Cogeneration

views updated Jun 08 2018

Cogeneration

Cogeneration is the simultaneous generation from a single energy source of two forms of energy, usually heat and electricity. Traditional generating systems produce only heat or electricity by burning a fuel. Burning fuel generates a lot of heat, and the exhaust gases can be hotter than 932°F (500°C). Traditionally, this “waste heat” would be vented into the environment for disposal. Cogeneration facilities capture some of that waste heat and use it to produce steam or more electricity. Both systems release the same amount of energy, but cogeneration obtains more end-use from that energy.

Cogeneration is widely used in some European countries, such as Denmark and Italy, where fuel costs are particularly large. In the United States, where fuel costs are relatively small, cogeneration produced about 8% of the electricity supply by 2006. Some researchers estimate that if all large U.S. industrial plants used cogeneration technology, there would be enough energy-generating capacity to last until 2020 without building any new power plants.

Why cogenerate?

There are several reasons why cogeneration is a beneficial technology. Cogeneration is an excellent method of improving energy efficiency, which has positive environmental and economic results. It also buys time to find new energy sources, and is a reliable, well-understood process.

The most important environmental reason to cogenerate is that vast amounts of precious, non-renewable resources are being wasted by inefficient uses. For example, in the United States, only 16% of the energy used for industrial processes creates useful energy or products. About 41% of the waste is unavoidable because some energy is always lost whenever energy is transformed. However, 43% of the wasted energy could potentially be used in a more energy-efficient process. Cogeneration is an excellent way to increase energy efficiency, which reduces both environmental impacts and operating costs.

Another benefit of cogeneration is that it is an off the-shelf technology. It has been used in some forms for over a century and therefore most technical problems have been solved. Because cogeneration is a reliable, proven technology, there are fewer installation and operating problems compared with new, untested technology.

History of cogeneration

At the beginning of the twentieth century, steam was the main source of mechanical power. However, as electricity became more controllable, many small “power houses” that produced steam realized they could also produce and use electricity, and they adapted their systems to cogenerate both steam and electricity. Then from 1940–1970, the concept developed of a centralized electric utility that delivered power to the surrounding area. Large utility companies quickly became reliable, relatively inexpensive sources of electricity, so the small power houses stopped cogenerating and bought their electricity from the utilities.

During the late 1960s and early 1970s, interest in cogeneration began to revive, and by the late 1970s the need to conserve energy resources became clear. In the United States, legislation was passed to encourage the development of cogeneration facilities. Specifically, the Public Utilities Regulatory Policies Act (PURPA) of 1978 encouraged this technology by allowing cogenerators to connect with the utility network to purchase and sell electricity. PURPA allowed cogenerators to buy electricity from utility companies at fair prices, in times of shortfall, while also allowing them to sell their electricity based on the cost the utility would have paid to produce that power, the so-called “avoided cost.” These conditions have encouraged a rapid increase in cogeneration capacity in the United States.

In Europe, there has been little government support because cogeneration is not seen as new technology and therefore is not covered under “Thermie,” the European Community’s (EC) energy program. Under Thermie, 40% of the cost for capital projects is covered by the EC government. However, some individual European countries, like Denmark and Italy, have adopted separate energy policies. In Denmark, 27.5% of their electricity is produced by cogeneration, and all future energy projects must involve cogeneration or some form of alternative energy. In Italy, low-interest loans are provided to cover up to 30% of the cost of building new cogeneration facilities.

Barriers to cogeneration

There are several barriers to the large-scale implementation of cogeneration. Although the operating costs of cogeneration facilities are relatively small, the initial costs of equipment and installation are relatively large. Also, multinational oil companies and central utility companies have substantial political influence in many countries. These companies emphasize their own short-term profits over the long-term environmental costs of inefficient use of non-renewable resources. Other barriers to cogeneration are the falsely depressed costs of fossil fuels, relative to their true, longer-term costs and future scarcity. In a world of plentiful, seemingly inexpensive energy, there is little

KEY TERMS

Avoided cost— Under PURPA, the price that the utility company must pay to buy electricity from a cogenerating company. It is calculated as the amount the utility would have paid if the utility company had generated the electricity itself.

Public Utilities Regulatory Policies Act (PURPA) —United States federal legislation that is designed to encourage the development of cogenerating plants.

Waste heat— Heat that is released as fuels are burned but is not used.

incentive to use fuel wisely. In addition, national energy policies can have a tremendous effect, like the EC’s Thermie policy that does not support cogeneration, and the recent cutbacks in the U.S. energy conservation policies and research, the effects of which remain to be seen.

In the United States, much of the energy research dollar is devoted to developing new energy sources, despite the fact that most of the country’s current energy sources are wasted due to inefficient use. As the world’s largest user (and waster) of energy, the United States has a substantial impact on worldwide pollution and also sets a technological lead for others to follow; it therefore, some argue, has a special responsibility to use its resources efficiently. What is more, many energy experts argue that more efficient end use can be used to substantially increase profits for businesses and trim expenses for consumers.

Current research

Current cogeneration research is examining ways of improving old technology. One improvement involves steam-injected gas turbines, which would increase the electric output capacity of the turbines, and thereby increase the energy efficiency of cogeneration. Other improvements are making cogeneration more feasible for smaller plants. Currently, this technology is feasible only in larger facilities. Smaller cogeneration units would allow a more widespread application of this energy-efficient technology.

See also Electrical power supply.

Resources

BOOKS

Pehnt, Martin, et al. Micro Cogeneration: Towards Decentralized Energy Systems. New York: Springer, 2005.

PERIODICALS

Ribaudo, Al. “Cogeneration Systems Offer Benefits tov Owners, Developers.” Real Estate Weekly. 52 (2006): 10.

OTHER

United States Combined Heat and Power Association. “CHP Basics.” <http://uschpa.admgt.com/CHPbasics.htm>(accessed October 21, 2006).

Jennifer LeBlanc

The Gale Encyclopedia of Science

Cogeneration

views updated Jun 08 2018

Cogeneration

Cogeneration is the simultaneous generation of two forms of energy , usually heat and electricity , from one energy source. Traditional energy generating systems produce only heat or electricity by burning a fuel source. In both cases, burning the fuel generates a lot of heat and the exhaust gases can be hotter than 932°F (500°C). Traditionally, this "waste heat" would be vented into the environment for disposal. Cogeneration facilities capture some of that waste heat and use it to produce steam or more electricity. Both systems produce the same amount of energy but cogeneration uses about 35% less fuel because it is designed to be a highly efficient process.

Cogeneration is widely used in some European countries, such as Denmark and Italy, where fuel costs are particularly large. In the United States, where fuel costs are relatively small, cogeneration produces about 5% of the energy supply. Some researchers estimate that if all large U. S. industrial plants used cogeneration technology, there would be enough energy-generating capacity to last until 2020 without building any new power plants.

Why cogenerate?

There are several reasons why cogeneration is a beneficial technology. Cogeneration is an excellent method of improving energy efficiency , which has positive environmental and economic results. It also buys time to find new energy sources, and is a reliable, well-understood process.

Another benefit of cogeneration is that it is an offthe-shelf technology. It has been used in some forms for over a century and therefore most technical problems have been solved. Because cogeneration is a reliable, proven technology, there are fewer installation and operating problems compared with new, untested technology.

History of cogeneration

At the beginning of the twentieth century, steam was the main source of mechanical power. However, as electricity became more controllable, many small "power houses" that produced steam realized they could also produce and use electricity, and they adapted their systems to cogenerate both steam and electricity. Then from 1940 to 1970, the concept developed of a centralized electric utility that delivered power to the surrounding area. Large utility companies quickly became reliable, relatively inexpensive sources of electricity, so the small power houses stopped cogenerating and bought their electricity from the utilities.

During the late 1960s and early 1970s, interest in cogeneration began to revive, and by the late 1970s the need to conserve energy resources became clear. In the United States, legislation was passed to encourage the development of cogeneration facilities. Specifically, the Public Utilities Regulatory Policies Act (PURPA) of 1978 encouraged this technology by allowing cogenerators to connect with the utility network to purchase and sell electricity. PURPA allowed cogenerators to buy electricity from utility companies at fair prices, in times of shortfall, while also allowing them to sell their electricity based on the cost the utility would have paid to produce that power, the so-called "avoided cost." These conditions have encouraged a rapid increase in cogeneration capacity in the United States.

In Europe , there has been little government support because cogeneration is not seen as new technology and therefore is not covered under "Thermie," the European Community's (EC) energy program. Under Thermie, 40% of the cost for capital projects is covered by the EC government. However, some individual European countries, like Denmark and Italy, have adopted separate energy policies. In Denmark, 27.5% of their electricity is produced by cogeneration, and all future energy projects must involve cogeneration or some form of alternative energy. In Italy, low-interest loans are provided to cover up to 30% of the cost of building new cogeneration facilities.

Barriers to cogeneration

There are several barriers to the large-scale implementation of cogeneration. Although the operating costs of cogeneration facilities are relatively small, the initial costs of equipment and installation are large. Also, multinational oil companies and central utility companies have substantial political influence in many countries. These companies emphasize their own short-term profits over the long-term environmental costs of inefficient use of non-renewable resources. Other barriers to cogeneration are the falsely low costs of fossil fuels , relative to their true, longer-term costs and future scarcity. In a world of plentiful, seemingly inexpensive energy, there is little incentive to use fuel wisely. In addition, national energy policies can have a tremendous effect, like the EC's Thermie policy which does not support cogeneration, and the recent cutbacks in the U. S. energy conservation policies and research, the effects of which remain to be seen.

In the United States, much of the energy research dollar is devoted to developing new energy sources, despite the fact that most of the country's current energy sources are wasted due to inefficient uses. In fact, energy efficiency has not increased much since 1985. As the world's largest user and waster of energy, the United States has a substantial impact on many forms of worldwide pollution , and therefore has a special responsibility to use its resources efficiently.

Current research

Current cogeneration research is examining ways of improving the old technology. One improvement involves steam-injected gas turbines, which would increase the electric output capacity of the turbines, and thereby increase the energy efficiency of cogeneration. Other improvements are making cogeneration more feasible for smaller plants. Currently, this technology is feasible only in larger facilities. Smaller cogeneration units would allow a more widespread application of this energy efficient technology.

Resources

books

Miller, Jr., G.T., Environmental Science: Sustaining the Earth. Belmont, CA: Wadsworth Publishing Company, 1991.

Orlando, J.A. Cogeneration Planner's Handbook. Lilburn, GA: Fairmont Press, 1991.

Payne, F.W., ed. Cogeneration Sourcebook. Atlanta, Fairmont Press, 1985.

periodicals

Ganapathy, V. "Recovering Heat When Generating Power." Chemical Engineering (February 1993): 94–98.

Shelley, S., and K. Fouhy. "All Fired Up About Cogeneration." Chemical Engineering (January 1992): 39-45.

Jennifer LeBlanc

KEY TERMS

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Avoided cost: —Under PURPA, this is the price that the utility company must pay to buy electricity from a cogenerating company. It is calculated as the amount the utility would have paid if the utility company had generated the electricity itself.
Public Utilities Regulatory Policies Act (PURPA): —This is U. S. federal legislation that is designed to encourage the development of cogenerating plants.
Waste heat: —This is heat that is released as fuels are burned but is not used.

The Gale Encyclopedia of Science

Cogeneration

views updated May 29 2018

Cogeneration

Cogeneration is the multiple use of energy from a single primary source. In burning coal , oil, natural gas , or biomass , it is possible to produce two usable forms of energy at once, such as heat and electricity. By harnessing heat or exhaust from boilers and furnaces, for example, cogeneration systems can utilize energy that is usually wasted and so operate at a higher efficiency.

The second law of thermodynamics states that in every energy conversion there is a loss of useful energy in the form of heat. It is estimated that nearly half of the energy used in the United States is wasted as heat. Energy conversion efficiencies vary in range but most systems fall below 50%: A gasoline internal combustion engine is 10–15% efficient, and a steam turbine operates at about 40% efficiency. A simple example of cogeneration would be the heater in an automobile , which utilizes the heat of the engine to warm the interior of the car.

Cogeneration is classified into a topping cycle or a bottoming cycle. In the topping cycle, power is generated first, then the spent heat is utilized. In the bottoming cycle, thermal energy is used first, then power is generated from the remaining heat. The basic component of a cogeneration system is the prime mover, such as an internal combustion engine or steam boiler combination, whose function is to convert chemical energy or thermal energy into mechanical energy. The other components are the generator which converts mechanical input into electrical output and a spent heat recovery system, as well as control and transmission systems. A cogeneration system utilizes the heat which the prime mover component has not converted into mechanical energy, and this can improve the efficiency of a typical gas turbine from approximately 12–30% to an overall rate of 60%.

In the United States, 40% of all electrical power is generated by burning coal, and coal-fired power plants lose two-thirds of their energy through the smokestack. Several large electric utilities have been using waste heat from their boilers for space heating in their own utility districts. This is known as district heating; zoning regulations and building locations permit this practice in New York City, New York; Detroit, Michigan; and Eugene, Oregon; among other cities. Waste heat from the generation of electricity has long been used in Europe to heat commercial and industrial buildings, and the city of Vestras, Sweden, produces all its electricity as well as all its space heating by utilizing the waste heat from industrial boilers.

In 1978, Congress passed the Public Utilities Regulatory Act, which allowed cogenerators to sell their extra power to utility companies. It has been estimated that if all waste heat generated by industry were used to cogenerate electrical power, there would be no need to construct additional power plants for the next two or three decades. The paper industry in the United States, which must produce steam for its industrial process, often uses cogeneration systems to produce electricity.

Experts maintain that half of the money consumers spend on electric bills pays not for the generation of power but for its distribution and transmission, including losses through transmission. Small, decentralized cogeneration systems that burn biomass, such as organic waste in agricultural areas, or garbage from large apartment buildings can minimize transmission losses and utilize waste heat for space heating. In Santa Barbara County, California, a hospital which operates a seven-megawatt natural gas turbine generator for its electrical power needs a cogeneration system installed to use thermal energy from the boiler to provide steam for heating and cooling. Extra steam not needed for these purposes is returned to the turbine, and excess electrical power is sold to the local utility.

A new technology for regeneration systems is coal gasification . Coal is heated and turned into a gas. The gas is burned to operate two turbines, one fueled by the hot gases and the other by steam generated from the burning gas. Scrubbers can remove 95% of the sulfur from the flue gases, and the result is a generating facility with high efficiency and low pollution .

[Muthena Naseri and Douglas Smith ]

RESOURCES

BOOKS

Heating, Ventilating, Air-Conditioning Systems and Equipment. Atlanta: American Society of Heating, Refrigeration, and Air-Conditioning Engineers, 1992.

Kaufman, D. G., and C. M. Franz. Biosphere 2000. New York: Harper-Collins, 1993.

Environmental Encyclopedia Naseri, Muthena; Smith, Douglas

Cogeneration

views updated May 17 2018

COGENERATION

Cogeneration is the production of two useful forms of energy in a single energy conversion process. For example, a gas turbine may produce both rotational energy for an electric generator and heat for a building.

During the energy conversion process, an energy converter converts some form of energy to a form having a more suitable use. A light bulb and a gasoline engine are two familiar converters. People invest in electric energy to operate a light bulb because light is useful; likewise, people invest in gasoline for energy to run the automobile internal combustion engine because automobiles are useful. The laws of nature require that there be no loss of energy in the conversion. If 100 joules of energy are converted, then 100 joules remain after the conversion. However, the laws of nature neither require the converted energy to be in the form we desire, nor do they require that the other forms be useful. If the converter of 100 joules were a light bulb, only about 10 joules would emerge as light. The other 90 joules would be heat. Touching an ordinary light bulb when lit attests to the heat that is produced.

Efficiency is a practical measure of the performance of a converter: efficiency is equal to the desired form of energy divided by the total energy converted. If the light converted 100 joules of energy into 10 joules of light energy, we would say its efficiency is 10 ÷ 100 = 0.1 or 10 percent.

Heat is always produced to some extent in energy conversion. In fact, when energy has gone through all possible conversions, it ends up as thermal energy in the environment. The efficiency of a steam turbine at a large electric power plant is about 50 percent. This means that 50 percent of the energy converted is rejected as heat to the environment by massive cooling towers that are prominent at power plant sites. Heat is a useful energy commodity, so one must wonder why rejected heat is not put to some use. The idea of cogeneration is to do just that.

Evaluating the practical worth of thermal energy in a substance such as water requires consideration of both temperature and the amount of the substance. To understand this we say the thermal energy of a substance is equal to the number of molecules times the energy per molecule. The thermal energy per molecule (i.e., the second factor) increases with increasing temperature. So, even if the temperature is high, making energy per molecule larger, the total will still be small if there are only a few molecules. Similarly, if the temperature is low and a large number of molecules is involved, the total thermal energy can be large. The temperature of the water removing heat from a steam turbine is relatively low—only 10 to 15°C above the temperature of the environment—but a huge amount of water is needed to remove the heat from the turbine, so the thermal energy transferred to the water must be quite large. The thermal energy, although low-grade (about 80°F or 30°C), is appropriate for heating buildings. In a scheme of relatively small scale called district heating, buildings are heated in some towns and cities. But usually a power plant, especially a nuclear power plant, is well removed from the city and the economics of piping the heat to where it is needed is very unfavorable—requiring not only longer runs of piping, but resulting in greater heat loss from those longer runs. Consequently, for remotely sited plants, the thermal energy is rejected to the environment and goes unused.

Industry needs both electricity and heat. It is possible for an industry to produce its electricity from gas-fired turbogenerators and use the rejected heat for industrial purposes. The rejected heat can be at relatively high temperature, making it more useful if some sacrifice is made in the efficiency of the turbogenerator. It is in areas like this that cogeneration has its greatest potential and one sees commercial cogeneration enterprises evolving to provide a growing share of energy production.

Joseph Priest