improved reliability in natural gas energy measurement ... · improved reliability in natural gas...

Improved Reliability in Natural Gas

Energy Measurement with the Revised

ISO 10723 Standard

Gerard Nieuwenkamp - VSL

Improved reliability in natural gas

energy measurement with the

revised ISO 10723 standard Gerard Nieuwenkamp

VSL Research and Development

VSL/CEESI: 3rd European USM workshop

Noordwijk, 17 March 2015

VSL - Beyond all doubt 2

Natural gas measurement


Energy (MJ) = Quantity (m3) x Quality (MJ/m3)

quantity = flow measurement

quality = calorific value (H) composition

gas chromatography

Error / uncertainty in both parts have the same impact!!

Natural gas energy measurement - Why measuring flow and composition

Contribution of uncertainty sources


With: Uflow = 0.2% rel.

UH = 0.5% rel. } Uenergy = 0.54% rel.





To reduce Uflow from 0.2% to 0.1% can be big investment

To reduce UH from 0.5% to 0.2% can be a much smaller investment

Natural gas metering

Heat Exchanger

16"

16"

30"

30"

6"

10"

2"

10"

10"

NMi TraSys

65 m3/h

6500 m3/h

2500 m3/h

400 m3/h

10"

10"

2"

10"

10"

16"

24"

2"

8"

30"

10"

10"

10"

10"

Metering runs

Metering runs

usm

6500 m3/h

usm

30"

Gas Oil Piston Prover

Cross over line

Flow finetuning

Blower and

variable speed

driveGC


Gas Chromatograph: is it a “Black Box” and is that bad?

Bad: if output is simply taken for granted Not bad: if black box model is validated and output can be taken for granted

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What is gas chromatography ?

t0

t1

tr

Gas Chromatography : calibration

Peak area is proportional to concentration

Gas chromatogram of calibration gas (with Elster Encal 3000)

Result of GC analysis

Gas composition is used to calculate the Calorific Value (inferior and superior), Wobbe index, compressibility, density, viscosity (Reynolds number), V.O.S. (ultrasonic flow meter), etc.


Calculation of the unknown composition

In case of single point calibration (common practise in many gas metering stations):

Concentration X of component Y unknown sample

X Y, unknown = ________________ * X Y, cal gas Peak area Y, unknown

Peak area Y, cal gas

XCH4

XC2H6

XC3H8

…

XCO2

XN2

XĆH4

XĆ2H6

XĆ3H8

…

XĆO2

XŃ2

Normali-

sation

H

Z

W

ns

e.g.,

ISO 6976

AGA8

AGA10


X unknown = ________________ * X cal gas Peak area unknown

Peak area cal gas

Requires: reliable peak area (system efficiency and repeatability) equal detector sensitivity for both peaks! (detector linearity)

Measuring / integration peak area

Reliable peak area: system efficiency

12

Very critical! 0.1% error (abs) in N2 0.1% (rel) error in H

Poor integration, but less critical for H (normalization) Critical for Tdew

Channel 1: N2, CH4, CO2 and ethane

Channel 2: propane and higher

Detector linearity check with 7 PSMs

0

10000

20000

30000

40000

50000

60000

70000

80000

0 3 6 9 12 15

mole fraction

res

po

nse

‘true’ response

curve

assumed response

curve WRM response

WRM mole

fraction

unknown response

unknown mole fraction

bias WRM mole fraction


-during field operation: single point calibration ! -How the quantify the bias and the associated uncertainty?


X unknown = ________________ * X cal gas Peak area unknown

Peak area cal gas

Requires reliable values for all individual components: prepared in accordance with ISO 6142 or certified in accordance with ISO 6143 (ISO 6974) issued under ISO 17025 / ISO Guide 34 accreditation (with uncertainty that is fit for purpose!)

Calibration gas quality

Objectives for validation


Need for reliable measurement results - Confidence in analytical results - Confidence and trust between buyer / seller - Comply to contractual issues - Comply to legislation

In practice: Comply to e.g. EN 1776: Gas supply – Natural gas measuring stations – Functional requirements

For on-line GC: comply to ISO 10723: Natural gas – Performance evaluation for on-line analytical systems


Validation with ISO 10723

Component Unit Min Max

Methane cmol/mol 64.19 98.30

Nitrogen cmol/mol 0.200 11.66

Carbon dioxide cmol/mol 0.050 8.06

Ethane cmol/mol 0.114 13.933

Propane cmol/mol 0.051 7.990

i-Butane cmol/mol 0.01171 1.1856

n-Butane cmol/mol 0.01553 1.1943

neo-Pentane cmol/mol 0.01007 0.300

i-Pentane cmol/mol 0.0059 0.2973

n-Pentane cmol/mol 0.01149 0.351

n-Hexane cmol/mol 0.005254 0.3499

Reference gas ranges expressed in amount-of-substance fractions

Use of (at least) 7 high quality, traceable, natural gas reference gas mixtures: - to demonstrate proper peak seperation (for many combinations) - to calculate repeatability (U peak area) - to demonstrate reproducebility (calibration interval) - to determine “true” response function (linearity) - Calculate total uncertainty on gas properties


The revised ISO 10723

What has changed?

Maturity! -Improved uncertainty calculation (GUM compliant) -Benchmark evaluation -Monte Carlo simulation (a.o. implementation of non- linearity and uncertainty sources) Dedicated calculations for different measurement ranges Dedicated calculations based on the selected calibration gas

Results of linearity tests

18

Calibration curve Ethane – 1st order Goodness of Fit 5.9 (>2) Absolute X and Y residuals >2

Calibration curve Ethane – 3rd order Goodness of Fit 0.9 (<2) Absolute X and Y residuals <2

Not linear: advise on composition of calibration gas


Monte Carlo simulation

Simulate 10.000 compositions within range of interest (dedicated to the location/source)! - random, but with some restrictions - increasing concentrations for decreasing carbon number - rectangular distribution on the ranges -iso- and normal- isomers with the same carbon number concentrations within 10% relative

Calculate the peak area based on the “true” respons functions Calculate the composition based on single point calibration Compare calculated composition (single point) to generated composition Expres the results in terms of %error


Result of Monte Carlo simulation

-0.150

-0.100

-0.050

0.000

0.050

0.100

0.150

60 65 70 75 80 85 90 95 100 105

Erro

r gr

oss

cal

ori

fic

valu

e (

MJ/

m3)

amount-of-substance fraction methane (cmol/mol)


-0.250

-0.200

-0.150

-0.100

-0.050

0.000

0.050

0.100

0.150

60 65 70 75 80 85 90 95 100 105

Erro

r gr

oss

cal

ori

fic

valu

e (M

J/m

3)


-0.250

-0.200

-0.150

-0.100

-0.050

0.000

0.050

0.100

0.150

60 65 70 75 80 85 90 95 100 105

Erro

r gr

oss

cal

ori

fic

valu

e (

MJ/

m3

)


Cal gas contains 91 % CH4

Monte Carlo simulation, using different calibration gas composition

Cal gas contains78 % CH4


Result of ISO 10723 evaluation

Values from the GC can be taken for granted ( H, W, z, Tdew, ρ, ϑs ± UH, W, z, Tdew, ρ, ϑs )

Dedicated performance for the on-line analyzer within the used application Demonstrated effect of the calibration gas composition and uncertainty

Satisfactory / Acceptable

Not satisfactory / Not acceptable

Mean error in superior calorific value

Uncertainty in superior calorific value

Uncertainty in superior calorific value

Uncertainty in carbon dioxide emission factor

Chromatography (peak separation)

Traceability of the calibration gas(es)

summary of the performance of the GC:

VSL implementation of EN 1776 /

ISO 10723 (+additional issues)

- Factory Acceptance Test (FAT) based on ISO 10723 - At VSL or at the manufacturer’s site

- Site Acceptance Test (SAT) based on ISO 10723 - demonstrate performance on-site (NG, LNG, green gas)

and help to solve non-conformities on-site!

perform re-calibration under ISO 17025 accreditation

- Supply of traceable Certified Reference Materials (ISO 6142 / ISO 6143)

ISO 10723, ISO 6142 and ISO 6143 activities performed within the scope of VSL’s ISO 17025 accreditation

- Train operators to perform ISO10723 validation

- Perform type approval for new GC’s

- Organization of Proficiency Testing schemes (PT, round robin) under ISO 17043 accreditation

23


Proficiency Testing (ISO 17043): to prove good performance

CH4 (10-2 mol/mol)

Reported data

Lab ID Value std.dev U (k=2) n flag zraw z En Yref Uref

L001 83.12 0.00 0.18 5 -0.90 -0.42 -0.22 83.17 0.16

L002 83.32 0.03 1.17 5 2.56 1.45 0.15 83.14 0.16

L003 83.18 0.00 0.83 5 0.22 0.27 0.04 83.15 0.16

L004 82.72 0.11 0.03 5 * -7.68 -3.43 -2.63 83.15 0.16

L005 83.17 0.00 0.02 3 -0.03 0.23 0.18 83.14 0.16

L006 83.15 0.00 0.13 3 -0.35 0.08 0.05 83.14 0.16

L007 83.14 0.00 0.21 2 -0.53 -0.16 -0.08 83.16 0.16

L008 83.17 0.02 0.08 5 0.00 0.00 0.00 83.17 0.16

L009 83.21 0.02 0.93 5 0.76 0.44 0.06 83.16 0.16

L010 83.20 0.01 0.22 5 0.57 0.43 0.20 83.15 0.16

L011 82.86 0.00 0.66 5 * -5.29 -2.23 -0.41 83.14 0.16

L012 83.20 0.01 2.64 5 0.48 0.39 0.02 83.15 0.16

L013 83.02 0.01 0.22 5 -2.63 -1.07 -0.49 83.15 0.16

L014 83.21 0.00 0.18 2 0.72 0.50 0.26 83.15 0.16

L015 83.21 0.01 0.26 4 0.67 0.48 0.20 83.15 0.16

Individual cylinders with natural gas mixture, certified by VSL, send to 15 participants:


Proficiency Testing results

80.56

81.56

82.56

83.56

84.56

85.56

L00

1

L00

2

L00

3

L00

4

L00

5

L00

6

L00

7

L00

8

L00

9

L01

0

L01

1

L01

2

L01

3

L01

4

L01

5

(10

-2 m

ol/

mo

l)

Laboratory ID

Results for CH4

-2.00

-1.50

-1.00

-0.50

0.00

0.50

1.00

1.50

2.00

L00

1

L00

2

L00

3

L00

4

L00

5

L00

6

L00

7

L00

8

L00

9

L01

0

L01

1

L01

2

L01

3

L01

4

L01

5

E n-n

um

be

r

Laboratory ID

En-numbers for CH4


VSL: related activities

Leading role in world-wide metrology for preparation of energy-gas Primary Reference materials - organizer of all CCQM Key comparisons for natural gas - organizer of first CCQM Key comparison on biogas - co-ordinator of EMRP LNG I and II - co-ordinator of EMRP biogas - participant (WP-leader) in EMRP energy gases - active in ISO TC 158 gas analyses - active in ISO TC 193 natural gas (ISO 6976, ISO 10723) Accredited laboratory for organization of Proficiency Testing schemes (PT’s, PT on demand)


Conclusion:

ISO 10723 describes a good method to obtain reliable results from an on-line natural gas analyzer The revision of the standard has improved the quality of the results and gives the possibility to match the results with the actual on-site situation (implementation of the standard may have become more complicated / more specialized)

VSL

PO Box 654

2600 AR Delft

The Netherlands

T

F

E

I

+31 15 269 15 00

+31 15 261 29 71

[email protected]

www.vsl.nl

Any Questions ? - ISO 10723 - VSL - gas chromatography - EMRP/EMPIR - PT-schemes - etc.

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