Uncertainties in the calculation of the energy unloaded from

Transcription

Uncertainties in the calculation
of the energy unloaded
from LNG tankers
GERG Academic Network Event
3rd & 4th June 2010
Susana Sanz Barberán
Supervisor: Alberto Gonzalo Callejo
Contents
1. Introduction
2. Model development
3. Implementation in Excel
4. Application of the model
5. Comparison with Custody Transfer
6. Conclusions
7. Future works
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Contents
1. Introduction
6. Conclusions
7. Future works
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1. Introduction
Liquefied natural gas (LNG) in the world
377.4 million m3/year LNG transported by sea
LNG carrier fleet: 298 vessels
20 Liquefaction Plants
63 Regasification Plants
LNG carrier
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Source: LNG Industry 2008, GIIGNL
1. Introduction
Measurement system of the unloaded energy
E = V · D · GCV - Egas displaced
[kWh]
[m3] [kg/m3] [kWh/kg]
VOLUME
Initial and final liquid level
Trim / List
Vapour temperature
DENSITY
LNG composition
Liquid temperature
GCV

LNG composition
ENERGY gas displaced
Gas displaced composition
Gas displaced volume
Vapour temperature
Pressure inside the tanks
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[kWh]
1. Introduction
Importance of proper measurement
331 700 GWh / year LNG
150.000 m3
1.000 GWh
20.5 Million €
1% = 10 GWh
331.700 GWh
6 800 Million €
205 000 €
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1%= 3317 GWh
6.8 Million €
1. Introduction
Uncertainty of the unloaded Energy
“LNG Measurement”, N.B.S.
“LNG Custody Transfer Handbook”, GIIGNL
Independent companies studies
Do not apply the Law of propagation of uncertainty
Terms confusion related to uncertainty
This project intends to:
Deepen in the field of uncertainty
Establish bases to future work
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1. Introduction
AIMS
Study of the energy measurement system
Development of a mathematical model
Implementation of the model in a spreadsheet
Historical study of Barcelona’s terminal unloadings
Comparison with Custody Transfer
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Contents
1. Introduction
6. Conclusions
7. Future works
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BASIC CONCEPTS
“Guide to the expression of uncertainty in measurement”, JCGM
Expanded uncertainty
Relative uncertainty
U = k ⋅ uC (x)
w( x) =
u ( x)
x
Combined standard uncertainty
2
⎡ ∂f ⎤ 2
- Uncorrelated input quantities uC2 ( x) = ∑ ⎢
⎥ u ( xi )
i =1 ⎣ ∂xi ⎦
N
- Correlated input quantities
Ci
2
N −1 N
⎡ ∂f ⎤ 2
∂f ∂f
2
u C ( x ) = ∑ ⎢ ⎥ u ( xi ) + ∑ ∑
u ( xi , x j )
i =1 j = i +1 ∂xi ∂x j
i =1 ⎣ ∂xi ⎦
N
Standard uncertainty
Type A:
u ( x) =
s ( x)
Type B:
n
u ( x) =
a
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9
;
u ( x) =
a
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METHODOLOGY
Determine the objective variable: Energy
Seek the sources of uncertainty and determine their values, u(x)
Express the objective variable in terms of its sources of
uncertainty
Calculate the combined standard uncertainty, uC(E)
Determine the expanded uncertainty, U(E)
Sources of uncertainty
Overall uncertainty of the measured energy
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Trim
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List
Revised
KLOSEK-McKINLEY
method:
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Standard deviation
Covariance
Calibration certificates
Enagas application
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Legistation
Contents
1. Introduction
6. Conclusions
7. Future works
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Contents
1. Introduction
6. Conclusions
7. Future works
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ENERGY
Different LNG carriers
Same LNG carrier
ENERGY
ENERGY
Correlation
Correlation
Volume
Volume
Density
Density
GCV (mass)
GCV (mass)
-0.10%
-0.05%
VOLUME
0.00%
0.05%
0.10%
0.15%
0.20%
-0.10%
VOLUME
Final Volume
Final Volume
Initial Volume
Initial Volume
0.02%
0.04%
0.06%
0.08%
0.10%
0.00%
0.05%
0.10%
0.15%
0.20%
0.10%
0.12%
Same LNG carrier
VOLUME
0.00%
-0.05%
0.12%
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0.00%
0.02%
0.04%
0.06%
0.08%
DENSITY
Same LNG carrier
DENSITY
DENSITY
Correlations
Correlations
Calculation
Calculation
V corrected
V corrected
V ideal
V ideal
M mix
M mix
-0.40%
GCV
-0.30%
-0.20%
-0.10%
0.00%
0.10%
0.20%
0.30%
-0.40%
GCV (mass)
Calculation
Calculation
Correlation
Correlation
M mix
M mix
GCV (mol)
GCV (mol)
-0.30%
-0.20%
-0.10%
0.00%
0.10%
0.20%
-0.20%
-0.10%
0.00%
0.10%
0.20%
0.30%
0.20%
0.30%
Same LNG carrier
GCV (mass)
-0.40%
-0.30%
0.30%
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-0.40%
-0.30%
-0.20%
-0.10%
0.00%
0.10%
MAXIMUM CASE
ENERGY
Correlation
Volume
Density
GCV (mass)
-0.05%
0.00%
0.05%
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0.10%
0.15%
0.20%
Contents
1. Introduction
6. Conclusions
7. Future works
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Custody Transfer as reference manual to LNG transactions
Does not apply the Law of propagation of uncertainty
Confuses terms as error and uncertainty
Modified
CUSTODY
CUSTODY
TRANSFER
TRANSFER
MÍNIMUM
MÁXIMUM
Volume
0.05%
0.21 %
0.006 %
0.061 %
Density
0.12%
0.23 %
0.059 %
0.058 %
GCV
0.06%
0.30 %
0.015 %
0.015 %
Correlation
-
- 0.039 %
- 0.019 %
ENERGY
0.14%
0.43
%
0.047 %
0.084 %
UNCERTAINTY MODEL
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Contents
1. Introduction
6. Conclusions
7. Future works
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6. Conclusions
New uncertainty model. Main factors:
Density
Volume
W(E)max = 0.17%.
Firstly, our model’s values were too far from the Custody
Transfer’s ones. After a detailed analysis, this difference has been
reduced in an important percentage.
Computer tool developed makes easier the application of the
model.
This model means an improvement in the determination of
uncertainty and can be used to reduce it.
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Contents
1. Introduction
6. Conclusions
7. Future works
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7. Future works
Complete the database of ships
Update the model with future regulations
Apply the model to all Enagas’ terminals
Joint Research Project: “Metrology for LNG”
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THANKS FOR YOUR ATTENTION
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