Developing improved sensors and controls for power plants offers the potential to cut costs for utility operators and customers by increasing efficiency, limiting outages, and reducing CO₂ emissions. The challenge for researchers is devising sensors that can provide real-time measurements of temperature, pressure, gas species and more amid harsh conditions.

The laser-heated pedestal growth (LHPG) system at the National Energy Technology Laboratory (NETL) allows researchers to fabricate optical fiber sensors that are ideal for the challenging environments associated with fossil fuel-based power generation systems. Modern sensor applications extend beyond traditional coal-fired power plants to include solid oxide fuel cells, gas turbines, boilers, and oxy-fuel combustion.

Optical fibers 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 fibers from single-crystal materials like sapphire and yttrium aluminum garnet (YAG), those same traits can be exploited in harsh environments. Single-crystal materials enable the use of fiber-optic technologies in these advanced power systems, where elevated temperatures, extreme pressures, and corrosive substances are commonly found.

LHPG is a crystal growth technique that involves using a CO₂ laser, combined with a complex beam delivery system and carefully controlled fiber-pulling mechanisms, to melt and reform bulk high temperature-resistant materials into single-crystal optical fibers. Researchers precisely control the LHPG process to ensure superior quality and incorporate novel sensor materials.

“Using this system, we’re able to create optical fiber sensors capable of surviving in some of the most extreme environmental conditions imaginable, including temperatures of more than 1,500 degrees Celsius,” Michael Buric, Ph.D., a researcher on NETL’s Functional Materials Team, said. “And we’re succeeding at reducing the cost of these new devices for real-world applications.”

Optical fibers 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 durable high-temperature optical cladding, or exterior light-guiding layer, to facilitate the integration of single-crystal fibers with opaque, 3D-printed machine components like gas turbine blades and solid oxide fuel cell interconnects.

Optical fiber sensors developed using the LHPG system 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.

Further fiber optics innovation at NETL will help to provide more accurate, real-time monitoring of conditions within advanced power systems to enable the safe and judicious use of America’s important fossil energy resources. In doing so, these vital tools will play an increasingly important role in the availability and security of our nation’s energy infrastructure.