Monday, July 7, 2008
Co- Generation Power Plant means to provide heat, power and environmental benefits:
Co- Generation Power Plant means to provide heat, power and environmental benefits:
‘Co-generation’ - known as combined heat and power, distributed generation, or recycled energy - is the simultaneous production of two or more forms of energy from a single fuel source. Cogeneration power plant simultaneously generates both electricity and useful heat from a common fuel source. It produces heat for industrial processes and uses a recovery boiler to generate electricity.
A. Cogeneration power plant generally includes reciprocating engines, combustion turbines, micro-turbines, backpressure steam turbines, and fuel cells. Cogeneration power plants often operate at 50 to 70 percent higher efficiency rates than single-generation facilities. In practical terms, what cogeneration usually entails is the use of what would otherwise be wasted heat (such as a manufacturing plant’s exhaust) to produce additional energy benefit, such as to provide heat or electricity for the building in which it is operating. Cogeneration is great for the bottom line and also for the environment, as recycling the waste heat saves other pollutant-spewing fossil fuels from being burned.
B. As of now, most of the thousands of cogeneration plants operating across the United States and Canada are small facilities operated by non-utility companies and by institutions like universities and the military. Cogeneration saves its customers up to 40% on their energy expenses, and provides even greater savings to our environment. Cogeneration, as previously described above, is also known as “combined heat and power” (CHP). Cogeneration is a proven technology that has been around in US for over 100 years. In fact, America’s first commercial power plant was a cogeneration plant that was designed and built by Thomas Edison in 1882 in New York.
C. Primary fuels commonly used in cogeneration include natural gas, oil, diesel fuel, propane, coal, wood, wood-waste and bio-mass. These "primary" fuels are used to make electricity, a "secondary" fuel. This is why electricity, when compared on a btu to btu basis, is typically 3-5 times more expensive than primary fuels such as natural gas. Due to competitive pressures to cut costs and reduce emissions of air pollutants and greenhouse gasses, owners and operators of industrial and commercial facilities are actively looking for ways to use energy more efficiently. One option is cogeneration, also known as combined heat and power (CHP). Cogeneration/CHP is the simultaneous production of electricity and useful heat from the same fuel or energy. Facilities with cogeneration systems use them to produce their own electricity, and use the unused excess (waste) heat for process steam, hot water heating, space heating, and other thermal needs. They may also use excess process heat to produce steam for electricity production. Cogeneration technologies are conventional power generation systems with the means to make use of the energy remaining in exhaust gases, cooling systems, or other energy waste stream. Typical cogeneration prime movers include: Combustion turbines, Reciprocating engines, Boilers with steam turbines, Micro-turbines, Fuel cells.
D. A typical cogeneration system consists of an engine, steam turbine, or combustion turbine that drives an electrical generator. A waste heat exchanger recovers waste heat from the engine and/or exhaust gas to produce hot water or steam. Cogeneration produces a given amount of electric power and process heat with 10% to 30% less fuel than it takes to produce the electricity and process heat separately. There are two main types of cogeneration techniques: (a) "Topping Cycle" plants, and (b) "Bottoming Cycle" plants.
(a) "Topping Cycle" plants - A topping cycle plant generates electricity or mechanical power first. Facilities that generate electrical power may produce the electricity for their own use, and then sell any excess power to a utility. There are four types of topping cycle cogeneration systems.
(i) The first type burns fuel in a gas turbine or diesel engine to produce electrical or mechanical power. The exhaust provides process heat, or goes to a heat recovery boiler to create steam to drive a secondary steam turbine. This is a combined-cycle topping system.
(ii) The second type of system burns fuel (any type) to produce high-pressure steam that then passes through a steam turbine to produce power. The exhaust provides low-pressure process steam. This is a steam-turbine topping system.
(iii) A third type burns a fuel such as natural gas, diesel, wood, gasified coal, or landfill gas. The hot water from the engine jacket cooling system flows to a heat recovery boiler, where it is converted to process steam and hot water for space heating.
(iv) The fourth type is a gas-turbine topping system. A natural gas turbine drives a generator. The exhaust gas goes to a heat recovery boiler that makes process steam and process heat. A topping cycle cogeneration plant always uses some additional fuel, beyond what is needed for manufacturing, so there is an operating cost associated with the power production.
(b) "Bottoming Cycle" plants - Bottoming cycle plants are much less common than topping cycle plants. These plants exist in heavy industries such as glass or metals manufacturing where very high temperature furnaces are used.
A waste heat recovery boiler recaptures waste heat from a manufacturing heating process. This waste heat is then used to produce steam that drives a steam turbine to produce electricity. Since fuel is burned first in the production process, no extra fuel is required to produce electricity.
E. An emerging technology that has cogeneration possibilities is the fuel cell. A fuel cell is a device that converts hydrogen to electricity without combustion. Heat is also produced. Most fuel cells use natural gas (composed mainly of methane) as the source of hydrogen. The first commercial availability of fuel cell technology was the phosphoric acid fuel cell, which has been on the market for a few years. Other fuel cell technologies (molten carbonate and solid oxide) are in early stages of development. Solid oxide fuel cells (SOFCs) may be potential source for cogeneration, due to the high temperature heat generated by their operation.
F. Environmental Issues - While cogeneration provides several environmental benefits by making use of waste heat and waste products, air pollution is a concern any time fossil fuels or biomass are burned. The major regulated pollutants include particulates, sulfur dioxide (SO2), and nitrous oxides (NOx). Some cogeneration systems, such as diesel engines, do not capture as much waste heat as other systems. Others may not be able to use all the thermal energy that they produce because of their location. They are therefore less efficient, and the corresponding environmental benefits are less than they could be. The environmental impacts of air and water pollution and waste disposal are very site-specific for cogeneration. This is a problem for some cogeneration plants because the special equipment (water treatment, air scrubbers, etc.) required to meet environmental regulations adds to the cost of the project. If, on the other hand, pollution control equipment is required for the primary industrial or commercial process anyway, cogeneration can be economically attractive.
G. Cogeneration Benefits - Cogeneration offers energy, environmental, and economic benefits, including:
(a) Saving money - By improving efficiency, cogeneration systems can reduce fuel costs associated with providing heat and electricity to a facility.
(b) Improving power reliability - Cogeneration systems are located at the point of energy use. They provide high-quality and reliable power and heat locally to the energy user, and they also help reduce congestion on the electric grid by removing or reducing load. In this way, cogeneration systems effectively assist or support the electric grid, providing enhanced reliability in electricity transmission and distribution.
(c) Reducing environmental impact - Because of its improved efficiency in fuel conversion, cogeneration reduces the amount of fuel burned for a given energy output and reduces the corresponding emissions of pollutants and greenhouse gases.
(d) Conserving limited resources of fossil fuels - Because cogeneration requires less fuel for a given energy output, the use of cogeneration reduces the demand on our limited natural resources—including coal, natural gas, and oil—and improves energy security.
Thus, co-generation units bring about the utmost economical and ecological advantage in a field where they can be meaningfully employed.