Academic journal article Environmental Health Perspectives

The Gas Is Greener ... (Innovations)

Academic journal article Environmental Health Perspectives

The Gas Is Greener ... (Innovations)

Article excerpt

According to studies done by the U.S. Environmental Protection Agency (EPA) and the Harvard School of Public Health, some 64,000 Americans die prematurely each year because of illnesses made worse by air pollutants. Despite fairly recent improvements in air quality made mainly through the improvement of automobile emissions technology, the American Lung Institute says that 66% of Americans live in areas failing to meet the National Ambient Air Quality Standards. Pollutants include ozone, particulate matter, carbon monoxide, and nitrogen dioxide, with industrial sources including electrical power generating plants producing the great majority. Some 25% of these plants will reach the end of their useful lives over the next five years and will require replacement, but with what?

The Energy Information Administration of the U.S Department of Energy (DOE) forecasts that U.S. electrical demand will increase by 15,000 megawatts (MW) annually through 2005. The World Energy Council puts additional global needs through 2010 at more than 550,000 MW. If obsolete plants are to be replaced by other plants burning hydrocarbon fuels, how can the addition of pollutants to the atmosphere be avoided? Clean Energy Systems (CES), a company founded by veterans of Aerojet's renowned rocket technology programs, may have an answer in its Environmentally Clean Power Generation System, which uses zero-emission steam technology, or ZEST.

A conventional gas turbine power plant works by mixing compressed air with fuel, which is then burned under constant pressure. The resulting hot gas is allowed to expand through a turbine to perform work. But burning substances such as petroleum in the presence of air creates a range of problems. At combustion temperatures, oxygen and nitrogen in the air combine to create nitrogen oxides. Additionally, when carbon-containing fuel is burned in the presence of air, the carbon combines with oxygen to form carbon dioxide (C[O.sub.2], a greenhouse gas implicated in global warming.

This C[O.sub.2] is either captured and processed for commercial use or sequestered. Current sequestering practices call for injecting the C[O.sub.2] into layers of sandstone, limestone, dolomite, or chert, or injecting it deep into underground aquifers, where it will theoretically remain in solution for thousands of years. "However," says Ian Kennedy, associate dean of the University of California at Davis College of Engineering and director of the university combustion laboratory, "that's based on the theory that these aquifers are stable. C[O.sub.2] is a bit like nuclear waste in that it has a long lifetime, and if it comes out it's like taking the top off the soda bottle, and the C[O.sub.2] is in the atmosphere anyway." The CES technology makes it easier and more economical to collect and sequester C[O.sub.2] by burning clean fuel in the presence of pure oxygen.

How It Works

In the CES system, a separation plant removes oxygen from the air, which is then mixed with fuel, compressed, and delivered to a steam generator and reheater. The gas is burned in the presence of water, creating a very-high-temperature gas (1,200-3,200 [degrees] F) that is composed almost entirely of C[O.sub.2] and water. The combustion gases, composed of approximately 90% water and 10% C[O.sub.2] by volume, are delivered to a high-pressure turbine. After expansion through the turbine, the gases flow through a second steam generator, called a reheater, which increases the temperature of the mixture. Next the gases flow through an intermediate pressure turbine, and then on to a low-pressure turbine, which generates electricity.

According to CES, this cycle will have a near-term operating efficiency of 56% (meaning that 56% of the thermochemical energy available in the oxygen and fuel is converted to electricity), versus a projected 60-65% efficiency--and C[O.sub.2] sequestration--when high-temperature turbines become available. …

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