1. Dynamic Measurement Solutions in LNG Custody Transfer
by Drew S. Weaver, P. E.
Director, Fluid Mechanics & Global Flow Labs
Daniel Measurement and Control, Inc.
Houston, Texas USA

2. Introduction This presentation will cover:
Update on LNG news & facilities
Challenges and goals for LNG measurement technology
Current volume & flow measurement technology and methods
Industry research and developments
Validation methods, standards and testing
Dynamic flow measurement solutions

3. LNG Basics
LNG (Liquefied Natural Gas): natural gas that is cooled to -162 °C (-260 °F) for change to a liquid state; storage is at essentially atmospheric pressure
Volumetric change: the liquefaction process reduces NG volume approximately 600 times – envision the volume of a beach ball reduced to the volume of a ping-pong ball !
Volume reduction allows international transport via cargo ships
After offloading / delivery, the LNG is heated to gaseous state for transportation via pipelines for distribution to power plants, processing plants, industry and homes

4. LNG Distribution Chain
Fuel stations (ship and road transport)
Ships
Locomotives
Trucks
Receiving terminal
Small ship
Road tanker
Buses
Ocean tanker
Pipeline gas
Distribution to Industry, Power & Process
Photos courtesy VSL

5. LNG News Topics 2015
“…unexpected plunge in the price of crude oil is throwing the energy markets in turmoil.”
“…could force energy companies to defer $150 billion in future projects.”
“…not expected to cause much near-term damage to LNG projects in the U.S. despite the fact that he price of oil is an important component in LNG prices around the world.”
“…pivotal year for America’s budding LNG industry.”
Source: LNG News 25 Jan 2015 / Wood Mackenzie
“The only constant in the liquefied natural gas industry again appears to be change – unpredictable change”
Source: Law February, 2015

6. LNG Facilities Worldwide
Existing LNG terminals
Africa – Algeria, Angola, Egypt,
Equatorial Guinea, Nigeria
Americas – Peru, Trinidad & Tobago
Asia - Brunei, Indonesia, Malaysia,
Russia
Australia
Middle East – Abu Dhabi, Oman,
Qatar, Yemen
Norway
USA – Kenai, Alaska
Major World areas importing LNG
- Asia, Europe, South America
Source – BP Statistical Review of World Energy 2006/2012

7. USA LNG Export Terminals Under Construction
Major US projects & expected startup year:
Sabine Pass, Louisiana (Cheniere)
Cove Point, Maryland (Dominion)
Freeport, Texas (Freeport LNG)
Cameron, Louisiana (Sempra Energy)

8. Challenges in LNG Measurement
There is concern that the basis for energy content uncertainty of transferred LNG (typically taken as ±0.5% to ±0.6%) may underestimate the true magnitude of measurement uncertainties
Dynamic methods of liquid flow measurement, gas flow measurement, product sampling, and composition determination conventionally applied in the energy industry may be utilized to reduce the measurement uncertainties at the LNG terminal as they relate to terminal balances
Measurement uncertainties for dynamic meters and flow measurement equipment utilized for LNG service may lead to reduced lost-and-unaccounted-for quantities at delivery or receipt terminals

9. LNG Energy Measurement Overview
Primary component LNG is methane
Natural gas liquefied by refrigeration process below -160° C at atmospheric pressure at export terminal
Transported to import terminals in ships
After storage, re-gasified for supply to pipeline distribution network
Measurement of LNG delivered to or received from ship’s tanks is currently made in the form of energy transferred*
The G.I.I.G.N.L. (International Group of Liquefied Natural
Gas Importers) Handbook reports inaccuracies involved in
the measurements of the parameters given in equation (1)
above and the overall inaccuracy in determining the LNG
energy transferred.
*Source: Flow Measurement Guidance Note No. 53 Liquefied Natural Gas Flow Measurement Technologies. NEL, East Kilbride, UK

10. LNG Volume Measurement Methods
Static Measurement Method
Tank Gauging (Shipboard /Onshore)
Level to volume correlation
May be affected by boil off vapor, stratification of liquid, vessel motion
Estimated uncertainty may be higher than desired

11. Challenges with LNG Tank Measurement
Temperature Measurement in Static Tanks
Loading and offloading of ships can involve volumetric rates of 5,000 to 15,000 m3/h
A 0.5°C change in the measured temperature can cause a 0.17% change in the calculated density
Small differences in liquid temperature of only a few tenths °C between cargo tanks have a detrimental influence on the combined standard uncertainty and overall uncertainty of the calculated energy transferred

12. Dynamic LNG Flow Measurement Technology – Primary Metering
Venturi (differential)
Coriolis (mass basis)
Ultrasonic (transit time basis)

13. Dynamic LNG Measurement
Dynamic measurement utilizes a flow meter at a designated point in a transfer line along with pressure & temperature measurement
Flow rate measurement requires:
Primary element (flow meter)
Upstream & downstream meter run
P & T instrumentation
Calibration or proving methodology T P S

14. Challenges - Dynamic LNG Measurement
LNG storage & transport in a state near its boiling point
Fluid state may change to two phase (liquid & gas)
Excessive pressure drop in the system
Reduced bore flow meters (full bore optimum)
Flow conditioners
Thermal hot spots on the pipeline

15. LNG Density and Gross Calorific Value
Direct measurement with a densitometer is not usually applied for LNG
Density is derived from gas composition and equations of state (e.g. Klosek – McKinley model)
Reliable and representative samples are critical to determine calorific value
Representative sampling over batch delivery
Vaporization of the fluid to maintain composition ratios
Conditioning of the gas sample
Transport to the analyzer
Analysis by Gas Chromatograph GC is common to traditional and new methodology

16. Uncertainty / errors contributing to “lost and unaccounted for” in LNG measurement
Dynamic flow measurement eliminates uncertainties associated with:
Error in tank volumes related to tank manufacturing and strapping tables
Changes in tank volumes due to continual temperature cycling
Errors in terminal inventory created by LNG transfers during tank measurements
Errors related to ship loading and offloading (list, trim and tank corrections)
Dynamic flow measurement of LNG on rundown lines and jetty lines complements existing tank gauging technology for Custody Transfer

17. Validation of Dynamic LNG Measurement
Weigh system
Lab facilities generally used for factory calibration of meters; difficult to apply for field measurement devices
Master meter as Reference Standard
Transfer standard method of meter calibration, can be affected by site conditions, requires periodic re-calibration of master meter by a traceable standard
Direct proving of the Flow Meter
In-situ field calibration of meter by comparison to a traceable volumetric standard; does not require short-term re-calibration of prover in the field

18. Industry Research – LNG
VSL (EMRP) in the Netherlands and other organizations (ISO, CEN, TUV, NEL, PTB, GIIGNL) are conducting research for development of measurement standards
Primary LNG mass flow standard operated and validated in 2013 at Gasunie Peakshaver - photos courtesy VSL, The Netherlands February 2015

19. LNG Direct Proving R & D
Engineering tools - CFD flow simulation & testing
Quantify & visualize flow phenomena
Simulations before lab testing
Testing to validate selected design
LNG proving concepts based on industry applied Custody Transfer prover designs:
Comparison of meter output to traceable standard
Meter factor from proving results applied to correct meter output
Correction of field measurement results to agreed or delivery contract conditions (standards)
Piston displacer with seals designed for application
Bi-directional operation - displacement prover
Previous experience with refrigerated butane or propane service at -46° C (-50 °F)

20. Previous Direct Proving Experience
Early 24 inch piston prover
Liquid propane -46 °C (-50 F°)

21. LNG - Direct Proving R & D
Prover pipe calibration section – design details
Volume for reference standard (distance between displacer detectors for selected prover pipe size)
Piston displacer w/ cryogenic seals
Materials for cryogenic service
Internal surface finish
Piston pre-run (run up) allowance
Piping configured for bi-directional piston movement
Flow diversion method
Bypass for end of piston travel
Configuration to eliminate “hot spots”
Purge /drain / vent lines and cool-down method

22. LNG - Direct Proving R & D
Detailed design requirements:
Piston
Free moving - fluid driving force
Weight minimized
Materials for cryogenic service
Position sensing – target ring
Seals
Cryogenic service materials
Operation with low driving force (low differential pressure)
Dual seals
Seal validity check necessary (double block & bleed)
Service life critical

23. LNG - Direct Proving R & D
Displacer position detection:
Non-contact & non wetted
Sealed 304 SS
Rated -364 F to 428 F (-220 C to 220 C)
Stainless steel MI cable extends through pipe insulation to ambient connection inside junction box
Detection of piston position by interaction with special target ring on piston

24. LNG - Direct Proving R & D
Testing of critical components
LN2 at -196 °C (-320 °F)
Linear Piston Position
Ambient and LN2
temperatures
Piston distance, repeatability & hysteresis using laser
Piston velocity range
Calibration at prover piston velocity equivalent to meter operational flow rates

25. LNG - Cryogenic Meter Prover Concept
Fully insulated

26. LNG Metering & Proving Module Concept
Insulation not shown

27. Summary - LNG Measurement
Changes in crude oil pricing affects LNG Trade
Reduction of measurement uncertainty is needed
LNG sampling & analysis is critical
Challenges of current and developing methodology are being solved
Dynamic measurement complements tank volume measurement
Importance of a traceable calibration system for dynamic flow measurement