Researchers at Sandia National Laboratories said they delivered electricity to the Sandia-Kirtland Air Force Base electrical grid using the Brayton Cycle.

The Brayton Cycle uses heated supercritical carbon dioxide instead of steam to generate electricity. It’s named after 19th century engineer George Brayton, who developed the method of using hot, pressurized fluid to spin a turbine, much like a jet engine.

Supercritical carbon dioxide is a non-toxic, stable material that is under so much pressure it acts like both a liquid and a gas. This CO2, which stays within the system and is not released as a greenhouse gas, can get much hotter than steam — 1,290 degrees Fahrenheit or 700 Celsius.

Partially because of this heat, researchers said the Brayton Cycle has the potential to be much more efficient at turning heat from power plants — nuclear, natural gas or even concentrated solar — into energy than the traditional steam-based Rankine cycle.

“Because so much energy is lost turning steam back into water in the Rankine cycle, at most a third of the power in the steam can be converted into electricity,” said laboratory researchers. “In comparison, the Brayton cycle has a theoretical conversion efficiency upwards of 50 percent.”

In a simple closed-loop Brayton cycle, the supercritical CO2 is heated by a heat exchanger. Then the energy is extracted from the CO2 in a turbine. After the CO2 exits the turbine, it is cooled in a recuperator before entering a compressor. The compressor gets the supercritical CO2 up to the necessary pressure before it meets up with waste heat in the recuperator and returns to the heater to continue the cycle. The recuperator improves the overall efficiency of the system.

In the Fall of 2019, Fleming began exploring how Sandia’s closed-loop supercritical CO2 Brayton Cycle test loop could be connected to the grid.

“We’ve been striving to get here for a number of years, and to be able to demonstrate that we can connect our system through a commercial device to the grid is the first bridge to more efficient electricity generation,” said Rodney Keith, manager for the advanced concepts group working on the Brayton Cycle technology. “Maybe it’s just a pontoon bridge, but it’s definitely a bridge. It may not sound super significant, but it was quite a path to get here. Now that we can get across the river, we can get a lot more going.”

On April 12, the Sandia engineering team heated up their supercritical CO2 system to 600 degrees Fahrenheit and provided power to the grid for almost one hour, at times producing up to 10 KW, something the teams said is a significant step.

The team’s goal is to demonstrate a 1 MW supercritical CO2 Brayton cycle system by Fall 2024.

You can read more on the Sandia National Laboratories’ announcement here.

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