Influence of flow disturbances on the performance of industry-standard LNG flow meters

In the last decade significant progress has been achieved in the development of measurement traceability for LNG inline metering technologies such as Coriolis and ultrasonic flow meters. In 2019, the world's first LNG research and calibration facility has been realised thus enabling calibration and performance testing of small and mid-scale LNG flow meters under realistic cryogenic conditions at a maximum flow rate of 200 m³/h and provisional mass flow measurement uncertainty of 0.30% (k = 2) using liquid nitrogen as the calibration fluid. This facility enabled, for the first time, an extensive test programme of LNG flow meters under cryogenic conditions to be carried out to achieve three main objectives; the first is to reduce the onsite flow measurement uncertainty for small and mid-scale LNG applications to meet a target measurement uncertainty of 0.50% (k = 2), the second is to systematically assess the impact of upstream flow disturbances and meter insulation on meter performance and the third is to assess transferability of meter calibrations with water at ambient conditions to cryogenic conditions. SI-traceable flow calibration results from testing six LNG flow meters (four Coriolis and two ultrasonic, see acknowledgment section) with water in a water calibration facility and liquid nitrogen (LIN) in the LNG research and calibration facility under various test conditions are fully described in this paper. Water and LIN calibration data were compared and it was observed that the influence of removing the meter insulation on mass flow rate measurement accuracy can be more significant (meter error > ±0.50%) than the influence of many typical upstream disturbances when the meter is preceded by a straight piping length equal to twenty pipe diameters (20D) with no additional flow conditioning devices, in particular for ultrasonic meters. The results indicate that the correction models used to transfer the water calibration to cryogenic conditions (using LIN) can potentially result in mass flow rate measurement errors below ±0.5%, however, the correction models are specific to the meter type and manufacturer. This work shows that the target measurement uncertainty of 0.50% can be achieved if the expanded standard error of the mean value measured by the meter is smaller than 0.40% (k = 2). It is planned to repeat these tests with LNG in order to compare the results with the LIN tests presented in this paper. This may reveal that testing with an explosion safe and environmentally friendly fluid such as LIN produces representative results for testing LNG flow meters.     

Development and evaluation of the calibration facility for high-pressure hydrogen gas flow meters

The calibration facility with the multi-nozzle calibrator was developed for the calibration of flow meters to be used with high-pressure, high-flow-rate hydrogen gas. The critical nozzles installed in the multi-nozzle calibrator were calibrated with traceability to the national standard. The relative standard uncertainty of the mass flow rates produced from the calibration facility is 0.09% when the flow rate is between 150 g/min and 550 g/min. In this study, the Coriolis flow meter was calibrated for a pressure range of 15–35 MPa. The relative standard uncertainty of the flow rates obtained from the Coriolis flow meter was 0.44% for the case of the worst fluctuations in the output of the flow meter; based on the calibration curve, this is 0.91%. The present result shows that there is a maximum 3% difference between the output of the Coriolis flow meter and the mass flow rates of the multi-nozzle calibrator, even though the Coriolis flow meter was calibrated using water. Therefore, for the development of a calibration facility that can calibrate a flow meter under the same conditions as those encountered in actual use, it will be important to develop a new flow meter.     

Effects of water in oil and oil in water on single-phase flowmeters

The effect of two-phase flow on the performance of a range of single-phase flowmeters has been investigated experimentally using the National Standard Multiphase Flow facilities at NEL. The flowmeters tested were 2-inch and 4-inch positive displacement meters, venturi meters, helicoidal and flat-bladed turbine meters, 2-inch U-tube, 3-inch and 1.5-inch straight tube Coriolis meters and a 4-inch vortex shedding meter. The flowmeters were tested in oil flow with water and water flow with oil. The second component fractions were varied from 3% up to 15% by volume. The aim of the project was to quantify the effect of second-phase fluid components on the basic uncertainty of a range of single-phase. These tests have provided evidence of the suitability of particular flowmeters for two-component flow applications. Comparisons have been made between generic type and size of flowmeter. The oil-in-water and water-in-oil tests indicated that the uncertainty in the outputs of the flowmeters tested were generally within ±1% relative to the reference flowrates, although some errors as high as 5–10% were also observed. Most of the measurements from the turbine flowmeters and the positive displacement flowmeters were within ±0.4% of the reference flowrates.     

The consistency of pressure effects between three identical Coriolis flow meters

Coriolis flow meters are one of the most popular flow measurement technologies in the world today for high accuracy measurement of single-phase liquids, gases and even slurries. They are capable of measuring both mass and density directly and can also infer the volume flow. They can be installed in challenging process environments and have been successfully deployed with non-Newtonian fluids, high viscosity fluids, pulsating flows and even at extreme temperatures and pressures.However, it is known that operating most Coriolis flow meters at a pressure which differs from the original calibration pressure requires compensation else significant measurement errors will occur. Pressure compensation coefficients appear to vary by manufacturer, meter geometry and sensor material. Furthermore, the manufacturer published pressure compensation coefficients are not fully traceable. To date, there has not been sufficient research exploring the consistency of the pressure compensation for identical Coriolis flow meters.This paper presents the findings of a research conducted at the TÜV SÜD National Engineering Laboratory (NEL) Elevated Pressure and Temperature (EPAT) oil flow facility to investigate the pressure effect uniformity for matching Coriolis devices. The first stage of the experimental programme calibrated three identical DN80 Coriolis flow meters at a range of pressures with no pressure compensation applied. A pressure compensation coefficient was then derived from the data and the Coriolis meters were then calibrated at two alternative pressures to ascertain the robustness of the coefficients and whether the compensation could be extrapolated successfully.From the experimental results, it can be concluded that the pressure effect for the three DN80 Coriolis flow meters was extremely repeatable and consistent with a discrepancy of less than 0.025% between the devices at 80 bar. Whilst the mass flow was significantly affected by fluid pressure, the fluid density did not appear to be influenced. The pressure corrected results were also well within the manufacturer specification of ±0.1%.     

Wet gas metering technique based on slotted orifice and swirlmeter in series

Wet gas flow is a subset of gas–liquid two-phase flow, and wet gas metering is gaining considerable attention due to its importance in the nuclear, oil and gas industry. Wet gas meter based on slotted orifice and swirlmeter combination in series was designed and investigated. A wet gas measurement model with the simultaneous equations from the two flowmeters' correlations has been established, and then an iterative solution algorithm is given. The novel proposed approach predicts the gas mass flow rate relative errors within ±6% from 89.2% tested samples, and the gas mass flow rate relative errors within ±20% from all tested samples, which is accepted for many wet gas applications. Therefore, it implies that the proposed wet gas metering technique may be used to meter both gas and liquid flow rates for wet gas flow at the Lockhart Martinelli parameter X≤0.12.     

Hydrogen refuelling station calibration with a traceable gravimetric standard

Of all the alternatives to hydrocarbon fuels, hydrogen offers the greatest long-term potential to radically reduce the many problems inherent in fuel used for transportation. Hydrogen vehicles have zero tailpipe emissions and are very efficient. If the hydrogen is made from renewable sources, such as nuclear power or fossil sources with carbon emissions captured and sequestered, hydrogen use on a global scale would produce almost zero greenhouse gas emissions and greatly reduce air pollutant emissions.The aim of this work is to realise a traceability chain for hydrogen flow metering in the range typical for fuelling applications in a wide pressure range, with pressures up to 875 bar (for Hydrogen Refuelling Station - HRS with Nominal Working Pressure of 700 bar) and temperature changes from −40 °C (pre-cooling) to 85 °C (maximum allowed vehicle tank temperature) in accordance with the worldwide accepted standard SAE J2601. Several HRS have been tested in Europe (France, Netherlands and Germany) and the results show a good repeatability for all tests. This demonstrates that the testing equipment works well in real conditions. Depending on the installation configuration, some systematic errors have been detected and explained. Errors observed for Configuration 1 stations can be explained by pressure differences at the beginning and end of fueling, in the piping between the Coriolis Flow Meter (CFM) and the dispenser: the longer the distance, the bigger the errors. For Configuration 2, where this distance is very short, the error is negligible.     

Improved hydrogen consumption detection method with flow meter of fuel cell vehicle

With the vigorous development of fuel cell vehicles, the hydrogen consumption in the driving process of fuel cell vehicles has become a major concern of automobile manufacturers and fuel suppliers. However, the measurement accuracy of flow meter in hydrogen medium cannot meet the requirements. In this paper, computational fluid dynamics software is used to simulate the velocity distribution of water and hydrogen in Coriolis flow meter with different mass flow rates without tube vibration. Aiming at the measurement error of Coriolis flow meter, a flow calibration device based on sonic nozzle was designed, and the results of measuring hydrogen mass flow by Coriolis flow meter and thermal flow meter were calibrated. Finally, the accuracy of the calibrated flow meter for measuring hydrogen mass flow under stable and dynamic conditions is tested. The test results show that the accuracy of calibrated Coriolis flow meter for hydrogen mass flow is less than ±1%, which can meet the accuracy requirements of fuel cell vehicle hydrogen consumption measurement. This study provides an important reference for the application of flow meter method in fuel cell vehicle economic evaluation method.     

Design and development for amelioration of primary water flow standard and calibration systems

The present study outlines the efforts made to improve national primary water flow standards and calibration systems through design and development. The facility has been designed and developed in accordance with ISO 4185 standard in the flow range 0.03 m³/h to 650 m³/h to calibrate various types of flow meters up to DN200 (Nominal diameter) using 12 kg, 300 kg, 3000 kg, and 6000 kg weighing systems. In the flow range up to 530 m³/h, the expanded uncertainty in flow meter calibration in totalized mode is found to be ±0.01% to ±0.025% (k = 2), whereas it is ±(0.03–0.05) % (k = 2) up to DN200 size (test rigs) for mass flow rate (MFR) and volume flow rate (VFR) in the flow range 0.1 m³/h to 650 m³/h. The measurement uncertainty achieved is comparable to that of state-of-the-art water flow measurement capabilities available at numerous National Metrology Institutes (NMIs). Thus, the present designed and developed system at CSIR-National Physical Laboratory (CSIR-NPL) is a solution to maintain traceability to the users and industries.     

Measurements of the flow of supercritical pressure carbon dioxide through Venturi flow meter

The Venturi flow meter exhibits relatively low pressure loss, simple design, and low manufacturing costs. This study describes flow rates measurements for supercritical pressure CO₂ using the Venturi flow meter with pressure ranging 7.379–7.836 MPa and 5.84–7.272 MPa for in supercritical and gaseous regions, respectively. The flow rates of supercritical pressure CO₂ were accurately measured using a Venturi flow meter with a diameter ratio of 0.6468, having large and small diameters of 87.32 mm and 56.48 mm, respectively. The convergent and divergent angles were 21 $°$ ± 1 $°$ and 15 $°$ ± 1 $°$, respectively. The averaged discharge coefficient of 0.9975 was obtained, which was independent of the pressure ratio. Additionally, the expansion factors were also calculated using the experimental results, which ranged from 0.99976 to 0.99987 and 0.99945–0.99995 for the supercritical and gaseous regions, respectively. The experimental results showed that the Venturi flow meter had uncertainties ranging from 0.1 to 2.8%.     

Uncertainty analysis of the high pressure closed loop gas flow standard facility in NIM

High pressure air flow standard facilities, including the pVTt facility, sonic nozzle facility and closed loop facility were built in NIM at the end of 2014. The high pressure closed loop gas flow facility was the first closed loop facility in China. The system has 4 sets of 100 mm diameter turbine meters for the reference meters with a flow range of (40–1300) m³/h and a pressure range of (190–2500) kPa. To avoid uncertainties introduced during installation, the reference meters were designed to be calibrated in situ using the sonic nozzle facility. The uncertainty in the pressure measurement was reduced by installing an absolute pressure transducer in the manifold upstream of the reference meters, with differential pressure transducers used to measure the pressure drops across the reference flow meter and the test flow meter. The relative expanded uncertainty for the test meter can reach 0.20% (k = 2) as verified by comparison the sonic nozzle facility and the closed loop facility measurements.     

Coriolis mass flow metering for three-phase flow: A case study

Previous work has described the use of Coriolis mass flow metering for two-phase (gas/liquid) flow. As the Coriolis meter provides both mass flow and density measurements, it is possible to resolve the mass flows of the gas and liquid in a two-phase mixture if their respective densities are known. To apply Coriolis metering to a three-phase (oil/water/gas) mixture, an additional measurement is required. In the work described in this paper, a water cut meter is used to indicate what proportion of the liquid flow is water. This provides sufficient information to calculate the mass flows of the water, oil and gas components. This paper is believed to be the first to detail an implementation of three-phase flow metering using Coriolis technology where phase separation is not applied.Trials have taken place at the UK National Flow Standards Laboratory three-phase facility, on a commercial three-phase meter based on the Coriolis meter/ water cut measurement principle. For the 50 mm metering system, the total liquid flow rate ranged from 2.4 kg/s up to 11 kg/s, the water cut ranged from 0% to 100%, and the gas volume fraction (GVF) from 0 to 50%. In a formally observed trial, 75 test points were taken at a temperature of approximately 40 °C and with a skid inlet pressure of approximately 350 kPa. Over 95% of the test results fell within the desired specification, defined as follows: the total (oil+water) liquid mass flow error should fall within ±2.5%, and the gas mass flow error within ±5.0%. The oil mass flow error limit is ±6.0% for water cuts less than 70%, while for water cuts between 70% and 95% the oil mass flow error limit is ±15.0%.These results demonstrate the potential for using Coriolis mass flow metering combined with water cut metering for three-phase (oil/water/gas) measurement.     

Water collection techniques at very low flow rates including strong capillary effects

Milli-, micro- and nano-flow calibrations are important in several areas of pharmaceutical, flow chemistry and health care applications where volumetric dosage or delivery at given flow rates are crucial for the process. After developing a facility for the micro-flow range, METAS has developed a facility for flow rates from 50 nL/min up to 400 mL/min. The continuous collection of the flowing water into a beaker on a balance without having droplet formation for a continuous increase of the weighing values is a challenge (dynamic gravimetric method). This technique is often used to determine the flow rate over several orders of magnitude. In this paper, we describe the newly developed METAS piston provers and focus on the water collection techniques used for the flow rate determination of very low flow rates going as low as 50 nL/min by means of the dynamic gravimetric method. One water collection technique is to immerse the outlet needle into the water in the beaker. To reduce evaporation either a saturated environment is created or a layer of oil is added on top of the water. Another water collection technique is applied at the METAS facilities, where the outlet needle is positioned just over glass filters on top of the beaker to collect the water by means of a constant water bridge obtained independently of the flow rate. These two techniques are investigated for comparing the stability of the flow rate determination and the influence of the capillary forces acting due to the water or water-oil surface on the outlet needle and on the water bridge between the outlet needle and glass filters. The technique applied at METAS with the water bridge between outlet needle and glass filter reveals to be more stable for the flow rate determination and corrections due to capillary forces acting on the outlet needle can be neglected compared to the water collection technique with the immersed needle.     

Wet gas meter based on the vortex precession frequency and differential pressure combination of swirlmeter

A wet gas meter, based on combination of two dissimilar output signals from swirlmeter, i.e. the vortex precession frequency and the differential pressure of swirlmeter, was designed and investigated in low pressure wet gas flow. A wet gas measurement model with the simultaneous equations from the two correlations of swirlmeter has been established, and then the iterative solution algorithm is given. The proposed wet gas meter predicts the gas mass flow rate errors within ±8% from 91.3% tested samples, and the liquid mass flow rate errors within ±20% from 89.2% tested samples, which may be used to meter both gas and liquid flow rates for wet gas flow with X?0.12$X?0.12$. In view of installation, maintenance and cost, the proposed approach is cost-effective due to using only a flow sensor.     

Blow-down calibration of a large ultrasonic flow meter

Oil and gas production industries use large (diameter > 0.8 m) ultrasonic flow meters (USMs) to measure exhaust gas from flare stacks, emissions from smokestacks, flow of natural gas, etc. Since most flow laboratories do not have compressors with sufficient flow capacity (>10 kg/s) to calibrate large flow meters, calibrations are performed using the blow-down method where flow is generated by discharging high pressure tanks, leading to significant flow transients. We used an array of critical flow venturis (CFVs) in a blow-down facility to calibrate a large (D = 89.5 cm) 8-path ultrasonic flow meter. The flow transients associated with the blow-down process caused large spatial and temporal variations in temperature that dominated (40%–67%) the uncertainty budget. Our uncertainty analysis accounts for transient-generated uncertainties and provides guidelines for improving blow-down calibrations of large flow meters.     

Interference effects of three sonic nozzles of different throat diameters in the same meter tube

For calibration of a large capacity gas flow meter, a sonic nozzle bank may be used as a reference system. International standards (ISO9300:1990) allow installation of a single nozzle in a meter tube as a flow transfer standard. For multiple nozzles in a single tube, the effect of interference between sonic nozzles and the chamber wall must be measured to predict the discharge coefficient of a nozzle array from those of single nozzles. The interference effect between neighboring nozzles can be additional error sources in mass flow measurement. Sonic nozzles with three different throat diameters (d=4.3, 8.1, and 13.4 mm) were tested in a single meter tube in three geometrical arrangements. The mass flow rate was measured against a primary gas flow standard system. Three installation plates for sonic nozzles were made to vary the distance between nozzles and distance from the chamber wall. Discharge coefficients of the three individual nozzles were in agreement with the ISO recommended equation within ±0.2%. Discharge coefficients of the nozzle bank calculated from those of the individual sonic nozzle were the same as the direct measurements within ±0.098% at the 95% confidence level for all cases. For these experiments, the results were not influenced by the proximity of the tube wall or the interaction of the nozzles.     

Micro-flow facility for traceability in steady and pulsating flow

This paper describes a primary standard for liquid micro-flow, which covers the flow rate range from 1 ml/min down to 100 nl/min with uncertainties in the range from 0.1% to 0.6% (coverage factor 95%). To realize stable flow rates, METAS applies the principle of generating flow by means of a constant pressure drop over a capillary tube according to the law of Hagen–Poiseuille. The constant pressure drop is mainly possible due to the fact that the relative pressure at the outlet needle remains constant as the outlet needle is positioned just above the beaker collecting the water. The special beaker and the adjustments for the weighing zone to control evaporation will be discussed in the paper as well as measurement results from flow sensors and flow generators, which highlight the repeatability and the reproducibility of the facility.     

The Coriolis mass flow meter as a volume meter for the custody transfer in liquid hydrocarbons logistics

In recent years, the Coriolis mass flow meters (CMF), devices based on the Coriolis effect over a vibrating pipe, have developed better metrological performance and they are now a reasonable alternative for the custody transfer measurements. Nowadays, many custody transfer operations require measurement of the net volume (volume measured at a certain reference temperature) and, therefore, it is not feasible to use the CMF as a mass flow meter. However, the actual CMF can be used as net volume meters because they have special equipment to measure density and temperature, and a flow computer. In this work, firstly a mathematical simplification of the physical model is proposed for the CMF. We part from the dimensional analysis of the flow-phase relationship produced by the Coriolis force, the main physical principle behind these devices. A simplified formula is obtained and it permits identifying the magnitudes of influence of the CMF as a mass meter. Secondly, its metrological properties are characterized. For such purpose, a 4” straight tube commercial meter has been calibrated in volume, in the 50 to 165 m³/h range against a standard container and a bidirectional prover, employing gas oil and kerosene (JET-A1). These calibrations have turned out to be compatible with the ones performed by the manufacturer in mass and using water. Then it is verified that the CMF fulfills the requisites of the legal metrology: maximum error allowed, linearity and repeatability. Skewness is observed in the relative error (expressed in %) of the CMF and it has been researched to be due to systematic effects related to constructive parameters of the meter. Lineal correlation is verified between relative error and temperature, and between relative error and flow rate, with negative slopes of −0.03% °C⁻¹ and −0.001% h/m³ respectively.     

Modeling temperature effects on a Coriolis mass flowmeter

Coriolis mass flowmeters are used for many applications, including as transfer standards for proficiency testing and liquified natural gas (LNG) custody transfer. We developed a model to explain the temperature dependence of a Coriolis meter down to cryogenic temperatures. As a first step, we tested our model over the narrow temperature range of 285 K to 318 K in this work. The temperature dependence predicted by the model agrees with experimental data within ± 0.08 %; the model uncertainty is 0.16 % (95 % confidence level) over the temperature range of this work.Here, basic concepts of Coriolis flowmeters will be presented, and correction coefficients will be proposed that are valid down to 5 K based on literature values of material properties.     

Orifice plate meter wet gas flow performance

Orifice plate meters are often used to measure wet gas flows. Research into the wet gas response of the horizontally installed orifice plate meter is discussed in this paper. Consideration is given to the significant influence of the wet gas flow pattern, as this has previously been found to be relevant to the wet gas response of other differential pressure type flow meters. A wet gas flow correlation for 2″ to 4″ orifice plate meters has been developed from multiple data sets from four wet gas flow test facilities. This corrects the liquid induced gas flow rate error for a known liquid flow rate to ±2% at a 95% confidence level.