Researchers at Sandia National Laboratories in New Mexico have announced that they have successfully tested a new power generation technology. Energy conversion systems could be used to power local grids, greatly improving the efficiency of power plants across the United States, and possibly the world.

In a news release from the U.S. Department of Energy’s (DOE) Office of Nuclear Energy, the researchers said supercritical carbon dioxide (CO₂) as working fluid. According to the lab, the gas flows through a continuous loop of pressurization, heating and expansion in a turbine to generate electricity. After the fluid exits the turbine, it is cooled in the recuperator before returning to the compressor to complete the cycle.

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This group tested the system for several months. A successful test earlier this year used an electric heater to boost the temperature of supercritical CO.₂ to 600F. It then used advanced power electronics, modified from an elevator control company, to power the electrical grid at nearby Sandia Kirtland Air Force Base.

According to the researchers, during the test the grid received power continuously for 50 minutes and generated as much as 10 kW of power at peak times. That’s about a third of the electricity the average U.S. home uses every day, according to the Institute.

Recent tests show that military base grid operators have agreed for the first time to draw power from the system. Previously, the power generated during testing was “dumped” into a load bank to avoid potential grid interruptions.

“We have been working for years to get here. Being able to demonstrate that the system can be connected to the grid via commercial devices is the first bridge to more efficient power generation,” said the manager. said Rodney Keith of Brayton at the Albuquerque-based lab for the Advanced Concepts Group where he is working on cycle technology.

Many power plants in operation today, including thermal generators such as coal-fired, nuclear, and natural gas-fired units, use the steam-based Rankine cycle to convert the heat they produce into electricity. The researchers noted that these systems could lose two-thirds of the energy they could have produced when converting steam to water to repeat the cycle.

Researchers Logan Rapp and Darrin Fleming Spoke Sept. 12 power The Sandia project is “different than what is being done at SWRI’s STEP pilot plant, primarily due to power levels. , a more traditional technology adopted from the Steam Rankine industry. We are working on very small machines of less than 1MWe.”

Researchers said: This power level and turbomachinery configuration uses a permanent magnet rotor that can operate in either motoring or generating mode. This means that power can be supplied to rotate the rotor in motoring mode at startup, and power can be extracted in generating mode when the cycle operates at temperature. ”

“This requires power electronics that control the direction of power flow and ensure that the power generated is of sufficient quality to be fed into the commercial AC power grid,” Rapp and Fleming said. says. The Sandia project “was the first successful test of the new power electronics, demonstrating its ability to consume power from the grid in motoring mode and return power to the grid in generating mode,” the researchers said. .

Sandia researchers said the supercritical Brayton cycle system could improve its efficiency by up to 50%, mainly due to the higher temperatures (1,290F) the material can reach. This could dramatically improve the efficiency of thermal power plants and improve the performance of concentrator photovoltaic (CSP) systems, they say.

According to researchers, supercritical CO₂ “It’s a non-toxic, stable material that can be under very high pressure and behaves like both a liquid and a gas. It heats up to 1,290 degrees Fahrenheit or 700 degrees Celsius.Partly because of this heat, the Brayton cycle is more powerful than the traditional steam-based Rankine cycle in power plants (nuclear, natural gas, and even light It can be much more efficient to convert heat into energy in the Rankine cycle.Since so much energy is lost in the Rankine cycle to turn steam back into water, steam can consume up to 3 minutes of power. can be converted into electricity, compared to a theoretical conversion efficiency of over 50% for the Brayton cycle.”

The lab said on Sept. 1 that it is already working to scale up its supercritical Brayton cycle technology. In future tests, the researchers will “demonstrate a recompressive closed Brayton cycle, after which he will proceed to a 1 MW scale generator that does not require power from the grid to heat the supercritical carbon dioxide.” said.

The Sandia project is supported by DOE’s Supercritical Transformed Power (STEP) program. The program is jointly sponsored by the Offices of Nuclear Energy, Fossil Energy and Carbon Management, and Energy Efficiency and Renewable Energy. The DOE said the STEP program “will work with industry to develop and mature technologies that will help commercialize supercritical carbon dioxide power cycle systems.”

—Darrell Proctor Senior Associate Editor at POWER (@power magazine).