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Linde engineers are working with partners to optimise CO2 management at algae cultivation plants in order to manufacture products as efficiently and cost-effectively as possible. The advantage of algae farms is that they can be built on land that is of no agricultural value, such as arid desert regions – meaning that they do not compete with food production.
The special abilities of algae are due to their metabolism. During photosynthesis, algal cells convert sunlight, water and CO2 into the energy-rich molecules they need in order to grow. In small quantities, the microorganisms can directly create fats or oils. Researchers from Sapphire Energy in the USA have optimised the metabolic process of the algal cells and developed a powerful strain capable of producing considerably larger volumes of oil. The microorganisms are cultivated in a briny nutrient solution and fed with CO2-rich air. In the presence of high levels of CO2, the algae grow at an accelerated rate. The main advantage of algae is that they can thrive in a particularly high concentration of CO2 of up to ten percent. This means that they produce two to three times more biomass than rooted plants over the same period of time and area. This makes algae a better source of biofuel than, say, maize.
In May 2011, Linde teamed up with Sapphire Energy, one of the world's leading producers of renewable algal oils, to develop a cost-effective carbon dioxide management system for commercial-scale open-pond algae cultivation plants. To produce one barrel (1 barrel = 159 litres) of bio-oil, or "green crude", the algae require around 600 kg of carbon dioxide.
The result: a negative CO2 footprint
Within this project, Linde engineers are responsible for identifying possible sources of CO2 as well as capturing, purifying and transporting the gas. The primary sources are flue gases from coal-fired power plants and refineries. An intelligent gas management system guarantees that the algae can do their job properly and that the end product has a negative carbon footprint, i.e. removes carbon dioxide from the earth's atmosphere.
It is estimated that commercial-scale algae farms will need a great deal of CO2 in the future – perhaps 10,000 tonnes per day. This corresponds to around 30 percent of the current merchant volume per day in the US. Compared with conventional fossil fuels, green crude has the potential to cut CO2 emissions by as much as 80 percent.
To produce biofuel, Sapphire Energy has developed proprietary technologies for the entire algae-to-biofuel value chain, from the biological reaction through cultivation, harvesting and extraction to refining. The resulting green crude can be used to produce fuels like kerosene, diesel and petrol. It thus fits optimally in existing industrial infrastructures and has great potential as an environmentally friendly raw material. By 2018, the company wants to take up commercial production and produce up to 10,000 barrels of green crude a day.
Turning CO2 into algal oil