|
Alternative fuel, also known as non-conventional fuels, is any material or substance, other than petroleum (oil), which is consumed to provide energy to power an engine. Some alternative fuels are biodiesel, ethanol, butanol, chemically stored electricity (batteries and fuel cells), hydrogen, methane, natural gas, wood, and vegetable oil. The need for the development of alternative fuel sources has been growing, due to concerns that the production of oil will no longer supply the demand. See future energy development for a general discussion. In a battery or fuel cell powered vehicle, the "fuel" is the set of chemicals which is oxidized and reduced to provide the electricity. In some circumstances, however, electricity may be provided directly to a mobile electric engine, such as an electrified trolley or train, or a magnetically levitated train. In such cases, electricity itself may be treated as an alternative "fuel," since it replaces fuel energy used in transportation. Electricity will be treated as a "fuel" in this article. Alternative fuel has become a topic of rapidly increasing interest due to global warming, rising gasoline prices, and the increasing pressure put on crude oil stocks. In the year 2000, there were about eight million vehicles around the world that ran on alternative fuels, indicating the increasing popularity of alternative fuels. Categorization Some of these come into the category of renewable energy. Renewable energy includes electricity generation for the home, while the term "alternative fuels" tends to refer to mobile energy (the source of which energy is usually renewable, but is not required to be). Some alternative fuels and the cars they power are: Gasoline type biofuels Diesel type biofuels Others with internal combustion External combustion No combustion Some less conventional alternative fueled cars are: Most alternative fuels are designed to be cheap, non-polluting, non-finite sources of energy. No such fuels currently exist globally, or they would by now be rapidly replacing current fossil fuels. Few countries, for example, have the natural resources of Brazil which enables its attempt to switch to an alternative ethanol economy. Renewable energy Main article: Renewable energy A possible solution to a potential future energy shortage would be to use some of the world's remaining fossil fuel reserves as an investment in renewable energy infrastructure such as wind power, solar power, tidal power, geothermal power, hydropower, thermal depolymerization, methanol, ethanol and biodiesel, or in an oil lamp; try olive oil, canola oil, safflower oil, or sunflower oil which do not suffer from finite energy reserves, but do have a finite energy flow. The construction of sufficiently large renewable energy infrastructure might avoid the economic consequences of an extended period of decline in fossil fuel energy supply per capita. Most alternative fuels assume a source of renewable energy or at least sustainable energy (such as nuclear power) as a source of the fuel. A few alternative fuels (for example, hydrogen) may be made by sustainable or nonsustainable means. If they are made by non-sustainable means, such fuels are offered as alternatives usually because they offer to cause less pollution at the point of use, and perhaps less pollution overall. Non-conventional oil Non-conventional oil is another source of oil separate from conventional or traditional oil. Non-conventional sources include: tar sands, oil shale and bitumen. Potentially significant deposits of non-conventional oil include the Athabasca Oil Sands site in northwestern Canada and the Venezuelan Orinoco tar sands. Oil companies estimate that the Athabasca and Orinoco sites (both of similar size) have as much as two-thirds of total global oil deposits, but they are not yet considered proven reserves of oil. Extracting a significant percentage of world oil production from tar sands may not be feasible. The extraction process takes a great deal of energy for heat and electrical power, presently coming from natural gas (itself in short supply). There are proposals to build a series of nuclear reactors to supply this energy. Non-conventional oil production is currently less efficient, and has a larger environmental impact than conventional oil production. Other fossil fuels and the Fischer-Tropsch process It is expected by geologists that natural gas will peak 5-15 years after oil does. There are large but finite coal reserves which may increasingly be used as a fuel source during oil depletion. The Fischer-Tropsch process converts carbon dioxide, carbon monoxide, and methane into liquid hydrocarbons (Gas To Liquid, see GTL) of various forms. The carbon dioxide and carbon monoxide are generated by partial oxidation of coal and wood-based fuels (see Biomass To Liquid BTL). This process was developed and used extensively in World War II by Germany, which had limited access to crude oil supplies. It is today used in South Africa to produce most of that country's diesel from coal. The Karrick process is an improved methodology for coal liquefaction, with higher efficiency. Since there are large but finite coal reserves in the world, this technology could be used as an interim transportation fuel if conventional oil were to become scarce. There are several companies developing the process to enable practical exploitation of so-called stranded gas reserves, those reserves which are impractical to exploit with conventional gas pipelines and LNG technology. Another potential source of methane is methane hydrate. This substance consists of methane molecules trapped within the crystalline structure of water ice and is found in naturally-occurring deposits under ocean sediments or within continental sedimentary rock formations. It is estimated that the global inventory of methane hydrate may equal as much as 10x the amount of natural gas. With current technology, most gas hydrate deposits are unlikely to be commercially exploited as an energy source. In addition, the combustion of methane results in the formation of carbon dioxide and would thus continue to contribute to global warming (methane hydrate may not actually be derived from true "fossil" sources (i.e., previously living matter), but in other respects it has the same problems of fossil fuel). Methanol (methanol economy) from any source can be used in internal combustion engines with minor modifications. It usually is made from natural gas, sometimes from coal, and could be made from any carbon source including CO2. Flexible fuel vehicles may run with a high share of ethanol (ethanol economy) (up to 85% Ethanol plus 15% gasoline for cold-starting vapor pressure). However, methanol or ethanol are not sources of energy, but merely a convenient way to store the energy for transportation. They represent a way to obtain liquid fuel, but require a net loss of energy in manufacture, which must come from a source like fossil fuel planetary reserves, solar radiation (either through photosynthesis or photovoltaic panels), or hydro, wind or nuclear energy (see below). Use of energy to produce alcohol fuels would proceed via production of hydrogen by electrolysis or possibly (in the case of heat from nuclear energy) by the sulfur-iodine cycle; then use of the hydrogen in the Fischer-Tropsch process along with CO2 from another source. Such a process might store and use hydrogen more efficiently than attempting to use hydrogen directly as fuel (a gallon of alcohol contains about 50% more hydrogen by weight than a gallon of liquid hydrogen). Since such a process would not liberate net new CO2 at the point of combustion, it would be greenhouse neutral, similar to alcohols made from biomass. Nuclear power and transportion energy and fuel The U.S. would require at least an eightfold increase in nuclear power production, from 10% of all energy supplied to about 90%, to replace both the current amount of electricity generated from fossil fuels and gasoline usage. Fission reactors Nuclear engineers estimate that the world could derive 400,000 quads (quadrillion, 1015, British thermal units), or about 420,000 EJ (exojoules = 1018 joules), of energy (1000 years at current levels of consumption, assuming new technology) from uranium isotope 235, if reprocessing is not employed. As uranium ore supplies are limited, a majority of this uranium would have to somehow be cost-effectively extracted from seawater. But, this technology does not exist. However, at the current technology and consumption, the reserves will last 50 years. Fast breeder reactors are another possibility. As opposed to current LWR (light water reactors), which burn the rare isotope of uranium U-235 (producing and burning about an equal amount of plutonium in the process), fast breeder reactors produce much larger amounts of plutonium from common U-238, then fission that to produce electricity and thermal heat. Because there is about 139 times more U-238 than U-235 on Earth, it has been estimated that there is anywhere from 10,000 to 5,000,000,000 years' worth (sustainable but not renewable, depending on future technology) of U-238 for use in these power plants, and that they can return a high ratio of energy returned on energy invested (EROEI), and avoid some of the problems of current reactors by being automated, passively safe, and reaching economies of scale via mass production. In addition, wastes produced by these plants are less toxic than those of conventional reactors. There are a few such research projects working on fast breeders. Lawrence Livermore National Laboratory is currently working on the small, sealed, transportable, autonomous reactor (SSTAR). Problems arise from the higher levels of heat and radiation produced by this reactor. There are other, more exotic nuclear projects (such as pebble bed reactors), each with their own technical problems. The long-term radioactive waste storage problems of nuclear power have not been solved, although on-site spent fuel storage in casks has allowed power plants to make room in their spent fuel pools. Today, the only industrial solution lies with storage in underground repositories. Because automobiles and trucks consume a great deal of the total energy budget of developed countries, some means would be required to deliver the energy generated from nuclear heat to these vehicles. The most direct solution is to use electric vehicles. Mass transit will be an important aspect of this solution, as it is readily electrified. Some think that hydrogen may play a role (see below). If so, it would be produced by electrolysis, either conventionally or at high temperatures supplied by reactor heat. Another possibility for producing hydrogen by nuclear power is the heat-driven sulfur-iodine cycle. Hydrogen need not be used directly in transportation. A hybrid chemical-energy storage process might use such hydrogen to produce methanol from CO2 (see above), which would then feed into the present internal-combustion-engine transportation infrastructure with far less modification than would be needed for hydrogen. See methanol economy. Fusion reactors It is relatively easy to start nuclear fusion reactions, which generate large amounts of energy (cf. nuclear weapons). However, the energy input needed in achieving the necessary temperature and electromagnetic confinement for controlled and sustained fusion is too large presently to maintain a significant energy gain. Electricity produced in a typical fusion facility would not involve the creation of millenary radioactive waste, neither would it involve a risk of nuclear meltdown*. The natural resources required for the implementation of the DT (Deuterium-Tritium) fuel cycle (the option that is most likely to be put into effect) are essentially inexhaustible. *. The research to make fusion power possible started in 1950, and has made notable progress since then *. ITER will be the first fusion reactor which reaches ignition, will cost €10 billion ($12.1 billion) and its construction will start in 2006, while in 2015 it should be ready*. The European Union, Japan, Russia, the USA, South Korea, India and China are jointly participating in ITER. However, ITER is only a scientific project. It will not generate electricity. If the current rate of research is maintained, fusion power may become a viable economic alternative to oil around 2050 *. Electricity from fusion power suffers from the same limitations as electricity from fission, solar, or other sources: it is an alternative to oil only in generating electricity, and functions well for transportation (assuming liquid fuels) only if an intermediate chemical energy storage economy (such as hydrogen economy, methanol economy or ethanol economy exits which can make use of nuclear power for chemical synthesis. Hydrogen Proponents of a hydrogen economy think hydrogen could hold the key to ongoing energy demands. Relatively new technologies (such as fuel cells) can be used to efficiently harness the chemical energy stored in diatomic hydrogen (H2). However, there is no accessible natural reserve of uncombined hydrogen (what there is resides in Earth's outer exosphere) and thus hydrogen for use as fuel must first be produced using another energy source; hydrogen would thus actually be a means to transport energy, rather than an energy source, just as common rechargeable batteries are. The most immediately feasible hydrogen mass production method is steam methane reformation, which requires natural gas, itself potentially in increasingly short supply. Another method of hydrogen production is through water electrolysis which can use electricity generated from any combination of: fossil fuels, nuclear, and/or renewable energy sources. Biomass or coal gasification, photoelectrolysis, and genetically modified organisms have also been proposed as means to produce hydrogen. According to the majority of energy experts and researchers, hydrogen is currently impractical as an alternative to fossil-based liquid fuels. It is inefficient to produce, insufficiently energy dense (hydrogen gas tanks would need to be 2-3 times as large as conventional gasoline tanks), and expensive to transport and convert back to electricity. However, theoretically it is more efficient to burn fossil fuels to produce hydrogen than burning oil directly in car engines (due to efficiencies of scale). Unfortunately, this does not take into consideration the significant energy cost of having to build hundreds of millions of new hydrogen powered vehicles plus hydrogen fuel distribution infrastructure. Research on the feasibility of hydrogen as a fuel is still underway, and the outcome is, at best, uncertain. Air engine The Air engine is an emission-free piston engine using compressed air as fuel. Liquid nitrogen A liquid nitrogen economy would extract energy from the temperature difference between air and liquid nitrogen. The Stirling engine or cryogenic heat engine offers a way to power such vehicles. A means to generate liquid nitrogen, which is only an energy storage medium, is needed. See also | |||||||
|
| ||||||||
 |
|
| |