LNG workshop

Flow Metering

Peter Lucas and Nikola Pelevic

Page

Physical Properties

Flow metering

Contents of this module

• Flow meter technology

• Fluid properties and measurement

• Calibration methods

• Field comparison tests and calibration

• Regulation

LNG allocation metering skid in Qatar LNG Floating Production Storage Offloading

LNG truck fuelling LNG buses LNG bunkering

LNG custody transfer at regasification terminal

Flow metering applications

Flow metering technologies

Requirements flow meters

• Low pressure drop to avoid (local) boiling

• Minimal moving parts

• The ability to function in cryogenic conditions

• Proven performance

Common technologies

• Coriolis flow meters

• (Clamp on) ultrasonic flow meter

Other technologies

• Turbine

• Laser Doppler Velocimetry (Anemometry)

Coriolis

Principle

Principle

• U – bend excited at natural frequency Ω

• Coriolis effect: perpendicular deflection of

moving parts

• Twist angle is a measure for mass flow

rate

• Natural frequency is a measure for density

• http://www.youtube.com/watch?v=NpX9oX

sbOfw

Practice

• Two vibrating tubes

• Phase difference (∆t) is a

measure for mass flow rate

• Natural frequency is a

measure for mass

∆t

- Not sensitive to flow profile (although there are discussions

with respect to sensitivity to Re)

- Relative large pressure drop

- Proper mounting and support required (internal stress

impacts zero reading)

- Zero procedure before calibration required

- Water flow calibration reflects a lot of other liquids

- Big and very heavy: limited available pipe sizes

Coriolis flow meter

General considerations

- ‘Proven technology’, already used for small and mid scale

- Relative large pressure causing (local) boiling not really an

issue

- Avoid internal stresses (due to contraction)

- Correct for contraction flow meter (density reading)

- Correct for Young’s elasticity modules (density and mass flow

rate reading)

- Meter factor based on calibration with LNG

- Meter factor based on calibration with water and

temperature (extrapolation) model

Coriolis flow meter

Application to LNG

Ultrasonic flow meter

Principle

Principle

• Travelling sound wave is convected

(transported) with flow

• Difference between upstream and

downstream sound wave is measure for

velocity

• Flow rate is velocity times surface area

Practice

• Various paths to get a ‘good’

average for the velocity

- Low pressure drop

- Sensitive to sound wave attenuation (damping),

reflection and deflection (particles/ impurities, boiling)

- Minimal pipe size (3” ~ 4”)

- Sensitive to flow profile

- Enough upstream pipe length

- Multi path flow meter

- Flow conditioner

- Calibration inclusive upstream piping

Ultrasonic flow meter

General considerations

- Becoming more common for large scale, however as of yet only to

monitor the process

- Not suitable for small scale LNG custody transfer (< 3” ~ 4”)

- Very sensitive to (local) boiling

- Low pressure drop

- Correct for contraction flow meter

- Meter factor based on actual calibration

- Meter factor based on calibration with water and temperature

(extrapolation) model

Ultrasonic flow meter

Application to LNG

Flow metering

Contents of this module

• Flow meter technology

• Fluid properties and measurement

• Calibration methods

• Field comparison tests and calibration

• Regulation

Density

Pre

ssure

Temperature

1 bar

10 bar

100 K 120 K

410

kg/m3

500

kg/m3 450

kg/m3

LNG at -165 oC

(108 K)

• ~ 1% / bar

• ~ 0.4% / oC

Water at 20 oC

• ~ 0.1% / bar

• ~ 0.1% / oC

NG 20 oC

• ~ 100% / bar

• ~ 0.3% / oC

Density required for

• Mass to volume conversion (or vice versa)

• Line pack corrections

V

m

Volume

mass

Pressure and temperature

The pressure and temperature are needed to

- Determine the density (together with composition)

- Determine the probability of no boiling, potential local

boiling or boiling

- Correct the flow meter reading in case of a significant

dependency on pressure and/ or temperature

Temperature

Elements

- RTD (Pt-100)

- Thermo well

- Transmitter

- Read out

Challenges

- Heat leakage

- Slow process

- Point measurement

- Close to the flow meter Flow

Elements

- Membrane (fast process)

- Transmitter

Challenges

- Measure close to meter

- No cryogenic membranes available

- The pressure in a liquid column follows from:

- Correction required in case pressure sensor and tap point are not located at the same height

- (Point measurement)

hgp

Pressure

Flow metering

Contents of this module

• Flow meter technology

• Fluid properties

• Calibration methods

• Field comparison tests and calibration

• Regulation

Calibration

Prior considerations

• Type of flow meter (USM, CMF)

• Use of the flow meter in the field (ambient conditions,

installation effects, insulation)

• What can we expect from the calibration facility

• Traceability required

• Required uncertainty

Calibration methods

Methods

• Gravimetric

• Pipe prover method

• Master meter method

• Piston prover tank

Gravimetric method

Principle

Gravimetric method

Application to cryogenic fluids

Open collection tank not possible:

• Fixed connection between scale and world (VSL, NL)

• No connection

• Fast and spill free decoupling mechanism (VSL)

• Road tanker (JV, NK)

• ‘Tank within a tank’ (NIST/ CEESi, USA)

Gravimetric method

Fixed connection

Subcooling

by pressurization

Calibration

mode

Cooling down by

depressurization

Stabilizing

mode

scale

scaleMUTMUT

m

mm

Gravimetric method

Fixed connection - considerations

• Permanent set up

• Fixed connection causes additional forces on

balance which are difficult to predict

• Steady and good control of flow conditions

• Continuous signal during calibration

• Small scale Qm = 0.5 - 4 kg/s

• Uncertainty 0.15 ~ 0.2%

LNG workshop - module 2C

Gravimetric method

Road tanker (no connection)

1 - Loading

of LNG road

tanker

2 – Weighing

full LNG road

tanker

4 – Weighing

empty LNG

road tanker

3 -

Unloading of

LNG road

tanker

Unloading

LNG road

tanker

Test Coriolis flow

meters Storage tank

scale

scaleMUTMUT

m

mm

Gravimetric method

Road tanker - considerations

• Temporarily set up

• Mass changes road tanker difficult to predict

• Unsteady flow and no control of flow conditions

• Only start and end mass available

• Uncertainty on mass ≤ 0.2%

Gravimetric method

‘Tank within tank’ - principle

Load cell

Calibration

weights

Weighing

tank

Gravimetric method

‘Tank within tank’ - considerations

• Permanent setup

• Steady and good control of flow conditions

• Buoyancy force difficult to predict

• Small scale Qm = 0.5 - 5 kg/s

• Uncertainty 0.12 ~ 0.15%

Master meter method

Principle

Master meter method

Considerations

• Permanent set up

• Not a primary standard

• Bootstrapping can be used to get traceability for

larger flow rates

• Good control of flow conditions

• Uncertainty follows from primary standard

LNG flow calibration standard (design schematics)

Front view

Flow metering

Contents of this module

• Flow meter technology

• Fluid properties

• Calibration methods

• Field comparison tests and calibration

• Regulation

Coriolis flow meter

Flow metering accuracy small scale

A

B

C

D Right scale

Field applications

Small scale custody transfer – results

- Good

reproducibility

- Good

agreement

From Mortensen and Kolbjørnsen, Field tests for the comparison of LNG static

and dynamic mass measurement methods, JV, 2013

Field applications

Large scale custody transfer – set up

Comparison volume USM and tank gauging1:

• Ship tank gauging based on GIIGNL

• Terminal tank gauging based on GIIGNL

• Volume measurement using an USM (dual path, 32”)

• Part of ‘Metrology for LNG’

• Location: Enagás Terminal Cartagena

• Date: April 2011 to April 2013

• Difference defined as: tank

tankUSM

V

VV

1) Benito et al, presented at LNG conference, Delft, 2013

Field applications

Large scale custody transfer – results

USM vs tank terminal USM vs tank ship

- Poor

reproducibility

- Significant

deviation

Flow metering

Contents of this module

• Flow meter technology

• Fluid properties

• Calibration methods

• Field comparison tests and calibration

• Regulation

Page

• Law states that all transactions based on mass

(NAWI) or volume of liquids (MID) must be metered

with approved meters

• B2B transactions regarding gaseous fuels which are

not intended for residential, commercial or light

industrial use do not require MID approved meters

• The definition for light industrial use differs from member

state to member state

• E.g. in the Netherlands, limit is given by the condition that

the amount delivered > 170.000 m3(n)/year or a connection

to the local grid > Qmax 40m3/h

Legal requirements for Custody

Transfer B2B or B2C

Page

Measuring system

volume/mass of cryogenic liquids, EU

Into the market:

- The MPE on the complete metering system is 2,5%

(incl. the flow meter MPE set at 1,5%)

- The return gas flow should be seen as part of the

metering system and as such should also fit within the

2,5% MPE

In use: MPE for measuring system (National legislation):

- 2,5% with exception of Denmark, Iceland, Romania,

Slovakia, Slovenia and Switzerland. MPE > 2,5%

LNG Custody Transfer Study P 38

Page

LNG Custody Transfer related standards

LNG Custody Transfer Study P 39

LNG Metrology/ custody transfer

ISO 12991'12

construction

requirements for

refillable fuel

tanks for LNG

ISO 18132-2'11

verification testing

of automatic level

gauges

ISO /DIS 12614 Part 1 -18

different issues, reqrmnts, Test

methods, Safety issues, Temperature

sensors etc

ISO 8943'07

the continuous

and intermittent

sampling of LNG

Design metering systems, test

protocols

GIIGNL

Int. Group

importers of LNG

custody transfer

handbook

ISO 18132-1'11

calibration and

verification of

automatic tank

gauges

ISO 10976'12

Procedure for

custody transfer

on board ships

ISO /DIS 12617 fuelling nozzles and

receptacles constructed

GERG 2008

Equations of State

for NG / LNG

NFPA 57

design,

installation,

operation,

maintenance of (LNG) engine fuel

systems and

dispensers

API 521

pressure-relieving

and vapour-

depressuring

systems

EU MID

2004/22/ec annex 1&5

European Legal Metrology

OIML Int. Org. For

Legal Metrology

OIML R81

Dynamic

measurement

devices for

cryogenic liquids

However: No

Massflow meters

OIML R117

Dynamic

Measurement

Systems Liquid

other than Water

Combine R81,105,117&solve

inconsistencies

OIML R105Massflow meters

However non cryogenic

Interpretation by NOBO

MID certificateOIML testreports

GAP/not ready

Large/Mid scale Applicable in general Small scale

ISO/DIS 16924 designing LNG filling stations/ dispenser

systems

Legend

EU Directive

23/2009/EG

Class III type

approved

weighing

instruments (non

automatic

weighing

instruments:

NAWI

AGA Report No.5

NG energy measurement

ISO 6976:1995

Natural gas,

Calculation of

calorific values,

density, etc.

NG Metrology/ custody transfer

ISO 6974:2012

Natural gas,

composition , gas

chromato graphy.

VSL

PO Box 654

2600 AR Delft

The Netherlands

T

F

E

I

Erik Smits

E

+31 15 269 15 00

+31 15 261 29 71

info@vsl.nl

www.vsl.nl

fsmits@vsl.nl

Peter Lucas:

nl.linkedin.com/in/lucaspeter

VSL group:

http://lnkd.in/Bif3Sy

VSL Fluid Flow Metrology group:

http://lnkd.in/DF2zJx

Questions ?

Peter Lucas

E plucas@vsl.nl