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Widescale Biodiesel Production from Algae
Michael Briggs, University of New Hampshire, Physics Department
As more evidence comes out daily of the ties between the leaders of petroleum producing countries and terrorists (not to mention the human rights abuses in their own countries), the incentive for finding an alternative to petroleum rises higher and higher. The environmental problems of petroleum have finally been surpassed by the strategic weakness of being dependent on a fuel that can only be purchased from tyrants.
In the United States, oil is primarily used for transportation - roughly two-thirds of all oil use, in fact. So, developing an alternative means of powering our cars, trucks, and buses would go a long way towards weaning us, and the world, off of oil. The best alternative at present is clearly biodiesel, a fuel that can be used in existing diesel engines with no changes, and is made from vegetable oils or animal fats rather than petroleum.
In this report, we will first examine the possibilities of producing biodiesel on the scale necessary to replace all petroleum transportation fuels in the U.S.
I. How much biodiesel?
First, we need to understand exactly how much biodiesel would be needed to replace all petroleum transportation fuels. So, we need to start with how much petroleum is currently used for that purpose. Per the Department of Energy's statistics, each year the US consumes roughly 60 billion gallons of petroleum diesel and 120 billion gallons of gasoline. First, we need to realize that spark-ignition engines that run on gasoline are generally about 40% less efficient than diesel engines. So, if all spark-ignition engines are gradually replaced with compression-ignition (Diesel) engines for running biodiesel, we wouldn't need 120 billion gallons of biodiesel to replace that 120 billion gallons of gasoline. To be conservative, we will assume that the average gasoline engine is 35% less efficient, so we'd need 35% less diesel fuel to replace that gasoline. That would work out to 78 billion gallons of diesel fuel. Combine that with the 60 billion gallons of diesel already used, for a total of 138 billion gallons. Now, biodiesel is about 5-8% less energy dense than petroleum diesel, but its greater lubricity and more complete combustion offset that somewhat, leading to an overall fuel efficiency about 2% less than petroleum diesel. So, we'd need about 2% more than that 138 billion gallons, or 140.8 billion gallons of biodiesel. So, this figure is based on vehicles equivalent to those in use today, but with compression-ignition (Diesel) engines running on biodiesel, rather than a mix of petroleum diesel and gasoline. Combined diesel-electric hybrids in wide use would of course bring this number down considerably, but for now we'll just stick with this figure.
One of the biggest advantages of biodiesel compared to other alternative transportation fuels is that it can be used in existing diesel engines. This completely eliminates the "chicken-and-egg" dilemma that other alternatives have, such as hydrogen powered fuel cells. For fuel cells, even when (and if) vehicle manufacturers eventually have production stage vehicles ready, nobody would buy them unless there was already a wide scale hydrogen fuel production and distribution system in place. But, no companies would be interested in building that wide scale hydrogen fuel production and distribution system until a significant number of fuel cell vehicles are on the road, so that consumers are ready to start using it.
However, with biodiesel, since the same engines can run on conventional petroleum diesel, manufacturers can comfortably produce diesel vehicles before biodiesel is available on a wide scale. As biodiesel production continues to ramp up, it can just go into the same fuel distribution infrastructure, just replacing petroleum diesel. Not only does this eliminate the chicken-and-egg problem, making biodiesel a much more feasible alternative than fuel cells, but also eliminates the huge cost of revamping the nationwide fuel distribution infrastructure.
II. Large scale production
There are two steps that would need to be taken for producing biodiesel on a large scale - growing the feedstocks, and processing them into biodiesel. The latter step would perhaps be best accomplished by existing oil refineries within the US being converted to biodiesel refineries, but could also be accomplished by new companies building new plants. The main issue that is often contested is whether or not we would be able to grow enough crops to provide the oil for producing the amount of biodiesel that would be required to completely replace petroleum as a transportation fuel. So, that is the main issue that will be addressed here.
The Office of Fuels Development, a division of the Department of Energy, funded a program from 1978 through 1996 under the National Renewable Energy Laboratory known as the "Aquatic Species Program". The focus of this program was to investigate high oil yield algaes that could be grown specifically for the purpose of wide scale biodiesel production1. Some species of algae are ideally suited to biodiesel production due to their high oil content (some as much as 50% oil), and extremely fast growth rates. From the results of the Aquatic Species Program2, algae farms would let us supply enough biodiesel to completely replace petroleum as a transportation fuel in the US (as well as its other main use - home heating oil).
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