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Gas Turbines: Cycle Innovations

Performance Characteristics of an Operating Supercritical CO2 Brayton Cycle

[+] Author and Article Information
Thomas Conboy

 Advanced Nuclear Concepts, Sandia National Laboratories, Albuquerque, NM 87185tmconbo@sandia.gov

Steven Wright, James Pasch, Darryn Fleming, Gary Rochau

 Advanced Nuclear Concepts, Sandia National Laboratories, Albuquerque, NM 87185

Robert Fuller

 Barber Nichols, Inc., Arvada, CO 80002

J. Eng. Gas Turbines Power 134(11), 111703 (Sep 28, 2012) (12 pages) doi:10.1115/1.4007199 History: Received June 26, 2012; Revised July 03, 2012; Published September 28, 2012; Online September 28, 2012

Supercritical CO2 (S-CO2 ) power cycles offer the potential for better overall plant economics due to their high power conversion efficiency over a moderate range of heat source temperatures, compact size, and potential use of standard materials in construction. Sandia National Labs (Albuquerque, NM) and the U.S. Department of Energy (DOE-NE) are in the process of constructing and operating a megawatt-scale supercritical CO2 split-flow recompression Brayton cycle with contractor Barber-Nichols Inc. (Arvada, CO). This facility can be counted among the first and only S-CO2 power producing Brayton cycles anywhere in the world. The Sandia-DOE test-loop has recently concluded a phase of construction that has substantially upgraded the facility by installing additional heaters, a second recuperating printed circuit heat exchanger (PCHE), more waste heat removal capability, higher capacity load banks, higher temperature piping, and more capable scavenging pumps to reduce windage within the turbomachinery. With these additions, the loop has greatly increased its potential for electrical power generation, and its ability to reach higher temperatures. To date, the loop has been primarily operated as a simple recuperated Brayton cycle, meaning a single turbine, single compressor, and undivided flow paths. In this configuration, the test facility has begun to realize its upgraded capacity by achieving new records in turbine inlet temperature (650 °F/615 K), shaft speed (52,000 rpm), pressure ratio (1.65), flow rate (2.7 kg/s), and electrical power generated (20 kWe). Operation at higher speeds, flow rates, pressures, and temperatures has allowed a more revealing look at the performance of essential power cycle components in a supercritical CO2 working fluid, including recuperation and waste heat rejection heat exchangers (PCHEs), turbines and compressors, bearings and seals, as well as auxiliary equipment. In this report, performance of these components to date will be detailed, including a discussion of expected operational limits as higher speeds and temperatures are approached.

Copyright © 2012 by American Society of Mechanical Engineers
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References

Figures

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Figure 1

Photograph of the Sandia S-CO2 Brayton loop

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Figure 2

SolidWorks drawing of the Sandia S-CO2 Brayton loop [5]

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Figure 3

Flow schematic of the S-CO2 test loop configuration

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Figure 4

Schematic of the turbo-alternator-compressor [5]

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Figure 5

Schematic of the motor/generator controller cabinet [5]

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Figure 6

(a) System-wide temperatures as a function of run-time; (b) system-wide pressures as a function of run-time; (c) turbo-alternator-compressor speed and power generation

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Figure 7

Test data for speed coastdown during test termination

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Figure 8

Temperature-entropy diagram for the test loop at peak power generation, 20 kWe

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Figure 9

Performance map of the compressor (test data indicated by open circles)

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Figure 10

Performance map of the turbine (test data indicated by open circles)

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Figure 11

Turbine pressure ratio and u/co as a function of time (compare with temperatures and speeds of Fig. 6)

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Figure 12

(a) Photo of the high temperature PCHE recuperator; (b) photo of the low temperature PCHE recuperator

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Figure 13

Heat exchanger performance versus time (compare with temperatures and speeds of Fig. 6)

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Figure 14

Photo of a partially disassembled thrust bearing [5]

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Figure 15

Front and rear journal and thrust bearing temperatures as a function of time (compare with temperatures and speeds of Fig. 6)

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Figure 16

Pie-chart illustrating a break-down of the consumption of apparent turbine work at 20 kWe

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Figure 17

Photograph of S-CO2 turbine and inlet nozzle [5]

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