LNG sampling and composition measurement

Jianrong Li (VSL)

LNG III Training

26 October 2018, Aberdeen, Scotland

Measurements involved in LNG custody transfer

2

Energy metering setup (simplified)

p

T

GC

Flow computer

Density

Calorific value

Wobbe number

Methane number

Speed of sound

…

Quantity (v, m)

Pressure

Temperature

LNG LNG

Composition

LNG composition measurement – What is important?

3

Accurate sampling Representative & Homogeneous

Accurate vaporizing

(for GC method)Complete and Instant

Conditioning of the

gaseous sampleConstant Pressure & Temperature

Accurate

measurementsAccurate method with lower uncertainty

LNG sampling precautions

Sampling is the most critical part of the LNG measurement chain

Avoid changing composition in every step

Control P, T to get representative sample

Locate sample probe at points where LNG is in a sub-cooled condition

Ensure LNG remains sub-cooled in sampling pipe during sampling

(pipe with good insulation, as short as possible, diameter as small as possible)

Guarantee complete and instant vaporizing (sufficient heat supply)

4

LNG sampling period

5

Sampling during constant flow rate…

LN

G f

low

rate

Time

Sampling period

LNG phase diagram

6

Reference:

1. Markus Richter, PhD thesis, Ruhr-Universität Bochum, Germany.

2. Angel Benito and Enagás, S.A., Accurate determination of LNG

quality unloaded in Receiving Terminals: An Innovative Approach.

LNG composition

7

Methane

Ethane

Propane

n-butane

iso-butane

C5 +

Nitrogen

Other impurities

Reference gas composition

8

Reference gases:

Components Mol fractions

(% mol/mol)

Nitrogen 0.15 - 1.5

Methane 78.5 - 99.7

Ethane 0.1 - 14

Propane 0.03 - 4

iso-Butane 0.01 – 1.1

n-Butane 0.01 – 0.9

iso-Pentane 0.005 – 0.15

n-Pentane 0.005 – 0.15

Reference gas composition should be

selected to cover low – medium – high

fractions

LNG composition measurement techniques

9

Gas Chromatography Raman Spectroscopy

https://teaching.shu.ac.uk/hwb/chemistry/tutorial

s/chrom/gaschrm.htm

http://www.horiba.com/scientific/products/raman-

spectroscopy/raman-academy/raman-faqs/hardware-

required/

Gas Chromatography vs. Raman Spectroscopy

10

Gas Chromatography

Currently used in ISO standard

Measure gas phase

Require sampling and vaporizing steps

before analysis (higher cost ?)

Raman Spectroscopy

Under developement

Can measure liquid & gas phase

Avoid sampling and vaporizing steps before

analysis (direct, lower cost ?)

Picture source: Shell Global Solutions

Gas Chromatography

11

Columns

Packed columns

− High capacity

− Good separation properties

− Relatively short in length

Capillary columns

− Low capacity

− Greater variety of columns

− Length (25 – 60m)

12

DetectorsThermal conductivity detector (TCD)

− Sensitivity varies between components

− Linear over 1-2 decades (µTCD)

− Capable of detecting non-combustibles

Flame Ionisation Detector (FID)

− Very sensitive

− Linear over 3-4 decades

− Detects only hydrocarbons

− Signal grossly proportional to carbon number

13

Gas chromatogram

14

Integration of peaks

min30 35 40 45 50

pA

4.8

4.9

5

5.1

5.2

5.3

FID1 A, (2006\20060901\004F0404.D)

46

.84

0

FID1 A, (2006\20060901\006F0604.D)

46

.84

5

FID1 A, (2006\20060901\010F1004.D)

46

.78

2

FID1 A, (2006\20060901\012F1204.D)

46

.84

3

15

Calibration standards

Three main types

− Primary Reference Materials (PRM)

− Certified Reference Materials (CRM)

− Working Reference Materials (WRM)

From PRM to WRM

− Uncertainty usually increases

− Stability may be less well established

In order to be an Reference Material

− Values must be metrologically traceable

− Uncertainty must be stated

16

Metrological traceabilityComposition measurements should be traceable to SI units

Composition can be expressed as

− Amount fractions (mol/mol)

− Mass fractions (kg/kg)

− Volume fractions (L/L)

− Concentration (g/L)

− Molar concentration (mol/L)

− …

Ultimate realisation by

− Gravimetry

− Volumetry

Pure substances

− Known impurities (identity and composition)

− Known molar mass

17

LNG sampling and composition measurementfacilities at Maasvlakte

18

Reference

Sampler &Vaporizer

LNG loop

LNG based calibration gases

Commercial

Sampler &Vaporizer

Reference Result

Qua

ntity

(uni

t)

Service

Measurement 1

(Reference)

Measurement 2

(Result)

LNG reference sampler and vaporizer

19

Progress in LNG sampling and compositionmeasurement tasks at Maasvlakte

20

Reference sampler and vaporizer

installed

MUSTANG sampler and vaporizer

installed

Commissioning tests planed for

Jan/Feb 2019

Experimental tests will be followed

Composition measurements (GC vs.

Spectroscopy)

Thank you for your attention!

Questions??

Contact details:

VSL

Thijsseweg 11

2629JA Delft

The Netherlands

T +31 15 269 15 00

F +31 15 261 29 71

E info@vsl.nl

I www.vsl.nl

Dr. Jianrong Li

Tel. +31 15 269 1573

Email: jli@vsl.nl