Supercritical carbon dioxide Brayton cycle developments at Sandia

From NextBigFuture.com

Eurekalert – Sandia National Laboratories researchers are moving into the demonstration phase of a novel gas turbine system for power generation, with the promise that thermal-to-electric conversion efficiency will be increased to as much as 50 percent — an improvement of 50 percent for nuclear power stations equipped with steam turbines, or a 40 percent improvement for simple gas turbines.

Research focuses on supercritical carbon dioxide (S-CO2) Brayton-cycle turbines, which typically would be used for bulk thermal and nuclear generation of electricity, including next-generation power reactors. The goal is eventually to replace steam-driven Rankine cycle turbines, which have lower efficiency, are corrosive at high temperature and occupy 30 times as much space because of the need for very large turbines and condensers to dispose of excess steam. The Brayton cycle could yield 20 megawatts of electricity from a package with a volume as small as four cubic meters.

The Brayton cycle, named after George Brayton, originally functioned by heating air in a confined space and then releasing it in a particular direction. The same principle is used to power jet engines today. “This machine is basically a jet engine running on a hot liquid,” said principal investigator Steve Wright of Sandia’s Advanced Nuclear Concepts group.

A competing system, also at Sandia and using Brayton cycles with helium as the working fluid, is designed to operate at about 925 degrees C and is expected to produce electrical power at 43 percent to 46 percent efficiency. By contrast, the supercritical CO2 Brayton cycle provides the same efficiency as helium Brayton systems but at a considerably lower temperature (250-300 C). The S-CO2 equipment is also more compact than that of the helium cycle, which in turn is more compact than the conventional steam cycle.

Operation and Analysis of a Supercritical CO2 Brayton Cycle (101 pages)

Schematic of supercritical compression loop using a 50 kWe motor driving a radial compressor at 75,000 rpm with a flow rate of 3.51 kg/s

Schematic drawing of the motor-driven S- CO2 compressor. This configuration uses ball bearings and has no turbine.

Simple diagram of the heated un-recuperated supercritical CO2 Brayton loop.

Photo of the heated, but un-recuperated, Brayton Loop. The foreground shows the heaters, the back ground shows the modified S-CO2 test loop with the turbomachine configured as a turbo-alternator-compressor.

Expected operating conditions of the S-CO2 compression test loop at the design point and on the liquid and vapor sides of the dome.

Wikipedia on the Brayton cycle

The proposed design of a 300 MWe nuclear plant with a supercritical CO2 brayton cycle system (24 pages from 2004)

FURTHER READING

Coverage from 2009 on supercritical CO2 recompression cycle

MIT CANES – Supercritical CO2 Brayton Cycle for Medium Power Applications (2007)

This final report summarizes the results of the study of a supercritical CO2 (SCO2) power cycle for medium power application. The objective of these investigations is to establish a 5 – 30MWe power conversion system for an indirect cycle that (1) achieves high net efficiency in conversion from thermal to electrical energy, (2) is compact with minimum volume and weight, (3) is robust, resilient to accidents and has high long term reliability and performance, and (4) exhibits good controllability and fast response to requested power changes.

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