Реферат: Hydrogen

– Fuel Of The Future Essay, Research Paper

HYDROGEN – THE POWER SURCE OF THE FUTURE

Since the beginning of the scientific revolution in the early nineties the mankind looks for an energy source that is clean and renewable; solution of this problem would be probably the most common thing in our life – WATER.

Water consists of two chemical elements, hydrogen and oxygen. Each molecule of water consists of two hydrogen (H2) atoms and one oxygen (O) atom. Chemical binding between these three atoms is very stable and strong. Therefore, the reaction of hydrogen and oxygen is under normal circumstances very intense and generates a lot of energy.

2H2 + O2 ? 2H2O + energy

Both, hydrogen and oxygen are gases at normal temperatures and pressures and the product of this reaction is pure water, usually in its gaseous form – steam.

Now it may look like hydrogen is the ideal power source that mankind is ever since looking for. More than 70 % of the Earth surface is covered by water, therefore hydrogen is renewable and unlimited. Reaction of hydrogen with oxygen generates a lot of energy and it does not have any negative output, only water. But, the respectable power hidden in water is known for more than 200 hundred years and as long scientists are trying to find a way to extract this energy, rather how to split the water molecules into hydrogen and oxygen. Hydrogen can be used to power cars, rail engines, airplanes, to produce electricity and heat. But, although the technical breakthrough in 19th and 20th century brought hydrogen into experimental use in many applications, there are still many problems to deal with.

There sure is a lot of misinformation about hydrogen gone to public, so here are the basic facts about hydrogen as a power source according to the Nuts & Volts Magazine (May 1999, WWW).

Hydrogen on earth is not a fuel. It is only an energy carrier. Following the definition of the word fuel, fuel is a substance that is capable of delivering new energy when burning or other chemical reaction occurs. On the other hand energy carrier is a substance that is only able to move previously acquired energy from one place to another. To be accurate, water molecule is energetically very advantageous for both oxygen and hydrogen atoms and needs much energy to disintegrate it again into hydrogen and oxygen atoms, or better H2 and O2 molecules, therefore H2 and O2 are only carrying energy.

There is more hydrogen in gasoline than there is in liquid hydrogen. Configuration of hydrogen atoms in gasoline is much more space saving than in pure liquefied hydrogen, therefore larger storage tanks are needed to store it.

Electrolysis is not usually the best way to generate hydrogen. Most of the today’s hydrogen comes from raw petrol as one of the by-products of petroleum processing. According to United States Alternative Fuels Data Center (2000, WWW) now, hydrogen is made using the following two methods. Electrolysis: Uses electrical energy to split water molecules into hydrogen and oxygen. Applying low DC voltage will result in releasing hydrogen on one electrode and oxygen on the other. The electrical energy can come from electricity production sources including renewable fuels. United States Department Of Energy (DOE) has concluded that electrolysis is unlikely to become the predominant method for large quantities of hydrogen production in the future. (2000, WWW) The best electrolysis is only 62 percent efficient. Synthetic gas (methane) reformation: Predominant method of Hydrogen producing is stream reforming or partial oxidation of natural gas, where other hydrocarbons can be used as feedstocks (for example biomass or coal can be gasified and used in a steam reforming process to create hydrogen). Commercial methane reformation can be around 68 percent efficient. According to Stanford University research of hydrogen (2000, WWW) the main present way of getting hydrogen is steam methane reformation and this will probably remain the most economical way as long as methane (natural gas) is available cheaply and in large quantities. When the price of methane goes up to more than three times it will be cheaper to produce hydrogen by splitting water molecules – H2O into hydrogen – H2 and oxygen – O2.

2H2O + energy ? 2H2 + O2

This is accomplished by electrolysis. If fossil fuels e.g. coal, oil or natural gas, are used to generate the electricity, there is no advantage over using fossil fuels directly. Indeed you still get CO and CO2 and there is a considerable loss of energy. Therefore the large-scale use of hydrogen depends on using either nuclear or solar electricity. In both nuclear and solar cases, there are possible technologies that do not use electricity as an intermediate form of energy.

For example it is possible to “resonate” the water molecule and make it to “fall apart”, but the frequencies to do this are in microwave and infrared range. There are no energy advantages to doing so, because emitting these frequencies is very energy demanding.

There is some hope that this process could be somewhat more efficient than electrolysis, but all of these technological procedures are still in development and are mostly only in a position of an experimental project. Besides new energy uses, hydrogen gets widely used to make ammonia, to stabilize fats, for welding, rocket fuel, acid manufacture, balloon filling, radioactivity studies and cryogenic research.

According to he Nuts & Volts Magazine (1999, WWW), the actual available energy in hydrogen flame is very low. Gasoline offers around 9000 watt-hours per liter and 13 000 watt-hours per kilogram of storage. Hydrogen at normal temperature and pressure offers an outstanding 39 000 watt-hour per kilogram, but only a pitiful 3,5 watt per liter. The major problem is that hydrogen gas uses too much volume to be very useful, as an energy carrier and compressing it into a liquid will increase the costs and loses. Efficiency goes down, safety and infrastructure issues appear and still are four-time les hydrogen atoms in any liter of liquid hydrogen than in a liter of gasoline. So the key problem is to find a way to store hydrogen in a safe and dense way.

No hydrogen flame has the ability to truly melt tungsten. There is much disinformation about hydrogen burning, mainly because the burning temperature of hydrogen flame is very unstable; therefore hard to measure and dependant on many factors, like volume and cleanliness of hydrogen and oxygen used in the reaction, temperature, pressure and any other chemical elements in touch with the reacting system. Almost any chemical element or compound can serve as a catalyst or inhibitor of the hydrogen oxidation reaction. Illusion of tungsten melting could be easily created with side reactions.

Hydrogen improperly burned in air creates polluting nitrogen oxides. University of Stanford (May 2000, WWW) argues that although some nitrogen compounds may also be produced and may have to be controlled the main problem of global warming – carbon dioxide is not produced in any quantity.

Hydrogen can rot metal through an embrittlement and will easy diffuse through most other materials. Hydrogen can form various compounds with almost all metals, except non-reactive metals like gold and platinum, and because hydrogen H2 molecules are very small they can diffuse through many materials, like most hydrocarbon-based materials (plastic, rubber). Consequently it means that special materials and their combinations need to be used.

Water is not a fuel. It is an ash. Often, water is mistaken to be the source of power but water is only the product of the hydrogen and oxygen reaction, not the actual fuel.

Normally, a monoatomic gas only briefly exists in tiny amounts. There is a lot of free hydrogen on our sun and on other moons and planets, but on Earth only a few very rare gas wells release some free hydrogen, but only in very small amounts and not clean enough for industry use.

Hydrogen creates severe and largely unresolved safety issues. This is one of the main problems of hydrogen as a power source, it forms a high explosive mixture with air and has to be handled with extreme care, special and expensive materials should to be used to avoid potential explosion.

These statements are generally quite disincentive, but all of those problems can be solved, it is only a matter of time and money spent in researches. For example use of hydrogen, as a fuel for combustion engines looks very positive, there are still many problems to solve, but hydrogen would be probably the fuel of our cars in the future. One of the important benefits of hydrogen is that it can be used directly in an internal combustion engine very similar to engines used with gasoline. Positive is also that hydrogen supplies three times the energy of gasoline; this could result in a lower fuel consumption and better mileage. On the other hand, three main disadvantages of hydrogen as a car fuel are its low density, safety problems and, since the insulation is not perfect yet, also evaporating of hydrogen, that is typically about 1,7 percent a day. Hydrogen uses too much volume to be very useful, as an energy carrier and compressing it into a liquid will increase the costs and loses. Efficiency goes down, safety and infrastructure issues appear and still are four-time les hydrogen atoms in any liter of liquid hydrogen than in a liter of gasoline. “In terms of containment, 9,5 kg of hydrogen is equivalent to 25kg of gasoline, but storing 25 kg of gasoline requires only a tank with mass of 17 kg, whereas the storage of 9,5 kg of hydrogen requires 55 kg” (Peschka, 1987, WWW). Part of the reason for this difference is that the volume of hydrogen is about four times greater for the same energy content of gasoline. “Although the hydrogen storage vessel is large, hydrogen burns 1.33 times more efficiently than gasoline in automobiles” (Bockris and Was, 1988, WWW). So the key problem is to find a way to store hydrogen in a safe and dense way. The solution is probably in metal hydrides. Metal hydride represents a special way of storing hydrogen atoms in a special metal grid, wherefrom hydrogen can be evolved at any time. Almost two times more hydrogen atoms could be stored this way in the same sized tank, but the whole system is very heavy because of the metal included in the hydrogen tank.

BMW and Mazda are demonstrating that it is anyway possible to run a hydrogen-powered car that is reliable and safe. BMW operates an experimental BMW 745hi (”hi” for hydrogen injection) vehicle that has a hybrid engine able to burn liquefied hydrogen as well as gasoline. “This vehicle is equipped with a 75 kg liquid-hydrogen tank with energy equivalent of 40 liters of gasoline and has a cruising range of 400 km, or fuel efficiency of around 10 km per liter” (2000, BMW official web page). Mazda is the pioneer of hydrogen use in internal combustion engines. According to Mazda’s homepage (2000, WWW) now there are three experimental vehicles operated by Mazda. First project of Mazda was a small Mazda HR-X van that just successfully completed a two years trial period. This car was lent to Hirohata Steel Mill for use as their company van and drove at least 20 000 kilometers on public roads. This vehicle uses pressurized, but not liquefied, hydrogen as the only fuel. The second car was the HR-X2, with the same chassis and engine but with a new fuel tank storing the hydrogen in its hydride form. This greatly improved the amount of stored hydrogen and increased its economy and cruising range. The last Mazda’s hydrogen powered project is the popular roadster Mazda MX-5 powered by hydrogen and a fuel tank using the hydride advantages. All these cars are about 400 kg heavier than the standard models; this is mainly because a 300 kg hydrogen tank was installed instead of a 50 kg fuel for a full gasoline tank. Mazda plans for the future are to bring a serial-produced vehicle with either hybrid or only hydrogen-powered engine to the world market before 2010. According to Mrs. A Martiniskova, only Japan government now supports this courageous idea, with a plan of building hydrogen filling stations (May 6, 2000 personal communication). Bockris and Wass (1998, WWW) estimate that assuming $0,05 per kWh of electricity from a nuclear power plant during low demand, hydrogen would cost $ 0,09 per kWh. This is the equivalent of $0,67 per liter of gasoline. Gasoline sells at the pump in the United States for about $0.30 per liter. “However estimates of real cost of burning a liter of gasoline range from $1.06 to $1.32, when production, pollution and other external cost are included” (1998, Worldwatch institute, WWW). Therefore based on these calculations hydrogen fuel may eventually become competitive. Although this statement seems to me to be somewhat biased, because taxes seem to be included in gasoline prices and in hydrogen prices not.

Significant change to hydrogen as a power source could be the development of a so-called FUEL CELL. “Fuel cell is an electric cell in which chemical energy from the oxidation of a gas fuel is converted directly to electrical energy in a continuous process” (2000, CD-ROM). Here, hydrogen again is used as the source of power and identical reaction occurs but the engine principle is completely different, instead of using the combustion to power a rotary engine fuel cell turns hydrogen and oxygen in a very special device, that outputs electric energy to power the vehicle. According to U.S. governmental web page Fuelcellworld (2000, WWW) this device converts hydrogen gas into negatively charged electrons (e-) and positively charged ions (H+). The electrons (e-) flow through an external load to the cathode. The Hydrogen ions (H+) flow through migrate through the electrolyte to the cathode where thy combine with oxygen and the electrons (e-) to produce water. Individual cells produce a small voltage. They are arranged in stacks to provide the required level of power. As all fuel cells also this one should provide a range of critical benefits that no other single power technology can match. According to United States Alternative Fuels Data Center vehicle powered by a fuel cell can be highly efficient and can reduce emissions significantly (2000,WWW). This technology is relatively young and still dealing with many issues; most of the problems are similar to “conventional” hydrogen powered engines. Almost all of the problems are associated with the hydrogen attributes that complicate its use, such as complicated handling, fueling and storage. Yet, there is no working fuel cell engine that is possible to mount into a conventional car; there is a working prototype of a fuel cell engine working with liquefied propane gas that is operated by University of Berlin. Propane Gas essential attributes are very similar to hydrogen attributes, so there is a hope that soon there will be also a hydrogen-powered fuel cell developed.

Whereas world petroleum reserves could not last forever it is very important to research other possible non-petroleum based fuels that are better for the nature and at least as good as gasoline to us. U.S. senator Harry Reid office (2000, WWW) Germany, Japan, Belgium, United States and Saudi Arabia are further researching and expanding the possibilities of hydrogen as a fuel that can replace gasoline one time. Relying on the Middle East petroleum resources weakens national strength of all the countries that do not have any important petroleum resources and every country could be self-sufficient with hydrogen. For example U. S. trade balance sheets show that oil imports drain 1 billion dollars from the U. S. economy every week. Important is also the “clean transport effect”, thanks to an engine that does not produces any carbon dioxide or other environmentally dangerous emissions. Hydrogen could be considered to be more safe than gasoline, if safety prescriptions are not violated, in case of an accident hydrogen would quickly evaporate and ascend in the atmosphere, while gasoline would stay spilled on the ground. Hydrogen caries much more energy than gasoline, is more engine saving and also the fuel cell technology promises further development and increasing reliability of hydrogen powered cars. Following United States Department of Energy we can expect regular hydrogen-powered traffic in 20 maybe 30 years (2000, WWW). Although, until now no hydrogen-powered cars are in production and hydrogen-powered engine is only under development hydrogen stays the main alternative fuel of the future.

Bibliography

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