SANDIA REPORT SAND2010-0171 Unlimited Release Printed September 2010 Operation and Analysis of a Supercritical CO2 Brayton Cycle Steven A. Wright, Ross F. Radel, Milton E. Vernon, Gary E. Rochau, and Paul S. Pickard Prepared by Sandia National Laboratories Albuquerque, New Mexico 87185 and Livermore, California 94550 Sandia is a multiprogram laboratory operated by Sandia Corporation, a Lockheed Martin Company, for the United States Department of Energy’s National Nuclear Security Administration under Contract DE-AC04-94AL85000. Approved for public release; further dissemination unlimited. Issued by Sandia National Laboratories, operated for the United States Department of Energy by Sandia Corporation. NOTICE: This report was prepared as an account of work sponsored by an agency of the United States Government. 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This report has been reproduced directly from the best available copy. Available to DOE and DOE contractors from U.S. Department of Energy Office of Scientific and Technical Information P.O. Box 62 Oak Ridge, TN 37831 Telephone: (865) 576-8401 Facsimile: (865) 576-5728 E-Mail: [email protected] Online ordering: http://www.osti.gov/bridge Available to the public from U.S. Department of Commerce National Technical Information Service 5285 Port Royal Rd. Springfield, VA 22161 Telephone: (800) 553-6847 Facsimile: (703) 605-6900 E-Mail: [email protected] Online order: http://www.ntis.gov/help/ordermethods.asp?loc=7-4-0#online 2 SAND2010-0171 Unlimited Release Printed September 2010 Operation and Analysis of a Supercritical CO2 Brayton Cycle Steven Wright, Ross Radel, Milton Vernon, Gary Rochau, and Paul Pickard Advanced Nuclear Concepts Department Sandia National Laboratories P.O. Box 5800 Albuquerque, New Mexico 87185-MS1136 Abstract Sandia National Laboratories is investigating advanced Brayton cycles using supercritical working fluids for use with solar, nuclear or fossil heat sources. The focus of this work has been on the supercritical CO2 cycle (S-CO2) which has the potential for high efficiency in the temperature range of interest for these heat sources, and is also very compact, with the potential for lower capital costs. The first step in the development of these advanced cycles was the construction of a small scale Brayton cycle loop, funded by the Laboratory Directed Research & Development program, to study the key issue of compression near the critical point of CO2. This document outlines the design of the small scale loop, describes the major components, presents models of system performance, including losses, leakage, windage, compressor performance, and flow map predictions, and finally describes the experimental results that have been generated. 3 THIS PAGE IS INTENTIONALLY BLANK 4 CONTENTS NOMENCLATURE ................................................................................................................................................................... 10 1 INTRODUCTION ............................................................................................................................................................ 11 2 S-CO2 COMPRESSION TEST LOOP SUMMARY ..................................................................................................... 14 2.1 S-CO2 COMPRESSION TEST LOOP AND HARDWARE ........................................................................................................ 14 2.2 S-CO2 HEATED BUT UN-RECUPERATED BRAYTON LOOP AND TURBOMACHINE ............................................................. 17 2.3 SUMMARY OF LOOP OPERATING CONDITIONS NEAR THE CRITICAL POINT .................................................................... 20 2.3.1 Thermodynamic cycle analysis of the compression loop ...................................................................................... 22 3 S-CO2 TURBOMACHINERY AND TEST-LOOP COMPONENTS .......................................................................... 24 3.1 TURBOMACHINERY ......................................................................................................................................................... 24 3.1.1 Rotor Cavity ......................................................................................................................................................... 26 3.1.2 Stress Analysis of Turbomachinery Housing ........................................................................................................ 28 3.2 GAS CHILLER .................................................................................................................................................................. 30 3.2.1 Analysis and Modeling of the Gas Pre-cooler ...................................................................................................... 31 3.3 WATLOW HEATERS ........................................................................................................................................................ 34 3.4 MOTOR ALTERNATOR AND CONTROLLER ....................................................................................................................... 35 3.5 INSTRUMENTATION ......................................................................................................................................................... 37 3.6 CONTROL SYSTEM .......................................................................................................................................................... 37 4 SYSTEM ANALYSIS OF THE COMPRESSION LOOP ............................................................................................ 40 4.1 COMPRESSOR MODEL DESCRIPTION ............................................................................................................................... 40 4.2 ORIFICE MODEL .............................................................................................................................................................. 41 4.3 INVENTORY CONTROL MODEL ....................................................................................................................................... 41 4.4 RESULTS OF DYNAMIC SIMULATION FOR THE S-CO2 COMPRESSION LOOP .................................................................... 41 5 TEST RESULTS AND OBSERVATIONS ..................................................................................................................... 43 5.1 CONTROL OF THE S-CO2 COMPRESSION LOOP ................................................................................................................ 43 5.1.1 Control Example .................................................................................................................................................. 44 5.1.2 Operating near the Pseudo-Critical Line ............................................................................................................. 45 5.1.3 Entering the Dome (Saturation Curve) ................................................................................................................ 47 5.2 HIGH SPEED SPIN TEST ................................................................................................................................................... 50 5.3 COMPRESSOR PERFORMANCE ......................................................................................................................................... 52 5.3.1 Measured Compressor Maps ................................................................................................................................ 54 5.4 WINDAGE LOSSES ........................................................................................................................................................... 58 5.4.1 Measured Windage Losses ................................................................................................................................... 62 5.5 SEAL LEAKAGE LOSSES .................................................................................................................................................. 63 5.5.1 Measured Labyrinth Leakage Flow Rates ............................................................................................................ 68 5.5.2 Gas-Foil Bearings ................................................................................................................................................ 69 5.5.2.1 Gas-Foil Bearing Test Results ............................................................................................................................................ 71 5.6 ROTOR SHAFT DYNAMICS .............................................................................................................................................