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Five Fuels Driving the Future
Replacing the gasoline that fuels our cars is no easy thing. Petroleum-based fuels like gasoline and diesel pack a lot of energy and, even though they're not cheap these days, they still cost less than most - though not all - alternatives. That makes replacing these liquid fossil fuels with more environmentally friendly counterparts a real challenge.
Most of us are aware of the near-term alternatives in limited or demonstration use today, most notably E85 ethanol, biodiesel, and of course those "alternative" fossil fuels, propane (LPG) and natural gas. Beyond these fairly well understood alternatives are little known and somewhat exotic candidates that can also contribute to reducing our dependence on imported oil and decreasing carbon dioxide emissions.
To be successful, an alternative fuel must work with current engine designs, not the other way around. The reason is simple: Engines that run on gasoline, diesel, or their non-petroleum replacements will be in use and consume fuels in considerable volume far into the foreseeable future.
There are two basic categories of feedstocks for advanced alternative fuels - fossil and biomass. Non-renewable fossil fuels include coal and natural gas. These can be converted to familiar liquid motor fuels through a process called liquefaction using coal-to-liquid (CTL) or gas-to-liquid (GTL) technologies. Biomass fuels produced with biomass-to-liquid (BTL) technology use renewable sources such as plants, organic waste, and algae.
Biomass-based equivalents exist for the three most commonly used transportation fuels today, allowing use of ethanol in place of gasoline, biodiesel rather than petroleum diesel (petrodiesel), and biogas instead of natural gas. In at least small quantities, usually less than about 20 percent, most of these fuels can be used in current engines with little or no modifications. Larger amounts may require some modification but not major engine redesigns. Here's how five top future fuels stack up.
Many see ethanol as displacing gasoline in the near term. In his 2007 State of the Union address, President Bush proposed expanding the production of ethanol to 35 billion gallons by 2017. That goal simply can't be reached with ethanol produced from corn, as is commonly done in the United States. At best, less than half of this can be corn-based ethanol because, in this case, the production of fuel must compete for a resource - corn - that's widely used for food.
This feeds controversy. Ethanol from corn is both land and energy intensive. Experts believe there is insufficient agricultural land to grow enough corn for both fuel and food. It also takes about 1,700 gallons of water to produce a gallon of ethanol. While some claim that producing ethanol requires more energy than is required for its creation, that's not quite true. The U.S. Department of Energy says corn-based ethanol provides 26 percent more energy than is required for its production, much of this due to fossil fuels used for fertilizer, diesel for tractors and trucks, and coal and natural gas for operating ethanol plants. Still, that's not an ideal scenario and some dismiss ethanol out-of-hand as a sustainable future fuel because of these issues.
These challenges will be resolved as the industry evolves from the use of food-based resources to cellulosic feedstocks to produce ethanol. Cellulosic ethanol yields 80 percent more energy than is required to grow and convert it into fuel. Since cellulose is present in every plant, there is an abundance of low cost feedstock materials available. There is no difference between corn and cellulosic ethanol in end-use since both are ethyl alcohol.
Most of the cellulosic ethanol research being conducted today is focused on switchgrass because of its high levels of cellulose. An acre of grasses or other crops grown to make ethanol could produce more than twice the number of gallons of ethanol compared to corn. This is partly because the whole plant can be used to make ethanol rather than just the grain, as is the case with corn ethanol. Plus, switchgrass is hardy. This native prairie grass can be grown in most of the U.S. including swamplands, plains, streams, and along shores. It grows fast, is resistant to many diseases and pests, and can produce high yields with low amounts of fertilizer and wildlife-harming chemicals. It is also tolerant to poor soils, flooding, and drought, plus it improves soil quality and prevents erosion.
It's also worth mentioning that cellulosic ethanol can be produced from an estimated 325 million tons of materials discarded annually including urban wood waste, mill residues, corn stover, and wheat straw. There's potential that these sources could provide as much as 30 percent of America's current fuel needs.
While cellulosic biomass is cheaper to grow than corn because it requires less energy, fertilizer, and herbicides, at present this isn't the industry's favored method of creating alcohol fuels. Simply, it's still substantially more expensive to process biomass into ethanol than it is to use corn. The current costs for producing cellulosic ethanol is about $2.25 per gallon, about twice as much as creating ethanol from corn. This cost translates to the equivalent of $120 a barrel oil, something that doesn't seem as distant as in the past. The target is to cut cellulosic ethanol production costs in half by 2012.
Production facilities for producing at least demonstration quantities of cellulosic ethanol are now coming on line. Verenium Corp. plans to produce 1.4 million gallons annually starting this year at its Louisiana plant. Mascoma Corp. has announced plans to build a demonstration facility with a capacity of about a half million gallons annually. SunOpta Inc. is currently producing cellulosic ethanol from corn stover in China. Abengoa Bioenergy is building a five million gallon cellulosic ethanol facility in Spain. Range Fuels in Georgia is raising the bar by building the first commercial-scale, 100 million gallon-per-year cellulosic ethanol plant in the U.S.
COAL-TO-LIQUID FUEL Both indirect and direct liquefaction - the process for creating a liquid from a solid or gas - are already used to produce liquid fuels from coal on a large scale in China, India, Indonesia, and the Philippines. South Africa uses coal liquefaction to provide a substantial percentage of its transportation fuels. In indirect coal liquefaction, intense heat and pressure turns coal into hydrogen and carbon monoxide. After impurities are removed, the synthesis gas is converted into clean liquid fuels and other chemical products through what's called the Fischer-Tropsch (FT) process. Diesel fuel produced by FT synthesis is virtually sulfur-free with low aromatics, has a high cetane number, and burns more completely with less emissions than the recently introduced low-sulfur diesel fuel that's enabling a new generation of "clean" diesel vehicles. In direct coal liquefaction, coal is pulverized and mixed with oil and hydrogen in a pressurized environment, converting the coal into a synthetic crude oil that can then be refined into a variety of fuel products.
Both indirect and direct liquefaction - the process for creating a liquid from a solid or gas - are already used to produce liquid fuels from coal on a large scale in China, India, Indonesia, and the Philippines. South Africa uses coal liquefaction to provide a substantial percentage of its transportation fuels.
In indirect coal liquefaction, intense heat and pressure turns coal into hydrogen and carbon monoxide. After impurities are removed, the synthesis gas is converted into clean liquid fuels and other chemical products through what's called the Fischer-Tropsch (FT) process. Diesel fuel produced by FT synthesis is virtually sulfur-free with low aromatics, has a high cetane number, and burns more completely with less emissions than the recently introduced low-sulfur diesel fuel that's enabling a new generation of "clean" diesel vehicles. In direct coal liquefaction, coal is pulverized and mixed with oil and hydrogen in a pressurized environment, converting the coal into a synthetic crude oil that can then be refined into a variety of fuel products.GAS-TO-LIQUID FUEL
The U.S. military wants to obtain about half of its aviation fuel from alternative sources by 2016 to reduce dependence on foreign-sourced crude oil. In 2006, the USAF - the Pentagon's largest consumer of fuel - for the first time flew a B-52 on a 50-50 blend of the military's conventional JP-8 fuel and Syntroleum synthetic fuel produced from natural gas using a GTL process. The B-52H was fully certified to use the FT blend based on this success. In 2007, this blend was demonstrated in the widely used C-17 Globemaster III cargo plane. The USAF intends to test certify every aircraft in its inventory for the fuel by 2011.
This has important implications for the civilian world. Not only can GTL fuel be used in civilian jet-powered aircraft, but also in diesel engines. Jet fuel and diesel are both kerosene based and quite similar. JP8, and the Navy's JP5, is now the standard fuel for the U.S. military's jet aircraft, helicopters, tanks, fighting vehicles, and trucks.
Synthetic fuels are not targeted exclusively for heavy-duty or military use. In the automotive realm, Audi has used GTL diesel in its R10 TDI Le Mans racers for the past two seasons. The automaker also provided numerous Audi 8 models with 3.0 liter V-6 TDI engines operating on Shell GTL diesel fuel for the World Economic Forum in Switzerland. Unlike petrodiesel, GTL fuel has no sulfur or aromatic compounds. It also offers the benefit of 93 percent less carbon monoxide and 30 percent less NOx emissions with no required engine modifications.
Biogas is primarily comprised of methane and carbon dioxide. It's produced by either fermentation or anaerobic digestion, in which microorganisms break down biodegradable material such as manure, sewage sludge, municipal waste, agricultural wastes, and energy crops. It also goes by varying names such as swamp, marsh, landfill, or digester gas. Biogas can be used for generating electricity, space heating, water heating, and process heating. If compressed, it can be used in natural gas vehicles.
Biogasmax is a large-scale integrated project funded by the European Commission to promote biogas as a vehicle fuel. The Biogasmax project is creating a network of biogas-related demonstrations to share best practices in managing sustainable urban transportation. The cities involved include Stockholm, Gothenburg, Lille, Rome and Berne.
CARBON DIOXIDE FUEL
Okay, while this seems far-fetched, it's grounded enough in reality to prompt a U.S. national laboratory to be seriously involved in the effort. In the future, there's potential that fuels could be produced from carbon dioxide, solving two problems - dependence on imported oil and dealing with CO2 greenhouse gases. The Department of Energy's Sandia National Laboratories in Albuquerque, New Mexico, is attempting to do this in the "Sunshine to Petrol" project, which would use concentrated solar energy to chemically "reenergize" carbon dioxide into carbon monoxide. The carbon monoxide would then be used to synthesize a liquid combustible fuel, such as methanol or even gasoline, diesel, and jet fuel.
Don't look for this solution in the short term, though. Sandia researchers say that if the technology pans out, it will probably be 15 or 20 years before its liquid solar fuel could be available commercially. Like you, we're hoping for a shorter time frame that allows this solar fuel to shine.
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