Superfund Research Program
Promising Developments are Made in the Real-Time Analysis of Combustion Emissions
Our society relies greatly on combustion processes, which support our modern lifestyle in a variety of ways. Combustion is used in incinerators as a method for destroying the country's growing volume of hazardous, medical, and municipal wastes, and it also accounts for approximately 85 percent of the world's energy production. Industrial burners and furnaces, as well as metal smelters and cement kilns, also employ thermal oxidation at high temperatures to accomplish their given purposes. Unfortunately, these various combustion processes can generate unintentional by-products that have the potential to impact public health, diminishing the benefits derived from combustion applications.
When any type of material is burned, whether to produce energy from fossil fuel or to destroy high volumes of hazardous wastes, the combustion process rarely results in complete thermal oxidation of the material to carbon dioxide and water. Depending on the chemical nature of the material burned and the combustion conditions, small amounts of a variety of substances can be formed or released. For example, when organic materials are combusted, pyrosynthesis can produce by-products such as hydrocarbons, dioxins, and furans. Heavy metals such as arsenic, chromium, and lead can also be released during the combustion of coal, metal ores, and metal-containing waste materials. Some of these combustion by-products pose carcinogenic and other health risks to humans. Thus, there is a great deal of concern when they escape into the atmosphere, because from there they can potentially come into contact with humans.
The emissions from combustion processes represent one of the most controversial issues surrounding the use of combustion, which remains the largest source of air pollutants in this country. Toxic emissions from combustion systems can be reduced, however, by engineering interventions such as advanced control systems that signal when toxic species are being released in combustion exhausts. One means for preventing emissions of toxic pollutants into the ambient air, continuous emissions monitoring, is now considered essential to fully assess the operating condition of large-scale combustion systems, such as waste incinerators. Monitoring systems capable of detecting a broad spectrum of toxic and hazardous chemicals are in particular demand at this time.
A team of researchers at the University of California-Berkeley is collaborating with scientists at the Lawrence Berkeley National Laboratory in Berkeley, California to develop a technique for real-time, continuous monitoring of a variety of compounds commonly found in combustion effluents. The technique under development uses excimer laser fragmentation fluorescence spectroscopy (ELFFS), a method that is offering the potential for detecting and quantifying multiple components in combustion exhausts.
The ELFFS technique uses high-energy photon beams from an excimer laser to convert non-fluorescent compounds into smaller fragments. The fragmented species are then detected optically by laser-induced fluorescence. The fluorescence signal is proportional to the concentration of substance detected. Because the photons are efficiently absorbed and the fluorescence lifetime falls within the range of nanoseconds, the process is rapid and also allows for sensitive detection of low concentrations of compounds. Metallic elements not requiring fragmentation can also be detected through this technique.
In laboratory experiments, ELFFS is proving to be a versatile tool for the simultaneous detection of different airborne compounds under simulated combustion conditions. During studies carried out in the post-flame gases of a laboratory burner, the researchers have shown that ELFFS is effective for detecting chlorinated hydrocarbons, barium, chromium, manganese, nickel, lead, and tellurium -- in real time and in situ. The method is also powerful: minute traces (in the ppb range) of the aforementioned species can be detected and identified based on their unique fluorescence.
Because the laboratory scale tests with ELFFS were so promising, a Cooperative Research and Development Authority (CRADA) was undertaken by the Department of Energy and Thermatrix (a company specializing in hazardous waste destruction) to advance the commercialization of this system for continuous emissions monitoring.
When fully developed, the ELFFS based system will have a major advantage over conventional emissions monitoring methods. Current monitoring practices of the above combustion by-products involve lengthy procedures that include extractive sampling and preparation of samples for chemical analysis, which can take up to several weeks to produce results. By using ELFFS, monitoring data can be produced as emissions are formed, allowing for rapid response and corrective actions if pollutants are being released. This capability will ultimately be useful for reducing the amount of pollutants released into the atmosphere by combustion processes.
Even as major efforts are underway to move away from society's dependence on combustion processes, combustion will continue to be an integral part of our society until new waste management strategies and energy production technologies are developed and in place. This research on continuous emissions monitoring is motivated in part by the need to protect human health and prevent environmental damage from the inadvertent by-products of combustion. Thus, these breakthroughs in emissions monitoring have far-reaching effects for both public health and environmental protection by offering a novel approach to control combustion processes in way that reduces their risks.
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To learn more about this research, please refer to the following sources:
- Buckley SG, Sawyer RF, Koshland CP, Lucas D. 1996. In situ monitoring of toxic metal emissions using excimer lawer fragmentation fluoresence spectroscopy. Combustion Science and Technology 118:169-188.
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