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 3
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
VSL - Beyond all doubt 4
With: Uflow = 0.2% rel.
UH = 0.5% rel. } Uenergy = 0.54% rel.
With: Uflow = 0.1% rel.
UH = 0.5% rel. } Uenergy = 0.51% rel.
With: Uflow = 0.2% rel.
UH = 0.2% rel. } Uenergy = 0.28% 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
VSL - Beyond all doubt 6
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
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.
VSL - Beyond all doubt 10
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
X´CH4
X´C2H6
X´C3H8
…
X´CO2
X´N2
Normali-
sation
H
Z
W
ns
e.g.,
ISO 6976
AGA8
AGA10
VSL - Beyond all doubt 11
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
VSL - Beyond all doubt 13
-during field operation: single point calibration ! -How the quantify the bias and the associated uncertainty?
VSL - Beyond all doubt 14
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
VSL - Beyond all doubt 15
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
VSL - Beyond all doubt 16
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
VSL - Beyond all doubt 17
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
VSL - Beyond all doubt 19
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
VSL - Beyond all doubt 20
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)
VSL - Beyond all doubt 21
-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)
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 (
MJ/
m3
)
amount-of-substance fraction methane (cmol/mol)
Cal gas contains 91 % CH4
Monte Carlo simulation, using different calibration gas composition
Cal gas contains78 % CH4
VSL - Beyond all doubt 22
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
VSL - Beyond all doubt 24
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:
VSL - Beyond all doubt 25
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 - Beyond all doubt 26
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)
VSL - Beyond all doubt 27
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
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Any Questions ? - ISO 10723 - VSL - gas chromatography - EMRP/EMPIR - PT-schemes - etc.