Cultivating algae for liquid fuel production
Thomas F. Riesing, Ph.D. - Permaculture Activist
With the increasing interest in biodiesel as an alternative to petrodiesel, many have looked at the possibility of growing more oilseed crops as a solution to the problem of peak oil. There are two problems with this approach: first, growing more oilseed crops would displace the food crops grown to feed mankind. Second, traditional oilseed crops are not the most productive or efficient source of vegetable oil. Micro-algae is, by a factor of 8 to 25 for palm oil. and a factor of 40 to 120 for rapeseed, the highest potential energy yield temperate vegetable oil crop. Michael Briggs at the Univ. of N. Hampshire Biodiesel group estimates that using open. outdoor, racetrack ponds, only 15,000 square miles could produce enough algae to meet all of the USA's ground transportation needs. Transportation accounts for 67% of US oil consumption according to the Atlantic Monthly, July/August 2005. We'll say more about the 15,000 square mile number below. If all of this land were in one rectangular piece, it would be 120 miles by 125 miles—about 1/7th of the area of the state of Colorado.
In this article we will first look at some of the publicly available research that has been done on the use of algae as a source for biodiesel. We will then examine some current projects that are using or trying to use algae to produce biodiesel. Finally, we will look at the implications of these for our energy future.
The National Renewable Energy Laboratory
During the oil crisis of the 1970s, Congress funded the National Renewable Energy Laboratory (NREL) within the Department of Energy to investigate alternative fuels and energy sources. Between 1978 and 1996, the Aquatic Species Program (ASP) focused on the production of biodiesel from high lipid-content algae growing in outdoor ponds and using CO2 from coal-fired power plants to increase the rate of algae growth and reduce carbon emissions. Prior to this program, very little work had been done to understand the growth process and metabolic composition of algae. As a result of the ASP there are now some 300 species, mostly diatoms and green algae, in a collection stored at the Marine Bioproducts Engineering Center that is available to researchers interested in developing algae as an energy source. (2)
Some results listed in the Close Out Report of the ASP are:
· Under optimum growing conditions micro-algae will produce up to 4 lbs./sq. ft./year or 15,000 gallons of oil/acre/year. Micro-algae are the fastest growing photosynthesizing organisms. They can complete an entire growing cycle every few days.
· One quad (1015 BTU or 7.5 billion gal.) of biodiesel could be produced on 200,000 ha of desert land (equivalent to 772 sq. mi., roughly 500,000 acres). (To produce one quad from a rapeseed crop would require 58 million acres or 90,000 sq. mi.)
· The outdoor race-track pond production system is the only economically feasible approach given the cost of petroleum in 1996. (One of the problems with growing algae in any kind of pond is that only in the top 1/4" or so of the water does the algae receive enough solar radiation. So the ability of a pond to grow algae is limited by its surface area, not by its volume.)
· Algae contains fat, carbohydrates, and protein. Some of the micro-algae contain up to 60% fat. Once the fat is 'harvested'— some 70% can be harvested by pressing—what remains becomes a good animal feed or can be processed to produce ethanol.
· The desert test location in New Mexico had sufficient sunlight, but low nighttime temperatures limited the ability to achieve consistently high productivity.
· There were problems getting lab-cultured algae to grow in the outside pond environment.
· No tests were carried out on mechanisms and procedures for harvesting the algae nor on the extraction of oils from the algae.
GreenFuel bioreactor in field test
GreenFuel Technologies in Cambridge, MA is field testing a closed system that uses the CO2 in power plant flue gases (13% of flue gases in the test) to feed algae. (3,4) In so doing, it significantly reduced the CO2 concentration in the exhaust by 82.3% (+/-12.5%) on sunny days and by 50.1% (+/- 6.5%) on cloudy days during the beta-test at the Cogeneration Plant at MIT. (5) The process also removed 85.9% (+/- 2.1%) of nitrogen oxides. And, not only will the GreenFuel Bioreactors reduce carbon and NOx emissions, but the company estimates the cost of a full-scale system installation to be 20% to 40% less than that of a comparable SCR system (pollutant scrubbers).
Using technology licensed from a NASA project, GreenFuel constructs triangular-shaped bioreactors from polycarbonate tubing two to three meters long and 10-20 cm in diameter. The hypotenuse of the triangles face the sun. Flue gases are introduced at the bottom of the hypotenuse and flow up while the media containing the algae flow in the opposite direction. From 15% to 30% of the algal media are harvested each day. The use of tubes in which to grow the algae overcomes the usual surface area limitation of ponds. In this case the turbulent mixing of the algal media with CO2 in the tubes and the speed at which the fluid moves determine how fast the algae grow.
"Until now, it was proving that the technology works. Now, basically, it's proving that the economics behind the technology work," said Isaac Berzin, chief technology officer. "The idea behind all this is that it's not a charity. If it makes sense economically, it will happen." "I read descriptions of all this (previous) research, and it was clear to me that the limiting factor was the engineering side of the system," he said. "Algae can take (carbon dioxide), eat it, and produce algae, that's a known fact. But if your system fails, it's a problem with the system, not the algae."
GreenFuel estimates that 70% of the power plants in the United States have enough space and 'food' to install a full complement of Bioreactor arrays. In the United States about 60% of the oil we use is for ground transportation—cars, vans, and trucks—while only about 25% is used as electricity. Potentially this means that GreenFuel reactors might be able to provide 2025% of the fuel needed to meet our transportation needs.
The GreenFuel Bioreactors could be used to fuel the power plant from which the algae are being fed. So you could build a power plant—including the reactors—and only have to provide it with enough fuel to get the bioreactors going! These reactors could also be used in breweries, fed from the excess CO2 that most breweries just waste.
Large-Scale Algae Production
Michael Briggs, a physicist in the University of New Hampshire (UNH) Biodiesel group, calculated the annual equivalent amount of biodiesel needed to meet all US ground transportation needs. (6) He assumes that all gasoline-powered vehicles could be replaced over time—the average life of a car in the US is 20 years—by biodiesel vehicles. He assumes no change in the current average fleet mileage, but does factor in that diesel engines are more efficient. With these assumptions—and a correction for the 2% lower mileage for biodiesel—he arrives at 140.8 billion gallons of biodiesel a year to meet US ground transportation needs. He does note that if people began to buy diesel hybrids (Mercedes showed its diesel hybrid concept car in June and it gets 70 mpg), the total fuel required might be reduced by a factor of three or more. (7)
Briggs used the numbers from NREL's Aquatic Species Program—that one quad (7.5 billion gallons) of biodiesel could be produced on 200,000 ha (roughly 500,000 acres) or about 780 square miles—to compute that 140.8 billion gallons of biodiesel would requre 19 quads (140.8 ÷ 7.5).This would require about 15,000 square miles (19 x 780), or about 9.5 million acres—which he notes is only about 12.5% of the area of the Sonoran desert of the Southwest. So using algae as a source of oil for biodiesel with the NREL productivity assumption, the acreage required is less than 3% of the 450 million acres now used to grow crops.
Based on a UNH research project, (8) Briggs then estimates the total cost of producing 140.8 billion gallons of oil (unrefined) for biodiesel at $46.2 billion—substantially less than the $100150 billion that the US currently spends to purchase foreign crude oil. Thus the large-scale algae farms envisioned by NREL would generate many jobs and substantially reduce the US trade deficit.
Other researchers have proposed a mammoth-scale algae production scheme to meet US requirements at fully amortized costs ranging from about $19 to $57 per equivalent barrel of petroleum. (9) This project assumes that an aqueduct could be built from the Pacific ocean to the Salton Sea and another from there to Death Valley and more aqueducts to other desert locations in Nevada, Arizona, and New Mexico. Such a scheme might have been possible in another era, but it hardly seems likely today.
Small-scale algae production in SolaroofTM greenhouses (10) could allow small-scale farmers to produce their own fuels. SolaroofTM greenhouses dramatically reduce the amount of heat required to operate a greenhouse through the winter. Most new commercial greenhouses use two layers of greenhouse plastic. The two layers are separated by an air space which is inflated by a small fan to provide more rigidity to help the roof deflect wind and shed rain and snow. The SolaroofTM greenhouse has two complete skins—one outside and one inside. During the daytime, this space may also be filled with air, but when the nights are cold or when the days are excessively hot, the space between the two skins is filled with soap bubbles.
The thermodynamics of heat transfer are such that any airspace more than about 1/4 inch has an R-value of 1. As a result, when the 12 to 18 inch space between the skins on a Solaroof greenhouse is filled with soap bubbles, it has an R-value between 20 and 40. During a hot summer day, the soap bubbles act like a cloud over the sun, leaving the inner skin of the roof cool, and appearing to the plants as if it were open sky. This can actually increase growth rates.
In high snow areas, the conventional two-layer plastic covering sheds snow because the greenhouse heating system keeps the inner skin at 50°F (10°C). This temperature is high enough to melt the snow fast enough so that there is no structural loading due to the snow. The system uses a bubble generator to fill the space with bubbles generated from water and soap that are at the ambient temperature of the greenhouse, which would also be about 50°. But unless the bubbles are continuously regenerated during a snow storm, it is doubtful that the snow would melt and relieve the structural loading.
Greenhouses can be modified to produce algae all year round. The surface area limitation which applies to ponds could be overcome in a greenhouse by adding a third layer of plastic inside the other two layers over which the pond water could flow in a thin enough film that it would receive enough solar radiation to grow algae. This should allow the SolaroofTM greenhouse to produce more algae than the surface area of a normal pond would. This mechanism for exposing the pond water to sunlight is similar to that employed by GreenFuel Technologies.
The greenhouse would also overcome two problems observed in the ASP trials in outdoor ponds—the greenhouse allows for better control of both the temperature and the air in the greenhouse. This should allow optimum growth as well as eliminate the possibility of contamination with local algae.
For small-scale operations to be effective, local co-operative biodiesel processing plants would also have to be constructed to convert the raw oil into fuel. A biodiesel cooperative in LaPlata County, Colorado, just completed a feasibility study that found it feasible to construct a 1-million gallon processing facility there to provide biodiesel for the county and a handful of other large users.
The research work carried out by the National Renewable Energy Laboratory seems to be on the verge of paying off. The bioreactors developed by GreenFuel Technologies could substantially reduce power plant carbon emissions. The biodiesel that these reactors produce could potentially replace 20-25% of the petroleum-based fuel used for transportation. If the GreenFuel technology can be adapted to greenhouses, they could become a small-scale, highly distributed source of fuel oil and perhaps prevent the emergence of a new fuel monopoly like Big Oil.
Tom Riesing, a former investment banker, with his partner Christie Berven, a retired elementary school teacher, operate Oakhaven Permaculture Center. Both trained in Permaculture Design at Central Rocky Mountain Permaculture Institute and in Permaculture Teaching at Earthaven Ecovillage. They designed their own home near Durango, Colorado and garden extensively throughout the year thanks to their 2,200 sq.ft. greenhouse.
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