September 2008

Ultrasonic the choice

Natural gas has emerged as an important source of energy, particularly for electric power generation. However, the major markets for natural gas are far away from the major gas reservoirs.

ARC Advisory Forum reported many pipeline projects are underway. To traverse intercontinental distances, converting the gas to LNG is the most economical alternative.

Flow measurement in LNG applications poses many challenges.

Flowmeters used for allocation and custody transfer applications should have no moving parts, the ability to perform in cryogenic applications, proven reliability and accuracy in liquid custody transfer applications, and built-in diagnostics.

Flowmeters used in LNG applications should also have low-pressure drop, to avoid vaporization of the LNG. As in any custody transfer application, flow measurements also need to be verifiable with check meters or provers.

Two different meter types satisfy these requirements for LNG applications: Coriolis and ultrasonic.

Ultrasonic flowmeters have a straight flow path and do not obstruct or impede the flow of gas or liquid through a pipeline, resulting in essentially no pressure drop and reduced risk of vaporization and the resulting multiphase fluid, which makes it difficult to measure and can introduce significant measurement uncertainty.

They are also available in larger diameter sizes than Coriolis meters, making them a more cost effective alternative for LNG applications.