Tomasz Olewski

Blanketing effect of expansion foam on liquefied natural gas (LNG) spillage pool.

With increasing consumption of natural gas, the safety of liquefied natural gas (LNG) utilization has become an issue that requires a comprehensive study on the risk of LNG spillage in facilities with mitigation measures. The immediate hazard associated with an LNG spill is the vapor hazard, i.e., a flammable vapor cloud at the ground level, due to rapid vaporization and dense gas behavior. It was believed that high expansion foam mitigated LNG vapor hazard through warming effect (raising vapor buoyancy), but the boil-off effect increased vaporization rate due to the heat from water drainage of foam. This work reveals the existence of blocking effect (blocking convection and radiation to the pool) to reduce vaporization rate. The blanketing effect on source term (vaporization rate) is a combination of boil-off and blocking effect, which was quantitatively studied through seven tests conducted in a wind tunnel with liquid nitrogen. Since the blocking effect reduces more heat to the pool than the boil-off effect adds, the blanketing effect contributes to the net reduction of heat convection and radiation to the pool by 70%. Water drainage rate of high expansion foam is essential to determine the effectiveness of blanketing effect, since water provides the boil-off effect.

Modeling of Fischer-tropsch Product Distribution over Fe-based Catalyst

Modeling of Fischer-Tropsch Product Distribution over Fe-based Catalyst Branislav Todic, Tomasz Olewski, Nikola Nikacevic, Dragomir B. Bukur* a Chemical Engineering Program, Texas A&M University at Qatar, PO Box 23874, Doha, Qatar b Faculty of Technology and Metallurgy, University of Belgrade, Karnegijeva 4, Belgrade, Serbia c Artie McFerrin Department of Chemical Engineering, Texas A&M University, 3122 TAMU, College Station, TX 77843, USA dragomir.bukur@qatar.tamu.edu

Small-scale experimental study of vaporization flux of liquid nitrogen released on water.

A small-scale experimental study was conducted using liquid nitrogen to investigate the convective heat transfer behavior of cryogenic liquids released on water. The experiment was performed by spilling five different amounts of liquid nitrogen at different release rates and initial water temperatures. The vaporization mass fluxes of liquid nitrogen were determined directly from the mass loss measured during the experiment. A variation of initial vaporization fluxes and a subsequent shift in heat transfer mechanism were observed with changes in initial water temperature. The initial vaporization fluxes were directly dependent on the liquid nitrogen spill rate. The heat flux from water to liquid nitrogen determined from experimental data was validated with two theoretical correlations for convective boiling. It was also observed from validation with correlations that liquid nitrogen was found to be predominantly in the film boiling regime. The substantial results provide a suitable procedure for predicting the heat flux from water to cryogenic liquids that is required for source term modeling.

Modelling of LNG Pool Spreading on Land with Included Vapour-Liquid Equilibrium and Different Boiling Regimes

This paper presents a source term model for estimating the rate of unconfined LNG pool spreading on land. The model takes into account the composition changes of a boiling mixture, the variation of thermodynamic properties due to preferential boiling in the liquid mixture and the effect of boiling regime on conductive heat transfer. The heat, mass and momentum balance equations were solved for continuous and instantaneous spills. A sensitivity analysis was conducted to determine the relative effect of each of these phenomena on pool spreading. The model was compared to a commonly used gravityinertia integral pool-spreading model with one-dimensional conductive heat transfer. 1. Introduction Although some pool spreading models have been developed as outlined by Webber et al. (2010), most of them are integral models and based on work carried out in the early 1970’s on non-volatile liquid spills. These early models tend to overlook the complexity associated with cryogenic pool spreading. Cryogens (e.g. LNG: boiling point = -162 °C) exhibit vigorous boiling upon being released on land or water at ambient temperature. In the case of an LNG release, some of the LNG will flash while rest will spread very quickly. The conditions of heat transfer from the surroundings and the composition of the LNG mixture may affect the spread rate and the vaporization rate. Most of the current modelling work on LNG spillage estimates the LNG properties either using fixed thermo-physical properties of a mixture or using those of pure methane as an analogue. This is questionable since the vaporization behaviour of a mixture is different from that of a pure fluid due to preferential boil-off of the lighter hydrocarbons, which in turn results to time varying properties of the spilled mixture. The complex phenomena governing the spread and vaporization of a LNG pool have to be accounted for and their relative importance must be understood to develop a comprehensive model that is both adaptable and applicable to a variety of scenarios. In this paper, a pool-spreading model that takes into account the composition changes of a boiling LNG mixture, the effect of different boiling modes on conductive heat transfer as well as the varying mixture thermodynamics and vapour liquid equilibrium effects is proposed. A sensitivity analysis is conducted to identify the relative importance of each of the governing parameters on the pool spreading process. The model incorporates the multicomponent nature of LNG and its effect on the behaviour of the spill with the aim of developing the most accurate and comprehensive representation of the pool spreading process.

Qatar, LNG, Spill Experiments and Process Safety

Publisher Summary The Liquefied Natural Gas (LNG) industry is developing rapidly throughout the world. The need for internationally accepted design standards and risk assessment procedures for land based LNG facilities is stressed. Risk assessments necessitate modeling worst credible scenarios using the best available techniques. The Health and Safety Laboratory (HSL) and National Fire Protection Association (NFPA) have summarized LNG field trial data that can be used for validation of models and software. The LNG industry has an enviable safety record: this includes offshore exploration and production, onshore processing, storage, tanker loading, transportation and offloading, and storage and re-gasification. But because of the international aspect of LNG trading a single major incident would probably have worldwide ramifications. Operations in all parts of the LNG industry must be subjected to the most rigorous risk assessments and facilities designed so that they remain adequately safe for both operators and the public even during worst credible maloperations.