Source Term Modeling Of Cryogenic Liquid Vapor Formation By Experimental Investigation - Evaporation Regime And Convection Effect

Abstract

Safe handling, storage and transportation of Liquefied Natural Gas (LNG) has been the root concern in the process industry due to the growing demand for ecological and clean alternative energy namely natural gas. Due to economic advantages in transportation, natural gas is transported in the liquid form. This calls for a thorough research in LNG safety due to its hazardous flammability properties. The study of consequence of loss of containment of LNG is critical to the risk assessment for LNG facilities. This is especially important for Qatar since it is the largest exporter of LNG accounting for about 32 % of the global LNG exports as of 2013. It is important to conduct fundamental and applied research to enrich the knowledge of LNG related safe operations. It is necessary to be able to model consequences of accidental LNG spill to assure sustainability of its production. The loss of containment of LNG leads to the generation of flammable vapor that gets dispersed in the atmosphere. This phenomenon is the same for any cryogenic liquid and is usually split into two stages: vapor formation (source term) and atmospheric dispersion. The vapor formation rate will be determined by its storage conditions (temperature and pressure) and the condition of the release (geometry and location of the dike/bund and the release point, ground temperature and weather data). During the dispersion stage, the behavior of the fluid is controlled by the atmospheric conditions (atmosphere stability class, wind speed, air temperature). The division of the phenomenon into two stages is a convenient approach from modeling perspective. Historically, less attention has been given to source term modeling. Simultaneously, the output of source term is the input into dispersion modeling, and thus, if the former is not accurately estimated the latter cannot be. Moreover, source term modeling is very complex and it cannot be well defined and validated since there is a lack of useful experimental data. This work aims at filling the gap and improving the experimental database. The scope of this part of project includes study of the convective heat flux to the cryogenic liquid pool, which is a part of source term model and study of evaporation regime. It also looks at different scales (small and medium) of experiments and the effect of spilled liquid composition. Currently, experimental results are available for spill of liquid nitrogen at small (0.001 m3) and medium scale (0.023 m3). The aim is to study the transition to evaporation regime and to validate existing evaporation models. It was determined that at the small scale five of the six models were valid but at the medium scale only one model gave close prediction. The deviation increase with scale up, which could be expected as most of the existing models were developed utilizing small scale experimental data. In near future, more investigations will be carried out at the large scale for better understanding of the phenomena.