Energy conversion engineering— the process of changing one form of energy to another— is an important and growing field with a large variety of applications. For example, energy conversion can be used to change the chemical energy in coal to thermal and mechanical energy that can turn a power plant’s turbine.
At the U.S. Department of Energy’s (DOE) National Energy Technology Laboratory (NETL)— America’s only national laboratory dedicated to fossil fuel research—researchers work to tackle, discover, refine, and disseminate new technologies that embrace the abundance of fossil fuels, while carefully considering and addressing the challenging requirements and opportunities of an energy-hungry world.
Many of NETL’s energy conversion engineering efforts focus on increasing power cycle efficiency, enabling more power generation for less fuel and fewer emissions.
The Laboratory’s Senior Fellow for Energy Conversion Engineering, Geo Richards, explained that the research can be sorted into short-term and long-term efforts.
“Near-term, we focus on improving existing coal or natural gas power plants to make them more efficient, and flexible, meaning they are able to operate in tandem with variable wind and solar energy” he said. “That includes work like improving power plant turbine blades, developing better sensors and control systems, and investigating how advanced manufacturing approaches can help create components that make power plants more efficient and productive.
“The benefit is that we get more energy out of our coal or natural gas, thereby extending our natural resources, reducing emissions, and insuring that the nation can benefit from low-cost energy while protecting the environment.”
An example of near-term efforts includes the continuing development of advanced, low-emission, high-efficiency gas turbine technology. The gas turbine is a workhorse of today’s power generation and NETL researchers are discovering approaches for a high-efficiency, near-zero-emission turbine power systems that depend on advancements in thermal protection using thermal barrier coatings and aerothermal cooling technologies. Recent advances in so-called “additive” will to enable innovative cooling designs that were not possible before. NETL is combining its lab capability with research partnerships to test new designs versus the current state of the art. The best concepts could be adopted in new engine designs, providing a boost to generating efficiency in the years ahead.
In the long-term, Richards explained that NETL’s energy conversion engineering efforts are developing a spectrum of innovative technologies in a wide range of topic areas, from future combustion technologies to solid oxide fuel cells, and the potential for using geothermal energy sources. Here are just a few of the energy conversion engineering research areas in which NETL researchers are active.
The combustion of fossil fuels in nearly pure oxygen, rather than air, presents an opportunity to simplify CO2 capture in power plant applications. While oxy-combustion power production provides oxygen to the combustion process by separating oxygen from air using a cryogenic air separation unit or an ion transport membrane, chemical looping systems produce oxygen internal to the process using oxidation-reduction cycling of an oxygen carrier. The chemical looping process can eliminate large capital and operating investments and other energy costs associated with oxygen generation. Chemical looping is considered a “transformational” technology with the potential to meet cost and performance goals for commercial applications. The concept of chemical looping can be applied to coal combustion, or to coal gasification, where it is known as chemical looping gasification. Development of efficient oxygen carriers, usually a metal oxide that transports oxygen to the fuel, is key to the success of chemical looping combustion. NETL has been testing carriers in its own pilot-scale 50 KWth chemical looping combustion reactor.
Direct Power Extraction
NETL researchers are developing technologies for oxy-fuel combustion using magnetohydrodynamics (MHD) to directly extract power from fossil energy combustion products. The process, which has no moving parts, can be more efficient in power production because it operates at temperatures that are only possible by using oxy-fuels. High-temperature oxy-fuel combustion products accelerate through a magnetic field to produce electric current, essentially creating an electromagnetic turbine expander. Hot exhaust from the expander can be used in conventional steam boilers, potentially enabling a high-efficiency retrofit to existing powerplants. In contrast to earlier attempts to harness MHD physics for power generation, recent scientific advances in low-temperature plasma generation, material science, and numeric models suggest that the concept can achieve high-efficiency power generation, with inherent control of carbon dioxide. At NETL, work is underway to develop durable electrodes, extend plasma conductivity, and optimize the process performance with validated numeric models.
Pressure Gain Combustion (PGC)
PGC can improve the efficiency of turbine generators by increasing the pressure using a transient, rather than steady, combustion process. While conventional gas turbine engines undergo a pressure loss during steady combustion, PGC uses constant volume combustion to create a pressure rise across the combustor, while consuming the same amount of fuel as the conventional, steady combustion. NETL researchers are working on technical challenges including fuel injection, fuel and air mixing, backflow prevention, wave directionality, controlling emissions of NOx and CO, unsteady heat transfer, and cooling flow challenges. The goal of the work is to develop PGC systems for integration with combustion gas turbines.
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 within 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 there is a range of potential geothermal opportunities at the facility, but additional research is needed to determine costs and resource assessment. Richards said NETL is leading research into using one well to recover natural gas while incorporating a second passage at the well site to simultaneously allow geothermal energy to be used locally as a steady supply of heat.
Supercritical carbon dioxide turbomachinery
The supercritical carbon dioxide power cycle operates similarly to other turbine cycles, but uses CO2 as the working fluid in the turbomachinery. The cycle is operated above the critical point of CO2 so that it does not change phases (from liquid to gas), but rather undergoes drastic density changes over small ranges of temperature and pressure allowing a large amount of energy to be extracted at high temperature from equipment that is relatively small. Fossil fuels, particularly coal, can provide an ideal heat source for SCO2 cycles with the potential to significantly increase efficiency over other power cycle configurations with potential for near 100 percent CO2 capture.
Solid Oxide Fuel Cells (SOFC)
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. They have no moving parts, which enables them to be highly efficient. NETL’s R&D is resulting in innovations 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.
NETL’s pursuit of these and other energy conversion engineering projects led to the development of critical capabilities that are used daily to tackle emerging energy challenges. NETL maintains advanced research capabilities in clean energy systems; multiphase flow science, combustion science, innovative energy concepts, reaction engineering and diagnostics and controls. The Laboratory’s researchers use a supercomputer and complex modeling devices, sophisticated sensors and multiphase flow science tools that show how liquids and gases mix and flow.
NETL’s Associate Director of Energy Conversion, Dave Berry, explained that, “The core of the laboratories capabilities and research success resides in the excellence and dedication of our research staff and cutting-edge facilities without which, achievement and innovation would not be possible.”
A robust fossil-based economy supports a high quality of life for millions of Americans, sustains its manufacturing and high-tech industries, and fosters economic growth. Using abundant fossil energy resources with sustainable environmental stewardship is critical. The advanced energy conversion technologies being explored by NETL can enable efficiencies that increase power production and reduce overall power generation costs.
Gerrill Griffith is a writer for NETL. For more than 40 years, he has worked in West Virginia as a journalist, higher education administrator, marketer for a private research laboratory and congressional staffer. He is a graduate of West Virginia University.