Working with experts in the private sector, the National Energy Technology Laboratory (NETL) is on a quest to increase the efficiency and durability of energy-producing advanced gas turbines using ceramic matrix composites (CMCs)—an objective that could help meet the nation’s increasing demand for additional energy while addressing environmental concerns.

A composite material is made up of two or more materials that have different physical or chemical properties. When combined, those materials produce a material that has characteristics different from the individual components. CMCs represent a major step forward in development of material capabilities for gas turbines because they have the strength of metals and the temperature capability of ceramics. CMCs are made up of ceramic fibers that are embedded in a ceramic matrix. Ceramics like silicon carbide or tungsten carbide are attractive because they can withstand very high temperatures and resist abrasion.

The Advanced Turbines Program at NETL is focused on R&D activities to develop technologies that will accelerate turbine performance, efficiency, and emissions reduction beyond current state-of-the-art and reduce the risk to market for novel and advanced turbine-based power cycles.

As gas turbine performance and efficiency goals increase, the resulting temperatures are increasingly higher than the melting temperatures of the super alloys traditionally used in turbines. For metal parts to survive at these temperatures, they are cooled with air. The high temperature capabilities of CMCs reduce the amount of air needed for cooling, which delivers benefits in output and efficiency. 

High strength CMC material is a uniquely U.S.-based technology enabling gas turbine parts to operate 500°F hotter than turbine parts made with exotic metal alloys. According to researchers, the efficiency benefit of CMCs in a single set of nozzles in a gas turbine is equivalent to the energy needed to power 3,700 typical U.S. homes.

The latest generation of CMCs features temperature capabilities and a recently developed ability to produce complex geometries at relevant scales, presenting an attractive opportunity for enhancing the capability of turbine parts. The aviation industry paved the way by using CMCs in jet engines. Those lessons learned are being incorporated into the design of much larger energy-producing gas turbines.

In an ongoing effort sponsored by NETL, GE Energy Inc., is building upon earlier DOE programs to apply its high-temperature CMC material system to hot gas path nozzles to contribute to the ultimate turbine efficacy improvement goals.

GE’s CMC nozzle development efforts, sponsored by NETL, play a key role in meeting challenging objectives for revolutionary, near-zero-emission advanced turbines technologies. The work directly targets the Department of Energy’s goal for advanced gas turbine efficiencies that are greater than 65 percent in combined cycle applications.