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Carbon dioxide biofixation

We have two pilot plants in operation that produce bio-oil from the intensive cultivation of microscopic algae, powered by CO2 captured from our upstream operations.

Technology

We are developing two different technologies for fixing CO2 through the cultivation of microalgae. We have commissioned the first pilot plant to obtain bio-oil from microalgae crops, powered by concentrated sunlight and “fertilised” by CO2 captured from upstream wells managed by our subsidiary Enimed, at the technological centre in Ragusa. The crude hydrocarbon obtained is then sent to the Gela bio-refinery to be transformed into the biodiesel with which we enrich Eni Diesel +. Its special industrial design means that the Ragusa plant is able to carry the carbon dioxide to photobioreactors that use natural light where we then cultivate the microalgae in water. The water is enriched with captured carbon dioxide and the sunlight concentrated in order to intensify the growth process. The plant-based substance produced is then harvested, dried and transformed into an algal flour rich in lipids from which we extract the bio-oil, whilst the water is purified and made available for other purposes. Furthermore, the same flour can be used as a component of agro-industrial and pharmaceutical products. Staying in this field, we are also developing an additional biofixation technology in which the algae are fed by artificial light that uses the preferred wavelengths of plants for photosynthesis at the Renewable Energy and Environmental R&D Centre in Novara, in conjunction with the Politecnico di Torino.

Context

Finding new ways to capture carbon dioxide and reuse it in industrial processes is of strategic importance if we are to reduce climate-changing gas emissions. Such operations use the circular economy approach, which already features in our business model, to allow them to “close the anthropic carbon cycle”, whereby CO2 molecules are captured by means of a natural process, namely biofixation by microscopic algae that are intensively cultivated in our photobioreactors. As well as reducing the emissions generated by our upstream operations, from which the carbon dioxide used to grow algal crops is sourced, the system presents the double advantage of not taking up any agricultural land, since it is contained within one of our industrial sites, not to mention the opportunities for local development that launching business initiatives based on these plants could bring to the area.

Technological challenge

Like all plants, algae need the sun to grow. This being the case, in a marine environment, they will grow as far as the sunlight reaches and in a manner that is inversely proportional to the depth, leaving a dark area beneath them where plant life struggles to survive. In order to make our cultivation system efficient we had to allow light to penetrate the entire water column, which is how we came to invent the “photobioreactor” - a system that incorporates solar energy and algal aquaculture -, of which we have created two different types by adapting them to our two different technologies. We have installed special panels made up of thousands of Fresnel lenses that track the sunlight and capture and concentrate it via special optical fibres on the roof of the Ragusa plant. These fibres, resembling long light filaments, descend right to the bottom of fourteen five-metre-high cylindrical tanks filled with salt water enriched with CO2 sourced from upstream wells, creating an artificial habitat that is perfectly conducive to the development of aquatic flora in which algae can then be intensely cultivated. The water in the tanks is stirred continuously to ensure even exposure and consequently optimise the cycle, allowing us to capture 1.8 tonnes of CO2 for each tonne of algal flour. This carbon dioxide capturing process is ultimately very efficient, enabling us to produce 250 tonnes of biomass per hectare in the space of a year, with which we can then trap some 450 tonnes of CO2. For the purposes of comparison, one hectare of wheat crop captures only 6.5 tonnes of carbon dioxide per year. The secret to these results is the possibility of recreating up to 30 growing seasons over the course of a single year. With regards to the technology we are developing at the Renewable Energy and Environmental R&D Centre in Novara together with the Politecnico di Torino, however, we have created multi-layer photobioreactors in which the algae are lit by an LED system powered by solar panels, combined with flow batteries to ensure 24-hour operation. These lamps emit light on the wavelengths favoured by algae, thus intensifying their growth process as much as possible. Being able to run uninterrupted day and night allows the plant to produce as much as 650 tonnes of biomass per hectare per year, consequently trapping 1,000 tonnes of CO2 - an exceptional result that can be obtained by recreating up to 70 seasons a year.

Industrial integration

The experimental plant in Ragusa where bio-oil is produced from microalgae works in perfect symbiosis with the upstream operations of the nearby Eni Oil Centre managed by our Enimed subsidiary. Being able to use the CO2 associated with the oil produced by the wells to obtain plant-based biofuels offers the double advantage of reducing the emissions generated by our activities and making new products available on the market. This initiative is currently at the advanced experimental stage required to optimise each step and maximise the efficiency of the entire process. Once we have access to actual production facilities based on this technology it could be applied in countless fields, both within our business and within the energy sphere in general. Its specific design means that the photobioreactor system is compact enough to allow it to be easily installed in very wide variety of industrial situations, wherever there is carbon dioxide to be captured.

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Catturare CO2 per produrre bio-olio algale - #innovation4energy | Eni Video Channel

Environmental impact

The strengths of the technologies we have developed for producing bio-oil from microalgae lie in their simplicity, compactness and ability to use concentrated sunlight or LEDs on the best possible wavelengths to eliminate carbon dioxide by transforming it into valuable substances. These factors make them suitable for applications in the most varied of contexts and compatible with the different operational scenarios that might be encountered in the energy industry. Once they have been developed on an industrial level, these plants could make a significant contribution to reducing the CO2 emissions generated by our upstream operations and other industrial sectors, with the added bonus of obtaining a finished product such as algal flour, which can be used in the downstream sector or sold for use in other production processes. Both of these factors mean that this technology could be adopted on a broad scale, thus boosting the potential positive impact that it could have in terms of limiting carbon dioxide emissions.