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Bioreactor: how to make oil growing algae on exhaust gas piped from power stations and remove 75 per cent of CO2 from power station exhaust

Posted by gasweek on 12 October, 2007

For its supporters the idea of growing single-celled algae on exhaust gas piped from power stations was the ultimate in recycling; and now one of them, CleanTech, has developed a bioreactor based on a patent held by a group of scientists at the Ohio Coal Research Centre, at the University of Ohio, reported The Economist, (8/9/2007, p. 6).

How it works – first method: The GS Cleantech bioreactor used a parabolic mirror to funnel sunlight into fibre-optic cables that carried the light to acrylic “glow plates” inside the reactor. These diffused the light over vertical sheets of polyester that formed the platform on which the algae grew. Eventually the polyester was unable to support the weight of the algae, and they fell off into a collection duct positioned underneath.

How it works – alternative method: GreenFuel Technologies, based in Cambridge, Massachusetts, had a different approach:

• its reactor is composed of a series of clear tubes, each with a second, opaque tube nested inside. This arrangement made it possible to bubble the exhaust gas down the outer compartment and then bubble it back up through the opaque middle;

• bubbling gas caused turbulence and circulated the algae around the reactor.

• the constant shift between light and darkness as the algal cells circulated increased the amount of carbon they fixed, probably by promoting chemical reactions that occurred naturally only at night.

75 per cent CO2 cut: A preliminary test of GreenFuel’s reactor design, which was performed at the Massachusetts Institute of Technology’s campus power plant, suggested that it can remove 75 per cent of the carbon dioxide from a power station’s exhaust. A more serious test is now being carried out by Arizona’s Public Service, at that state’s Redhawk power utility. Another test was planned in Louisiana

One hectare makes 30,000 litres of oil: GreenFuel claimed over the course of a year one hectare (2.5 acres) of its reactors should be able to produce 30,000 litres (8,000 American gallons) of oil, which could be used as biodiesel, and enough carbohydrates to be fermented into 9,000 litres of ethanol, which can be used as a substitute for petrol.

The Economist, 8/9/2007, p. 6

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