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Solving a sticky problem in power plants

Photonics Spectra
Dec 2008
Laura S. Marshall,

As energy costs rise and the economy falls, there is no room for inefficiency in power production.

In coal-fired power plants, a problem known as slagging occurs when coal ash minerals get sticky and latch onto the boiler tubes that transport steam, reducing heat transfer to the steam tubes and sometimes requiring a full shutdown of the boiler for cleaning or repair. Slagging-related breakdowns in efficiency cost coal-fired power plants $2.4 billion every year, according to a report by the Palo Alto, Calif.-based Electric Power Research Institute.

Given that these plants generate half the electricity in the US and that the price of coal has doubled in just a year, a solution to slagging is overdue.

That’s where LIBS comes in. Laser-induced breakdown spectroscopy, that is. It’s an optical technology developed by Energy Research Co. (ERCo) of Staten Island and the Energy Research Center (ERC) at Lehigh University in Bethlehem, Pa., and it will allow plant operators to detect slagging in its earliest stages.

Laser-induced breakdown spectroscopy for use in coal-fired power plants was developed by the Energy Research Co. of Staten Island, N.Y., and the Energy Research Center at Lehigh University in Bethlehem, Pa. Courtesy of Carlos E. Romero, Lehigh University.

Carlos E. Romero, principal research scientist and associate director at Lehigh’s ERC, was quick to point out that the development process was collaborative. “ERCo has developed the LIBS system,” he said. “The ERC has provided the power plant expertise and artificial intelligence tools for the LIBS application in coal-fired power plants.

“This particular application, where we used artificial neural networks to correlate LIBS data with ash fusion temperature, was designed with coal-fired power plants in mind.”

LIBS originally was designed for the fiberglass and scrap aluminum industries, according to Robert De Saro, ERCo president. The system is made up of a pulsating laser, a sample chamber, an optical spectrometer and photodiodes, an amplifier unit and a processing computer.

“A laser beam is directed onto a sample that is gathered from a sampler,” he said. “The laser vaporizes and ionizes micrograms of the coal. The resulting emitted radiation is collected by a spectrometer, which records the wavelength and the intensity of the radiation.”

De Saro said that the amplitude of the light signal reveals the concentration of the carbon, hydrogen, sulfur, oxygen, trace metals such as mercury, and ash components such as silicon or aluminum that can be identified in the coal sample. “The wavelengths uniquely identify each element, and the intensities determine their concentrations,” he said. “The measurements are made continuously and simultaneously.”

LIBS already has been tested at Brayton Point Station, a working coal-fired power plant in Somerset, Mass. ERCo and ERC personnel tested coal samples for ash minerals and ash fusion temperatures using both LIBS and standard laboratory methods, which take about three days. “The results were outstanding,” De Saro said.

He said the demonstration showed that hourly LIBS coal analyses would provide fusion temperature feedback with enough resolution to predict changes in fuel quality, which means plant operators would be able to tell when slagging was likely to occur next.

Best of all, according to De Saro, the system costs less than existing testing methods. Nuclear source instruments using gamma neutron activation analysis range from $250,000 to $500,000, he said, and have additional costs associated with the isotope source and its permitting and handling.

“LIBS is relatively inexpensive and provides a significant cost savings to the power plant,” he said. “It is easy to use, and little operator training is required. It does not have a nuclear source and can measure any element on the periodic table. Its operating and maintenance costs are very low.

“Its only disadvantage is that it is still in the development stage.”

ash mineralsboiler tubescoal-fired power plantsenergyResearch & TechnologyspectroscopyTech Pulse

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