targets set by the EU's Renewable Energy Directive for transport (RED II). Solid residue, on the other hand, is made inert by recovering the remaining energy within the process itself, while the water is used in the production of biogas and biomethane and then purified for subsequent reuse in agriculture. In addition, if adopted in countries with economies where agriculture predominates, the system could provide an industrial outlet for the large amounts of waste biomass, and contribute to the supply of fuels for local markets.