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12-26-2002, 12:52 PM
Here's some general info about using hydrogen as a fuel...
Hydrogen Fuel
Since the early 19th century, scientists have recognized hydrogen as a potential source of fuel. Current uses of hydrogen are in industrial processes, rocket fuel, and spacecraft propulsion. With further research and development, this fuel could also serve as an alternative source of energy for heating and lighting homes, generating electricity, and fueling motor vehicles. When produced from renewable resources and technologies, such as hydro, solar, and wind energy, hydrogen becomes a renewable fuel.
Composition of Hydrogen
Hydrogen is the simplest and most common element in the universe. It has the highest energy content per unit of weight—52,000 British Thermal Units (Btu) per pound (or 120.7 kilojoules per gram)—of any known fuel. Moreover, when cooled to a liquid state, this low?weight fuel takes up 1/700 as much space as it does in its gaseous state. This is one reason hydrogen is used as a fuel for rocket and spacecraft propulsion, which requires fuel that is low?weight, compact, and has a high energy content.
In a free state and under normal conditions, hydrogen is a colorless, odorless, and tasteless gas. The basic hydrogen (H) molecule exists as two atoms bound together by shared electrons. Each atom is composed of one proton and one orbiting electron. Since hydrogen is about 1/14 as dense as air, some scientists believe it to be the source of all other elements through the process of nuclear fusion. It usually exists in combination with other elements, such as oxygen in water, carbon in methane, and in trace elements as organic compounds. Because it is so chemically active, it rarely stands alone as an element.
When burned (or combined) with pure oxygen, the only by products are heat and water. When burned (or combined) with air, which is about 68% nitrogen, some oxides of nitrogen (or NOx) are formed. Even then, burning hydrogen produces less air pollutants relative to fossil fuels.
Producing Hydrogen
Hydrogen bound in organic matter and in water makes up 70% of the earth's surface. Breaking up these bonds in water allows us produce hydrogen and then to use it as a fuel. There are numerous processes that can be used to break these bonds. Described below are a few methods for producing hydrogen that are currently used, or are under research and development.
Most of the hydrogen now produced in the United States is on an industrial scale by the process of steam reforming, or as a byproduct of petroleum refining and chemicals production. Steam reforming uses thermal energy to separate hydrogen from the carbon components in methane and methanol, and involves the reaction of these fuels with steam on catalytic surfaces. The first step of the reaction decomposes the fuel into hydrogen and carbon monoxide. Then a "shift reaction" changes the carbon monoxide and water to carbon dioxide and hydrogen. These reactions occur at temperatures of 392° F (200 ° C) or greater.
Another way to produce hydrogen is by electrolysis. Electrolysis separates the elements of water—H and oxygen (O)—by charging water with an electrical current. Adding an electrolyte such as salt improves the conductivity of the water and increases the efficiency of the process. The charge breaks the chemical bond between the hydrogen and oxygen and splits apart the atomic components, creating charged particles called ions. The ions form at two poles: the anode, which is positively charged, and the cathode, which is negatively charged. Hydrogen gathers at the cathode and the anode attracts oxygen. A voltage of 1.24 Volts is necessary to separate hydrogen from oxygen in pure water at 77° Fahrenheit (F) and 14.7 pounds per square inch pressure [25° Celsius (C) and 1.03 kilograms (kg) per centimeter squared.] This voltage requirement increases or decreases with changes in temperature and pressure.
The smallest amount of electricity necessary to electrolyze one mole of water is 65.3 Watt-hours (at 77° F; 25 degrees C). Producing one cubit foot of hydrogen requires 0.14 kilowatt-hours (kWh) of electricity (or 4.8 kWh per cubic meter).
Renewable energy sources can produce electricity for electrolysis. For example, Humboldt State University's Schatz Energy Research Center designed and built a stand-alone solar hydrogen system. The system uses a 9.2 kilowatt (KW) photovoltaic (PV) array to provide power to compressors that aerate fish tanks. The power not used to run the compressors runs a 7.2 kilowatt bipolar alkaline electrolyzer. The electrolyzer can produce 53 standard cubic feet of hydrogen per hour (25 liters per minute). The unit has been operating without supervision since 1993. When there is not enough power from the PV array, the hydrogen provides fuel for a 1.5 kilowatt proton exchange membrane fuel cell to provide power for the compressors.
Steam electrolysis is a variation of the conventional electrolysis process. Some of the energy needed to split the water is added as heat instead of electricity, making the process more efficient than conventional electrolysis. At 2,500 degrees Celsius water decomposes into hydrogen and oxygen. This heat could be provided by a solar energy concentrating device to supply the heat. The problem here is to prevent the hydrogen and oxygen from recombining at the high temperatures used in the process.
Thermochemical water splitting uses chemicals such as bromine or iodine, assisted by heat. This causes the water molecule to split. It takes several steps—usually three—to accomplish this entire process.
Photoelectrochemical processes use two types of electrochemical systems to produce hydrogen. One uses soluble metal complexes as a catalyst, while the other uses semiconductor surfaces. When the soluble metal complex dissolves, the complex absorbs solar energy and produces an electrical charge that drives the water splitting reaction. This process mimics photosynthesis.
The other method uses semiconducting electrodes in a photochemical cell to convert optical energy into chemical energy. The semiconductor surface serves two functions, to absorb solar energy and to act as an electrode. Light-induced corrosion limits the useful life of the semiconductor.
Biological and photobiological processes use algae and bacteria to produce hydrogen. Under specific conditions, the pigments in certain types of algae absorb solar energy. The enzyme in the cell acts as a catalyst to split the water molecules. Some bacteria are also capable of producing hydrogen, but unlike algae they require a substrate to grow on. The organisms not only produce hydrogen, but can clean up pollution as well.
Recently, research funded by the U.S. Department of Energy has led to the discovery of a mechanism to produce significant quantities of hydrogen from algae. For 60 years, scientists have known that algae produce trace amounts of hydrogen, but have not found a feasible method to increase the production of hydrogen. Scientists from the University of California (UC), Berkeley, and the U.S. DOE's National Renewable Energy Laboratory found the key. After allowing the algae culture to grow under normal conditions, the research team deprived it of both sulfur and oxygen, causing it to switch to an alternate metabolism that generates hydrogen. After several days of generating hydrogen, the algae culture was returned to normal conditions for a few days, allowing it to store up more energy. The process could be repeated many times. Producing hydrogen from algae could eventually provide a cost-effective and practical means to convert sunlight into hydrogen.
Another source of hydrogen produced through natural processes is methane and ethanol. Methane (CH4) is a component of "biogas" that is produced by anaerobic bacteria. Anaerobic bacteria occur widely throughout the environment. They break down or "digest" organic material in the absence of oxygen and produce biogas as a waste product. Sources of biogas include landfills, and livestock waste and municipal sewage treatment facilities. Methane is also the principal component of "natural gas" (a major heating and power plant fuel) produced by anaerobic bacteria eons ago. Ethanol is produced by the fermentation of biomass. Most fuel ethanol produced in the United States is made from corn.
The United States, Japan, Canada, and France have investigated thermal water splitting, a radically different approach to creating hydrogen. This process uses heat of up to 5,430°F (3,000°C) to split water molecules.
Potential Uses for Hydrogen
The transportation, industrial, and residential sectors in the United States have used hydrogen for many years. Many people in the late 19th century burned a fuel called "town gas," which is a mixture of hydrogen and carbon monoxide. Several countries, including Brazil and Germany, still distribute this fuel. Airships (dirigibles and blimps) used hydrogen for transportation. Currently, industries use hydrogen for refining petroleum, and for producing ammonia and methanol. The Space Shuttle uses hydrogen as fuel for its rockets.
With further research, hydrogen could provide electricity and fuel for the residential, commercial, industrial, and transportation sectors in the United States.
When properly stored, hydrogen as a fuel burns in either a gaseous or liquid state. Motor vehicles and furnaces can easily be converted to use hydrogen as a fuel. Since the 1950s, hydrogen has powered some airplanes. Automobile manufacturers have developed hydrogen-powered cars. Hydrogen burns 50% more efficiently than gasoline, and burning hydrogen creates less air pollution. Hydrogen has a higher flame speed, wider flammability limits, higher detonation temperature, burns hotter, and takes less energy to ignite than gasoline. This means that hydrogen burns faster, but carries the danger of pre-ignition and flashback. While hydrogen has its advantages as a vehicle fuel it still has a long way to go before it can be used as a substitute for gasoline. This is mainly due to the investment required to develop a hydrogen production and distribution infrastructure.
Fuel cells are a type of technology that use hydrogen to produce useful energy. In fuel cells, electrolysis is reversed by combining hydrogen and oxygen through an electrochemical process, which produces electricity, heat, and water. The U.S. space program has used fuel cells to power spacecraft for decades. Fuel cells capable of powering automobiles and buses have been and are being developed. Several companies are developing fuel cells for stationary power generation. Most major automobile manufacturers are developing fuel cell powered automobiles.
Hydrogen could be considered a way to store energy produced from renewable resources such as solar, wind, biomass, hydro, and geothermal. For example, when the sun is shining, PV systems can provide the electricity needed to separate the hydrogen (as in the Humboldt State University's describednaboveResearch Center descibed abvoe). The hydrogen could then be stored and burned as fuel, or to operate a fuel cell to generate electricity at night or during cloudy periods.
Storing Hydrogen
In order to use hydrogen on a large scale, safe, practical storage systems must be developed, especially for automobiles. Although hydrogen can be stored as a liquid, it is a difficult process because the hydrogen must be cooled to ?423° Fahrenheit (-253° Celsius). Refrigerating hydrogen to this temperature uses the equivalent of 25% to 30% of its energy content, and requires special materials and handling. To cool one pound (0.45 kg) of hydrogen requires 5 kWh of electrical energy.
Hydrogen may also be stored as a gas, which uses less energy than making liquid hydrogen. Because hydrogen is a gas, it must be pressurized to store any appreciable amount. For large?scale use, pressurized Hydrogen gas could be stored in caverns, gas fields, and mines. The hydrogen gas could then be piped into individual homes in the same way as natural gas. Though this means of storage is feasible for heating, it is not practical for transportation because the pressurized metal tanks used for storing hydrogen gas for transportation are very expensive.
A potentially more efficient method of storing hydrogen is in hydrides. Hydrides are chemical compounds of hydrogen and other materials. Research is currently being conducted on magnesium hydrides. Certain metal alloys such as magnesium nickel, magnesium copper, and iron titanium compounds, absorb hydrogen and release it when heated. Hydrides, however, store little energy per unit weight. Current research aims to produce a compound that will carry a significant amount of hydrogen with a high energy density, release the hydrogen as a fuel, react quickly, and be cost-effective.
A company in Utah, Power Ball Technologies, has developed a process in which sodium metal is pelletized and encapsulated with polyethylene plastic. The pellets can then be containerized, transported, and then opened in a patented hydrogen generator to produce hydrogen gas. According to the company, each gallon of these pellets is capable of producing 1,307 gallons of hydrogen gas, which is an equivalent hydrogen storage density more than 7 times greater by volume than a compressed hydrogen tank storing hydrogen at 3,000 psi.
The Cost of Hydrogen
Currently the most cost-effective way to produce hydrogen is steam reforming. According to the U.S. Department of Energy, in 1995 the cost was $7.39 per million Btu ($7.00 per gigajoule) in large plant production. This assumes a cost for natural gas of $2.43 per million Btu ($2.30 per gigajoule). This is the equivalent of $0.93 per gallon ($0.24 per liter) of gasoline. The production of hydrogen by electrolysis using hydroelectricity at off peak rates costs between $10.55 to $21.10 per million Btu ($10.00 to $20.00 per gigajoule).
Hydrogen Research in the United States
Recognizing the potential for hydrogen fuel, the U.S. Department of Energy (DOE) and private organizations have funded research and development (R&D) programs for several years. The DOE's Fiscal Year 2002 budget includes 31 million dollars for hydrogen energy programs.
Reading List
The following publications provide additional information about hydrogen fuel. Contact sources to confirm availability and prices before ordering. This list was reviewed in March 2002, with subsequent additions.
Articles and Conference Papers
Articles from Home Power Magazine, P.O. Box 520, Ashland, OR 97520; Phone: (800) 707-6585; Email: hp@homepower.com ; World Wide Web: www.homepower.com. Selected articles include:
"Cookin' on Hydrogen Stove Burner Conversion," D. Booth, W. Pyle, (No. 33) pp. 28-30, 2-3/1993.
"Heatin' with Hydrogen," W. Pyle, J. Healy, R. Cortez, D. Booth, (No. 34), pp-26-29, 4-5/1993.
"Hydrogen Basics," A. Potter, M. Newell, (No. 32) pp. 42-45, 12/1992 - 1/1993.
"Hydrogen Fuel," L. Spicer, (No. 22) pp. 32-34, 4-5/1991.
"Hydrogen Storage," W. Pyle, (No. 59) pp. 14-20, 6-7/1997.
"Solar Hydrogen by Electrolysis," W. Pyle, J. Healy, R. Cortez, (No. 39) pp. 32-38, 2-3/1994.
"The Schatz PV Hydrogen Project," R. Perez, (No. 22) pp. 26-30, 4-5/1991.
"Water Electrolyzers," L. Spicer, (No. 26) pp. 34-35, 12/1991-1/1992.
Articles from Solar Today, American Solar Energy Society (ASES), 2400 Central Avenue, Unit G 1, Boulder, CO 80301: Phone: (303) 443 3130; Email: ases@ases.org ; World Wide Web: www.ases.org. Selected articles include:
"Florida's Hydrogen Research," I. Melody, (7:5) pp. 14-16, 9-10/1993.
"Hydrogen Fuel from the Sun," P. Lehman, C. Parra, (8:5) pp. 20-22, 9-10/1994.
"Hydrogen Powered Ice Cream," C Para, S. Ornelas, and J. Zoellick, (13:4) pp. 30--33, 8-9/1999.
"Renewable Hydrogen Energy Systems," J. Ogden, (7:5) pp. 17-18, 9-10/1993.
"Solar Energy Hydrogen - Partners in a Clean Energy Economy," C. Linkous, (13:4) pp. 22-25, 8-9/1999.
"Solar Hydrogen: A Sustainable Energy Option," C. Thomas, (7:5) pp. 11-13, 9-10/1993.
"Solar Hydrogen for Transportation," J. Ogden, (9:1) pp. 25-27, 1-2/1995.
Miscellaneous Articles and Conference Papers
"The Car of His Dreams," C. Levesque, Public Utilities Fortnightly,(139:4) pp. 23-26, February 15, 2001.
"The Development of a Hydrogen-Fueled Internal Combustion Engine," J. Fiene, et al., Solar Forum 2001: Annual American Solar Energy Society Conference, Washington, DC, April 21-25, 2001.
"From Fuel Cells to a Hydrogen-based Economy," A.Lovins and B. Williams, Public Utilities Fortnightly, (139:4) pp. 12-21, February 15, 2001.
"Hydrogen Station Using Solar Becomes First Such Facility in Los Angeles Area," Ed., Solar & Renewable Energy Outlook, (27:15) p. 170, August 1, 2001.
"Let's Be Rational About Hydrogen as a Vehicular Fuel," H. Linden, Public Utilities Fortnightly, (140:6) pp. 8-9, March 15, 2002
"Metal Hydrides for Solar Thermal Applications," G. Lloyd, K. Kim, and A. Razani," Solar 98: Annual American Solar Energy Society Conference, Albuquerque, New Mexico, June 14-17, 1998; pp. 439-444.
"Routes To a Hydrogen Economy," S. Dunn, Renewable Energy World, (4:4) pp. 19-29, July/Aug 2001.
"Sustained Photobiological Hydrogen Gas Production upon Reversible Inactivation of Oxygen Evolution in the Green Alga Chlamydomonas reinhardtii," A. Melis, et al. Plant Physiology, (122) pp. 127-136, January 2000.
Books
Energy: The Solar-Hydrogen Alternative, J. Bockris, John Wiley & Sons, New York, New York, 1976. 376 pp., Out of print. ISBN 0-470-08429-4.
Fuel from Water: Energy Independence with Hydrogen, M. Peavey, Merit Inc., 1993. Available from Real Goods/Gaiam Inc., 360 Interlocken Boulevard, Suite 200, Broomfield, CO 80021-3492; Phone: (800) 762-7325; World Wide Web: www.realgoods.com . 251 pp., $25.00, Product No. 80-210.
Hydrogen Fuel for Surface Transportation, J. Heffel, et al, Society of Automotive Engineers (SAE), 1996. Available from SAE, 400 Commonwealth Drive, Warrendale, PA 15096-0001; Phone: (724) 776-4970; Fax: (724) 776-5760; World Wide Web: www.sae.org. $99.00, ISBN: 1560916842.
Hydrogen Futures: Towards a Sustainable Energy System, S. Dunn, Worldwatch Institute, 2001. Available from Worldwatch Institute, Publications, P.O. Box 879, Oxon Hill, MD 20797; Phone: (888) 544-2303 or (301) 567-9522; Fax: (301) 567-9553; Email: wwpub@worldwatch.org ; World Wide Web: www.worldwatch.org . 90 pp., $5.00, Worldwatch Paper 157.
The Keys to the Car, J. MacKenzie, World Resources Institute, 1994. Available from World Resources Institute Publications, c/o Hopkins Fulfillment Service, P.O. Box 50370, Baltimore MD 21211-4370; Phone: (800) 537-5487 (publications); Fax: (410) 516-6998; World Wide Web: www.wri.org. $20.00.
The Phoenix Project, H. Braun, Sustainable Partners, Inc. Available from Sustainable Partners, 6245 North 24th Parkway, Suite 209, Phoenix, AZ 85016; Phone: (602) 955-4555; Fax: (602) 955-5444; Email: info@phoenixproject.net; World Wide Web: www.phoenixproject.net. 366 pp., $28.00.
The Solar-Hydrogen Energy Economy: Beyond the Age of Fire, L. Skelton, Van Nostrand Rheinhold, 1984. 200 + pages, Out of print. ISBN 0-442-28221-4
Solar Hydrogen: Moving Beyond Fossil Fuels, J. Ogden and R. Williams, World Resources Institute, 1989. 123 pp., Out of print. ISBN 0-915825-38-4.
Tomorrow's Energy - Hydrogen, Fuel Cells and the Prospects for a Cleaner Planet, P. Hoffman, The MIT Press, 2001. Available from MIT Press, c/o Triliteral, 100 Maple Ridge Drive, Cumberland, RI 02864; Phone: (800) 405-1619 or (401) 658-4226; Fax: (800) 406-9145 or (401) 531-2801; Email: mitpress-orders@mit.edu ; World Wide Web: www.mitpress.mit.edu. 320 pp., $32.95, ISBN: 0262082950.
Reports
Unless otherwise indicated, the reports cited below can be purchased from the:
National Technical Information Service (NTIS)
5285 Port Royal Road, Springfield, VA 22161
Phone: (800) 553?6847 or (703) 605-6000; Fax: (703) 605-6900
Email: orders@ntis.gov
World Wide Web: www.ntis.gov
NTIS adds costs for shipping and handling. Check the price and availability before placing an order.
Assessment of Methods for Hydrogen Production Using Concentrated Solar Energy, G. Glatzmaier, D. Blake, and S. Showalter, National Renewable Energy Laboratory, 1998. 24 pp., $ 23.00, NTIS Order No. DE98001924.
Conversion of Municipal Solid Waste to Hydrogen, J. Richardson, et al., Lawrence Livermore National Laboratory, 1995. 27 pp., $28.50, NTIS Order No. DE95016063.
Costs of Storing and Transporting Hydrogen, W. Amos, National Renewable Energy Laboratory, 1998. 220 pp., $47.00, NTIS Order No. DE00006574.
FY 2002 Annual Operating Plan: Hydrogen Program, U.S. Department of Energy, 2001. Available on the World Wide Web at: www.eren.doe.gov/hydrogen/news.html. 231 pp.
The Green Hydrogen Report. The 1995 Progress Report of the Secretary of Energy's Technical Advisory Panel, National Renewable Energy Laboratory, 1995. 23 pp., $28.50, NTIS Order No. DE95009213.
Hydrogen and the Materials of a Sustainable Energy Future, M. Zalbowitz (ed.), Los Alamos National Laboratory, 1997. 180 pp., $44.00, NTIS Order No. DE97002453.
Hydrogen as a Transportation Fuel: Costs and Benefits, G. Lawrence, Lawrence Livermore National Laboratory, 1996. 116 pp., $41.00, NTIS Order No. DE96010888.
Hydrogen Energy for Tomorrow: Advanced Hydrogen Production Technologies, National Renewable Energy Laboratory, 1995. 4 pp., $10.00, NTIS Order No. DE95000270.
Hydrogen Energy for Tomorrow: Advanced Hydrogen Transport and Storage Technologies, National Renewable Energy Laboratory, 1995. 4 pp., $10.00, NTIS Order No. DE95000271.
Hydrogen Program Plan: FY1993-FY1997, National Renewable Energy Laboratory, 1992. 94 pp., $34.00, NTIS Order No. DE92010556.
Hydrogen Storage for Vehicular Applications: Technology Status and Key Development Areas, S. Robinson, J. Handrock, Sandia National Laboratories, 1994. 47 pp., $28.50, NTIS Order No. DE94011626.
Integrated Technical and Economic Assessments of Transport and Storage of Hydrogen, G. Berry and J. Smith, Lawrence Livermore National Laboratory, 1994. 12 pp., $28.50, NTIS Order No. DE94013145/WDE.
On-Board Hydrogen Storage Systems Using Metal Hydrides, L. Heung, Westinghouse Savannah River Company, 1997. 18 pp., $23.00, NTIS Order No. DE97060222.
Survey of the Economics of Hydrogen Technologies, C. Padro and V. Putsche, National Renewable Energy Laboratory (NREL), 1999. Possibly available from the NREL Document Distribution Service, 1617 Cole Blvd, Golden, CO 80401. 54 pp.
Sustainable Hydrogen Production, D. Block, Florida Solar Energy Center, 1996. 103 pp., $41.00, NTIS Order No. DE96006063/LL.
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This brief was reviewed for accuracy and updated in March 2002.
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