Technology Circular economy

A tankful of algae

 By Luca Longo
Circular economy

Eni’s researchers are serious about their plan to eliminate the carbon dioxide produced by oil wells and transforming it into bio-oil (and then into vehicle fuel) using just solar energy and… algae!

They have attained their objective thanks to ten years of intense multidisciplinary research which involved Eni Renewable Energy and Environmental R&D Centre in Novara and Eni Upstream Research Centre in San Donato. The technological effort involved the Upstream and Downstream business areas and the Energy Solutions Division. The pilot installation being used for the production tests is located in Ragusa. At this site Enimed recovers the carbon dioxide extracted from the oil wells, along with the hydrocarbons, where it is separated and sent to Eni Renewable Energy  Centre and injected in 14 large transparent cylinders produced by Sun Algae Technology, an Austrian start up now belonging to an Italian group.

Sun Algae Technology pilot plant in Ragusa

These fibreglass cylinders, five meters high, contain a swirling green liquid composed of swarms of microscopic algae suspended in saltwater. To enhance the air of science fiction, the cylinders are in darkness yet glow in a strange manner.
Looking up at the roof we discover the source of these strange lights: large solar concentrators that revolve slowly tracking the sun. Each concentrator is made of thousands of brilliant Fresnel lenses that concentrate the sunlight on as many optical fibres that transmit it into the cylinders below to illuminate the algae. This is why such systems are called photobioreactors.
With the sunlight focused on the algae and the fossil carbon dioxide gurgling below them, the microscopic aquatic plants have all they need to grow and multiply.
Once they are grown enough, the algae are extracted from the liquid, dried and transformed into an algae cake rich in lipids, from which an oil is extracted and sent to the Eni’s biorefinery nearby, replacing palm oil, the biomass presently used.
In the meantime, their water content is separated, purified and piped back into the photobioreactors where the next generation of microalgae is now growing.

Flour sample obtained by the algae drying process

A look into the future

The pilot plant in Ragusa has the capacity to capture, fix and re-use 80 tonnes of carbon dioxide each year, producing 40 tonnes of algae cake, which in turn can annually produce 20 tonnes of bio-oil thanks to the energy of the sunlight captured by the 320 square meters of solar concentrators.
But this is just the beginning: on the basis of the running datasets obtained from this first pilot plant – up and running since September 2017 – Eni is planning to build a plant with the capacity to treat up to 1,500 tonnes of CO2 each year, again within the Enimed plant in Ragusa.

System of solar concentrators that feed the photobioreactors

This result is the fruit of skills acquired by Eni researchers in several areas: processing and growing of microalgae, development of innovative solar technologies, processes to refine oil products, the formulation of green-chemistry products and biorefinery construction technologies.
In short: the fossil carbon dioxide is removed from oil installations and – thanks to Eni’s biorefineries – converted into green fuel with the help of sunlight. This creates a virtuous cycle between the traditional oil plants and the advanced refineries. Lastly, it is worth remembering that the third generation bio-oil produced turns into a biodiesel that does not compete with food crop cultivation.

READ MORE: Swimming solar the renewables of the future by Amanda Saint

about the author
Luca Longo