Vapor Explosion Research Articles

Predicting the vaporization rate of a spreading cryogenic liquid pool on concrete using an improved 1-D heat conduction equation

The accidental spilling of cryogenic liquid leads to formation of a spreading pool, which may result in pool fires, BLEVE(boiled liquid evaporate vapor explosion) or vapor cloud fire, such as liquefied natural gas, is flammable. The key aspect of evaluating the consequence of such a disaster is to predict vaporization rate of the spreading cryogenic liquid pool. In this study, an empirical function was established to predict the temperature gradient of concrete. Afterwards an improved 1-D heat conduction equation was established to predict heat conduction of the spreading cryogenic liquid, and then vaporization rate was measured. In addition, to validate accuracy of the improved 1-D heat conduction equation, small-scale experiments were conducted to calculate vaporization rate for a spreading cryogenic liquid pool. The resulting vaporization rate decreased with discharge time, and increased with spill rate. The established empirical function was used to predict the temperature gradient displayed satisfactory accuracy with absolute average relative errors (AAREs) less than 10%; the improved 1-D heat transfer model AAREs were less than 13% compared with the experimental value. In summary, the improved 1-D heat transfer model can be applied to predict vaporization rate if the spill rate and discharge time are confirmed.

Simulation and preliminary validation of a three-phase flow model with energy

This paper is devoted to the simulation of the three-phase flow model [20], in order to account for immiscible components. The whole model is first recalled, and the main properties of the closed set are given, with particular focus on the Riemann problem associated with the convective subset that contains non-conservative terms, and also on the relaxation process. The model is hyperbolic, far from resonance occurrence, and a physically relevant entropy inequality holds for smooth solutions of the whole system. Owing to the uniqueness of jump conditions, specific solutions of the one-dimensional Riemann problem can be built, and these are useful (and mandatory) for the verification procedure. The fractional step method proposed herein complies with the continuous entropy inequality, and implicit schemes that are considered to account for relaxation terms take their roots on the true relaxation process. Once verification tests have been achieved, focus is given on the simulation of the experimental setup [8, 9], in order to simulate a cloud of droplets that is hit by an incoming gas shock-wave. Finally, the study of a three-phase flow setup involving thermal effects is presented, it is based on the KROTOS experiment [25] which focuses on vapour explosion simulation.

Inhibition of the Wall-attached Fuel Combustion and the Formation of Aerosol Particle

The wall-attached fuel layer of the combustor usually leads to an unstable combustion and produces an unexpected emission, such as aerosol particles and unburn hydrocarbons. In this study, the impaction of ethanol droplet on a heated liquid surface was examined for investigating the factors those could effectively control the fuel atomization and avoided the formation of wall-attached fuel layer. We accelerated the volatilization of ethanol droplets after contacting the liquid surface and even achieved the flash evaporation condition to burst the oil layer, which was conducive to cleaning the inner wall of the combustors and reducing emissions. A 3.12-mm ethanol droplet was used to impact a glycerol pool. The Weber number (WE, 303–1343) and pool temperature (T, 50–260°C) were two controlled parameters to explore the impaction characteristics. There were four typical phenomena observed, including surface dissolving, penetrating dissolution, vapor explosions, and nucleate boiling. Results showed that the maximum volume and surface area of the crater increased with the WE and the liquid pool temperature during impaction. Meanwhile, the boundary temperatures between the penetrating dissolution and the vapor explosion decreased. Additionally, the vapor explosion time increased with the WE but negatively correlated to the liquid pool temperature. The entire vapor explosion process was very short, lasting about 200 milliseconds. Furthermore, the increasing WE had a negative effect on the nucleate boiling intensity when the liquid pool temperature significantly enhanced it. Consequently, the fuel droplet atomization and explosion could be sensitively controlled by varying the WE and the temperature of impaction surface. This finding provides valuable information to the designer of combustor control unit to inhibit and destroy the wall-attached fuel layer during the spry combustion and further inhibit the formation of combustion aerosol particles.

Оценка динамических нагрузок на стены и перекрытие подреакторного помещения РБМК-1000 при паровом взрыве

One of the conditions for the safe operation of a nuclear power plant (NPP) unit is a comprehensive design and experimental justification of its failure-free operation in all operating modes and limitation of accident radiation consequences, including those in the case of severe beyond design basis accidents. According to the nuclear power industry development plans in Russia, new NPPs equipped with RBMK-1000 reactors are not supposed to be constructed in the future. Although the assigned service life of RBMK-1000 based power units that remain in operation is close to expiration, these power units account for most of the electricity generation in the total amount of nuclear power capacities in Russia (about 40%); therefore, the relevant industry organizations have decided to extend their operation. This article analyzes the severe accident evolvement scenario at an RBMK-based NPP during the stage of severe core damage, in the course of which fuel-containing masses collapse into the subreactor space filled with water. Once fuel-containing masses emerge in the sub-reactor room, they come in interaction with the reactor base concrete. There is a potential danger of the concrete floor slab melting and the corium collapsing into the bubbler pool water. The main strategy foreseen for keeping the molten core within the reactor space boundaries involves decay heat removal from the reactor and cooling of the support metal structures by supplying water. However, the filling of the subreactor space with liquid may give rise to conditions under which vapor explosion can occur. The maximum dynamic impact applied to the RBMK-1000 subreactor room walls in the event of possible interaction between the molten corium and water during a severe beyond design basis accident is estimated. It is shown that when the corium melt interacts with a large amount of water in the subreactor room, the kinetic energy of the resulting water vapor is sufficient to cause significant destruction of the power unit building. When the water level in the subreactor room falls below one meter, the destruction hazard becomes less probable. The mass of hydrogen released as a result of the interaction is also estimated.

Heat Transfer Considerations on the Spontaneous Triggering of Vapor Explosions—A Review

Vapor explosions have been investigated both theoretically and experimentally for several decades, focusing either on the vapor film, or on mechanical aspects. Where the main interest for industry lies in the safety risks of such an event, fundamental research is focusing on all partial processes that occur during a vapor explosion. In this paper, vapor explosions are discussed from a heat transfer point of view. Generally accepted knowledge of heat transfer between hot surfaces and liquids is compared to early investigations regarding the origin of vapor explosions. Both steady state and transient models are discussed. The review of available literature suggests that vapor explosions trigger spontaneously by the collapse of the boiling film. Better understanding of the fundamental aspects of vapor explosions might give rise to future ideas on how to avoid them.

Drying and heating of scrap metal at steelmaking: industrial safety, economics, ecology

At steel production based on scrap metal utilization, the scrap heating before charging into a melting facility is an important way of energy efficiency increase and ecological parameters improving. In winter time scrap metal charging with ice inclusions into a metal melt can result in a considerable damage of equipment and even accidents. Therefore, scrap preliminary drying is necessary to provide industrial safety. It was shown, that in countries with warm and low-snow climate with no risk of scrap metal icing up during its transportation and storing in the open air, the basic task being solved at the scrap drying is an increase of energy efficiency of steelmaking. InRussiathe scrap metal drying first of all provides the safety of the process and next - energy saving. Existing technologies of scrap metal drying and heating considered, as well as advantages and drawbacks of technical solutions used at Russian steel plants. In winter time during scrap metal heating at conveyers (Consteel process) hot gases penetrate not effectively into its mass, the heat is not enough for evaporation of wetness in the metal charge. At scrap heating by the furnace gases, a problem of dioxines emissions elimination arises. Application of shaft heaters results in high efficiency of scrap heating. However, under conditions of Russian winter the upper scrap layers are not always heated higher 0 °С and after getting into a furnace bath the upper scrap layers cause periodical vapor explosions. The shaft heaters create optimal conditions for dioxines formation, which emit into atmosphere. It was shown, that accounting Russian economic and nature conditions, the metal charge drying and heating in modified charging buckets by the heat of burnt natural gas or other additional fuel is optimal. The proposed technical solution enables to burnt off organic impurities ecologically safely, to melt down ice, to evaporate the wetness in the scrap as well as to heat the charge as enough as the charging logistics enables it. The method was implemented at several Russian steel plants. Technical and economical indices of scrap metal drying in buckets under conditions of EAF-based shop, containing two furnaces ДСП-100, presented.

Research of mechanisms of interaction of melt and coolant by means of small-sized experiments with solid and liquid metal samples

Several basic fragmentation hypotheses described in the literature for the case of fine-scale spontaneous vapor explosion, when single hot drops are falling in the coolant, are analyzed. It is shown that all of them, depending on the experimental conditions, describe the real physical phenomena. It is highlighted, that the process of fragmentation during the spontaneous vapor explosion is directly connected to the regime of the film boiling collapse of the underheated liquid, which is still underexplored. The experiments on the liquid drops fragmentation are complemented by those with surface boiling at the solid metal samples of semi-spherical form. The connection between the vapor explosion of water and the increase of the surface wettability is confirmed. The video material, indicating the possibility of formation of liquid jets that strike the hot surface during the collapse of the vapor shell, is obtained. The time interval (duration of the contact) between the first contact of the coolant with the hot surface and the explosion boiling of the liquid is experimentally determined. The dependence of the contact duration on the temperature of the overheated wall is determined and its comparison with the theoretical estimations is provided.

An innovative and comprehensive approach for the consequence analysis of liquid hydrogen vessel explosions

Hydrogen is one of the most suitable solutions to replace hydrocarbons in the future. Hydrogen consumption is expected to grow in the next years. Hydrogen liquefaction is one of the processes that allows for increase of hydrogen density and it is suggested when a large amount of substance must be stored or transported. Despite being a clean fuel, its chemical and physical properties often arise concerns about the safety of the hydrogen technologies. A potentially critical scenario for the liquid hydrogen (LH2) tanks is the catastrophic rupture causing a consequent boiling liquid expanding vapour explosion (BLEVE), with consequent overpressure, fragments projection and eventually a fireball. In this work, all the BLEVE consequence typologies are evaluated through theoretical and analytical models. These models are validated with the experimental results provided by the BMW care manufacturer safety tests conducted during the 1990's. After the validation, the most suitable methods are selected to perform a blind prediction study of the forthcoming LH2 BLEVE experiments of the Safe Hydrogen fuel handling and Use for Efficient Implementation (SH2IFT) project. The models drawbacks together with the uncertainties and the knowledge gap in LH2 physical explosions are highlighted. Finally, future works on the modelling activity of the LH2 BLEVE are suggested.

Hazard analysis on LPG fireball of road tanker BLEVE based on CFD simulation

In order to research the hydrocarbon fireball characteristic of LPG tanker Boiled Liquid Evaporate Vapor Explosion (BLEVE) under different conditions, computational fluid dynamics (CFD) simulations of the hydrocarbon fireballs from the LPG tanker BLEVE accidents were carried out. Several new different factors, such as the mass of fuel, inlet velocity and airflow velocity, were considered to analyze the influence on the evolution of the characteristics of the fireball and the development of the LPG tanker BLEVE accidents. Results indicate that the fireball with a greater mass of fuel radiates more heat but slower. The large longitudinal diameter of the fireball and high radiation heat flux are observed in case of a faster inlet velocity used for the same mass. The airflow was found to shorten the initial phase of the fireball effectively. Some suggestions were proposed to prevent the LPG BLEVE accidents. Analysis performed show that various parameters like fireball diameter, radiative heat flux and lifting speed of fireball can be predicted well using FDS code.

Vapor explosion in steel mill industries: Chemical composition analysis on molten slag and coolant

AbstractIt is important to prevent vapor explosion for steel mill industries for the reason that explosions can produce overpressure which cause buildings and facilities to rupture. The spontaneous vapor explosion occurs when a molten slag contacts with coolant. In this research, the molten slag which includes more than 10 chemical compositions produced in actual steel mill industries is employed. Three types of coolant were employed which can be used in real industries such as tap water, freshwater, and yard coolant. Spontaneous vapor explosion occurred when the yard coolant, which has a higher concentration of salt than either tap water or freshwater, was used as coolant. When the vapor explosion occurred, the temperature of the yard coolant was exclusively investigated in the range of 40°C to 55°C. The vapor explosion was independent of the molten slag temperatures employed. The vapor explosion in this work was attributed to the high salt concentration of the yard coolant, which improved the heat transfer to the vapor film around the molten slag droplet. The heat transfer promoted the vapor film to collapse and triggered the spontaneous vapor explosion.

Water droplet impact on high-temperature peanut oil surface: The effects of droplet diameter and oil temperature

A series of experiments on water droplet interaction with high-temperature peanut oil were conducted and the effects of droplet diameter and oil temperature were discussed in the current study. Three typical regimes, including secondary jet, bubble and vapor explosion were observed during the impact process. Especially, water vapor explosion can be induced by solid-liquid contact (Toil≥241 °C) and liquid-liquid contact (Toil≥301 °C). The evolution model of water vapor was proposed and divided into three stages. Furthermore, to characterize the hazards of the vapor explosion, the heat values absorbed by single water droplet and itsmaximum fragmentized daughter droplet were both quantified. It is found that compared with the oil temperature, the droplet size has a more significant effect on the absorption heat of the droplet. For the solid-liquid explosion, with the decrease of the impact droplet diameter, the size of the vapor bubble increases, and resultantly the ratio of the absorption heat of the maximum daughter droplet to that of a single droplet increases. Additionally, the larger the impact droplet size is, the more daughter droplets are formed, resulting in a more violent explosion with long time.

A Study on the Impact of Damage Caused by an Explosion Accident at a Downtown Gas Station: Focusing on Radiant Heat

A common accident that can occur at a gas station is a gas explosion. Assuming that a boiling liquid expanded vapor explosion (BLEVE) occurred at a gas station, a total of 117 scenarios were considered at ambient temperatures of -5.9, 20, and 34.8 °C; relative humidities of 58%, 69%, and 84%; and fill rates of 30 to 90% by changing the storage tank volume by 5%. The scenario was compared and analyzed using the ALOHA BLEVE-Fireball Model. The damage prediction involves the formation of a fire ball by BLEVE that emits radiant heat, which can affect the human body. Human damages were classified as second degree burn, pain, and no pain. The damage evaluation confirmed that pain could be felt over a 987 m radius in the worst conditions. In addition, the second-degree burn and pain areas were significantly affected by the exposure time.

Numerical simulation of medium to large scale BLEVE and the prediction of BLEVE’s blast wave in obstructed environment

After the numerical study of medium-to-large-scale Boiling Liquid Expanding Vapour Explosion’s (BLEVE) in open space (Li and Hao, 2020), this second article focuses on the investigation of the interaction of blast wave with structures in obstructed environment. Currently, pressurized tanks are commonly used as the storage vessels in the oil and gas industry. Pressurized tanks contain high-energy liquid/vapour which, if accidentally released, originates a BLEVE. Although there are already a series of approaches available in literature to estimate blast waves generated from these pressurized tanks, most of these approaches are suitable to predict blast load in the open space only. In this paper, the authors intend to utilize their previously validated numerical approach to predict BLEVE’s peak pressure in different obstructed environments. By carrying out over 200 different simulations of BLEVE, the separation distance effect, obstacle geometry effect and BLEVE’s scale effect on blast wave generation and propagation are studied. A number of simulation-based correlations for pressure prediction are proposed. The Bologna BLEVE that occurred in 2018 is further modelled to investigate the accuracy of the proposed correlations in predicting the peak pressure in the event. The outcome of this study can be used to predict explosion loads for better assessment of their effects on structures.

Evaluation of energy and impulse generated by superheated steam bubble collapse in subcooled water

Collapse of superheated vapor bubbles in subcooled water is studied from the viewpoint of possible mechanisms of premixed zone formation in stratified vapor explosions. Numerical modeling is performed for spherically symmetric bubble collapse in subcooled water, with different initial vapor superheats. The kinetic energy of liquid flow generated due to vapor collapse is obtained. It is shown that the primary mechanism triggering vapor collapse and water flow is vapor cooling in the bubble by colder interface, lowering the vapor pressure and generating necessary pressure drop. Results are compared with an idealized case of bubble vapor maintained at the saturation conditions corresponding to water temperature. Two-dimensional simulations of bubble collapse near solid wall are performed by the boundary element method. Implications to stratified vapor explosions are discussed, and correlations for possible splashing of melt due to the impact of water jets generated by a collapsing steam bubble are obtained.

Fireball modeling and thermal hazards analysis of leaked 1,1-difluoroethane in fluorine chemical industry based on FDS

To better understand the boiling liquid expanding vapor explosions (BLEVE) risk in the fluorine chemical industry, the detailed BLEVE properties of 1,1-difluoroethane were investigated based on fire dynamics simulator code of computational fluid dynamics in this work. The BLEVE fireball was modeled using appropriate numerical models and parameters. The analysis was developed to predict the fireball hazard especially the thermal radiation of 1,1-difluoroethane. The empirical equations of the fireball diameter, height, and duration are modified according to the simulation results. Fireballs have extremely high temperatures and cause strong thermal radiation to the surroundings. In the fluorine chemical industry, the 1,1-difluoroethane fireball can form the thermal radiation of more than 37.5 kW m−2 in the range of 65 m, resulting in high death probability. In addition, the domino effect manifestation of toxic gases inhalation and environmental wind effect on the fireball are also discussed. The results show that the simulation method is accurate and can be used for evaluating the BLEVE scenarios and analyzing the impact on the fluorine chemical facility.

Studies of the TNT equivalence of propane, propane/oxygen, and ANFO

The TNT equivalences of equal masses of propane, a stoichiometric mixture of propane and oxygen, and ammonium-nitrate–fuel-oil (ANFO) were calculated based on the peak hydrostatic and dynamic pressures, the hydrostatic and dynamic pressure positive-phase impulses, and the positive-phase integrated work flux. It was assumed that the propane had been dispersed as a vapour/droplet cloud to form a stoichiometric mixture with atmospheric oxygen before detonation. This is the objective for fuel–air weapons and the worst-case scenario for accidental propane explosions such as boiling liquid expanding vapour explosions. The TNT equivalences of propane/oxygen and ANFO, which have energy yields less than TNT, show little variation when calculated using the different blast wave physical properties. In contrast, the equivalences for propane, which has a significantly higher energy yield than TNT, show a broad range of values, with those based on the impulses being significantly larger than those based on the peak values. The equivalence based on the positive-phase integrated work flux is intermediate between the peak and impulse values. The reasons for these differences are illustrated and discussed.

Risk Factors of Vapor Explosion of Molten Slag in Slag Yard for Steelworks

The risk of vapor explosions has always existed in steelworks that deal with a large amount of high-temperature molten slag. Previous studies on vapor explosions caused by the direct contact of high-temperature molten slag with cooling water were mainly focused on nuclear power plants, whereas there is hardly any research on vapor explosions concerning molten slag in steelworks. Therefore, there is a necessity to understand the causes of vapor explosions occurring during the work process at slag yards. This study analyzed risk factors of potential vapor explosions during the work process at slag yards in steelworks and conducted a small-scale experiment based on field conditions. The experiment found the risk factors that cause vapor explosions at the cooling stage and loading stages of the process and found that spontaneous vapor explosions occurred depending on the temperature of cooling water for molten slag and the contained salinity. Thus, it was confirmed that the significant causes of vapor explosions in the steel industry were the salinity of the cooling water concentrated by seawater desalination and high-water temperature at 50°C caused by the circulation structure of cooling water.

Effects of top vent locations and gasoline volumes on vented gasoline vapor explosion in closed small-scale vessel

In this study, experiments are conducted with a small-scale vessel (cross section of 100 mm × 100 mm and length of 1000 mm) to investigate the effects of a 60 mm × 60 mm vent set on the vessel roof in vented gasoline vapor explosion. Different vent locations and gasoline volumes are considered and compared. The results indicate that the initial gasoline volumes significantly affect the color and propagation characteristics of the flame generated by the explosion. Violent turbulence occurs around the side vent when the flame is ejected through it, and the turbulence near the side vent becomes more intense as the distance between the side vent and the ignitor increases. Subsequently, flame-oscillating propagation behavior is observed. The amplitude of the flame oscillating propagation decreases as the distance between the side vent and the ignitor increases. The maximum explosion overpressure and deflagration index in the pipeline increase linearly as the distance between the side vent and the ignitor increases. The release of power of the gasoline vapor explosion damage can be significantly enhanced by reducing the distance between the side vent and the ignitor. However, a shorter distance between the side vent and the ignitor prolongs the explosion noise, which is harmful to the human ear. The side vent locations and gasoline volumes have negligible effect on the maximum sound pressure level of the explosion noise, which is approximately 120 dB in all cases. Additionally, the flame propagation dynamic process can be reflected to some extent by the change curve of the sound pressure level.

Influence of thermal stratification by fire on heat-mass coupling response mechanism of the liquefied tank

In order to study the explosion-inducing process and thermal response of fire-induced BLEVE(boiling liquid expanding vapor explosion), a small experimental device was established. The radiant heating source was used to simulate the external fire heat effect, and superheated water was used as the medium. The pneumatic ball valve was used to simulate the leakage action. The gas-liquid flow, internal pressure and temperature transient response of the tank during the heating and venting processes were measured, and the superheated process of the medium in the tank was analyzed. The temperature-pressure coupling response after the explosion was traced to investigate the thermal action of the fire on the tank. The experiment found that the heating of the storage tank was the generation and gradual disappearance of temperature stratification. The crack action would result in the breaking of phase equilibrium and pressure rebound. There was an overheat delay in the detonation, and the temperature stratification would prolong the overheat time of the medium. There was a lower limit for the occurrence of the BLEVE accident, the critical stratification degree was used to quantify the limit and the limit of this experimental condition was ξ≤2.33.

A three-dimensional simulation of the effects of obstacle blockage ratio on the explosion wave in a tunnel

In this paper, a three-dimensional simulation has been performed to investigate the potential consequences of flammable vapor explosion in a tunnel with an obstacle, the obstacle with different area blockage ratios (10, 20, 30 and 40%). The blast wave shape, increase in the maximum explosion overpressure, and the arrival time of peak pressure in the vicinity of the obstacle with different blockage ratios have been characterized. The simulation results show that the configuration of the blast wave was remarkably compressed due to the effects of obstacle and the deformation process which can be divided into four stages. The influence of blockage ratio on the maximum overpressure and the arrival time of peak pressure were mainly reflected in the back of the obstacle 1 m from the ground, and the maximum overpressure for this location decreases as the blockage ratio increases. Meanwhile, the maximum overpressure of 10% blockage ratio is 57% higher than that of 40% blockage ratio for the location of the back of obstacle. The arrival time of peak pressures for the location of the back of obstacle is delayed as the blockage ratio increases. The maximum overpressure under the tunnel ceiling showed an opposite trend between the location of the front of the obstacle and the location behind the obstacle. In the front of the obstacle, the maximum overpressure under the tunnel ceiling increases as the blockage ratio increases; however, it decreases as the blockage ratio increases in the back of the obstacle. What’s more, the comparison of this paper’s data and the results from available are published. It was found that the simulation results in this article are consistent with the experimental results of studies.