UNCERTAINTY ON PERFORMANCE MEASUREMENT OF S-CO 2 COMPRESSOR OPERATING NEAR THE CRITICAL POINT

Transcription

1 UNCERTAINTY ON PERFORMANCE MEASUREMENT OF S-CO COMPRESSOR OPERATING NEAR THE CRITICAL POINT The 4th International Symposium - Supercritical CO Power Cycles September 9-10, 014, Pittsburgh, Pennsylvania Jekyoung Lee a, Seong Gu Kim a, Jeong Ik Lee a, Jae Eun Cha b a Korea Advanced Institute of Science and Technology b Korea Atomic Energy Research Institute

2 CONTENTS Introduction Uncertainty analysis Summary and further works

3 Introduction S-CO Brayton cycle development in KAIST research team Steam Rankine Cycle S-CO Brayton Cycle Economic benefit due to higher efficiency and compactness of power conversion system Difficulties on S-CO Brayton cycle Dramatic change on thermodynamic properties near the critical point Compressor Design methodology C p (kj/kg K) MPa 7.4 MPa 7.5 MPa 7.6 MPa 7.7 MPa 7.8 MPa 7.9 MPa 8 MPa Temperature ( O C) 3

4 Introduction S-CO Pressurization Experiment (SCOPE, constructed in KAIST) Components 1. Overview. Impeller 3. Main compressor 4. Pre-cooler 5. Booster pump 6. Vacuum pump Sensors PT100 Ohm RTDs Static temperature Rosemount 3051S Pressure Transmitter Static pressure Rheonik RHM0 mass flow meter Accuracy Sensor type Accuracy RTD ±0. o C Pressure transmitter ±0.09% Mass flow meter ±0.16% RPM ±0.1% Power ±0.5kW 4

5 Introduction Main compressor description TE PT Hot water Motor HS Vent Cold water PSV Main Main Compressor Pump PT FE TE HS PT Vent TE TE Heat exchanger Water Line Hot water TE Cold water Canned motor pump 6kW motor driver Sleeve journal bearing with working fluid lubrication Closed(shrouded) type impeller Recirculation flow exists Water jacket is equipped to maintain integrity of sleeve bearing Available RPM: 460(77Hz) S-CO Line Charging system Main compressor design conditions Inlet pressure, MPa Outlet pressure, MPa Pressure ratio 1.18 RPM 448 Mass flow rate, kg/s 4.49 Dimensions of mechanical parts Impeller type Closed Impeller diameter, mm 34 Journal bearing type Sleeve Thrust bearing type Plain Material SUS316 5

6 Introduction SCOPE operation purpose. 1 Experience to CO pressurization with various fluid conditions SCOPE operation purpose. V&V of KAIST_TMD Turbomachinery in-house code SCOPE operation purpose. 3 V&V of KAIST_HXD Heat exchanger in-house code Total to Total Efficiency (%) Turbomachinery Efficiency-Mdot Map On-design point rpm=3600 rpm=4500 rpm=5400 rpm=6300 rpm=700 Pressure Ratio Turbomachinery PR-Mdot Map On-design point rpm=700 rpm=6300 rpm=5400 rpm=4500 rpm= Mass Flow Rate (kg/s) Mass Flow Rate (kg/s) 6

7 Uncertainty Analysis Compressor performance variable Pressure ratio Isentropic efficiency hout, ideal h 1: η = h h : PR = P P η = out in out in in ( ho, out, isen ho, in ) m W Nomenclature PR : pressure ratio η : efficiency h : enthalpy m : mass flow rate W : input power U : impeller tip speed in : compressor inlet out : compressor outlet isen : isentropic process o : stagnation th : theoretical (Euler equation) loss : loss in compressor int : internal loss ext : external loss 3: h h h m th loss, int th U η = =,(where, hloss, ext >> loss, int ) hth + hloss, ext hth + hloss, ext W Internal losses : Losses occurred through primary paths of working fluid in a machinery External losses : Losses generated from the exterior of primary paths Primary path 7

8 Uncertainty Analysis Nomenclature h : enthalpy Uncertainty analysis m : mass flow rate Relative(fractional) uncertainty [] W : input power 1/ ω f 1 f U : impeller tip speed in : compressor inlet = ϖ x i out : compressor outlet f f x i isen : isentropic process Pressure ratio o : stagnation 1/ ω : uncertainty ω PR o ωp ω o, out P o, in = + PR o P o, out P o, in Isentropic efficiency ω η 1 ho, out, isen h o, out ( 1) 1: = ωh + ω o, isen h + ω oin, h o, out η ho, out, isen h o, in ( ho, out ho, in )( ho, out, isen ho, in ) ho, out h o, in 1/ ω η : = ωh + ω o, out, isen h + ω oi, n m + ω W η ho, out, isen h o, in ho, out, isen h o, in m W 1/ ω η 1 1 3: = ωu ω + m + ω W η U m W 1/ [] Holman, J. P., 001, Experimental Methods for Engineers, McGraw-Hill, New York, NY, USA 8

9 Uncertainty Analysis Data cases Case 1, 83 bar, 40 o C, above the critical operation Case, 74.4 bar, 3.5 o C, near the critical operation Mass flow rate (kg/s) Inlet P (kpa) Outlet P (kpa) Inlet T ( o C) Outlet T ( o C) RPM Mass flow rate (kg/s) Inlet P (kpa) Outlet P (kpa) Inlet T ( o C) Outlet T ( o C) RPM Measured data Measured data Pressure (bar) Temperature ( o C) Case1 (.0kg/s) Case1 (1.5kg/s) Case1 (1.0kg/s) Case1 (0.5kg/s) Case (1.0kg/s) Case (1.5kg/s) Case (.0kg/s) Case (.8kg/s) 9

10 Uncertainty Analysis Uncertainty calculation results PR = η η = P P out in h -h out,ideal in = h out -h in ( ho, out, isen ho, in ) U η = W m m W Mass flow rate kg/s PR ωpr PR η ωη η ωη η ωη Case 1, Supercritical operation Case, Near the critical operation , (%) / η , (%) / η Time 0.53 (s) , (%) / η Efficiency (%) Efficiency / * 1 : Even near the steady ω η state, a large fluctuation 1 (50%-150% Range) of efficiency 1 was observed due to very small 1 background noise 1 in temperature and pressure measurement. Thus it is = not possible to report efficiency ωh based on + equation (3). ω o, out, isen h + ω oi, n m + ω W η ho, out, isen h o, in ho, out, isen h o, in m W 10

11 Uncertainty Analysis Issue 1 Peak region on property variation of S-CO near the critical point causes high uncertainty on efficiency measurement Inherent characteristic of S-CO near the critical point Strong correlation with specific heat and measurement uncertainties 11

12 Uncertainty Analysis SCOPE Recompression Layout Issue Performance measurement to low isentropic enthalpy rise (which is related with pressure ratio) compressor has high uncertainty on efficiency measurement for temperature and pressure measurement S-CO Integral Experiment Loop (SCIEL) 1

13 Uncertainty Analysis Issue 3 Applying of density measurement at compressor inlet and outlet reduces uncertainty on efficiency measurement [1]. T: Temperature, P: Pressure, D: Density Inlet : T P Outlet : T - P 1% Improvement Inlet : D P Outlet : T - P 33% Improvement Inlet : D P Outlet : D - P [1] Wahl, G. D., 009, "Efficiency Uncertainty of a Turbine Driven Compressor in a Supercritical CO Brayton Cycle", Proceedings of S-CO Power Cycle Symposium, RPI, Troy, NY 13

14 Uncertainty Analysis Issue 4 Approximation on efficiency calculation is necessary for low pressure ratio S-CO compressor with near the critical operation condition Due to uncertainty of enthalpy terms on efficiency calculation equations, high uncertainty always involves when S-CO compressor inlet condition is near the critical point Approximation on efficiency calculation for main compressor of SCOPE h h h m th loss, int th U η = = hth + hloss, ext hth + hloss, ext W 1 1 = ω + ω + ω η ω η U m W U m W 1/,(where, h >> ) loss, ext loss, int Out Basis Recirculation (High pressure) low specific speed design Some portion of high(discharge) pressure S-CO recirculates through shaft Thus, it is fair assumption that external losses are greater than internal losses High friction In It doesn t represent actual isentropic efficiency of machinery. However, it can be utilized for the base data for operation with low uncertainty 14

15 Uncertainty Analysis Issue Actual enthalpy input Approximation on efficiency calculation is necessary for low pressure ratio S-CO compressor with near the critical operation condition Due to uncertainty of enthalpy terms on efficiency calculation equations, high uncertainty always involves when S-CO compressor inlet condition is near the h critical point th + hext, loss Approximation on efficiency calculation for main compressor of SCOPE hth hloss, int hth U m η = = hth + hloss, ext hth + hloss, ext W 1 1 = ω + ω + ω η ω η U m W U m W Enthalpy (J/kg) 1/ 5000,(where, h >> ) h th loss, ext loss, int h ext, loss Evaluated enthalpy input Ideal enthalpy rise Out Recirculation (High pressure) High friction In Basis low specific speed design Mass flow rate (kg/s).5 3 Some portion of high(discharge) pressure S-CO recirculates through shaft Thus, it is fair assumption that external losses are greater than internal losses It doesn t represent actual isentropic efficiency of machinery. However, it can be utilized for the base data for operation with low uncertainty 15

16 Summary and further works Issues on uncertainty on efficiency measurement of near the critical operation S-CO compressor 1. Peak region on property variation of S-CO near the critical point causes high uncertainty on efficiency measurement Inherent characteristics of S-CO near the critical point. Performance measurement on low isentropic enthalpy rise (which is related with pressure ratio) compressor has high uncertainty on efficiency measurement Machine dependency At.7 pressure ratio, this issue will be mitigated with under 0.1 of relative uncertainty. 3. Applying of density measurement at compressor inlet and outlet reduces uncertainty on efficiency measurement [1]. It is true that it increases measurement confidence. However it doesn t provide remarkable improvement for low pressure ratio S-CO compressor. 4. Approximation on efficiency calculation is necessary for low pressure ratio S-CO compressor with near the critical operation condition Just for SCOPE compressor which has relatively high external losses It doesn t represent actual efficiency but it can be used for performance indicator for operation with low uncertainty 16

17 Summary and further works Further works Uncertainty analysis for the compressor of S-CO Integral Experiment Loop (SCIEL) Construction field : Korea Atomic Energy Research Institute (KAERI) 014 construction : Simple cycle demonstration analysis on each loss model will be carried out to make better approximation on performance measurement. 17

18 THANK YOU..