Benefits of Dynamic Metering in LNG Custody Transfer

by | Aug 18, 2015 | Flow, Measurement Instrumentation | 0 comments

The LNG industry has a bright future, considering the demand for clean-burning natural gas. And as the LNG fleet and terminal network grows to meet demand, the technologies must be developed to improve operations by trending away from unstable measurement variables and introducing ways to more accurately meter.

The complex algorithm used to calculate the energy value of LNG involves sampling, measuring the quantities and calculating the derived quantities. This is a major metrological challenge, as these measurements must take into consideration different scenarios and parameters such as tank shape, possible deformation, tank table errors, surface conditions, cargo boil-off gas rates and a cargo’s equilibrium state.

Ultrasonic meter measurement techniques are rapidly being enhanced to solve for these challenges. Namely, the Rosemount 3818 LNG ultrasonic meter, is designed to reduce flow measurement uncertainty across the LNG value chain. Able to overcome most of the LNG dynamic measuring problems, this latest ultrasonic meter technology has already been accepted by the industry as a reliable solution for improving accuracy.

The best uncertainty value under ideal measurement conditions is 0.5 percent. However, in normal operations this value can increase to as much as 0.9-1.0 percent uncertainty. So, when it comes to measurement techniques, every improvement is important.

Some of the most significant benefits of ultrasonic meters are:

  • Mitigated pressure drops
  • Operating at relatively low velocities
  • Remotely mounted electronics avoid proximity to pipe
  • Integral insulation to facilitate installation of user’s primary insulation
  • Anticipated uncertainty as low as 0.3 percent
  • Included proving system for meter calibration
  • Increased operational efficiency
  • Reduced reactive maintenance
  • Increased capital efficiency
  • Improved measurement system reliability

The most sophisticated models of ultrasonic meter technology have also overcome many of the problems associated with earlier versions, such as hot spots and large pressure drops. Even so, these problems are inherent to the unstable nature of LNG storage and transportation.

Another effective way to overcome problems with traditional measurement techniques is to install additional flowmetering points. This can improve operational efficiency as well as reduce unaccounted-for quantities.

With a complete measurement system – one that uses technologies like advanced diagnostics, wireless solutions, and new-generation control systems – issues in sampling complexity and high maintenance costs are reduced as well.

Challenges in metering and measuring LNG are associated with strong fiscal risks; however, dynamic metering allows increased accuracy and reliability with a reduction of this risk. The growth of the industry requires innovation, and is leading companies to embrace new facilities while looking for opportunities to exert changes in typical dynamic methods. The most successful future LNG projects will consider changing to dynamic methods per the API custody transfer standard for liquid transfer.

Check out the full LNG custody transfer white paper for more information on this topic.

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The opinions expressed here are the personal opinions of the authors. Content published here is not read or approved by Emerson before it is posted and does not necessarily represent the views and opinions of Emerson.

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