Duality in LNG tank-pressure behaviour and its relevance for ship-to-ship transfers to floating storage and regasification units

Abstract

Floating storage and regasification units (FSRU) are in high demand globally forming a specialized and growing fleet of ships to service a steadily expanding liquified natural gas (LNG) industry. Ship-to-Ship (STS) LNG cargo transfers are an inevitable part of the FSRU day-to-day operating patterns. It is little more than a decade since FSRU operations began and a lack of knowledge persists concerning their relatively complex tank pressure behaviour during STS transfers. In this work, based on details from more than thirty STS operations, FSRU tank pressure trends and influencing factors are explained. The interactions between the vapor space and liquid LNG are strongly influenced by the thin surface film between those phases in an LNG tank. The saturated vapor pressure of the LNG and the volumetric balance of gas and liquid movements in and out of the tank are also influential. These factors control the rate and extent of evaporation and condensation occurring at the surface film, thereby impacting tank pressure changes. This paper presents observations that reveal a duality in FSRU tank pressure behaviour that in over-pressured conditions allows tank pressure to rise significantly and rapidly. On the other hand, in under-pressured conditions tank pressure stabilizes at certain levels and inhibits significant reduction below those levels. Here, we explain the processes involved in determining FSRU tank pressure trends during STS transfers, and, based on observations of actual STS transfers, provide rules of thumb and empirical equations that can be used to estimate tank pressure behaviour in a range of operating conditions. These are supported by several generic cases of tank pressure, temperature and SVP trends reflecting the various tank scenarios commonly associated with routine operating patterns of FSRU during STS transfers. The principles described in this paper apply to LNG Carriers but tend to be disrupted by sloshing and wave movements also in the tanks during transit.

Cited as: Kulitsa, M., Wood, D.A. Duality in LNG tank-pressure behaviour and its relevance for ship-to-ship transfers to floating storage and regasification units. Advances in Geo-Energy Research, 2020, 4(1): 54-76, doi: 10.26804/ager.2020.01.06

References

Arjomandnia, P., Tade, M.O., Pareek, V., et al. Analysis of available data from liquefied natural gas rollover incidents to determine critical stability ratios. AIChE J. 2013, 60(1): 362-374.

Bates, S., Morrison, D.S. Modelling the behaviour of stratified liquid natural gas in storage tanks: A study of rollover phenomenon. Int. J. Heat Mass Trans. 1997, 40(8): 1875-1884.

Baudouy, B. Heat transfer and cooling techniques at low temperature. arXiv: 1501.07153 [physics.acc-ph], 2015.

Booth, D.A., Bulsara, A., Joyce, F.G., et al.. Wall film flow effects with liquefied natural gas. Cryogenics 1974, 14(10): 562-563.

Chen, Y.G., Price, W.G., Temarel, P. Numerical simulation of liquid sloshing in LNG tanks using a compressible two-fluid flow model. Paper ISOPE-I-09-532 Presented at the International Offshore and Polar Engineering Conference, Osaka, Japan, 21-26 July, 2009.

Deshpande, K.B., Zimmerman, W.B., Tennant, M.T., et al. Optimization methods for the real-time inverse problem posed by modelling of liquefied natural gas storage. Chem. Eng. J. 2011, 170(1): 44-52.

Dimopoulis, G., Frangopoulos, C. A dynamic model for lique-fied natural gas evaporation during marine transportation. Int. J. Thermodyn. 2008, 11(3): 123-131.

Dobrota, D., Lali ´c, B., Komar, I. Problem of boiloff in LNG supply chain. Trans. Marit. Sci. 2013, 2(2): 91-100.

GIIGNL. Rollover in LNG Storage Tanks. 2nd Edition, 2012-2015/Public Version, 2012.

Globe, S., Dropkin, D. Natural convection heat transfer in liquids confined by two horizontal plates and heated from below. J. Heat Trans. 1959, 81(1): 24-28.

Glomski, P., Michalski, R. Problems with determination of evaporation rate and properties of boiloff gas on board LNG carriers. J. Polish CIMAC 2011, 6(1): 133-140.

Grotle, E.L., Esoy, V. Dynamic modelling of the thermal response enhanced by sloshing in marine LNG fuel tanks. Appl. Therm. Eng. 2018, 135(5): 512-520.

Hashemi, H.T., Wesson, H.R. Cut LNG storage costs. Hydrocarb. Process. 1971, 50(1): 246-249.

Hayashi, K., Yarimizu, K., Furutani, S. Supercompact BOG recondensing system minimizes equipment lifecycle costs. World Oil 2016, 237(10): 41-44.

Kanazawa, T., Kazuhiko, K., Kuroda, A., et al. Experimental study on heat and fluid flow in LNG tank heated from the bottom and sidewalls. Heat Trans. Asian Res. 2004, 33(7): 417-430.

Kim, H., Shin, M.W., Yoon, E.S. Optimization of operating procedure of LNG storage facilities using rigorous BOR model. Paper Presented at the Proceedings of the 17th World Congress The International Federation of Automatic Control, Seoul, Korea, 6-11 July, 2008.

Kulitsa, M., Wood, D.A. LNG Cargo Handling-Conclusion: Tandem pressures between ships during STS transfers cuts gas losses. Oil Gas J. 2017a, 115(12): 65-70.

Kulitsa, M., Wood, D.A. LNG Cargo Handling: New approach improves ship-to-ship LNG transfers. Oil Gas J. 2017b, 115(11): 56-60.

Kulitsa, M., Wood, D.A. LNG rollover challenges and their mitigation on Floating Storage and Regasification Units: New perspectives in assessing rollover consequences. J. Loss Prevent. Proc. Ind. 2018a, 54: 352-372.

Kulitsa, M., Wood, D.A. Floating storage and regasification units face specific LNG rollover challenges: Consideration of saturated vapor pressure provides insight and mitigation options. Nat. Gas Ind. 2018b, 5(4): 391-414.

Kulitsa, M., Wood, D.A. Soft metal blanket with optional anti-sloshing conceptual designs to improve pressure control for floating and land-based liquefied natural gas tanks. Adv. Geo-Energy Res. 2019, 3(4): 424-447.

Laciak, M. Liquefied natural gas storage of variable composition. Arch. Min. Sci. 2015, 60(1): 225-238.

Lemmon, E.W., Huber, M.L., McLinden, M.O. NIST reference fluid thermodynamic and transport properties-REFPROP. Version 10, 2019.

Li, Y., Chen, X., Chein, M.H. Flexible and costeffective optimization of BOG (boil-off gas) recondensation process at LNG receiving terminals. Chem. Eng. Res. Des. 2012, 90(10): 1500-1505.

LMNO Engineering. Bernoulli Equation Calculator with Applications, 2019.

Ludwig, C., Dreyer, M.E., Hopfinger, E.J. Pressure variations in a cryogenic liquid storage tank subjected to periodic excitations. Int. J. Heat Mass Trans. 2013, 66: 223-234.

Munson, B.R., Young, D.F., Okiishi, T.H. Fundamentals of Fluid Mechanics. New York, USA, John Wiley and Sons, 2013.

Paine, S.N., Turner, D.D., Kuchler, N. Understanding thermal drift in liquid nitrogen loads used for radiometric calibration in the field. J. Atmos. Ocean Technol. 2014, 31(3): 647-655.

Prandtl, L. ¨Uber Fl ¨ussigkeitsbewegung bei sehr kleiner Reibung, Verhandlungen des Dritten Internationalen Mathematiker-Kongresses (Heidelberg 1904), 1905, pp. 484-491.

Roh, S., Son, G. Numerical study of natural convection in a liquefied natural gas tank. J. Mech. Sci. Technol. 2012, 26(10): 3133-3140.

Rudman, M., Prakash, M., Cleary, P.W. Simulation of liquid sloshing in a model LNG tank using smoothed particle hydrodynamics. Paper ISOPE-I-09-540 Presented at the International Offshore and Polar Engineering Conference, Osaka, Japan, 21-26 June, 2009.

Scurlock, R.G. Stratification, Rollover and Handling of LNG, LPG and Other Cryogenic Liquid Mixtures. United Kingdom, Springer International Publishing, 2016.

Sha, W., Ren, J., Wang, C., et al. Dynamic characteristics of the initial interface in stratified multi-composition liquid tanks during rollover. Appl. Therm. Eng. 2018, 145: 396-406.

Weyburne, D. A mathematical description of the fluid boundary layer. Appl. Math. Comput. 2006, 175(2): 1675-1684.

Weyburne, D. New thickness and shape parameters for describing the thermal boundary layer. arXiv: 1704.01120 [physics.flu-dyn], 2017.

Wood, D.A., Kulitsa, M. A review: Optimizing performance of Floating Storage and Regasification Units (FSRU) by applying advanced LNG tank pressure management strategies. Int. J. Energy Res. 2018, 42(4): 1391-1418.

Zakaria, Z., Kamarulzaman, K., Samsuri, A. Rollover phenomena in liquefied natural gas storage: Analysis on heat and pressure distribution through CFD simulation. Int. J. Innov. Eng. Technol. 2017, 8(1): 392-400.