Modelling the Vapourization Rate of LNG

Abstract

The use of natural gas has been on the increase for the past three decades and current consumption is expected to double by the year 2020. A rise in the number of transoceanic shipments will, logically, increase the risk of accidental spills, especially at terminal facilities. An LNG spill will generate a potentially dangerous cryogen vapour cloud. Consequently, the study of the rate of vapourization of this cryogen over water surfaces is of primary importance. Experimental measurements on confined LNG spills indicate the presence of high vapourization rates at early times after spillage. The present work introduces a vapourization model that has not been explored in previous studies. This model proposes the existence of a thin liquid layer at the cryogen-water interface that is not in thermodynamic equilibrium with the bulk of cryogen liquid. The implementation of the proposed model in a computer program allowed for the simulation of the boil-off process, and the estimation of the initial vapourization rates and heat transfer coefficients in confined and unconfined spills. The simulated cryogen spills offered a description of the vapourization rates that correlated well with experimental boil-off data. The simulations indicated the existence of early vapourization rates in the range of 0.03 to 0.06 gcm _2 s _1 , and an average initial heat transfer coefficient of 1576 Wm _2 K _1 for a typical LNG mixture.