GTI METERING RESEARCH FACILITY UPDATE Edgar B. Bowles, Jr. and Marybeth G. Nored GTI Metering Research Facility Program, Southwest Research Institute

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1 GTI METERING RESEARCH FACILITY UPDATE Edgar B. Bowles, Jr. and Marybeth G. Nored GTI Metering Research Facility Program, Southwest Research Institute 6220 Culebra Road, San Antonio, TX INTRODUCTION The Gas Technology Institute (formerly the Gas Research Institute) sponsors a comprehensive flow measurement research, development, and commercialization (RD&C) program aimed at improving natural gas metering performance in the field. This paper summarizes some of the recent accomplishments of the research program at the Gas Technology Institute (GTI) Metering Research Facility (MRF), a high-accuracy natural gas flow calibration laboratory capable of simulating a wide range of operating conditions for the industry s research, calibration, and testing needs. The MRF, located at Southwest Research Institute (SwRI) in San Antonio, Texas, supports a variety of GTI-sponsored research and third-party test and calibration activities. Major research initiatives currently being funded by GTI (formerly known as the Gas Research Institute or GRI) include ultrasonic and turbine flow meter research and gas sampling methods research. Over the past year, GTI has also funded Coriolis flow meter research and the development of a new energy flow rate meter concept. Through its portfolio of projects addressing priority research needs, the GTI natural gas measurement program provides significant benefits to the natural gas industry. Measurement Plan prepared by the Operating Section of the American Gas Association (AGA). This plan recommended the development of an independent, qualified flow test facility that would be operated under the sponsorship of the gas industry. This facility had to be capable of providing performance data on a broad spectrum of meter types and sizes over a wide range of flow conditions. In response to this recommendation, GTI initiated the MRF program with Southwest Research Institute in To cover the wide range of flow conditions necessary for the research and testing needs of the natural gas industry, development of the MRF 1 included three primary components: a High Pressure Loop (HPL), a Low Pressure Loop (LPL), and a Distribution Meter Test Stand (DTS). Table 1 lists the operational ranges for all three systems. The HPL and LPL are re-circulating flow loops, while the DTS is a blow-down type system. Each system can flow either natural gas or nitrogen. Parameter HPL LPL DTS Max. Rate (MSCFH) 7, Max. Rate (ACFH) 84,000 43,600 2,500 Pressure (psig) 150-1, Gas Temp. ( F) Ambient Pipe Size (inches) up to 2 Specific Gravity TABLE 1. Metering Research Facility Operational Ranges An on-line, laboratory-grade gas chromatograph is used for detailed analysis of the test gas. FIGURE 1. GTI Metering Research Facility METERING FACILITY DEVELOPMENT The Metering Research Facility program was initiated by GTI in the late 1980s in direct response to a growing need within the natural gas industry for improvement in the state-of-the-art of gas flow measurement. The concept of a natural gas industry metering research and calibration facility was first proposed in the Gas Industry Flow measurement accuracy on the order of 0.1 to 0.25% is achieved in the HPL, LPL, and DTS through the use of individual gravimetric primary calibration systems. Sonic nozzles, gas turbine meters, and laminar flow elements are also used as secondary transfer standards. The gravimetric calibration system for the High Pressure Loop is shown on Figure 2. An example of the performance of the MRF is illustrated by Figure 3, which plots orifice meter discharge coefficients (C d ) from the HPL against similar data from other international flow calibration laboratories. In addition to serving as a test bed for GTI-sponsored research, the MRF is available to any other interested parties for test and calibration services. The MRF PAGE PROCEEDINGS

2 This document represents the first industry guidelines on the use of ultrasonic flow meters for natural gas applications. Report No. 9 is fundamentally different from most other gas flow meter standards in that it is performance-based and does not include dimensional and other mechanical specifications associated with the meter installation. Instead, the report states that the flow meter must perform within specified measurement error limits when installed per the meter manufacturer s recommended installation configuration. Since the publication of Report No. 9, the AGA Transmission Measurement Committee has proposed that a flow performance verification test be included in the next revision of the report to help ensure that meters perform within the specified measurement error limits. This verification test would allow a manufacturer to validate recommended installation configurations and allow meter users to compare meter performance and installation requirements under a common set of piping configurations. It is also anticipated that the next revision of Report No. 9 will include a small number of recommended installation configurations. FIGURE 2. GTI MRF High Pressure Loop Weigh Tank technical staff also provides assistance with meter station design and helps troubleshoot metering problems in the field. In addition, the MRF offers training courses on meter station design and operation. During the past year, the MRF research program assisted the AGA TMC in developing a meter verification test protocol and, also, in identifying one or more acceptable piping installation configurations that could be recommended in the next revision of AGA Report No. 9. Commercially-available multipath ultrasonic gas flow meters from Daniel Flow Products, FMC/Kongsberg, and Instromet Ultrasonic were tested during the course of this project. Meter installations both with and without flow conditioners were evaluated. The test flow conditioners included in the research were the CPA-50E, the GFC TM TAS, the VORTAB TM, and the concentric 19-tube bundle (all pictured in Figure 4). ULTRASONIC GAS FLOW METER RESEARCH In June 1998, the AGA Transmission Measurement Committee (TMC) published its Report No. 9, entitled Measurement of Gas by Multipath Ultrasonic Meters. 2 Orifice C d mm Orifice Meter Tube Calibration β = 0.75 AGA - 3 (RG) equation for flange tapped orifice coefficient 95% confidence interval for RG equation Water data NEL DHL NIST Natural gas data Gasunie British Gas Ruhr Gas CEAT GRI MRF HPL Pipe Reynolds Number FIGURE 3. GTI MRF High Pressure Loop 10-inch Diameter Orifice Discharge Coefficient Data FIGURE 4. Flow Conditioners Used During MRF Ultrasonic Flow Meter Tests 2002 PROCEEDINGS PAGE 167

3 The test installation piping configurations evaluated in the MRF test program were based on recommendations from the flow meter and flow conditioner manufacturers and results of previous MRF research. 3, 4 The various installation configuration tests demonstrated that each flow meter/flow conditioner combination produced unique operational characteristics due to differences in the meters calculation algorithms and acoustic path configurations. The ability of a meter to compensate for a velocity profile distortion determines the amount of bias there will be in the meter error. The MRF research results indicated that effective flow conditioning can reduce errors caused by single and double elbow configurations located upstream of the meter. In most test cases, the CPA-50E, the GFC TM TAS, and the VORTAB TM flow conditioners reduced the meter error to within the 0.3% of the reading limit specified in AGA Report No. 9 for piping installation effects. Research has shown that for a meter and flow conditioner to effectively compensate for flow field distortions, the meter/flow conditioner combination should be flow calibrated as a package. A GTI Topical Report 5 summarizing the findings of the MRF research program on flow conditioner performance and piping installation configuration effects on ultrasonic meters was published in January that Coriolis meter technology showed enough promise for custody transfer applications with pressurized gas that an effort was initiated to produce an AGA report (i.e., industry guideline or standard). In 2001, GTI provided funding for an MRF research program to support the development of an industry standard for Coriolis gas flow meters. The research program focused on two technical areas: (1) baseline performance testing of five commercially-available meters in 2-inch to 4-inch diameter line sizes and (2) installation and operational effects testing. Results of the MRF research were recently published in a GTI Topical Report 8 on Coriolis mass flow meters for natural gas applications. The test meters were provided by Micro Motion, Incorporated (MMI), Endress & Hauser (E&H) and FMC Measurement Solutions. Though the internal geometry differed, these meters basically represented the split, bent-tube configuration (see Figure 5) and the single, straight-tube (or radial mode) design. In the installation effects tests, the meters were tested downstream of single and double elbow configurations (both in-plane and 90 out-of-plane relative to one another), a standard tee, and a standard concentric reducer. In addition to the recent installation effects testing, the MRF research program has quantified meter performance effects due to: (1) a diameter mismatch between the meter body and adjacent meter tube and (2) line pressure variations. 6 Diameter mismatches, in either the upstream or downstream direction, within the ±1.0% of pipe diameter limit specified in AGA Report No.9, did not result in any additional error for the ultrasonic flow meters tested. Variations in static line pressure, however, produced an appreciable meter bias error. The degree of error varied by meter design, but was shown to be as large as 0.09% of reading per 100 psig change in line pressure. The exact cause of this effect was still under investigation as of the publication date of this paper. Potential causes being considered included a shift in transducer delay time due to changes in line pressure or a Reynolds number dependency due to velocity profile changes. Ongoing ultrasonic meter research being funded by GTI will provide a clearer understanding of ultrasonic flow meter response to pressure variation. In addition, the current MRF research aims to study meter accuracy at low flow rates and the effects of temperature probe location in bi-directional flow applications. CORIOLIS GAS FLOW METER RESEARCH The AGA Transmission Measurement Committee recently published an Engineering Technical Note 7 on Coriolis flow meters used in high-pressure natural gas applications. After completing this Tech Note, the AGA TMC concluded FIGURE 5. Bent-tube Coriolis Meter Under Test at the MRF Results from this research program indicated that the meters exhibited unique operating characteristics, thus, each design had its own strengths and weaknesses. In PAGE PROCEEDINGS

4 general, the 2-inch diameter Coriolis meters maintained measurement reproducibility levels of 0.15% to 0.25% of reading in the baseline meter configuration. The meter zero for the bent-tube meter designs was relatively unaffected by line pressure changes, while the straighttube (radial-mode) meter showed a non-linear line pressure dependence in its meter zero. Compared to the straight-tube meter designs, the bent-tube designs were also less sensitive to flow field distortions resulting from the upstream piping configuration. The straight-tube designs experienced measurement biases from 1.5% to +4.0% of reading due to the upstream piping configurations. The results of the Coriolis flow meter research at the MRF also suggested that water-calibrated Coriolis meters could be used in high-pressure gas applications and still provide relatively accurate measurements. It is necessary to apply a correction factor for increased line pressure when using a water-calibrated meter in a highpressure gas application. Additional testing of a statistically significant sample of meters is needed in order to draw more definitive conclusions on this subject. The AGA Transmission Measurement Committee is currently pursuing the completion of a Coriolis gas flow meter report (i.e., industry standard or guideline) for custody transfer measurement applications involving high-pressure gas. This AGA report is expected to be published in TURBINE GAS FLOW METER RESEARCH Due to several recent advances in gas turbine flow meter technology, the AGA Transmission Measurement Committee is currently revising AGA Report No. 7 Measurement of Gas by Turbine Meters. 9 In support of this effort, GTI is funding a research program at the MRF to investigate the measurement performance of new high-capacity and dual-rotor meters, as well as installation and operational effects. In 2001, testing focused on nominal 6-inch diameter meters having 30 rotor blade angles (or extended-capacity meters) or dual-rotor configurations. The meter installation configurations referenced in AGA Report No. 7 (i.e., the recommended, short-coupled, and close-coupled configurations [see Figure 6] ) were evaluated, as well as the International Standards Organization (ISO) 9951 high-perturbation piping configuration. In addition, the research tests evaluated meter performance with and without a flow conditioner installed upstream. The effect of line pressure variation on meter accuracy was also investigated. The test meters were first flow calibrated using the AGA Report No. 7 recommended configuration. Subsequent flow tests were run using the AGA short-coupled and close-coupled configurations, as well as the ISO 9951 high-perturbation piping configuration, and the results were compared. For flow rates above 9,000 acfh, all test results agreed to within ±1.0% of reading (i.e., the current AGA Report No. 7 measurement uncertainty limit). FIGURE 6. Turbine Meter Under Test in a Close-Coupled Configuration at the MRF Furthermore, it was determined that with effective flow field conditioning at the meter inlet, the measurement uncertainty band was reduced to less than +0.25% of reading. The single-rotor and dual-rotor meter configurations did not exhibit significant differences in total measurement uncertainty and both meter types displayed improved measurement accuracy with effective flow field conditioning at the meter inlet. Additionally, the MRF test results found that changes in line pressure (between atmospheric and 160 psig) could produce significant shifts in meter calibration. The behavior and magnitude of the shifts were found to be a function of meter design. Further testing of meter calibration shifts due to line pressure variations is ongoing at the MRF. The current MRF research may provide a recommended dividing point (whereby meter performance specifications could be categorized by the expected operating pressure range) between low and high pressure applications. A summary of recent MRF turbine meter research results was presented in a technical paper 10 at the 2002 AGA Operations Conference and will be published in a GTI Topical Report scheduled for release in NATURAL GAS SAMPLING RESEARCH Proper natural gas sampling methodologies are critical to the accurate determination of natural gas heating value. Improper sampling technique can distort the composition of the natural gas sample, which will directly affect the accuracy of the heating value and indirectly affect the accuracy of the volumetric flow rate (through errors in the gas properties, such as gas density). Because of the importance of accurate sampling of the natural gas flowing through a pipeline, GTI, the American Petroleum Institute (API), and the U.S. Minerals Management Service (MMS) initiated a consortium 2002 PROCEEDINGS PAGE 169

5 research project to document the causes of gas sample distortion and to implement procedures that produce accurate sample analysis. Much of this consortium research work has been carried out at the MRF. The research results have lead to a recent revision of the industry standard for gas sampling methods, i.e., the API Manual of Petroleum Measurement Standards (MPMS), Chapter 14.1 Collecting and Handling of Natural Gas Samples for Custody Transfer. 11 This comprehensive research program has looked at all aspects of natural gas sampling methodology. Various types of spot- and composite-sampling methods, as well as on-line analysis methods, have been studied. Causes of gas sample distortion that have been identified include thermodynamic phase changes, molecular adsorption* (on the surfaces of solids or liquids), sample probe location, filtering of the sample gas, and cleanliness of the gas sampling equipment. Once a gas sample has been distorted, its composition has been altered and, thus, its heating value will be erroneously determined based on the altered composition. Recent MRF gas sampling methods research has been directed toward improving the accuracy of the hydrocarbon dew point temperature calculated from the common equation of state models used by the U.S. natural gas industry. Inaccurate prediction of the hydrocarbon dew point temperature by analytical means can be a contributing factor in sample gas distortion. Accurate estimation of the hydrocarbon dew point temperature is highly dependent on the percentages (or characterization) of the heavier hydrocarbons in a gas mixture. Recent sampling research at the MRF also investigated the Fill and Empty (Purging) Spot Sampling Method as a self-heating technique (see Figure 7). Initial analytical modeling of the Fill and Empty purging process suggested that the method showed promise at heating the gas sample bottle during the sample process. If enough heat could be generated by a reasonable number of Fill and Empty purge cycles, this spot sampling method could be used to heat the sample bottle to a sufficiently high temperature, thus ensuring the sample gas maintains a single phase during the gas sample collection process. Subsequently, experimental tests performed at the MRF revealed that the heating of the sample bottle by the purging process varied considerably and was a function of gas temperature and pressure, as well as ambient temperature. In particularly cold ambient test conditions, the purging process was unable to raise the gas sample bottle temperature above the hydrocarbon dew point temperature of the gas. Results of recent gas sampling research at the MRF were summarized in a technical paper 12 presented at the 2002 AGA Operations Conference. In addition, a GTI Topical *Adsorption is a process of attraction between gas molecules and the surfaces of solids or liquids. FIGURE 7. Testing of the Fill & Empty (Purging) Spot Sampling Method at the MRF Report 13 summarizing natural gas sampling research work completed through 1999 has been published. Two additional GTI Topical Reports summarizing subsequent research work are scheduled for publication in 2002 and should be available by the time of the American School of Gas Measurement Technology in September. OTHER GTI-FUNDED RESEARCH In addition to the ongoing work described above, the GTI MRF program has sponsored other flow measurement research. For example, a prototype energy flow rate meter is under development at the MRF. This work has received funding from both GTI and the U.S. Department of Energy. The device is designed to measure a small number of process variables (e.g., gas sound speed, diluent concentrations, pressure, temperature, and volumetric or mass flow rate) to determine energy flow rate in real time, and at normal pipeline operating conditions. This new device is expected to be a more cost effective approach to determining energy flow rate than the conventional approach of combining measurements from a volumetric flow meter and gas chromatograph. Further sensor development, laboratory testing, and field-testing at gas transmission pipeline sites are currently being completed. Two preliminary 14, 15 reports on this device are available from GTI. GTI is also funding an inter-laboratory test comparison of the MRF, the Colorado Engineering Experiment Station flow calibration lab in Ventura, Iowa, and the TransCanada Calibrations test facility in Winnipeg, Manitoba. These are the three high-volume natural gas flow meter test facilities in North America. This marks the first time that these three test labs have undergone a direct performance comparison. This project has federal government participation from the U.S. National Institute of Standards and Technology and Measurement Canada. Test results should be available by the end of PAGE PROCEEDINGS

6 CONCLUSIONS GTI s applied flow measurement research program continues to address the priority needs of the natural gas industry. This paper summarizes some of the recent measurement research activities at the MRF. A complete listing of all MRF research reports and technical papers is available from GTI ( or the MRF website ( REFERENCES 1. Johnson, J. E., et al., Metering Research Facility Design, GRI Topical Report No. GRI-91/0251, GRI, Chicago, IL, March Measurement of Gas by Multipath Ultrasonic Meters, American Gas Association Transmission Measurement Committee Report No. 9, American Gas Association, Arlington, VA, June Grimley, T. A., Performance Testing of Ultrasonic Flow Meters, 15th North Sea Flow Measurement Workshop, Kristiansand, Norway, October Grimley, T. A., The Influence of Velocity Profile on Ultrasonic Flow Meter Performance, Proceedings of the American Gas Association Operations Conference, Seattle, WA, May Grimley, T. A., Performance Testing of 12-Inch Ultrasonic Flow Meters and Flow Conditioners in Short Run Installations, GRI Topical Report No. GRI- 01/0129, GRI, Chicago, IL, January Grimley, T. A., Effects of Diameter Mismatch and Line Pressure Variations on Ultrasonic Gas Flow Meter Performance, GRI Topical Report No. GRI- 02/0031, GRI, Chicago, IL, April Coriolis Flow Measurement for Natural Gas Applications, American Gas Association Transmission Measurement Committee Engineering Technical Note, American Gas Association, Washington, D. C., July Grimley, T. A., Coriolis Mass Flow Meter Performance with Natural Gas, GRI Topical Report No. GRI-01/0222, GRI, Chicago, IL, January Measurement of Gas by Turbine Meters, American Gas Association Transmission Measurement Committee Report No. 7, American Gas Association, Arlington, VA, June George, D. L., Turbine Meter Test Results - Installation Configuration Effects, Proceedings of the American Gas Association Operations Conference, Chicago, IL, May Collecting and Handling of Natural Gas Samples for Custody Transfer, Manual of Petroleum Measurement Standards, Chapter 14.1, 4th Edition, American Petroleum Institute, Washington, D.C., August Kelner, E., D. L. George and M. G. Nored, Natural Gas Sampling Techniques - Recent Research Results, Proceedings of the American Gas Association Operations Conference, Chicago, IL, May Behring, K. A. and E. Kelner, Metering Research Program: Natural Gas Sample Collection and Handling-Phase I, GRI Topical Report No. GRI-99/ 0194, GRI, Chicago, IL, August Behring II, K. A., E. Kelner, A. Minachi, C. R. Sparks, T. B. Morrow, and S. J. Svedeman, A Technology Assessment and Feasibility Evaluation of Natural Gas Energy Flow Measurement Alternatives, Final Report, Tasks A and B, Southwest Research Institute for the U.S. Department of Energy, Morgantown Energy Technology Center, Morgantown, WV, May Morrow, Thomas B., E. Kelner, and A. Minachi, Development of a Low Cost Inferential Natural Gas Energy Flow Rate Prototype Retrofit Module, Topical Report to GRI and the U.S. Department of Energy, GRI Contract No , DOE Cooperative Agreement No. DE-FC21-96M33033, October Edgar B. Bowles, Jr PROCEEDINGS PAGE 171