uncertainties in the calculation

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Uncertainties in the calculationof the energy unloaded

from LNG tankers

GERG Academic Network Event

3rd & 4th June 2010

Susana Sanz BarbernSupervisor: Alberto Gonzalo Callejo


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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

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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

Source: LNG Industry 2008, GIIGNL

LNG carrier


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1. Introduction

Measurement system of the unloaded energy

E = V D GCV - Egas displaced[kWh] [m3] [kg/m3] [kWh/kg] [kWh]

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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1. Introduction

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Importance of proper measurement

20.5 Million 205 000

150.000 m3

1.000 GWh 1% = 10 GWh 331.700 GWh 1%= 3317 GWh

331 700 GWh / year LNG

6 800 Million 6.8 Million


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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 Barcelonas 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

Combined standard uncertainty

- Uncorrelated input quantities

- Correlated input quantities

Standard uncertainty

Type A: Type B: ;

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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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TrimList

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RevisedKLOSEK-McKINLEY

method:

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Standard deviation Covariance15


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Calibration certificates LegistationEnagas application

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Contents

1. Introduction

2. Model development3. Implementation in Excel



6. Conclusions

7. Future works

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Contents

1. Introduction

2. Model development3. Implementation in Excel



6. Conclusions

7. Future works

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ENERGYDifferent LNG carriers Same LNG carrier

VOLUMEDifferent LNG carriers Same LNG carrier

-0.10% -0.05% 0.00% 0.05% 0.10% 0.15% 0.20%

ENERGY

Correlation

Volume

Density

GCV (mass)

ENERGY

Correlation

Volume

Density

GCV (mass)

-0.10% -0.05% 0.00% 0.05% 0.10% 0.15% 0.20%

VOLUME

Final Volume

Initial Volume

VOLUME

Final Volume

Initial Volume

0.00% 0.02% 0.04% 0.06% 0.08% 0.10% 0.12%0.00% 0.02% 0.04% 0.06% 0.08% 0.10% 0.12%

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DENSITYDifferent LNG carriers Same LNG carrier

GCVDifferent LNG carriers Same LNG carrier

DENSITY

Correlations

Calculation

V corrected

V ideal

M mix

DENSITY

Correlations

Calculation

V corrected

V ideal

M mix

-0.40% -0.30% -0.20% -0.10% 0.00% 0.10% 0.20% 0.30%

GCV (mass)

Calculation

Correlation

M mix

GCV (mol)

GCV (mass)

Calculation

Correlation

M mix

GCV (mol)

-0.40% -0.30% -0.20% -0.10% 0.00% 0.10% 0.20% 0.30%

-0.40% -0.30% -0.20% -0.10% 0.00% 0.10% 0.20% 0.30%-0.40% -0.30% -0.20% -0.10% 0.00% 0.10% 0.20% 0.30%

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MAXIMUM CASE

ENERGY

Correlation

Volume

Density

GCV (mass)

-0.05% 0.00% 0.05% 0.10% 0.15% 0.20%

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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

UNCERTAINTY MODELCUSTODYTRANSFER MNIMUM MXIMUM

Volume 0.21 % 0.006 % 0.061 %

Density 0.23 % 0.059 % 0.058 %

GCV 0.30 % 0.015 % 0.015 %

Correlation - - 0.039 % - 0.019 %

ENERGY 0.43 % 0.047 % 0.084 %

0.05%

0.12%

0.06%

0.14%

Modified

CUSTODYTRANSFER

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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 models values were too far from the CustodyTransfers ones. After a detailed analysis, this difference has been

reduced in an important percentage.

Computer tool developed makes easier the application of themodel.

This model means an improvement in the determination ofuncertainty and can be used to reduce it.

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C t t


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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

uncertainties in the calculation

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