Break-Even Power Transients for Two Simple Recuperated S-CO2 Brayton Cycle Test Configurations

by Steven A. Wright, Tom M. Conboy, & Gary E. Rochau
Sandia National Laboratories

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Supercritical CO2 power plants offer the potential for better economics due to their small size, use of standard materials, and improved electrical-power-conversion efficiency at moderate temperatures (400-750°C). Sandia National Labs (SNL or Sandia) and the DOE-NE have been operating a supercritical CO2 (S-CO2) Brayton cycle power system that is currently located at Sandia’s contractor Barber Nichols Inc. in Arvada, Colorado. This loop is a re-configurable proof-of-principle Brayton cycle power loop that is being developed in stages. During 2010 the Brayton cycle loop was configured with a 260 kW heater, a Printed Circuit Heat Exchanger (PCHE) recuperator, and a PCHE water-to-CO2 gas chiller. In this configuration, the simple recuperated Brayton cycles have just enough power to reach break-even conditions. Break-even conditions occur when the turbine produces as much power as is being consumed by the compressor and required to overcome windage (friction). The test results from two break-even power generating test results are provided. The first test results were performed with the main compressor turbomachinery, while the second test was performed with the re-compressor turbomachinery. In each case, compressor inlet conditions were chosen to match their respective design points. Due the higher density at the compressor inlet in the main-compressor the flow rate was relatively high (1.6 kg/s or 3.5 lb/s), and thus it was only possible to reach a peak temperature of 477K (400°F). Nevertheless positive power was produced. In contrast, because of the lower density in the re-compressor turbomachine, a peak temperature of 589 K (600°F) was achieved and substantially more power (~ 8 kWe). The measured data for the two electrical power generating operations is presented along with a brief summary and comparison with model predictions.