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Shining a laser light on slagging
Slagging – the accumulation of coal ash at high temperatures on the tubes carrying steam in a power plant boiler – costs power plants $2.4 billion a year, according to a recent report by the Electric Power Research Institute (EPRI).
ERC researchers have worked with the Energy Research Co. (ERCo) of Staten Island, N.Y., to develop an optical technology that lets plant operators make real-time adjustments to prevent slagging and fouling problems. Using laser-induced breakdown spectroscopy (LIBS) and artificial intelligence, the system provides instant analysis of the elemental composition of the coal as it is being burned. LIBS also correlates the fusion temperature of the coal ash, which is affected by the ratio of the elemental ingredients.
The new technology was successfully tested at Brayton Point Station, a coal-fired power plant in Massachusetts. The two-year project was funded by DOE through the New York State Energy Research and Development Authority. The researchers have won a second DOE grant to develop a commercial prototype.
|Schuster seeks to control the shape of the plasma and of the radial profiles of plasma variables while keeping it free of magnetohydrodynamic instabilities.|
LIBS uses a pulsating laser with two frequencies, one infrared and one visible light. The laser vaporizes a sample and gives a distinct elemental signature represented by intensity and wavelength. From these data, a software package containing artificial neural network models estimates ash-fusion temperature and predicts coal slagging potential.
Traditionally, says ERC associate director Carlos Romero, operators measure coal composition and ash-fusion temperature by taking a sample from a boiler and testing it in a lab. This can take days. operators can also take measurements with a nuclear analyzer using gamma rays. But the analyzer has a large footprint, says Romero, and is potentially hazardous. LIBS is the size of a tabletop, is relatively safe to use and provides instantaneous data without interrupting the process.
“Our results have been very positive,” says Romero. “LIBS analyzes coal composition accurately and with good repeatability. It also predicts ash-fusion temperature with results that compare very favorably with results obtained using standards of ASTM International.”
Cleaner coal – through drying
Half the electricity in the U.S. is generated by coal-fired power plants, but many facilities burn low-rank coals. The moisture content in these coals can approach 40 percent, compared to 6 to 8 percent in high-rank coals, and it adversely affects a plant’s performance and emissions.
Engineers at Lehigh’s ERC and at Great River Energy (GRE) in North Dakota have developed a low-temperature coal-drying system that removes moisture from coal using heat rejected by the power plant. The 10-year project was funded by doe and GRE. GRE is installing the new technology at its 1,160-MW Coal Creek Station, making the station the world’s first to operate with 100 percent feed-dried coal.
Levy and ERC associate director Nenad Sarunac say that at Coal Creek the new technology will remove about a quarter of the moisture from low-rank coal, resulting in a 5 percent improvement in efficiency, a 5 percent reduction in CO2 emissions, and larger reductions in emissions of NOX, SOX and mercury.
The cost of retrofitting coal creek with the new technology is relatively low compared to the cost of constructing a new plant that would operate as efficiently, researchers say. Given that low-rank coals constitute more than half the world’s coal reserves, the patented technology could potentially be used on a global scale.
ERC researchers are working with U.S. and international companies to integrate the new system into an oxy-combustion power cycle and a coal-to-liquid plant.
The fusion vision
One of the most enticing – and elusive – sources of renewable energy is nuclear fusion, in which isotopes of H2 join under extreme heat (up to 100 million degrees) to create helium atoms. Fusion has the potential to provide unlimited supplies of clean, safe energy, says Eugenio Schuster, assistant professor of mechanical engineering and mechanics. It emits no pollutants or greenhouse gases, it produces minimal radioactive waste, and it poses no threat of a large-scale accident.
An international team of engineers and scientists is building ITER, a $10 billion tokamak, or fusion reactor, in France. Their goal is to generate more energy from fusion – five to 10 times more – than is required to heat the hydrogen plasma. Schuster has ties with ITER researchers and with leading U.S. fusion research centers, including General Atomics in San Diego and the Princeton Plasma Physics Laboratory. He has organized workshops on fusion for DOE and NSF.
Schuster studies the conditions for a highly confined, stable hydrogen plasma. He seeks to control the shape of the plasma and the radial profiles of plasma variables such as density, temperature and current, while keeping the plasma free of magnetohydrodynamic instabilities.
To understand the evolution of the plasma current profile, Schuster models the evolution of the related poloidal magnetic flux profile in normalized cylindrical coordinates. He uses a nonlinear partial differential equation called the magnetic diffusion equation.
By controlling the profile shape of the plasma’s toroidal current, says Schuster, scientists hope to enhance the confinement of the plasma, and the steadiness of the fusion reaction.
DOE regularly funds internships for Schuster’s students at the DIII-D tokamak at General Atomics. This year, Yongsheng Ou and Chao Xu, two Ph.D. candidates, contributed a paper that was selected as a finalist for the Best Paper Award at the American Control Conference, the largest event of its kind in the U.S.
Experts say it could take 30 years or more before humans enjoy abundant fusion energy, but Schuster is optimistic.
“I’m confident this will be something I can tell my grandchildren about.”