With research laboratories located in the heart of regions rich in fossil energy resources, NETL is on a mission to discover, integrate, and mature technology solutions to enhance the nation’s energy foundation and protect the environment for future generations. The Lab is leading efforts to resolve the environmental, supply, and reliability constraints of using America’s abundant fossil fuel resources—coal, natural gas, and oil. Energy conversion engineering is one of the Lab’s core competencies, specializing in technologies that enable low-carbon power production while optimizing environmental performance, water use, efficiency, and waste minimization.

Within this research area, NETL is investigating innovative approaches to making the nation’s power cycles more efficient while using less fuel. Playing a critical role in that effort are geothermal energy, supercritical carbon dioxide (sCO₂) turbomachinery, and solid oxide fuel cells (SOFCs).

Geothermal Energy

Geothermal resources are reservoirs of hot water that exist below the Earth’s surface. Deep wells can be drilled into these underground reservoirs to tap into a supply of steam, and the hot water can be brought to the surface to power many applications. Geothermal energy is renewable, domestic, and clean, and power plants operating from geothermal energy can produce electricity all day, every day.

Geothermal energy could be used to heat commercial office complexes and military installations with heat from deep within the Earth. In 2016, NETL investigated the geothermal potential for a military training facility located in a region where both geothermal and natural gas resources may be developed, possibly together. The technically accessible deep geothermal resources are thought to be suitable for “direct-use” applications, such as facility heating and industrial processes in manufacturing. NETL concluded that a range of potential geothermal opportunities exist at the facility, but additional research is needed to determine costs and resource assessment. The Lab is leading research into using one well to recover natural gas while incorporating a second passage at the well site to simultaneously mine geothermal energy for heat.

Supercritical Carbon Dioxide Turbomachinery 
At elevated temperatures and pressures, CO₂ becomes a supercritical fluid, meaning that it can fill a container like a gas, but has the density of a liquid. In this state, sCO₂ can be used as a working fluid in energy conversion power generation to increase plant efficiency, reduce fuel consumption and emissions, reduce cooling water requirements, and provide a compact design that will reduce capital costs. 

Fossil fuels, particularly coal, can provide an ideal heat source for sCO₂ cycles. NETL is researching sCO₂turbomachinery that can harness this benefit and more. Using the Lab’s High-Pressure Combustion Research Facility, which houses a dynamic gas turbine and simulation validation test rig, researchers model components of sCO₂ systems, analyze their costs, and subject them to laboratory testing to advance turbine cycles that rely on sCO₂—instead of steam—to more efficiently spin the rotating blade in turbines.

Solid Oxide Fuel Cells

SOFCs produce power by converting the chemical energy in fuel directly to electrical energy. SOFCs consist of two electrodes—a positive cathode and a negative anode—and an electrolyte sandwiched in between. The chemical reactions that produce electricity occur in the electrodes, while the electrolyte shuttles charged particles from one electrode to the other. A catalyst speeds the reactions at the electrodes. SOFCs operate at high-temperature, which increases their efficiency and allows them to use hydrogen and carbon monoxide that is produced through coal gasification as well as during reforming of hydrocarbons such as methane.

Compared to conventional power production technologies, SOFCs generate electricity with much higher efficiencies, fewer emissions and require less fuel. However, the technologies that make SOFCs practical on a large scale are expensive. NETL researchers are innovating technologies to improve performance in the anode and cathode, increase cell efficiency, and diminish SOFC system costs, all with the goal of transferring these breakthrough innovations to industry and facilitating commercial acceptance of SOFC technology.

The technologies being developed through NETL’s energy conversion engineering core competency are building a foundation for flexible power systems over a range of sizes that will be needed to meet future energy demands including smaller grids and further integration with renewables emerge.