Sapphire Could Make Coal More Energy Efficient

Only diamond is harder than sapphire.

That's why sapphire is being tested as a sensor that could relay critical information about extreme conditions present during gasification, the process of heating coal until it becomes a gas.

With such monitors in place, scientists can ensure that the gasifiers heat the coal to the exact temperature necessary to turn it into gas, thus ensuring that the process is running as efficiently as possible.

“There is a very high temperature, very high pressure, and a lot of chemicals reacting together,” said Hai Xiao, associate professor at the Missouri University of Science and Technology, and the chief researcher on the project.

Xiao and his team have been working on this problem because they know that synthetic gas made from coal burns with fewer emissions than coal alone. While burning coal has an efficiency of around 37 percent, Xiao said, the gasification process can increase the efficiency to more than 45 percent.

Unfortunately, no sensor has been developed that’s tough enough to withstand the intense environment inside a gasifier, where temperatures can surpass 3,000 degrees Fahrenheit.

Sapphire is one of the only known materials able to beat the heat. And it's already used for a variety of industrial applications, including optics and semiconductors,

Xiao and his colleagues are making the sensor from sapphire fibers, which they create by dropping a solid sapphire seed into a specific amount of molten sapphire and drawing it upward, allowing the sapphire to grow into single crystal sapphire fibers.

The scientists are experimenting with different diameters of the sapphire fibers to find which size works best. While sapphire is generally a very durable material, it is a gemstone, and can be fragile at diameters that are too thin. When completed, each fiber will be 3 feet to 6 feet long and smaller in diameter than the average human hair.

Ozzie Lomax, the combustion turbine plants manager for AmerenUE, an energy provider to Missouri, said, “We’re always looking for new temperature and pressure sensors to increase the reliability of our gas turbines.”

The Missouri University of Science and Technology team hope to test the sensors in AmerenUE production facilities.

“The sensors will be mounted in the coal gasification equipment or our gas turbines where they will give us information on how well the combustion process is occurring, “ Lomax said.

Once the technology is completed and becomes commonly applied, perhaps sapphires will be known for more then just the September birthstone.