Algae-to-Gas Route Gets Boost

The technology could provide the cheapest biofuel competitive with natural gas.

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A biomass gasification process developed at the U.S. Department of Energy's Pacific Northwest National Laboratory (PNNL), Richland, Wash., moved closer to commercialization in May when an exclusive license to the technology was granted to Genifuel Corp., Salt Lake City, Utah. That company hopes to begin piloting the algae-to-natural-gas route in 2010, says Jim Oyler, its president.

With this gasification process, we can convert the [aquatic] biomass to a clean fuel that is almost completely carbon-neutral.

– Jim Oyler, president, Genifuel Corp.
In the continuous process, algae is fed into the bottom of a fixed-bed catalytic tubular reactor operating at 350°C and 3,000 psi. It's almost instantaneously converted into a gas stream nearly identical in composition to natural gas. The gas typically contains 97.4% methane, 1.3% ethane, 0.5% hydrogen and 0.5% carbon dioxide. A small amount of ash also is produced. PNNL has been developing the process for about a decade. The latest catalyst, a ruthenium-based material, provides greater activity and longer life (over six months) — and enables the reactor to handle wet biomass such as algae without need for drying. Compared to anaerobic digestion, the process reportedly works 400 times faster and provides higher yields.

"At Genifuel, we have developed efficient growth and harvesting techniques for the aquatic biomass. With this gasification process, we can convert the biomass to a clean fuel that is almost completely carbon-neutral," says Oyler. The CO2 produced is separated and recycled to grow more algae, he explains.

The technology (Figure 1) should provide the cheapest biofuel, he believes, competitive with natural gas at $8 or more per 1,000 scf.

Investment costs should be relatively low, adds Oyler, because the algae can be grown in simple open-air ponds, harvesting is easy, and the reactor is just a vertical stainless-steel vessel with catalyst on a fixed screen or grid.

PNNL has run laboratory tests at scales of up to 33 L/hr. Genifuel hopes to build an acre or more of ponds for growing algae and a pilot plant that produces 1,000 scfd of gas, says Oyler. The site has yet to be selected but likely will be in the western or southern U.S. Trials should last a year.

Oyler foresees commercialization in 2011–2012. Genifuel is prepared to operate plants but also is open to licensing the technology. The catalyst isn't particularly exotic, he notes, so there shouldn't be any issues about supplying it in sufficient quantities.
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