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Application of CMFD to LNG transport: Safety and Optimization March 2015 C. Narayanan ASCOMP www.ascomp.ch chidu@ascomp.ch

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LNG related phenomena 2 Phenomena of interest (requiring modelling): 1.Rollover in LNG storage tanks (safety analysis) 2.Filling of LNG storage tanks 3.Sloshing-induced pressure loads 4.Boil-off and sloshing-induced boil-off

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1- Rollover in LNG storage tanks 3 Issues of interest: Start time of Rollover phenomenon End time of Rollover phenomenon Calculate flow from heat ingress in tank Production of BOG ASCOMPs solutions: TransAT LNG : a1D model to predict Rollover because the long times and multiscale nature of the problem make it expensive to perform 3D CFD. TransAT Multiphase : Use advanced CFD to address local-scale, deeper issues related directly or indirectly to LNG transport issues, including rollover, boil-off, etc..

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1D model to predict incipient rollover. The main uncertainty in modelling rollover time is the heat and mass transfer coefficients between the lower and upper layers. ASCOMP has developed a 1D model based on Ref [2] and has improved it further (TransAT LNG). [1] Heestand, Shipman, Meader (2004): A predictive model for rollover in stratified LNG tanks, AIChE J., 29(2).Heestand, Shipman, Meader (2004): A predictive model for rollover in stratified LNG tanks, AIChE J., 29(2). [2] Deshpande KB, Zimmerman WB et al. (2011): Optimization methods for the real-time inverse problem posed by modelling of LNG storage, Chem. Engg. J., 170(1), 44-52.Deshpande KB, Zimmerman WB et al. (2011): Optimization methods for the real-time inverse problem posed by modelling of LNG storage, Chem. Engg. J., 170(1), 44-52. 4 1D modelling of rollover: TransAT LNG Validation & Application

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la Spezia accident: 1971, La Spezia, Italy - This accident was caused by "rollover" where two layers of LNG with different densities and heat content form. The sudden mixing of these two layers results in the release of large volumes of vapor. In this case, about 2,000 tons of LNG vapor discharged from the tank safety valves and vents over a period of a few hours, damaging the roof of the tank. Well reported by Sarstens report (31h) Inputs: Mole fractions Temperature Layer height Heat fluxes through tank walls Outputs: Rollover time Boil off rate LayerMethan e EthanePropaneButaneNitroge n upper0.63620.24160.09360.02510.0035 lower0.62260.21850.12660.03210.0002 Layerheight [m]Temperature [K] upper5114 lower18119 bottom [W/m^2]lower wall [W/m^2] upper wall [W/m^2] top [W/m^2] 20.826.94 15.77 5 1D modelling of rollover: TransAT LNG Validation & Application

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If two liquefied natural gas from different sources are brought together in a storage tank, the lighter LNG ( red curve ) may lie over the heavier LNG ( blue curve ) and could eventually lead to rollover. heat leakage from the walls, the dome and the bottom Rayleigh recirculation flow between film and upper layer Vapour liquid equilibrium in the film Thermodynamic properties from Refprop 6 TransAT-RolloverDeshpande et al. (2011) 1D modelling of rollover: TransAT LNG Validation & Application

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Preferential boil-off. Species evolution in the lower layer (blue), upper layer (red), liquid film (yellow) and vapour film (black) 7 1D modelling of rollover: TransAT LNG Validation & Application

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M Modelling capabilities Cl 1Multiphase flow models a.Level Set model b.Mixture models Ready 2Compressible multiphase flow treatment Ready 3Multiphase phase change modelling framework a.Based on Antoine vapour-pressures for pure components and Raoult's law of mixing. b.Mass and heat transfer rates have to be modelled. Ready 4Turbulence modelling (RANS, LES, VLES) Ready 5Multicomponent gaseous mixture model Ready 7LNG-specific phase change model, EoS, material properties As per client requiremen t TransAT Multiphase 8

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9 CMFD model validation: TransAT Multiphase Example 1: LNG tank filling (without rollover phenomenon)

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10 CMFD model validation: TransAT Multiphase Example 2: Liquefacation of gas in a conduit

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t = 6.52 s t = 7.64 s t = 7.52 s t = 7.88 st = 7.76 s t = 7.44 s CMFD model validation: TransAT Multiphase Example 3: Sloshing in a tank (incompressible flow) Exp. Bredmose & Peregrine, JFM, 2006 (sloshing in a tank. TransAT dotted lines) 11

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12 Case # Scal e LiquidGasT0: initial temperature (C) P0: Ullage pressure (Bar) 61:1LNGNG-1621 CMFD model validation: TransAT Multiphase Example 4: Sloshing pressure; ISOPE Benchmark: compressible

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13 CMFD model validation: TransAT Multiphase Example 4: Sloshing pressure; ISOPE Benchmark: compressible

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14 Density Pressure CMFD model validation: TransAT Multiphase Example 4: Sloshing pressure; ISOPE Benchmark: compressible

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KEPCO: Korea Electric Power Corporation Nuclear reactor safety problem related to steam condensation in a subcooled suppression pool. Phenomena: Highly underexpanded compressible steam jet issuing into cold water. Steam jet expansion through oblique shock waves. Steam condensation. Effect of phase change on pressure wave sound speed. Predict pressure fluctuation due to condensing steam jet. Numerical Schlieren image of steam jet issuing into water Mass-flux 600 kg/m 2 s 10 mm diameter jet Inlet velocity: 500 m/s Water Saturated (100 o C) Large-eddy Simulation 15 CMFD model validation: TransAT Multiphase Example 5: Steam condensation in a subcooled suppression pool

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For a saturated system in thermal equilibrium (very small bubbles) Discontinuity in sound speed Sound speed as low as 1 m/s Sound speed for steam-water saturated system. Void fraction of 0.97 with and without phase change for a bubble diameter of 2 microns. CMFD model validation: TransAT Multiphase Example 5: Steam condensation in a subcooled suppression pool 16

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TransA T Haas & Sturtevant (Exp.) Naber (CFD) Incoming shock velocity (m/s) 411415419 Refraction shock velocity (m/s) 238240230 Interface velocity (m/s)73 17 CMFD model validation: TransAT Multiphase Example 6: Shock- Helium bubble interaction

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ASHRAE Research Project: CFD study of condensation induced hydraulic shocks in anhydrous ammonia refrigeration systems (currently ongoing). Key Phenomena: 1.Condensation-induced hydraulic shocks: The depressurisation of the gas pockets between the slugs and the end cap produce condensation- induced shocks. 2.Vapor-propelled liquid slugging: Slug formation is a prerequisite condition for the shocks to develop. Without slugs, shocks were not observed. 3.Highly compressible multiphase (single- component) flow with phase change. liquid slug vapour compression vapour collapse water hammer Shock Simplified problem being considered 18 CMFD model application: TransAT Multiphase Example 6: Condensation-induced hydraulic shocks

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GTT Safe Heating: Safe evaporation procedure for LNG container system in accident scenario. Multi-scale approach to simulate the response of the whole insulating layer to different heating scenarios. Cryogenic CFD computation of pressure drops through narrow gaps and porous media. Model to investigate accident scenario and formulate safe evaporation procedure. 3D 2D 0D 19 CMFD model application: TransAT Multiphase Example 7: Heat transfer in cryogenic insulation technologies

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Summary 20 1.ASCOMP has significant experience in dealing with compressible multiphase flows with phase change. 2.Advanced numerical methods have been developed to solve this very stiff problem and applied to many challenging problems. 3.The specific features of LNG phase equilibrium thermodynamics will have to be implemented in TransAT. 4.A simplified 1D model (TransAT LNG) to predict incipient rollover is available. 5.A detailed 3D CMFD model (TransAT Multiphase) to predict various LNG transport related issues is available (for lease or for services) If there is an interest in consulting then ASCOMP can prepare a project work plan and financial plan.