When considering metering solutions for custody transfer applications, there are several potential options for Liquefied Natural Gas (LNG) flow measurement.
Differential pressure meters and turbine meters are the oldest and most well-established methods; however, they are often not suitable for evolving LNG measurement needs. Older technologies have difficulties which include significant pressure drop in the flow line, limited flow range, and requirements of long, straight runs of pipe upstream and downstream. But the biggest challenge for these methods is the variable composition of LNG. Because LNG can and will vary in composition, it is not possible to assign default properties at the reference conditions (i.e., boiling point) to convert between volume and mass as is commonly done with purity cryogenic liquids.
Ultrasonic meters and Coriolis flow meters are the two ‘newcomer’ technologies, and these methods have already caught the attention of an industry in need of greater accuracy and flexibility. While ultrasonic has been widely accepted for use in metering natural gas, they are still in the early stages of demonstrating good measurement of LNG. Coriolis meters, on the other hand, have had well-established success in measuring both gaseous-phase natural gas and LNG.
Advantages of Coriolis Flow Meters
Coriolis metering presents several distinct benefits over other measurement options.
● Direct Mass Flow and Density Measurement
Coriolis meters measure quantity absolutely, unaffected by changing fluid properties such as viscosity, density, temperature, or pressure. When the flow rate measurement is made in direct mass units, there is much less uncertainty in quantifying net energy content delivered.
While traditional volumetric meters require either pure fluids or density-compensation correction systems to adjust the actual measured volume flows to reference conditions, this conversion adds uncertainty. Coriolis meters eliminate the extra complication and save costs because, by directly measuring mass, there is no need for density compensation.
Reducing the conversions and compensations for flow measurement lessens the chance of error and variability. Coriolis meter direct mass-flow measurement is a more straightforward way to calculate energy content, which inherently boosts measurement confidence.
● No Special Piping Requirements
Micro Motion Coriolis meters do not require special installation procedures, flow straighteners, or specific lengths of straight pipe for correcting the fluid flow profile. These excessive accessory requirements used to overcome the limitations of turbine, ultrasonic, and differential pressure systems are costly and cumbersome. By eliminating the external piping requirements, the costs and size of skid-based measurement systems are reduced. Instead, Micro Motion Coriolis meters enable a simple, cost-effective loading terminal design.
● No Calibration Drift
Unlike other technologies, Coriolis meters do not experience a drift in performance or calibration over time when operating on LNG. Micro Motion Coriolis meters hold their calibration for years at a time without needing maintenance. No intrusive moving parts means nothing to wear out or be sensitive to changing fluid composition.
In the case of LNG metering, traditional is not better. Coriolis’ modern technology offers benefits over outdated approaches. For direct measurement and a more streamlined system, Micro Motion Coriolis meters have proven the most reliable system for custody transfer applications.