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The New ISO 10723
Advances and new concepts in the
performance evaluation and benchmarking
of
on‐
line
natural
gas
analysers.
Dr Paul Holland
BD Director, EffecTech Group
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Natural gas quality measurementcomposition (content) of natural gas
• inert gases
nitrogen, carbon dioxide, helium, (argon & hydrogen)
• hydrocarbons
methane, ethane, propane, iso‐butane, n‐butane,
pentanes, hexanes + ......
properties (characteristics) of natural gas
• calorific value, Wobbe number, standard density (ISO 6976)
• compression factor,
line
density
(ISO
12213)
• hydrocarbon dew point (ISO 23874)
• emission factors
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Energy determination
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Risks
in
energy
metering
0
500,000
1,000,000
1,500,000
2,000,000
2,500,000
3,000,000
3,500,000
4,000,000
4,500,000
0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6
Annual Value / €
U(Energy) / %
Typical gas fired power station
Power output : 500 MW
Energy Price : €60 / MWh
Typical
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Gas quality measurement instruments
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Legal / commercial requirementslegislation
• customer protection (example in UK law)
Public Gas Transporters (PGTs) shall carry out performance evaluations of
gas quality
metering
instruments
in
accordance
with
ISO
10723
following
installation or maintenance. Provided that the results of the procedure show that the error on the calculated calorific value of transmission gas will not exceed 0.10 MJ.m‐3 for gas compositions allowed in the system, the PGT may then use that instrument for the determination of calorific values for the purposes of section 12 of the Gas Act 1986.”
• control of GHG emissions (example in EU directive)
commercial gas contracts
• sales gas
agreements
/ contracts
(end
‐users)
• allocation agreements (upstream)
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Revision of ISO 10723 : 1995revision to existing standard required for
• inclusion of measurement uncertainties
instrument precision, instrumental errors
working calibration gas
• compliance with GUM
• more rigorous assessment of errors and uncertainties of measurement
of
composition (gas content amount fraction)
gas properties (calculated from composition)
revision by
• ISO/TC193/WG15 (with liaison from ISO/TC158)
• Drafting by
G
Squire
(EffecTech,
UK)
and
D
Lander
(NGG,
UK)
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ISO/DIS 10723 : 2011 ‐ Scope
Determine E(x), E(P)
and U(x), U(P) over a
pre‐
defined
range
of
compositions for each
specified component
Determine a range of
compositions for each
specified
component
which satisfy pre‐
defined maximums in
E(x), E(P) and U(x), U(P)
using a specified calibration gas
composition and uncertainty
calibration gas redesign
composition
and
uncertainty
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Instrument errors
0 1 2 3 4 5 6 7 8 9 10
response / (peak area)
content / (% mol/mol)
y=Fass(x)
xcal
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Instrument errors
0 1 2 3 4 5 6 7 8 9 10
response / (peak area)
content / (% mol/mol)
y=Fass(x)
y=Ftrue(x)
xcal
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Instrument errors
0 1 2 3 4 5 6 7 8 9 10
response / (peak area)
content / (% mol/mol)
y=Fass(x)
y=Ftrue(x)
xcal
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Instrument errors
0 1 2 3 4 5 6 7 8 9 10
response / (peak area)
content / (% mol/mol)
y=Fass(x)
y=Ftrue(x)
xcal
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Challengemeasurement of TRUE (actual) response functions for
the instrument for all components (i=1..q)
• calibration functions
y = Fi,true(x)
• analysis functions
x = Gi,true(y)
function types for F & G
• polynomials of order 1, 2 or 3
yi = Fi,true(xi)
= a0 +
a1xi +
a1xi2 +
a3xi3
xi= Gi,true(yi) = b0 + b1yi + b2yi2 + b3yi
3
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Design of reference gasesa series of reference gases is measured by the
instrument being calibrated
components included
in
reference
gases
• depends on application
range
of
composition• equal or greater than that expected to be measured by the
instrument (no extrapolation)
number of
mixtures
• dependent upon expected order of F and G
3 (1st order), 5 (2nd order), 7 (3rd order)
• approximately equally
spaced
within
the
range
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ISO
10723 ‐ Performance
evaluations
of
on‐
line
analytical systems• ISO 17025 accredited calibration
gases
• well established
reference
values
&
uncertainties
• 7 ‐10 cylinders each containing 10,11
or 12 components
• wide range
natural
gas
compositions
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Experimental design
replicate measurements
r e f e r e
n c e
g a s e s
Batch‐wise calibration
simplest / manual / most practical ( p gas changes)
temporal drift has more significance
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replicate measurements
r e f e r e
n c e
g a s e s
Drift compensation calibration
compensates for temporal drift (due to sample size effects)
automation required
Experimental design
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Drift
correctionSamples are injected at (or with reference to)
ambient pressure.
response effective sample size ambient pressure
Batch‐wise calibration Drift compensation
calibration
yijk = y’ijk . Pref / Pijk
measure ambient pressure at time of
sample injection (Pijk)
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Gas fired power station
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Gas fired power station
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Witnessed factory evaluation
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LNG receiving terminal
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Custody
transfer
border
station
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Drift compensation calibration (automated)
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Offshore allocation / sales gas
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Regression
analysisparameters F and G are calculated using GLS
• maximum liklihood functions relationships (MLFR)
• uncertainties in both variables (amount and response)
• procedure identical to that prescribed in ISO 6143
response functions validated for each component
and in
each
domain
F and
G using
ISO
6143
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Calibration
results
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Errors content / amount fraction & properties
• assumed
• true
• measured amount following calibration
(where functions coincide)
• normalise
• errors
)(, i assi i y G x
)(, i truei i x F y
))((
))((.
,,,
,,,
,
*
,
calitrueiassi
trueitrueiassi
calimeasi
xFG
xFGxx
*
,
*
,
,
measi
measi
measix
xx
trueimeasimeasi xxx ,,,
truemeasmeas PPP
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Uncertainties
in
errors
contributions from
• calibration gas
• instrument precision
properties• any property / characteristic calculated from composition
)( ,calixu
)(&)( ,, measicali yuyu
),...,,,,...,,( 2121 mn wwwxxxf P
)()()( 2
1
2
2
1
2
2
i
m
i i
i
n
i i
c wuw
f xu
x
f Pu
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produce a off ‐line model of instrument
• errors as
a function
of
amount
fraction
• repeatability as a function of amount fraction
• uncertainties as a function of amount fraction
use Monte Carlo simulation
• generate 10,000 different gas compositions
• for each composition calculate
errors in physical properties
uncertainties in physical properties
Off ‐
line
model
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Errors and uncertainties on errors
-0.15
-0.10
-0.05
0.00
0.05
0.10
0.15
78 80 82 84 86 88 90 92 94 96 98
E(CVSUP) / MJ.m-3
methane content / (% mol/mol)
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Error distribution
-0.15
-0.10
-0.05
0.00
0.05
0.10
0.15
78 80 82 84 86 88 90 92 94 96 98
E(CVSUP) / MJ.m-3
methane content / (% mol/mol)
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Mean error (bias)
-0.16
-0.14
-0.12
-0.10
-0.08
-0.06
-0.04
-0.02
0.00
0.02
0.04
0.06
0.08
0.10
0.12
0.14
0.16
78 83 88 93 98
E(CVSUP) / MJ.m-3
methane content / (%mol/mol)
Maximum Permissible
Bias (MPB)mean error = bias ‐ B(P)
MPBP
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Uncertainty on mean error
-0.16
-0.14
-0.12
-0.10
-0.08
-0.06
-0.04
-0.02
0.00
0.02
0.04
0.06
0.08
0.10
0.12
0.14
0.16
78 83 88 93 98
E(CVSUP) / MJ.m-3
methane content / (%mol/mol)
Maximum Permissible
Error (MPE)uncertainty on the mean error≈ uncertainty on bias ‐ U(B(P))
MPE PUPc
d i i
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Errors and uncertainties ‐ summary
E l d i f lib i
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Example – design of calibration gas
E l d i f lib ti
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Example – design of calibration gas
xC1,cal = 0.88
mean E(CV) = 0.001 ± 0.061 MJ.m‐3
E l d i f lib ti
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Example – design of calibration gas
xC1,cal = 0.88
mean E(CV) = 0.001 ± 0.061 MJ.m‐3
xC1,cal = 0.81
mean E(CV) = 0.000 ± 0.028 MJ.m‐3
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Analysis function correction ‐ superior CV
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Dove House
Dove Fields
Uttoxeter
Staffordshire
ST14 8HU
United
Kingdom
tel : +44 (0)1889 569229
e‐mail : [email protected]
web‐site : www.effectech.co.uk
ISO9001:2008 FS 554539