Suppression of methane explosions in a field-scale pipe

Suppression of passive and active explosions has been investigated in a field-scale pipe in this paper. Water recognized effective in explosion suppression has been chosen as the extinguishing agent, and the water mist formed by home developed passive and active explosion suppressors has been proved successfully to meet the practical requirements. The experimental results showed that the suppression effects depend on the density and length of water mist suspended inside the pipe, and both passive and active explosion suppressors can fully quench the explosion of methane–air mixture with the filling of enough water. The larger the mist density and length is, the better the suppression effect becomes. For passive explosion suppression, two suppressors with different arrangements have been discussed. Moreover, a critical curve was plotted based on the experimental results of active explosion suppressions, which can be applied to evaluate the suppression effects practically.     

聚丙烯车间12m3釜聚合岗危险分析及安全措施

聚合岗位是石油化工厂聚丙烯车间重要且非常危险的岗位,一旦发生意外事故,将会导致人员的重大伤亡和巨大的经济损失。笔者依据聚丙烯车间生产现状,详细地介绍了12m3 釜聚合岗位工艺流程,用“系统安全”的理论和方法对其主要物质、生产工艺、操作过程的危险性进行了辨识,且绘制了主要危险点分布图;通过危险源辨识可知,聚合釜具有的超温、超压特点是该岗位众多危险源中最为严重的潜在危险,应用“事故树法”对聚合釜超温、超压爆炸事故进行了危险分析,找出其爆炸潜在的危险因素有2 4种,该事故树的最小割集共有6 6个,表明聚合釜爆炸可能性是很大的。依据分析结果,针对聚合釜爆炸可能性最大的危险因素,提出了安全对策与措施,以避免或减少爆炸事故的发生     

Modelling large-scale vented gas explosions in a twin-compartment enclosure

Natural gas and LPG are common fuels that have been used relatively safely in the home for many decades. However, when there is a release of gas within a dwelling, or gas from a leaking external pipeline migrates into a building, an explosion may occur. Most of the experimental research into vented gas explosions has been conducted in single enclosure, cuboid or spherical geometries which are not representative of accidental explosions in dwellings or process industries. This paper discusses the findings of a comprehensive large-scale experimental programme undertaken by British Gas Research and Development and also compares FLACS CFD (Computational Fluid Dynamics) simulations against a number of these experiments. The results suggest that the software is useful in gaining a greater understanding of the dynamics of explosion development in dwellings. The paper highlights areas of good performance of the software as well as areas of shortcomings where further understanding and modelling effort is needed.     

Suppression of cone discharges in a powder silo using a grounded metal rod

While filling a large silo with coarse nonconductive powders, strong electrostatic sparks known as a cone discharge, which can become sufficiently energized to ignite a flammable dust cloud, often occur on the surface of a powder heap. In an attempt to mitigate or eliminate a cone discharge, a long metal rod with a pointed tip or a flat tip was vertically installed in the center of an experimental silo (1.5 m in diameter, 2 m in effective height) with the objective that the static charge might be released by the corona discharges or the surface potential of the powder heap reduced by the electric field reducing effect. The experimental results are summarized as follows:(1) No cone discharges were observed while the silo was being filled with polypropylene pellets when either a pointed tip or a flat-tip rod was installed so that its lower end was located 10 cm above or 30 cm below the heap surface level. A corona discharge that occurred on the pointed tip was shown to be effective to some extent in reducing the charge of the powder heap.(2) Brush discharges were observed near the metal rod and its support. However, we assume that the maximum energy was not high enough to ignite a dust cloud with minimum ignition energy greater than 3 mJ.     

Process of accidental explosions at a refuse derived fuel storage

Accidental gas explosions occurred at a refuse-derived-fuel (RDF) storage in Japan, and two fire fighters on duty were dead. The flammable gases, which caused the gas explosions generated during a RDF fire. It means that gas explosions could occur in the use of solid fuels under certain conditions. This study has been conducted for exploring the process to gas explosions in the RDF storage. The temperature at a part of the RDF pile in the storage was inferred to spontaneously increase, and the prediction of the temperature increase was attempted on the basis of the Frank-Kamenetskii theory. It was shown that the critical temperature of RDF for spontaneous temperature rise depends on the size of the pile. Larger the pile, lower the critical temperature. The possibility of accumulation of flammable gas in the space of the RDF storage is discussed. It is indicated that the spread rate of thermal wave is slow and a high temperature region likely established. After the RDF pile ignites, the oxygen concentration near the burning site becomes low and the flammable species components in the generated gas increases. Those species pass through surrounding low temperature region and come out into the space over the RDF pile without combustion. An explosion would occur when a fresh air comes into the storage, mixes with the flammable gas coming out from the pile to form a flammable mixture, and then the flammable mixture ignites. The most effective means to prevent accidental explosions is to avoid spontaneous ignition by cooling the heated RDF. If spontaneous ignition occurs, elimination of flammable gases from the storage should be strongly recommended.     

Modelling the mitigation of a hydrogen deflagration in a nuclear waste silo ullage with water fog

During the decommissioning of certain legacy nuclear waste storage plants it is possible that significant releases of hydrogen gas could occur. Such an event could result in the formation of a flammable mixture within the silo ullage and, hence, the potential risk of ignition and deflagration occurring, threatening the structural integrity of the silo. Very fine water mist fogs have been suggested as a possible method of mitigating the overpressure rise, should a hydrogen–air deflagration occur. In the work presented here, the FLACS CFD code has been used to predict the potential explosion overpressure reduction that might be achieved using water fog mitigation for a range of scenarios where a hydrogen–air mixture, of a pre-specified concentration (containing 800 L of hydrogen), uniformly fills a volume located in a model silo ullage space, and is ignited giving rise to a vented deflagration. The simulation results suggest that water fog could significantly reduce the peak explosion overpressure, in a silo ullage, for lower concentration hydrogen–air mixtures up to 20%, but would require very high fog densities to be achieved to mitigate 30% hydrogen–air mixtures.     

Study of the propagation of kerosene explosions inside a partitioned vessel

The aim of this work is to present a simple modelling in order to predict the evolution of the thermodynamical characteristics of the combustion of kerosene droplets in each compartment of a closed or a vented vessel.A simple representation of the combustion phenomena based on energy transfers and the action of specific molecular species is presented.The fuel ratio of the mixture is defined by the experimental determination of the partial pressure of the kerosene vapors. The total mass rate of gaseous substances due to the difference of pressure between adjacent compartments or the surrounding atmosphere is calculated by the standard orifice equations. A calculation methodology is developed to simulate the transmission of the explosion from one compartment to another adjacent compartment in simple structures with a possible extension to complex multi-partitioned structures. The model allows the study in each compartment of the influence of various parameters such as the fuel ratio of the mixture, the size of the inner openings or the venting effects.Calculation and experimental results show that in all cases, overpressures appear in the adjoining areas to the ignition compartment.     

Development of a limit state approach for design against gas explosions

The design of topsides against explosions requires the definition of a design over-pressure, however, these values are often treated as deterministic and there is a wide variation within the industry in the treatment and interpretation of the loads.

This paper advocates the adoption of a number of limit state for explosion loading. Events of different magnitudes are differentiated on the basis of frequency and linked to appropriate degree of reliability thus avoiding disproportionate effects from minor events.

The two principal limit states considered are a limit state for all the safety critical systems for relatively high frequency events and a survival condition for low probability events. Parallels are drawn from other branches of engineering where extreme loads have to be designed for.     

Numerical simulation of gas explosions in linked vessels

The ability of the CFD code AutoReaGas to simulate a gas explosion in two linked vessels was investigated. These explosions present an anomalous destructive power because both peak pressures and rates of pressure rise are much higher than those generated in single vessel explosions. A fair agreement was observed between the computed results and experimental data taken from literature. Moreover, the computed values of the turbulence intensity at varying diameters of the connecting pipe demonstrate that turbulence induced in both vessels represent a major factor affecting the explosion violence.     

Flame-propagation behavior and a dynamic model for the thermal-radiation effects in coal-dust explosions

To reveal the flame-propagation behavior and the thermal-radiation effects during coal-dust explosions, two coal-dust clouds were tested in a semi-enclosed vertical combustion tube. A high-speed video camera and a thermal infrared imaging device were used to record the flame-propagation process and the thermal-radiation effects of the fireball at the combustion-tube outlet. The flame propagated more quickly and with a higher temperature in the more volatile coal-dust cloud. The coal-dust concentration also significantly affected the propagation behavior of the combustion zone. When the coal-dust concentration was increased, the flame-propagation velocity and the fireball temperature increased before decreasing overall. Based on the experimental results, a dynamic model of the thermal radiation was employed to describe the changes in the fireballs quantitatively and to estimate the thermal-radiation effects during coal-dust explosions.     

Gas-phase thermal explosions in catalytic direct oxidation of alkenes

The metal-based catalytic oxidation of alkenes to the corresponding epoxides is playing a significant role in the modern chemical industry. Nevertheless, these key processes are still lacking proper understanding with respect to the gas-phase runaway behaviour (thermal explosion) and to the hot spot formation on the catalytic surface, under the typical process conditions.This work aims to enlighten these aspects by considering either the catalytic or the gas-phase chemistry for the development of reactor operative diagrams, in order to define the best-operating conditions with respect to the selectivity, the productivity, and the process safety aspects.The proposed methodology has been applied to the oxidation of ethylene and propylene for the direct oxidation process by pure oxygen, considering a detailed kinetic model accounting for the homogeneous reactions, coupled with the heterogeneous catalytic mechanisms.Sensitivity and reaction path analyses were performed to individuate the ruling species and reactions determining the transition to runaway conditions.     

Evaluating the overall efficiency of a flameless venting device for dust explosions

Results from cornstarch explosion tests using a flameless venting device (mounted over a burst disc) on an 8 m³ vessel are presented and used to determine the overall efficiency of the device, which is defined as the ratio between its effective vent area and the nominal vent area. Because these devices are comprised of an arrestor element mounted over an impulsively-actuated venting device (such as a burst disc), the functional form of the overall efficiency is taken as the product of the area efficiency (i.e., the ratio between the effective vent area of the entire assembly to that of the venting device without the arrestor element) and the burst efficiency (i.e., the ratio of the effective vent area of the venting device without the arrestor element to the nominal vent area). The effective vent areas are calculated from measured overpressures using three different empirical correlations (FM Global 2001, NFPA 2007, and VDI 2002). Furthermore, due to significant variations in the effective reactivity from test to test, a correction factor proportional to the initial flame speed is applied when determining the area efficiency. In general, it was found that the FM Global and NFPA methodologies yield consistent results with less scatter than VDI 3673.     

Prevention of gasoline vapor explosions in portable fuel containers

Portable Fuel Containers (PFCs) made for consumer use can, under unusual circumstances, develop a flammable atmosphere in the container headspace. In order to prevent an inadvertent ignition from causing flame propagation into this headspace and a subsequent explosion or flame jetting, PFC manufacturers are developing prototype Flame Mitigation Devices (FMDs) for installation in the PFC. A test method is described in this paper to determine if the installed FMD will indeed prevent flame entry into the PFC in a high-challenge flame propagation scenario. The method entails the use of a butane-air mixture ignited in a 5 cm diameter, 12 cm long tube attached to either the container neck or a spout on the container neck. Two concept FMD designs have successfully prevented repeated attempts at flame propagation into the PFC and have also produced encouraging results in tests for fuel flow restriction, duel dispensing nozzle friction, and prolonged fuel exposure. Versions of these tests are currently being promulgated in a draft ASTM standard on PFC FMDs.     

Computational modeling of vapor cloud explosions in off-shore rigs using a flame-speed based combustion model

Computational modeling is a useful tool in determining the consequences from vapor cloud explosions. Here an approach that uses a flame-speed based combustion model is evaluated. Various scenarios of explosions in full-scale off-shore modules are simulated and compared to available test data. The ignition location of the cloud and available venting paths are found to affect the overpressure field in and outside the module. For end ignition cases, the combustion of gas pushed out of the module is found to play a key role. Using the flame-speed based model with appropriate effective flame speeds is found to provide accurate simulations.     

节能减排技术在3200m3高炉系统的应用

在唐钢3 200m3高炉系统建设中,通过采用大喷煤量、辅助热风炉预热助燃空气、明特克法炉渣处理工艺、干法煤气净化、厚料层烧结、TRT高炉余压发电等先进的生产工艺,合理开发利用资源,实现循环经济.坚持环保"三同时"制度,实现了3 200m3高炉及其配套系统的节能减排.     

10000M3煤气柜爆炸事故分析

2003年9月15日17时20分,陕西省某钢铁企业10000M3煤气柜发生爆炸,造成5人当场死亡,1人抢救无效死亡,3人受伤的重大生产安全事故,直接经济损失50多万元.     

Consequences assessment of explosions in pipes using coupled FEM-SPH method

Explosions often lead to destruction of equipment, which is a difficult problem including complicated fluid-solid interactions. Most traditional CFD methods cannot synchronously solve the movements of fluids and large deformation and fracture of solids because such problem is usually accompanied with constantly moving-and-changing boundary conditions. In this paper, a coupled Finite Element Method-Smoothed Particle Hydrodynamics (FEM-SPH) method was proposed to simulate the dynamic processes of explosions in pipes. The propagation of blast wave and the fracture of pipe were captured in every timestep, where the energy dissipation caused by plastic deformation and crack propagation were fully considered. A rate-dependent failure criterion for high-strain-rate load conditions was employed in the numerical simulation, which was presented in our previous work and has been verified in the dynamic fracture behavior of steels for pressure vessels and pipes. In addition, a simpler formula was proposed to describe the attenuation of blast wave outside the pipe and the consequences caused by the explosions were assessed. Results revealed the interaction between blast wave and pipe, the leakage of detonation products, the attenuations of peak overpressures outside the pipe and the corresponding consequences at different distances. It is found that when considering the energy consumption during plastic deformation and crack propagation in coupled FEM-SPH method, the assessment results are more rational than that without considering such energy consumption.     

Some aspects in testing and assessment of metal dust explosions

The dust explosion committee of the Association of Powder Process Industry and Engineering, Japan recently established two testing standards for dust explosions. In the investigations for the standardization, many experimental data have been obtained for the dusts currently used in Japanese industries. Data for zirconium, tantalum and silicone dusts are presented to discuss the use of test methods, which have been accepted internationally. The test methods for dust explosions have to consider a variety of kinds and forms of dusts to be tested.