Qualification of Ultrasonic Flow Meters for Custody Transfer of Natural Gas Using Atmospheric Air Calibration Facilities

摘要

Without the ability to measure flow accurately at atmospheric pressure, it is unlikely that this metering technology could have been developed without external help from a public agency or distribution concern. Even with low-pressure operation, the project was heavily dependent on computational physics not only for the fluid dynamics, but the acoustics and digital signal processing that completes the meter. Such modeling will become more important in the future, as standards are developed to use air as a calibration medium. As large ultrasonic meters outgrow all measurement facilities, a solid understanding of the principles will be required in order to use meters without calibration. Presently, low-pressure air calibration is only advisable in large pipe sizes where Reynolds mismatch can be minimized. The uncertainty analysis does show that it is possible to build meters with flow-weighted, mean uncertainties less than 0.4% without calibration, if installation guidelines are observed. Where we go from here, depends on how the natural gas international community deals with the definition and measurement of uncertainty, absolute or relative, and how this uncertainty propagates out to actual energy based unaccountables at the final point of delivery.