offshore lng unloading: new large-bore cryogenic hoses & bog analysis
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Offshore LNG† Unloading:
New Large-Bore Cryogenic Hoses & BOG* Analysis
Jose Casella
University of Salford. UK
+33(0)642382359
1 † LNG : Liquefied Natural Gas.
*BOG: Boil-off gas
Outline:
Objectives
2 2
Results
Methodology
Problem Definition
Introduction
Concluding Remarks
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Financial impact of Large-bore Cryogenic hoses in Offshore LNG Unloading.
Optimize the annual LNG shipping costs and energy consumption of a typical Floating Storage and Regasification Unit (FSRU).
Objectives:
Cryogenic Hoses Weakest link of the LNG Chain Friction losses and BOG (1.275 billion USD in BOG in 2007). Diameters smaller than those required for reasonable pressure drop
at the typical unloading rates.
Introduction
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Liquefied Natural Gas
Offshore LNG Unloading
Problem Definition.
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BOG:
Unloading at Low peak periods. Different operating conditions.
Forecast Energy costs?
Optimize Shipping costs?
LNG
Vaporizers
HP pumps
BOG Comp
Recondenser
Storage
LNG carrier
Transmission
LOW
SEND-OUT RATE!
Flaring, Venting
Approach: 1) CFD 2) Gas Processing Simulations 3) Financial Assessment
Methodology
LNG Composition & Properties: P-H generated using Peng-Robinson Equation [7].
CFD RANS Sparlat-Allmaras turbulent
model. Isothermal, Incompressible, No
vaporization Fluid domain length of 5D based DNS. Periodic conditions (Velocity – Eddy
Viscosity) Height of the First layer (y+=200)
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Results
CFD Flow detaches at the top of the primary corrugation
and recirculation vortices between consecutive corrugations.
Helical corrugations inducing swirl.
High pressure zone at 45º upstream the top of the corrugations while low pressure zones are expected at the top of the corrugation. (flow periodically detaches – Risk of Bubble formation).
4 Empirical Correlations Accuracy of 9.5% with Riley’s equation.
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Up to 70% of the total pressure drop!
Vaporization
Numerical Wall Shape
Optimization
Liners
Results
Analysis Tool:
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Lowest heat transfer and pressure drop in a 24” hose. BOG in 20” is smaller that 2x16” at unloading rates
lower than 10,500 m3/hr.
Results
BOG The friction losses are approximately 60%
lower with a single line of 24”
Optimum LNG Unloading rate for minimum BOG at the recondenser
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CAPEX of BOG Comp
Station
High Unloading rates at
Low Peak periods
Results
Financial Impact
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2x16”
1x20”
1x24”
Optimum Unloading Rates
Hose Unloading rate
Energy Shipping
2x16” 9,000 m^3/hr 0.2 MM$ 139 MM$
1x20” 8,000 m^3/hr -1.8% +0.95 %
1x24” 11,000 m^3/hr -15.4% -1.38 %
Annual Costs
Energy Costs Shipping Costs
Concluding Remarks
Optimistic solution looking towards cost reduction in the LNG Industry.
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Account with up to 70% of the total pressure drop. R&D of Liners
The size of BOG compression station (CAPEX) can be reduced significantly only by deployment of large-bore cryogenic hoses.
Financial impact not only in energy consumption but also is shipping costs (1.4 MMUSD per year).
Novelty: Integration of all components of the RT. Statistical treatment to forecast probability distribution. Coupling CFD, gas processing simulation and financial assessment.
Thanks
“Real knowledge is to know the extent of one's ignorance.” (Confucius, 551-479 BC)
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Acknowledgements
The author wish to acknowledge and thank to Dunlop Oil & Marine Ltd and Altair Engineering for permission to publish this work at the IGEM Competition. (UK, 2013)
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References
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