LNG Energy Determination for Custody Transfer: TrueValue

ASaP and Orbital joined forces and have developed an LNG Energy Determination solution using the GasPT product and the ASaP Phazer – LNG Probe-Vaporizer to provide accurate and continuous measurement of LNG properties so that operators can accurately and reliably account for every drop of LNG during transfer.

Continuous Measurement with True Value™

LNG Energy Determination Orbital + ASaP = TrueValue

Background of LNG Energy Determination

This note has been prepared for the purpose of illustrating the benefits of reliable, continuous measurement of LNG during loading and unloading of vessels for custody transfer.

In many countries in recent times there has been a significant shift from a single source of indigenous natural gas towards multiple sources of gas from new inter-connector pipelines and shipped LNG.  The terminal operations for LNG import and export require accurate monitoring of gas quality and flow at numerous points in order to satisfy energy accounting standards and trading contracts.

The GIIGNL equation to calculate net energy transferred is:

E = (V.ρ.GCV) – Egas displaced in tank ± Egas to Engine Room

Accurate measurement of the LNG density (ρ) and Gross Calorific Value (GCV) is therefore critical and these parameters will vary as loading/unloading operations proceed and boil-off gas is released.

LNG Energy Determination for Custody Transfer

Analysis of LNG

Cycle time of traditional GC analyzers is several minutes.  This can be an issue if gas is being exported out of specification and needs to be diverted rapidly for further process treatment. Furthermore, for accurate accounting when metering the LNG during transfer, the LNG flow data needs to be matched to instantaneous energy data as closely as possible; a GC cannot achieve this as it leaves significant data gaps between cycles.

Orbital GasPT2 Natural Gas Properties Transmitter BTU analyzerAlternative technologies like the GasPTi exist which is capable of providing the accuracy required for custody transfer applications within 10 seconds. Like a GC, the GasPTi does NOT require a permanent supply of support gases, such as carrier gas, calibration gas, instrument air, etc. Its compact footprint as well as significant infrastructure to protect the device from the hazardous area and marine environment.

Solution for LNG Energy Determination

True Value™ is a unique integration of LNG sampling, LNG vaporization, gas conditioning and gas analysis which provides rapid and accurate monitoring of gas quality, with T90 response time less than 10 seconds and to a CV error of less than ±0.5%.  The compact Phazer – LNG Probe-Vaporizer is linked to the system to ensure a homogenous gas mixture at its outlet. The system mounts directly onto a pipeline or can be post-mounted nearby with a short gas sample line.  Best response and accuracy is gained from pipeline mounted surfaces.

Depending on the application, GasPTi signal outputs can be either serial, Ethernet or analogue interfaces.  Calorific Value (Gross and Net), Relative Density, Wobbe Index, Compressibility, Methane Number, Motor Octane Number and others are all standard physical properties which are output from GasPTi.

In addition to ATEX, IECEx and CSA approvals, American Bureau of Shipping type approval has been obtained for GasPT marine LNG tanker applications.

The Zone 1 True Value™ has been developed specifically for LNG applications to improve speed of response and accuracy.

ASaP Phazer LNG Probe-Vaporizer Photo 2

Example LNG Energy Determination Applications

Project Company Location Application
Isle of GrainNational GridUKImportation terminal
South HookQatar PetroleumUKImportation terminal
DragonBG GroupUKImportation terminal
Teesside GasPortExcelerateUKFloating regasification
Cryostar MarineCNOOCChinaLNG tankers
KantoTokyo GasJapanImportation terminal
KansaiOsaka GasJapanImportation terminal
GwangyangPOSCOS.KoreaImportation termina

LNG Applications

Gas quality monitoring on LNG export and importation terminals:

  • LNG metering
  • Export sales gas
  • Boil-off gas recondensers inlet and outlet
  • Fuel gas for revaporisation heaters

Gas quality monitoring on marine LNG tankers:

  • Boil-off gas prior to reliquefaction
  • Ship-to-ship transfer

Benefits of True Value™

  • Proven technology.
  • Full compliance with ISO 8943.
  • Successful testing against EN 12838.
  • Sub-cooled cold section insures 100% LNG sample transport to Vaporizer section.
  • Integrated Zero Dead Volume™ accumulator.
  • Unique flash vaporization and flow control design.
  • No moving parts and practically maintenance free.
  • Phazer – LNG Probe-Vaporizer complements the GasPTi-LNG instrumentation to provide LNG sampling, vaporization, conditioning and analysis in one small, easily installed system which will operate at low LNG line pressure.
  • Measures at LNG pressures from 0,5 BarG.

Conclusion

Traditional GC analysers and vaporisers may have issues with speed of response and gas sample partial vaporisation.mTrue Value™ provides vaporization, gas sampling, gas conditioning and analysis to give rapid and accurate CV data which can be used for custody transfer, process control and alarms on LNG terminals.

Publications

A New Method for LNG Energy Determination

International Gas Research Conference, Rio de Janeiro 2017.

GasPTi – A New Method for LNG Energy Determination

LNG 18,    Perth 2016

Experiences in Gas Quality Monitoring in Natural Gas Markets

IGU World Gas Conference, Paris 2015

Put to the test Field study of LNG probe-vaporizers, LNGIndustry July, 2016.

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