Using algae for carbon mitigation at power plants is gaining momentum but there is disagreement over whether it's the best or most efficient use of the resource.
An Arizona Public Services' project at Cholla Power Plant in Holbrook, Ariz., is set to be the first integrated pilot-scale demonstration of capturing CO2 from a coal-fired power plant with algae in the U.S., according to Daniel Cicero, senior management and technology advisor for the U.S. DOE's National Energy Technology Laboratory in West Virginia. The 25-acre raceway pond project, which should be completed and operating in the next three to four years, is an expansion of APS's research and development endeavor at its natural gas-fired Redhawk Power Station near Phoenix, according to Cicero. "The algae technology is being considered to be an integral part of the electric power plant for its mitigation of CO2 emissions and for further reuse of the CO2 into a coproduct (substitute natural gas) with the electric power from the plant," he says. Researchers expect that the Cholla algae farm will reuse CO2 at a rate of 70 metric tons per acre per year.
The project received $70.5 million from the American Recovery and Reinvestment Act, one of many algal carbon mitigation endeavors awarded federal funding. "We began a program several years ago about using algae to absorb CO2 from power stations and further use that CO2 as opposed to just emitting it," says Cicero, who works in the DOE's Office of Fossil Energy. The ARRA also awarded a total of $7.02 million for design and evaluation of algae growth projects at industrial emitters, including some power plants, in Hawaii, Virginia, Ohio, Texas and California. More funds will be awarded after another competitive process to determine which projects will see the remaining three phases of development-detailed design, construction and operation. Those projects are expected to come on line shortly after the Cholla application, although they will be smaller.
Cicero sees promise for the practice from bench-scale results, but acknowledges work left to be done. "It's going to take a lot of land mass to capture significant amounts of CO2," he says, adding that some areas are more amenable to algae growth than others and applications must be tailored to specific locations. "We have been able to demonstrate that depending on the strain of algae you choose, it can be very effective in [certain areas], but you have to be careful which strains of algae are chosen and how you process those algae." On average, about 60 percent of the carbon dioxide can be captured daily, according to the Office of Fossil Energy.
The algae grown with carbon emissions can enhance domestic biofuel production and contribute to energy security, but carbon dioxide abatement is the most important benefit, according to Cicero. "Our primary focus is on CO2 capture and helping companies get renewable energy credit," he says.
Abandon All Hope
But some researchers believe that the focus should be changed, including John Benemann of Benemann Associates. The number of power plants with the right conditions for growing algae is small, according to Benemann, and it's difficult to match up a sufficient growth operation with plant size. "Even under the best circumstances, the amount of CO2 mitigated is not overwhelming," he says. At most a small fraction of a percent of total CO2 emissions from power plants could be abated by microalgae, he explains, so those who believe algae will solve the problem should abandon all hope.
Benemann has researched microalgae for more than 30 years and says there are a number of issues related to using it for carbon mitigation. The best way to look at such a project is in the benefit of biofuels production, not CO2 mitigation. "Rather than using algae to mitigate CO2 from power plants, use power plants to supply CO2 for algae biofuels production needs … Just like any other biofuel, it doesn't matter where the CO2 comes from," he says. "It doesn't matter if you take it from a power plant or from the atmosphere."
In his paper, "Microalgae Biofuels: A Brief Introduction," Benemann writes that contrary to common belief, CO2 use by algal cultures is not sequestration, nor even a greenhouse gas (GHG) abatement process by itself. "…that could only come from using the algal biofuels to replace fossil fuels, in the same way as all other biofuels are assumed to replace fossil fuels and thereby reduce greenhouse gas emissions and mitigate global warming." In actuality, algae-based biofuels using fossil fuel flue gas CO2 are less desirable for GHG abatement than higher plant biofuels, he writes. By depending on the consumption of fossil fuels they indirectly contribute to the atmospheric CO2 load and are by definition unsustainable. They enable fossil fuel use, he argues.
Of all the factors that limit the potential of algal biofuels, including suitable climate, land, water, nutrients and CO2 on-site, CO2 is likely the most limiting, according to Benemann. Carbon dioxide supply from power plants is not cost-free because of the necessary capital and operational costs of supplying the CO2 to the ponds. Capturing carbon dioxide from large fossil fuel power plants would require tens of thousands of hectares of algae ponds in close proximity to the plants, he continues. Further, large land and water resources are uncommon at most large power plants, and only about half the captured CO2 is captured in the biofuel.
"You can make a case for algae biofuels production, but you cannot make a case for algae saving coal-fired power plants from emitting CO2," he says. More concentrated fossil fuel CO2 sources such as refineries and ammonia plants would be more suitable, along with smaller-scale nonfossil fuel sources such as wastewater treatment plants.
Location, Location, Location
A Bard Holding Inc. pilot project in Pennsylvania will begin to produce 20 million gallons of algae oil for biofuels in April, using a nearby industrial and municipal wastewater treatment plant, along with emissions from three natural gas power plants, including Dominion, one of the largest in the northeast corridor. Bard has a purchase agreement on 38 of the 2,700 acres at the Keystone Industrial Port Complex in Fairless Hills. Once the pilot is operational, Bard plans to construct a full-scale 66 million-gallon-per-year photobioreactor algae production system.
"The reason we chose this site is the wastewater treatment plant is less than 500 yards from our site and adjacent to the Dominion power plant," said Surajit Khanna, Bard founder and chairman of the board. "This is the best scenario you could ever have." In addition, a number of other steam-generating plants operate within a 10-mile radius.
The relatively high content of carbon dioxide in flue gas significantly increases growth rates in the species of algae used in Bard's photobioreactor technology. The algae will be harvested every 30 minutes and the key to such vigorous harvesting is the amount and frequency of carbon dioxide pumped into the algae system, Khanna says. The company says its process can be used at virtually any power plant with the incorporation of slug flow technology to create favorable conditions for algae growth.
Contrary to Benemann's beliefs, the company says the main benefit of using industrial waste streams for algae growth is the atmospheric cleanup, but it also generates carbon credits and brings down operating and materials costs. "All these power plants will be penalized if they don't have a solution for taking CO2 and using it," says Sharon Miller, vice president of strategic planning for Bard. "You can't emit carbon dioxide anymore. If you can't emit carbon dioxide, then you don't have an industry. Everything emits carbon dioxide."
‘Little Green Factories'
Seattle-based Bioalgene Inc. will use its open pond algal carbon-capture process to generate carbon credits for coal-fired power plants and wastewater treatment facilities, as well as to produce algal biomass for products. "Both industries are awakening to the benefits of algae cultivation as a means to generate benefits from handling their waste products," says CEO Stan Barnes. He refers to the applications as "little green factories."
Bioalgene's three-phase process-evaluation, pilot and scale up-has the potential to dramatically reduce emissions at coal-fired power plants, allow the plants to reuse substantial amounts of water, and provide greater efficiency for their processes, according to Barnes. He says the most important benefit is the carbon credits. "We think that algae are the largest scale, most efficient, least costly means to do that."
Contrary to Benemann's argument, Barnes says his process is 30 percent more efficient when CO2 is gathered from a concentrated source, than when it's taken from an atmospheric source, although both can be efficient.
Both Barnes and Keven Vorce, vice president of finance for Bard, agree that growing algae with CO2 emissions and industrial waste is sustainable. "It's a permanent renewable source," Vorce says. "Power plants and wastewater treatment plants will continue operating until the world comes to an end."
A Bioalgene project at a coal-fired power plant in Boardman, Ore., will complete phase two this summer and a couple more locations are developing phase one, according to the company. Full commercialization of the Bioalgene process is three to four years away, Barnes says. "Neither we, nor anybody else has fully scaled these systems," he says. "We're confident we'll be able to do that. It's by no means an established industrial process yet, but we're all working hard at this because we see the potential." BIO
Lisa Gibson is a Biomass Magazine associate editor. Reach her at firstname.lastname@example.org or (701) 738-4952.