Fine Tuning Coriolis Flow Meter Calibrations Utilizing Piece- Wise Linearization

Transcription

1 Fine Tuning Coriolis Flow Meter Calibrations Utilizing Piece- Wise Linearization Tonya Wyatt Global Chemical Industry Manager Emerson Process Management Micro Motion, Inc. AGA Operations Conference and Biennial Exhibition 2015

2 New Developments to Improve Natural Gas Custody Transfer Applications with Coriolis Meters Including Application of Piecewise Linear Interpolation (PWL) Marc Buttler Midstream O&G Marketing Manager, Micro Motion Emerson Ron Gibson Senior Engineer, ONEOK, Inc. Gary McCargar Senior Engineer, ONEOK, Inc. Karl Stappert Americas Flow Solutions Advisor, Emerson Process Management Tonya Wyatt Process Gas and Chemical Marketing Manager, Micro Motion Emerson

3 Agenda Calibration Adjustment Methods for Gas Meters Coriolis Meter Calibration Options Principle of Operation Review Calibration Fluid Flexibility Pressure Effect Compensation Multi-Point Piecewise Linear Interpolation (PWL) Implementation of PWL PWL and Pressure Effect Compensation Together Results In-situ Secondary Verification of Calibration Impact of Zero

4 Error Error Error Error Calibration Adjustment Methods from AGA 11 Flow Weighted Mean Error (FWME) 0.50% 0.30% 0.10% -0.10% % As Found Error FWME Correction Corrected Data -0.50% Flow Rate, lbm per second 0.10% Polynomial Algorithm 0.05% 0.00% As Found Error Polynomial Algorithm Correction -0.05% Corrected Data -0.10% Flow Rate, lbm per second 0.10% 0.05% As Found Error Multi-Point Piecewise Linear Interpolation (PWL) 0.00% -0.05% Multi-Point Piecewise Linear Interpolation Correction (PWL) Corrected Data -0.10% Flow Rate, lbm per second 0.50% Piecewise Linearization (Step-wise) 0.30% 0.10% -0.10% -0.30% As Found Error Step-wise Correction Corrected Data -0.50% Flow Rate, lbm per second

5 Coriolis Meter Principle of Operation As a particle inside a rotating body moves toward or away from the center of rotation, the particle generates inertial forces that act on the body. The principle of operation dictates a Coriolis meter s performance characteristics Sensitive to bulk inertial forces of the fluid Insensitive to change in fluid properties and velocity profile

6 Theory of Operation Process fluid enters the sensor and flow is split with half the flow through each tube Drive coil vibrates tubes at natural frequency Pick-off coils on inlet and outlet sides generate raw measurement signals

7 Direct Mass Flow Measurement No Flow Isometric View At No Flow Flow Causes Twist

8 nsec of signal per g/sec of flow Coriolis Meter Raw Sensitivity Varies with Design Large Tube Geometry Medium Tube Geometry Short Tube Geometry 0 Flow Sensitivity Examples Raw Sensitivity Depends on Design of Tube Geometry Signal to Noise Ratio Depends on Raw Sensitivity and Stability Calibration Flexibility, Immunity to Secondary Effects, and Diagnostic Capabilities Depend on Signal to Noise Ratio

9 AGA Report No. 11 / API MPMS Ch Measurement of Natural Gas by Coriolis Meter First Edition Published by the American Gas Association (AGA) December 2003 Adopted by American Petroleum Institute (API) upon publication API Manual on Petroleum Measurement Standards (MPMS) Chapter 14.9 Similar to other AGA technology performance based specifications AGA 3: Orifice AGA 7: Turbine AGA 9: Multipath Ultrasonic

10 AGA Report No. 11 / API MPMS Ch Measurement of Natural Gas by Coriolis Meter 2 nd Edition Published February 2013 Covers all single phase natural gases as pure or a mixture of hydrocarbons and diluents API Standard API MPMS Chapter 14.9 Recommended Practice Specification, calibration, installation, operation, maintenance, and verification

11 Conversion of Mass to Volume at Standard Conditions SCF SCF SCF Mass b Mass Pb x Mr(Gas) Zb x R x Tb Mass Gr (Gas) x AGA11 Eqn. D.2 lbs/day lbs/ft3 = ft3/day (Air) AGA8 Detail Non-ideal gas law: P b, T b, R are constants Note: Z b does not vary more than 0.02% at base conditions. AGA8 Gross 1 or 2 No pressure or Temperature Measurement Required to Convert from Mass to Standard Volume Molar weight, Base Compressibility, and Specific Gravity Are All Determined by Gas Composition

12 Calibration Fluid Flexibility Purpose and Benefits Calibration fluid flexibility is a capability that allows a traceable liquid calibration to be used for traceable gas measurements Liquid medium meter calibration system benefits Easier to control liquid (e.g., water) system uncertainties Lower cost Greater safety Recognized in AGA Report No. 11 / API MPMS Ch Must demonstrate acceptable provenance for each Coriolis meter design

13 NMi Declaration of Water-to-Gas Calibration Transferability for Micro Motion Coriolis Meters Testing Included ½ to 12 inch Coriolis meters Conducted on following mediums Natural gas Nitrogen Ethylene Results CMF Model Coriolis meters calibrated on water at manufacturer may be applied to the following applications without requiring a field calibration or gas calibration Every gaseous medium with density greater than 4 kg/m3 Super-critical ethylene with density up to 450 kg/m3

14 NMi Euroloop Test for CMFHC Meters

15 Effect of Pressure on Coriolis Meters Internal pressure changes the shape of the flow tube Tube ovality becomes round Tube bends straighten Changes in flow tube shape increases stiffness of flow tube Changes in tube stiffness directly affects sensor calibration Magnitude of effect varies by meter size and design m FCF *time delay FCF tube stiffness

16 Application of Compensation for the Effect of Pressure on the Meter SCF SCF SCF Mass F b P Mass Pb x Mr(Gas) Zb x R x Tb Mass Gr (Gas) x F P factor can be employed to compensate for the effect of pressure on the meter. F P factor is not a correction for behavior of the gas. (Air) F F P P F P compensation is only required for some of the larger meter sizes

17 Flow Pressure Effect Correction and Potential Error Potential Error w/o Pressure Correction (Natural Gas)

18 Example Application of Pressure Effect Compensation - CMFHC2 Gas Test Results All data collected on natural gas using meter factory calibration on water Data shown with and without standard F P pressure compensation Max deviation of all compensated data < 0.25%

19 Error Multi-Point Piecewise Linear Interpolation (PWL) 0.10% 0.05% As Found Error 0.00% -0.05% Multi-Point Piecewise Linear Interpolation Correction (PWL) Corrected Data -0.10% Flow Rate, lbm per second Correction applied at selected linearization points is equal and opposite to the average of the as-found values at the same flow rate Correction values applied between neighboring points are determined by linear interpolation between the two points Correction above the highest flow rate point are held constant Correction below the lowest point is based on linear interpolation to zero error at zero flow to allow meter zero adjustment to control accuracy below Q t

20 PWL Procedure Optional PWL software must be ordered separately when the order is placed for a Micro Motion ELITE CMF meter PWL calibration and configuration is conducted by qualified third-party calibration laboratories selected and hired by end users Emerson has trained, equipped, and qualified three independent gas labs in NA to execute the procedure (to date) Colorado Engineering Experiment Station, Inc., Southwest Research Institute, and TransCanada Calibrations Basic Procedure at the third-party lab 1. Install and zero meter as necessary 2. Collect as-found data (pressure compensation active) 3. Select and program meter with up to 10 linearization points from the as-found data 4. Collect as-left data to verify accuracy of linearization

21 Error Error PWL and Pressure Comp. Together PWL As-Found Data Collected with Pressure Compensation Active P Cal remains the original factory water calibration pressure This method keeps pressure compensation and linearization independent from each other 0.60% 0.40% 0.20% 0.00% -0.20% As Found Error (PRESS. COMP ENABLED) Multi-Point Piecewise Linear Interpolation Correction (PWL) Corrected Data -0.40% -0.60% Flow Rate, lbm per second Alternative Method: PWL As-Found Data Collected with Pressure Compensation Inactive P Cal becomes the gas lab As-Found pressure for future pressure compensation This method resets the pressure compensation baseline pressure to the gas test pressure 0.60% 0.40% 0.20% 0.00% -0.20% -0.40% As Found Error (NO PRESS. COMP - CMFHC2 at 230 psig) Multi-Point Piecewise Linear Interpolation Correction (PWL) Corrected Data -0.60% Flow Rate, lbm per second

22 % Error % Error Results with PWL 1-inch Meter CMF As Found Averages by Flow Rate Verification Averages by Flow Rate lbm per second Averages at Each Flow Rate Observations Test turndown 58 : 1 All verification averages better than ± 0.08% Verification averages above 0.13 lbm/sec better than ± 0.027% All verification data better than ± 0.11% All Data As Found Data Verification Data lbm per second

23 % Error % Error Results with PWL 2-inch Meter CMF As Found Averages by Flow Rate Verification Averages by Flow Rate Observations Test turndown 45 : 1 All verification averages better than ± 0.09% All verification data better than ± 0.29% lbm per second Averages at Each Flow Rate All Data As Found Data Verification Data lbm per second

24 % Error % Error Results with PWL 3-inch Meter CMF As Found Averages by Flow Rate Verification Averages by Flow Rate Observations Test turndown 10 : 1 All verification averages better than ±0.08% All verification data better than ± 0.22% lbm per second Averages at Each Flow Rate All Data As Found Data Verification Data lbm per second

25 Secondary Verification Purpose and Benefits Secondary Verification is a capability that allows a measuring device to use an alternative method to confirm flow measurement accuracy without the need for a calibration to a traceable flow reference standard Reduce lost and unaccounted for (LAUF) product and reconciliations with the capability to perform more frequent checking without adding cost Work practices may use statistical data and secondary verification results to extend primary calibration intervals Recognized in AGA Report No. 11 / API MPMS Ch. 14.9

26 Secondary Verification Methods used for Coriolis Meters Structural observations Ignore all fluid effects to measure changes to the meter structure Example: Micro Motion Smart Meter Verification (SMV) method to measure stiffness of flow tubes 2 X 1 FRF F M jc K Fluid dependent observations Uses knowledge of current fluid properties to test meter response to fluid Fluid properties must be accurately measured and controlled Example: Micro Motion Known Density Verification method (KDV) to observe Compact Density Meter (CDM) behavior when fluid density is known

27 Coriolis Meters are like Simple Springs Stiffness Influences Measurement Spring Natural Frequency proportional to Spring Stiffness Spring Mass Weight Density proportional to Tube Stiffness Tube Mass Fluid Mass Mass Flow proportional to Tube Stiffness Mass Inertial Forces

28 Using Resonant Modal Analysis to determine Coriolis Flow Tube Stiffness Quick, reliable indication of complete sensor health from tube structure to electronics Proactive maintenance to eliminate calibrations and improve process uptime Test tones Response Okay Not Okay

29 Span vs. Zero y mx b Meter Zero FCF

30 Zeroing Best Practices Most applications Use factory zero Insure no flow condition Insure meter is full Insure process conditions are stable Example: Micro Motion Zero Verification monitors 8 parameters to check stability of process and check current zero value

31 Conclusions Some Coriolis meters have demonstrated the capability to be calibrated on liquid in order to measure gas Some Coriolis meters can be adjusted with PWL in gas calibration labs to improve gas flow measurement PWL must be implemented together correctly with pressure compensation Secondary verification methods exist to confirm Coriolis meter accuracy after primary flow calibrations including span and zero

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