Luc Véchot

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.

Evaluation of the Thermal Runaway Decomposition of Cumene Hydroperoxide by Adiabatic Calorimetry

Many industrial accidents in the recent past showed that the thermal decomposition of Cumene Hydroperoxide (CHP) can lead to runaway reactions and subsequent fires and explosions. Still this organic peroxide is extensively used in the petrochemical industry. This paper is aimed at a better understanding of the possible consequences of CHP decomposition by analyzing its thermal behavior when dissolved in a high boiling point solvent using two different adiabatic calorimeters. The experimental data obtained allowed us to assess the general trends on the main runaway parameters and to characterized the thermal decomposition of the mixture with respect to the peroxide concentration, as well as the influence of the thermal inertia of the equipment. The gas generation rate for each of experiment was calculated and then corrected to adiabatic conditions. The data generated can assist as a guidance for designing processes where CHP is involved, along with their safeguards.

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.

Vent sizing: analysis of the blowdown of a hybrid non tempered system.

The runaway and blowdown of a non tempered hybrid chemical system (30% cumene hydroperoxide) exposed to an external heat input was investigated using a 0.1l scale tool. The maximum temperature and the maximum temperature rise rate were showed to be sensitive to the vent size. An Antoine type correlation between the maximum temperatures and pressures was observed. These resulted from the presence of vapour, mainly generated by the reaction products. Increasing the initial filling ratio resulted in an earlier vent opening but did not have a significant influence on the blow-down. Three types of mass venting behaviour were observed, when changing the vent area to volume ratio (A/V): • for large A/V, two-phase venting occurred from the vent opening until the end of the second pressure peak; • for medium A/V, two-phase venting occurred before and after the turnaround. The data seem to indicate that gas only venting occurred at turn-around; • for low A/V, two-phase venting was observed only after the second pressure peak. Two-phase venting after the second pressure peak probably results from the boiling of the hot reaction products at low pressure.

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.