Laser-induced breakdown spectroscopy is starting to light the way for power plant operators who want to reduce coal ash deposition in their boilers.
The most significant ash-related problem in coal-fired power plants is deposition, according to Steam, the authoritative work published by the Babcock & Wilcox Co. During the combustion process, coal ash can be released in a molten fluid or sticky plastic state. A portion of the ash, which is not cooled quickly to a dry solid state, impacts on and adheres to the furnace walls and other heating surfaces; this phenomenon is commonly referred to as slagging. Because such large total quantities of ash are involved, even slagging created by a small fraction of the total ash can seriously affect with boiler operation.
| Slagging and associated problems cost U.S. coal-fired power plants approximately $2.4 billion each year. |
Specifically, slagging occurs when coal ash accumulates, at high temperatures, outside the tubes that carry steam inside a power plant boiler. Slagging reduces heat transfer from the flue gas to the steam tubes and decreases a plant’s efficiency. In extreme cases slagging can require a boiler to be shut down while heat transfer surfaces are cleaned or repaired. According to a 2007 report by the Electric Power Research Institute, slagging and associated problems cost U.S. coal-fired power plants approximately $2.4 billion each year.
The variability of ash behavior is one of the biggest problems for boiler designers and operators. Although boilers are often designed to burn a wide range of coals satisfactorily, no one unit can perform equally well with all types of coal.
Recently, a new technology has been developed to assist power plant personnel in dealing with ash-related challenges. During the past two years, Lehigh University’s Energy Research Center (ERC) has worked with the Energy Research Co. (ERCo) of Staten Island, N.Y., in developing an optical technology that will allow power plant operators to make rapid adjustments to prevent boiler slagging and fouling problems (Figure 1). The project was funded by the U.S. Department of Energy’s (DOE’s) State Technologies Advancement Collaborative (STAC) program, which was managed by the New York State Energy Research and Development Authority (NYSERDA) and a Phase I Small Business Innovation Research program from the DOE’s National Energy Technology Laboratory.
1. Preventing sticky buildup. Laser-induced breakdown spectroscopy (LIBS) technology is designed to analyze coal composition and provide fusion temperature feedback to power plant staff who handle coal-fired boiler operations. Courtesy: Energy Research Center, Lehigh University
The ERC and ERCo have applied laser-induced breakdown spectroscopy (LIBS) technology to provide instant analysis of the elemental composition of the coal being burned and correlation of that analysis with the fusion temperature of the coal ash, which is affected by the concentration of the elemental coal ingredients.
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