Custody Transfer Accuracy in an 8-Path Ultrasonic Flow Meter with 5D Upstream Straight Run

Transcription

1 Custody Transfer Accuracy in an 8-Path Ultrasonic Flow Meter with 5D Upstream Straight Run Author: Nick Mollo, Principal Engineer Presenter: Gerard Bottino, Global Sales Manager Flow 2017 Baker Hughes, a GE company, LLC - All rights reserved.

2 Presentation Summary The need for compact metering skids used in offshore applications where footprint is critical, and land based applications where cost is important, require meter installations that can tolerate the reduced straight inlet lengths. Meters utilizing multiple, cross-plane, measurement paths to cancel swirl effects is a common practice. Opposing tangential velocity vectors are automatically subtracted from each other. Is a long, straight pipe, calibration of such a flow meter sufficient to provide custody transfer level accuracy in disturbed, short length inlet installations?

3 Presentation Overview Product description Definitions and equations Test matrix Case studies Results analysis Conclusion

4 Sentinel LCT8 Ultrasonic Flow Meter Flowcell body based off of our successful Sentinel LCT4, transit time, ultrasonic meter The hardware and software in the electronics was upgraded for 8 channels The eight, off diameter, chordal, acoustic paths, and located with four in each vertical plane Paths are symmetrical about all three pipe centerline axis 90 crossed-planes for swirl insensitivity

5 Ultrasonic Flow Meter Theory For the sake of time, I will not cover the theory of operations for ultrasonic flow meters. If anyone would like information on how these meters work, see us during the break at our booth.

6 ሶ Definitions and Equations Meter Accuracy The error of the flow rate measurement compared to a calibrated reference %Err = V MUT Vሶ MM 100% Vሶ MM k-factor The meter factor needed for correction at a given flow condition k factor = ሶ V MM ሶ V MUT Meter Repeatability The delta between max and min meter accuracy over three consecutive runs (OIML) Repeat = %Err max %Err min ቚ three points Meter Linearity The span of min to max error across the entire calibration range Linearity = %Err max %Err min ቚ full range Velocity Ratio An indication of the flow profile shape, correlated to Reynolds number; Sentinel LCT linearization tables are based on VR, not velocity VR σ Velocity inner σ Velocity outer VR

7 Velocity Ratio Velocity ratio, VR, is a measure of flow profile shape, with a range from 1.0 to around 2 The Sentinel LCT8 k-factor (correction) tables are built up based on Velocity Ratio this is still a Reynolds correction, but density and viscosity do not need to be known or entered into the meter.

8 Velocity Ratio and Other Diagnostics

9 Test Matrix No flow conditioners were used for any test case Case # Meter Size 6in 6in 6in 10in Lab Information Alden Labs Water Alden Water CEESI Oil CEESI Multi-oil CEESI Multi-oil Base Case 20D Straight FLOW at least 20D LCT8 X X X X DEIP Double Elbow in Plane Long Radius Elbows 2x FLOW 5D LCT8 X X X X DEOP Double Elbow out of Plane Long Radius Elbows 2x X X X X 4EIP Four Elbows in Plane FLOW Long Radius Elbows 4x 5D LCT8 X 6EOP Six Elbows out of Plane X Static Mixer FLOW 5D LCT8 X Globe Valve FLOW 5D LCT8 X

10 Labs Flow Uncertainty Alden Labs (Water) Gravimetric reference / weigh tank for volumetric flow rate Reference is NIST traceable Best quoted uncertainty is 0.20% CEESI (Oil) Turbine master meter references for volume Lab is ISO certified Facility uncertainty across all oils and Re range is 0.05%

11 Early 8Path Prototype The original 8path prototype, using the same acoustic path chord locations as our Sentinel LCT4 4path meter, was our first look into our capabilities 5 diameters behind common disturbances. 6in meter, straight inlet, BASE case 6in meter, double elbow, out of plane case 6in meter, double elbow, in plane case

12 Early 8Path Prototype The %Error for each case shown come for a k(vr) curve derived from the straight inlet case only. No additional corrections were done for the elbows. These preliminary results were very promising, and demonstrated just how the additional, cross plane of measurements help with disturbance insensitivity.

13 8 Path vs. 4 Path Raw Errors Equivalent 4 path planes vs. combined 8 path performance (Ballard 2017)

14 Redesigned Chord Locations The measurement chord locations were adjusted based on numerical analysis from the previous flow test data and were relocated to better handle swirl flow and a wide Reynolds range. The second round of disturbance testing used water and included additional, uncommon pipe configurations, on the redesigned flowcell. 6in meter, four elbows, in plane case 6in meter, six elbows, out of plane case

15 Redesigned Chord Locations The new chord locations remarkably improved the out of the box accuracy to the extent that no k-factor table was needed to better linearize the straight pipe case. The other pipe cases, also without any correction table, were also quite successful. The performance was verified, within a tolerance, by a quick test of this particular flowcell, at CEESI at a slightly lower Re range.

16 6in Final Design Multi-Oil Testing at CEESI A joint test program was developed along with CEESI to independently verify two LCT8 meters after they were calibrated in three oils, in a straight pipe, base configuration. CEESI were also given freedom to come up with a third disturbed configuration. Scheduling decided which oils would be used for the different configurations. 6in meter, double elbow, out of plane 6in meter, inline static mixer 6in meter, double elbow, in plane

17 6in Final Design Multi-Oil Testing at CEESI The results for the elbow cases were post-processed using the k(vr) curve that linearized the base case, as the table was disabled after the base case and prior to the elbow and mixer tests. The meter became more susceptible to the presence of the disturbances as the Reynolds number decreased. Repeatability issues arise in and around transition, but the elbows do cause the repeatability to wander to less than desirable levels. The static mixer was a very turbulent case that caused extremely unsymmetrical flow with VR 0.7 this is not a recommended installation! Oil Drakeol 32 Drakeol 5 Exxsol D80 Kinematic Viscosity 160cSt 16cSt 2.5cSt Reynolds Range 1,335 10,700 15, ,000 95, ,000

18 10in Final Design Multi-Oil Testing at CEESI The 10inch meter was part of the joint test program. Disturbance testing was carried out independently after the straight pipe base case calibration was completed. CEESI selected a full open globe valve as the third configuration. 10in meter, double elbow, out of plane 10in meter, full open globe valve

19 10in Final Design Multi-Oil Testing at CEESI A single k(vr) curve, obtained from the straight pipe calibration, across the whole Re range was used; the curve for lower Re was only marginally effective due to scheduling Transition and laminar flow appear to have a noticeable impact on disturbance sensitivity. Globe valve was only tested using the single fluid, but showed promising results. Oil Drakeol 32 Drakeol 5 Exxsol D80 Kinematic Viscosity 146cSt 16.1cSt 2.44cSt Reynolds Range ,800 6, ,000 59,000 1,200,000

20 Results Analysis In general, the Sentinel LCT8 shows good insensitivity to many of the standard disturbances, especially above an Re of 10,000 Some disturbances have more of an effect on repeatability, rather than directly on accuracy. Expecting a meter, installed behind a severely disturbed pipe configuration, flowing a wide range of products, to perform within tight accuracy specifications will likely need engineering review and potential tuning. Steps can be taken to reduce the uncertainty; this may include in situ proving/master metering, a calibration that closer models the application; a better understanding of the trends can result in the ability to shift a straight pipe calibration curve to the expected, disturbed condition.

21 Conclusions BHGE 8path Sentinel LCT8 meter is a good balance between having just enough acoustic paths, which do not overly influence the actual flow, while still being able to account for swirl caused by upstream piping, without the need for flow conditioning. Meeting custody transfer accuracies downstream of disturbances is possible, but may be limited in some applications.

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