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NETL’s manufacturing system provides new opportunities for optical sensors

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World Coal,

In 1917, when Albert Einstein suggested that it might be possible, under the right conditions, to produce light rays that could be directed at atoms to produce energy in beams of light, he created the theory behind what would become light amplification by stimulated emission of radiation – what we call lasers today.

Einstein never dreamed that researchers would someday use this principle to improve fossil fuel-based power generation systems – but that is just what is happening at NETL. NETL researchers are using lasers to make better sensors that work more efficiently inside the harsh environments of power generation systems, from traditional coal-fired power plants to solid oxide fuel cells, gas turbines, boilers and oxy-fuel combustion.

The results of that work are improved controls for power plants, lower costs for power producers, lower bills for customers, reduction in power outages, lower CO2 emissions, and increased power production efficiencies.

The challenge for researchers has been to devise sensors that can provide real time measurements of temperature, pressure, gas species and more amid harsh conditions. That is where lasers come into the picture.

The laser-heated pedestal growth (LHPG) system at NETL allows researchers to fabricate optical fibre sensors that are ideal for the challenging environments associated with fossil fuel-based power generation systems.

LHPG is a crystal growth technique that involves using a CO2 laser, combined with a complex beam delivery system and carefully controlled fibre-pulling mechanisms, to melt and reform high temperature-resistant materials – into single crystal optical fibres.

Optical fibres are flexible, transparent light guides slightly thicker than a human hair and typically made of glass or plastic. Their resistance to electromagnetic interference and ability to fit into confined spaces make them useful for transmitting light and communications; their most well-known uses. By fabricating optical fibres from single crystal materials such as sapphire and YAG (yttrium aluminum garnet), those same traits can be exploited in harsh environments.

Michael Buric, Ph.D., with the NETL’s Functional Materials Team explained that researchers precisely control the LHPG process to ensure superior quality and incorporate novel sensor materials.

“Using this system, we’re able to create optical fibre sensors capable of surviving in some of the most extreme environmental conditions imaginable, including temperatures of more than 1500°C,” Buric said. “And we’re succeeding at reducing the cost of these new devices for real world applications.”

Optical fibres created through LHPG are integrated into sensor assemblies and tested for performance to determine which materials and configurations show the most promise, thereby guiding future research. For instance, scientists are exploring options to develop a durable high temperature optical cladding, or exterior light-guiding layer, to facilitate the integration of single crystal fibres with opaque, 3D printed machine components such as gas turbine blades and solid-oxide fuel cell interconnects.

By using the LHPG system, NETL researchers can create optical fibre sensors that are more reliable than traditional alternatives because they eliminate electrical connections, a common cause of sensor failure. They also offer versatility through embedded, remote and distributed sensing technologies.

NETL’s fibre optics innovation is just one example of how the Lab is using cutting-edge tools like lasers to enable the safe and judicious use of America’s important fossil energy resources. These vital innovations will play an increasingly important role in the availability and security of our nation’s energy infrastructure.

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