EXTENDED APPLICATION OF CORIOLIS METERSFOR MEASURING NATURAL GAS Keven Conrad, Flow Product Business Manager, Endress¹Hauser, Inc 1oel Clancy, Operations Manager, CEESI Iowa High Flow Test Facility Prepared Ior: 2005 AGA Operations ConIerence and Biennial Exhibition April 27-29, 2005 __________________________________________________ Abstract Coriolis mass Ilow measurement Ior natural gas proves to minimize the uncertainties associated with volumetric Ilow measurement. The installation requirements and overall cost can be greatly simpliIied and reduced. The need Ior proper straight run and Ilow proIile dependencies are shown to be virtually eliminated. While simulating such high level perturbation and installation eIIects, Coriolis continues to perIorm well within the accuracy speciIication oI AGA 11 over and extended range oI Ilow. Testing on a new 10¨ Coriolis mass Ilowmeter will be discussed. __________________________________________________ Introduction Coriolis mass Ilowmeters have been used to improve the accuracies oI liquid measurement since the 1980`s. It is no secret that gas measurement has become a major Iocus Ior this technology. At the time oI the release oI AGA Report No. 11 (1) and the prior issuing oI AGA Engineering Technical Note (2) , the available Coriolis meter sizes were only up to 6 inch. Coriolis is a viable option to be used in gas Ilow measurement, yet typically thought oI Ior smaller line sizes. Coriolis manuIacturers continue to advance the development oI meter sensitivity, their immunity to noise, the ability to be mechanically selI supporting and most recently, larger available sizes commercially up to 10 inch. There are manuIacturers who custom make meter bodies which can even exceed this. Older designs may not have been able to operate within the needed accuracies at lower pressure, total allowable pressure drop and were subject to noise and vibration eIIects. As a result oI manuIacturers overcoming these technical hurdles, Coriolis has gained worldwide recognition Irom standards and approving organizations like, AGA (American Gas Association), API (American Petroleum Institute), NMI (Dutch Weights and Measures), PTB (German Weights and Measures) and OIML (Organisation Internationale de Metrologie Legale). The ability to deliver meters which continue to operate and maintain custody transIer level oI perIormance regardless oI pressure, temperature, noise, vibration, pipe stress and installation is unparallel by any other metering technology available to this industry. Since Coriolis Ilow meters measure direct mass, many issues are eliminated which aIIect the uncertainty oI volumetric based metering. Some Coriolis manuIacturers do not rely on any particular velocity proIile and in turn can reduce the amount oI piping and external equipment needed to achieve the accuracies desired. Coriolis meters with this capability are able to register bi-directional just as accurate. This can Iurther eliminate the need oI additional piping, Ilow conditioning and auxiliary equipment. Since not all Coriolis meters are alike, it is recommended that the manuIacturer be consulted in regards to their speciIic recommendations on upstream piping conIigurations. For Coriolis to report out in standard volumetric Ilow, it simply divides the mass Ilow by the standard or base density oI the Iluid being measured. The need to actually measure and compensate Ior the temperature, pressure or compressibility oI the gas is virtually eliminated. For single component gases, common databases exist to look this inIormation up. For mixtures, the gas composition can be measured or estimated, depending on the level oI accuracy required. II measured, a gas chromatograph is typically used allowing the operator to back calculate the base density by the use oI AGA Report No. 8 (5) . Individual manuIacturers may have compensation Ior temperature and pressure and its eIIects on the meter itselI and will be discussed later in this report. For the reasons mentioned above and others, the installation can be simpliIied and reduced in size and overall cost. Principle of Operation When a Iluid particle inside a rotating body moves away or toward the center oI rotation, the particle creates an inertial Iorce (known as the Coriolis Iorce) that acts on the body. (1) In this case, the tube oI a Coriolis Ilow meter is the body. Coriolis meters typically comprise oI one or two tubes which oscillate amongst their own axis. In a dual tube meter, the tubes are typically reIerenced to each other with electro- dynamic sensors or 'pickoII¨ coils which are located near the inlet and outlet oI each tube. An exciter or drive coil is typically placed near the center oI each oI the tubes and will oscillate the tubes at a Irequency determined by the design oI the meter and the Iluid which is present at the time. In liquid or gas measurements, the oscillation Irequency is inversely proportional to the density oI the Iluid. The heavier the Iluid the lower the oscillation Irequency will be. With gases, the use oI oscillation Irequency does not provide a satisIactory level oI resolution to properly determine the Ilowing density oI the gas accurate enough and at this point is not typically utilized. Knowing the mass Ilow and diIIerential pressure across the meter is actually a much better way to back into the Ilowing density oI a gas stream iI needed. On the other hand, Ior liquids, the resolution oI density can be evaluated in the order oI +0.0005 g/cc. When a mass oI Iluid (gas/liquid) Ilows through the meter, each tube experiences what is called the Coriolis Iorce. The Iorce causes each tube to deIlect where the inlet and outlet become out oI phase. The detection oI the phase shiIt, or 'oIIset¨ as it is commonly reIerred to, is measured by the electro-dynamic sensors at the inlet and outlet oI the meter. This amount oI phase oIIset is dependent on individual manuIacturer`s designs and is directly proportional to the mass Ilow. Figure 1 is an example oI a dual tube design which shows the tubes with an exaggerated amount oI movement in an oscillatory state with zero Ilow. Figure 2 gives a visual oI what the tube looks like when Ilow oI either gas or liquid begins to move through this rotational Irame. A Coriolis Iorce is experienced and the tubes begin to deIlect. Figure 1: Dual tube design with zero Ilow Figure 2: Dual tube design with Ilow Figure 3 is an example oI a single tube with Ilow along with the graphing oI each individual pickoII coil signal. Figure 3: Single tube with Ilow rate illustrating the pickoII coils plotting out phase oIIset detection DiIIerent manuIacturers will have diIIerent amount oI movement or amplitude depending upon designs. One particular manuIacturer moves the tubes less than .050 mm. This in itselI is an indication oI how sensitive the measuring techniques have become with modern technology. On the other hand, they are resistant to vibration and other external inIluences and these become proprietary discussions and techniques utilized by the diIIerent manuIactures. The ability to read several phase oIIsets and update the mass Ilow measurement in the order oI milliseconds is just another example oI how Iar technology has allowed Coriolis to advance. Benefits in Using Coriolis Flow Meters Coriolis Mass Flowmeters oIIer great advantage over volumetric based Ilow measurement technologies, including: No moving parts or bearings which will wear in dry gas. No straight run requirements needed Ior the majority oI manuIacturer`s designs. No Ilow conditioning needed Ior the majority oI manuIacturer`s designs. Tolerable to solids/liquid particulates which can damage oriIice plates and turbines. Can handle an over range oI Ilow which can damage mechanical metering. No external temperature or pressure measurement required in most cases. Immune to Iluid property and compositional changes. Coating oI the tubes can actually be detected. (Dependent on manuIacturer). Diagnostics which allow continuous monitoring Ior corrosion, erosion or buildup. No sensing lines to plug, Ireeze or leak Wide turndown ratio demonstrated at 150:1* * Typical spec. oI 50:1 and dependent on allowable dp, gas density and velocity) 150:1 was on testing oI high pressure natural gas at CEESI (1190 Psia & 77 F) SpeciIic manuIacturers have designs which are mechanically built to isolate the measuring tubes Irom mechanical stress and external Iorces. Immunity to pipeline vibration, with excellent stability and accuracy is also a Ieature that can now be sourced. To put it simply, this means no brackets or supports required Ior the installation. II the piping system will support the meter, then there is no need to provide isolative support. This will lower the installation costs. The stability oI the zero point is also very important when evaluating perIormance oI a Coriolis Ilow metering. Stability means there is no signiIicant shiIt or phase oIIset detected when there is zero Ilow. The beneIits that come with mass Ilow are enormous. Although there is a substantial install base and several reports out that prove how tolerable this technology is on gas Ilow measurement, there still seems to be hesitancy or a lack oI knowledge within the gas measurement industry on the implementation oI Coriolis and the use oI mass Ilow i.e. 'standard volume¨ Ior their measurement needs. One reason would be the thought that these meters can`t handle the range oI gas Ilow and that size limitation would eliminate the ability to select Coriolis. This report will give an update on what`s new Ior the industry as well as detail some testing which was perIormed by Colorado Engineering Experiment Station, Inc. (CEESI) in Iowa. Cost could also be a Iactor when one is initially evaluating the use oI Coriolis Ilowmeters. They tend to be more pricy than your traditional volumetric based primary elements, but when the total installed and operating cost is evaluated in more detail, one will see the beneIits really stand out and can outweigh the cost diIIerence. Installation eIIects have been evaluated by several independent testing Iacilities and one speciIically on natural gas was perIormed several years ago by Southwest Research Institute (SwRI) and showed that the 'bent-tube designs showed insigniIicant Ilow measurement error when subjected to a variety oI upstream piping conIigurations.¨ (3) This report will highlight continued testing and proven perIormance in multiple high level Ilow disturbances. What`s New for the Industry in Gas Measurement? Large Coriolis Flow Meters! Independent testing, conducted by the Colorado Engineering Experiment Station, Inc. (CEESI) conIirms a newly released 10-inch Coriolis Ilowmeter to perIorm well within the custody transIer gas accuracy speciIications oI 1.0° as described in the American Gas Association (AGA) Report No. 11. Meter perIormance shown later in this report is within the speciIied accuracy oI +0.35° + |(Zero Stability/Actual Reading)*100| ° taking into account the uncertainty oI the calibration Iacility oI +0.23°. Meter proved to perIorm extremely well in both ideal and non-ideal piping orientations. Turndown ratio or range ability exceeded all expectations and demonstrated custody transIer level accuracies in the range oI 150:1. Typical speciIications would more likely be in the range oI 50:1 or less depending on the gas density and allowable pressure drop. Velocities tested at CEESI were way outside oI typical pipeline or gas Ilow standard practices. The Ilow rate through the Coriolis meter was compared to three Daniel 12-inch turbine meters at 300 lb/s (Velocity oI 158 It/s in a 10-inch pipeline) and went all the way down to one 4-inch Daniel turbine at 2 lb/s (Velocity oI 1 It/s in 10-inch pipeline). In between each test point the metering system was given a suIIicient amount oI time to stabilize prior to taking the data. Third Party Testing of Large Size Coriolis in Natural Gas PerIormance speciIications within AGA 11 are describe and illustrated below in Figure 4. The meters ability to repeat within +1.0° below Q transitional and +0.5° above and with an average mean error oI less than +1.0° is aIter the Iinal meter Iactors are applied. This allows an Operator/Designer to have the meter third party certiIied and adjust the Iinal meter Iactor to match up with an accredited calibration Iacility. CEESI, which was used to test the newly released 10 inch Promass Irom Endress¹Hauser has an advertised uncertainty on mass Ilow oI +0.23° and is ISO/IEC 17025 certiIied by the National Voluntary Laboratory Accreditation Program (NVLAP). See Appendix A Ior copy oI their certiIicate. All in all, Coriolis meters are perIorming out-oI-the-box near the uncertainty oI the calibration Iacility. Several tests have shown that Coriolis meters, depending on the manuIacturer and design, could meet the speciIications eliminating the need Ior any additional meter Iactors. It is still the option oI the Operator/Designer to have the meter re-calibrated iI they still desire. They can Iine tune the meter with multiple k Iactors or implement other linearization and adjustment Iunctions in either a Ilow computer or within the electronics oI the meter depending on the manuIacturer`s capability. AGA 11 Repot No. 11 Performance Requirements Figure 4: AGA PerIormance SpeciIication Summary Previously, a 6 and 4-inch Ilowmeter were conIirmed to perIorm within the same custody transIer speciIications at Pigsar/Ruhrgas in Germany. Figure 5: Illustration oI Endress¹Hauser Promass Coriolis meter installed at Pigsar Figure 6: Results oI tests oI natural gas measurements in the PIGSAR calibration institute. Endress¹Hauser Promass F, the DN 150 / 6¨ model, proved just as eIIicient as the smaller versions oI the meter tested prior at both 20 and 50 bar. In 2004, CEESI conducted calibration water, air, dry gas and wet-gas tests on Coriolis Mass Flowmeter. This testing was sponsored by the Gas Research Institute and the results are reported in GRI-04/0172. The single calibration Iluid tests show that a water calibration oI the Coriolis mass Ilowmeter can be used Ior transIerability over to speciIied accuracies in natural gas applications without deviation in the k-Iactor. (4) This was also proven by the calibration test which was run on a new 10-inch Coriolis at CEESI. The meter was certiIied and calibrated on water (see Appendix B calibration certiIicate oI a particular manuIacturer). It then perIormed in gas within the speciIication which is +0.35° plus the zero stability. See the sizing, accuracy curve and pressure drop calculation Irom a sizing program in Figure 8. Figure 7: Installation oI 10-inch Promass Coriolis oI Endress¹Hauser at CEESI in Iowa Figure 8: Example oI a sizing and speciIication soItware giving expected accuracy data as well as pressure drop inIormation. Results and Test Description of 10-Inch Coriolis Meter at CEESI Natural gas Ilowing through CEESI`s Iacility in Iowa is taken Irom the Northern Border Pipeline, ran through the calibration Iacility where temperature, pressure and gas composition is evaluated and compensated Ior compressibility. It is then converted to mass by taken the volumetric Ilow in standard cubic Ieet and simply multiplying it by the reIerence or standard density in lbs/It`3 at 519.67 degrees Rankine and 14.696 Psia . The gas is compensated Ior compressibility and composition according to AGA 8 (5) calculations. This is then compared directly to the mass Ilow reading Irom the Coriolis meter. The Coriolis meter does not need the temperature or pressure reading to make any adjustments to the Iluid component. On the other hand, diIIerent manuIacturers will speciIy an accuracy eIIect due to the pressure and temperature eIIect it has on the metering tubes themselves. For the highest degree oI accuracy, this needs to be corrected Ior. For one particular manuIacturer, the temperature correction is +0.0001° oI Iull scale per degree F and is compensated Ior in the meter. The pressure eIIect has a higher negative bias oIIset due to the stiIIening oI the tubes at higher pressure. For the 10 inch model, this oIIset is speciIied at -0.0006/psi, so Ior 1200 psi operating conditions at CEESI in Iowa, it is determined to be .72° adjustment. II the pressure condition is constant or stable, one can program directly into the meter the pressure value. II the operating condition is more dynamic and has extreme pressure swings, then taking a pressure reading live into the meter electronics is also possible Ior optimization oI accuracy. Test 1 & 2: Straight Run Test This was a baseline test which we allowed over 40 diameters oI straight pipe coming into the meter aIter it reduced Irom 12 inch to 10 inch and then the downstream Ilow had at least 20 diameters prior to expansion back into the larger size diameter pipeline. The meter was installed with no support and also no Ilow conditioning. The meter zero was checked under pressure conditions and the amount the value had changed Irom Iactory calibration was very small. Flange alignments were centered by the technicians, yet no dowel pin alignment was used. Pressure drop data was captured yet showed extreme deviation Irom calculated hydraulics and appears to be a result oI the pressure tap location downstream oI the meter. Future testing may be needed to veriIy the entire pressure recovery zone downstream oI the Coriolis meter. Results were extremely good and showed a slight tail oII on the low end yet were still in the speciIied accuracy oI the meter as well as within the requirements oI AGA 11. Test 2 was a reproducibility check which looked good as well. The data in Figure 10 has the uncertainty oI +0.23° Irom CEESI`s calculation indicated on the graph. Test 1 & 2 Figure 9: Picture oI Installation with Pressure measurements upstream and downstream oI meter Test 1 & 2 Results Figure 10: Testing oI 10-Inch in over 40 diameter oI straight run 10" Endress+Hauser PromassCorioIisMeter Straight run of pipe wi th over 40 diameters from 12" x 10" reducer, no flow conditi oner -2.0 -1.5 -1.0 -0.5 0.0 0.5 1.0 1.5 2.0 0.00 50.00 100.00 150.00 200.00 250.00 300.00 Mass Flow Rate, lb/ s P e r c e n t D e v i a t i o n Test #1 Test #2 Q-min Qt (10%of Qmax) Q-max Uncertainty of CEESÌ Natural Gas Data +/ - 0.23% 585 487 97 292 195 390 0 MMSCFD Test 3: Elbows Out of Plane and 10 Diameters Upstream of Meter In this setup we reconIigured the piping to create a Ilow disturbance which would likely exist in the real world due to piping or space limitations. Again, no Ilow conditioner was used and the piping was aligned by best practices like beIore. Results were quite impressive and seem to be very repeatable and Ilat in comparison to the straight run test. See Figure 12 below. Test 3 Figure 11: Picture oI Installation Ior Ilow disturbance and only 10D Figure 12: Results Irom Test 3 with elbows out oI plane and only 10D 10" Endress+Hauser PromassCorioIisMeter (2) 90 degree elbow out of plane with 5D, 90 degree elbow and 10D straight pipe, no flow conditioner -2.0 -1.5 -1.0 -0.5 0.0 0.5 1.0 1.5 2.0 0.00 50.00 100.00 150.00 200.00 250.00 300.00 Mass Flow Rate, lb/ s P e r c e n t D e v i a t i o n Test #3 Q-min Qt (10%of Qmax) Q-max Uncertainty of CEESÌ Natural Gas Data +/ - 0.23% 585 487 97 292 195 390 0 MMSCFD Test 4 & 5: Elbows Out of Plane and 0 Diameters Upstream of Meter In this setup we reconIigured the piping to create an extreme or high level perturbation. We bolted the 90 degree elbow directly to the meter and on test 5 the Coriolis meter was purposely allowed to drop within the bolt slop. This gave us approximately a 1/4 inch oI misalignment on the Ilanges (Figure 14). Again, no Ilow conditioner was used. Results were even more impressive so on Test 5 the meter was evaluated all the way down to 1.9 lb/s which equates to less than 1 It/s velocity in the 10 inch pipeline and the perIormance was dead on. The disturbed Ilow proIile seem to register even more accurately on the low end than it did with over 40 diameters oI straight pipe. (Figure 15) Test 4 & 5 Figure 13: Picture oI Installation Ior Ilow disturbance and only 10D Figure 14: Picture oI Flange Misalignment Test 4 & 5 Results Figure 15: Results Irom Test 4 & 5 with elbows out oI plane and 90 bolted directly to Coriolis Summary of All Tests Figure 16: Results Irom all tests with the manuIacturer speciIication curves 10" Endress+Hauser PromassCorioIisMeter Double elbows out of plane with 12" x 10" reducer between, 5D, 90 bolted directly to Coriolis meter -2.0 -1.5 -1.0 -0.5 0.0 0.5 1.0 1.5 2.0 0.00 50.00 100.00 150.00 200.00 250.00 300.00 Mass Flow Rate, lb/ s P e r c e n t D e v i a t i o n Test #5 Test #4 Q-min Qt (10%of Qmax) Q-max Uncertainty of CEESÌ Natural Gas Data +/ - 0.23% 585 487 97 292 195 390 0 MMSCFD 10" Endress+Hauser PromassCorioIisMeter CEESÌ High Flow Natural Gas Calibration Testing Facility - All Data -2.0 -1.5 -1.0 -0.5 0.0 0.5 1.0 1.5 2.0 0 50 100 150 200 250 300 Mass Flow Rate, lb/ s P e r c e n t D e v i a t i o n Test #CP Test #1 Test #2 Test #3 Test #4 Test #5 UCL LCL Q-min Qt (10%of Qmax) Q-max Typical flow range for natural gas pipeline operation Uncertainty of CEESÌ Natural Gas Data +/ - 0.23% 585 487 97 292 195 390 0 MMSCFD Example of Total Installed and Operating Cost Comparison Below is an example oI a study perIormed by a major petrochemical company on an allocation meter Ior a particular gas coming into the plant. Figure 17 below points out all oI the diIIerent issues which could play a Iactor in the overall installed and operating cost outside oI the initial purchase price. In the example below, the payback was calculated to less than six months just due to the improvement on the uncertainty oI the measurement only. As one can see, there is much more than just the measurement accuracy which can aIIect the total installed or operating cost oI a measurement point. Other items like leak points and secondary containment issues were not discussed in detail, yet are all positive issues with the Coriolis meter and that the Iact there are little or no moving parts, the overall maintenance oI the measurement will be reduced. Figure 17: Example oI radar plot between Coriolis and InIerred mass volumetric meter Conclusion Meter sizes, perIormance and overall immunity to Ilow proIile and compositional Iactors have surpassed most expectations within the industry. The Iollowing are conclusions which were drawn Irom the independent testing and data made available in this report. 1. Calibration oI Coriolis Ilow meters on water is transIerable over to gas measurement within the gas speciIication oI each individual manuIacturer. 2. Customers should get the manuIacturers speciIications on the eIIects oI Pressure and Temperature Ior their particular design and iI needed, plug the values into the meter Ior proper compensation. 3. Depending on manuIacturer, Coriolis Ilow meters can have extremely good turndown ratios in excess oI 50:1. Typically seen on higher pressure gases. 100:1 20:1 50:1 10:1 5:1 2 4 6 8 25 15 10 5 0. 5 0. 1 1. 0 5. 0 0. 1 0. 5 1. 0 5. 0 .0 1 1 2 6 1 4 8 12 2 4 8 12 % of reading Turndown RepIacement period (years) Human Intervention (times / year) No. of components % drift per year caIibration frequency (times / year) Points of potentiaI Ieakage Coriolis meter Inferred mass meter 4. Flow proIile disturbances and swirl Ilow have little or no impact on the measurement accuracy. In this particular report, it enhanced the measurement. 5. Mass based measurement oI natural gas eliminates many Iactors which go into the calculation oI the overall measurement uncertainty in volumetric based measurement. Temperature, pressure, compressibility, expansion coeIIicients, Ilow proIile and wear on moving parts is just to name a Iew. 6. Larger size Coriolis meters and their extreme sensitivity on the low end oI the measurement allows one to properly size these meters with an acceptable pressure drop. It should also be pointed out that Ilow strainers, long runs oI piping and Ilow conditioners can all be removed and thereIore will help in the overall pressure drop evaluation. References 1. AGA |2003|. Measurement oI Natural Gas by Coriolis Meter. American Gas Association Transmission Measurement Committee, AGA Report No. 11 / API MPMS 14.9. Arlington, VA. 2. AGA |2001|. Coriolis Flow Measurement Ior Natural Gas Applications. American Gas Association Transmission Measurement Committee, Engineering Technical Note. Arlington, VA. 3. Pipeline & Gas Journal |2002|. Coriolis Suggests It Can Serve In Custody TransIer Applications. Terrence A. Grimley, Southwest Research Institute. San Antonio, TX 4. Gas Research Institute, GRI-04/0172 |2004|. Coriolis Mass Flow Meter PerIormance With Water, Air, Dry-Gas & Wet-Gas. Charles L. Britton / Josh Kinney, Colorado Engineering Experiment Station, Inc. Nunn, CO 5. AGA |1994|. Compressibility Factor oI Natural Gas and Related Hydrocarbons. American Gas Association Transmission Measurement Committee, AGA Report No. 8. Arlington, VA. Appendix A Appendix B