Concentrated CO2 gives algae growth spurt

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Concentrated CO2 gives algae growth spurt

The University of Twente recently developed a new technology to cheaply and efficiently capture CO2 from ambient air. The CO2 thus captured is used by the university to grow algae, but can also be used to store solar and wind energy in a closed cycle.

The ‘CO2 air capture unit’, the machine used by the University of Twente to capture CO2 from the air, was designed to capture at least 500 grams of CO2 from the air per day. The CO2 is present in the air a strongly diluted form (approximately 400ppm). As a result, around 1400 cubic meters of air is needed to get one kilo of CO2.

Four trees

The test set-up used by the university captures CO2 from the ambient air rather than specific flue gases. The capacity of the new air capture unit can be compared to that of four big trees, each planted on a surface area of 50 square meters. The University of Twente will be using the device that captures CO2 from the air to grow algae, a valuable resource for food ingredients and various chemicals in it the bio-based economy. The growth rate of the algae is increased drastically under the influence of CO2.

Cycle

To achieve the current capacity with which the university aims to capture CO2 from the air the researchers use sorbents, small particles to which CO2 binds. In an ‘adsorber’, the researchers bring non-charged particles into contact with a huge air flow that moves through the unit with a very low pressure drop. As soon as the particles are charged with CO2, they travel up to the top of the unit, which is about six meter in height. From there, gravity propels them to flow down through a heated column, the ‘desorber’, where they deliver their CO2 load. After this, the sorbents will repeat the same cycle again.

Opportunities for greenhouse horticulture

The CO2 -rich gas subsequently travels from the air capture unit to the algae reservoir. Although cooling down and heating requires energy, the net energy consumption of the capture unit is relatively low. The energy costs (estimated at about 75 euros per 1,000 kilograms of CO2) are relatively limited and in line with the current prices on the market for CO2. It is expected that the greenhouse horticulture industry will able to benefit from this technology. “The use of ‘CO2 air capture’ makes it possible to produce CO2 more sustainably, no matter where in the world”, says project leader Dr Wim Brilman.

Sustainable natural gas

The CO2 thus captured can also be used to store solar or wind energy. Using CO2 from the air, together with hydrogen, it is possible to produce methanol and sustainably produced methane (‘natural gas’). Thanks to this interim step, peaks in the supply and demand of energy can be responded to adequately, without any need for batteries. This ‘natural gas route’ will be tested in a ‘Power-to-Gas’ system connected to an existing apartment building complex in Rozenburg.

Source: NWO/Universiteit Twente. Photo: Gijs van Ouwerkerk.

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