氯碱生产中氢气火灾爆炸事故树分析

氢气火灾爆炸事故是氯碱生产中最常见的事故之一.在对焦作化电集团实际调研的基础上,采用系统安全分析方法中的事故树分析方法对氢气火灾爆炸事故进行了定性、定量分析.给出了氢气火灾爆炸事故树图,事故树的最小割集、最小径集以及3种重要度.最后基于事故树分析提出了预防事故发生的安全防范措施.     

Current status and expected future trends in dust explosion research

In spite of extensive research and development for more than 100 years to prevent and mitigate dust explosions in the process industries, this hazard continues to threaten industries that manufacture, use and/or handle powders and dusts of combustible materials. Lack of methods for predicting real dust cloud structures and flame propagation processes has been a major obstacle to prediction of course and consequences of dust explosions in practice. However, work at developing comprehensive numerical simulation models for solving these problems is now on its way. This requires detailed experimental and theoretical studies of the physics and chemistry of dust cloud generation and combustion. The present paper discusses how this kind of work will promote the development of means for prevention and mitigation of dust explosions in practice. However, progress in other areas will also be discussed, e.g. ignition prevention. The importance of using inherently safe process design, building on knowledge in powder science and technology, and of systematic education/training of personnel, is also emphasized.     

Does your facility have a dust problem: Methods for evaluating dust explosion hazards

The hazards of dust explosions prevailing in plants are dependent on a large variety of factors that include process parameters, such as pressure, temperature and flow characteristics, as well as equipment properties, such as geometry layout, the presence of moving elements, dust explosion characteristics and mitigating measures. A good dust explosion risk assessment is a thorough method involving the identification of all hazards, their probability of occurrence and the severity of potential consequences. The consequences of dust explosions are described as consequences for personnel and equipment, taking into account consequences of both primary and secondary events.While certain standards cover all the basic elements of explosion prevention and protection, systematic risk assessments and area classifications are obligatory in Europe, as required by EU ATEX and Seveso II directives. In the United States, NFPA 654 requires that the design of the fire and explosion safety provisions shall be based on a process hazard analysis of the facility, process, and the associated fire or explosion hazards. In this paper, we will demonstrate how applying such techniques as SCRAM (short-cut risk analysis method) can help identify potentially hazardous conditions and provide valuable assistance in reducing high-risk areas. The likelihood of a dust explosion is based on the ignition probability and the probability of flammable dust clouds arising. While all possible ignition sources are reviewed, the most important ones include open flames, mechanical sparks, hot surfaces, electric equipment, smoldering combustion (self-ignition) and electrostatic sparks and discharges. The probability of dust clouds arising is closely related to both process and dust dispersion properties.Factors determining the consequences of dust explosions include how frequently personnel are present, the equipment strength, implemented consequence-reducing measures and housekeeping, as risk assessment techniques demonstrate the importance of good housekeeping especially due to the enormous consequences of secondary dust explosions (despite their relatively low probability). The ignitibility and explosibility of the potential dust clouds also play a crucial role in determining the overall risk.Classes describe both the likelihood of dust explosions and their consequences, ranging from low probabilities and limited local damage, to high probability of occurrence and catastrophic damage. Acceptance criteria are determined based on the likelihood and consequence of the events. The risk assessment techniques also allow for choosing adequate risk reducing measures: both preventive and protective. Techniques for mitigating identified explosions risks include the following: bursting disks and quenching tubes, explosion suppression systems, explosion isolating systems, inerting techniques and temperature control. Advanced CFD tools (DESC) can be used to not only assess dust explosion hazards, but also provide valuable insight into protective measures, including suppression and venting.     

旋风除尘器静动态强度分析

对旋风除尘器在静态载荷下的强度进行了分析,发现头部顶板是较薄弱部件.通过动态载荷系数(DLF)方法,研究了旋风除尘器承受动态粉尘爆炸压力载荷时提高使用强度的可能性,结果表明,一般情况下,由于载荷的动态特性导致设备强度的变化可以忽略.     

Parametric study of the explosivity of graphite-metals mixtures

The explosivity of dust clouds is greatly influenced by several parameters which depend on the operating conditions, such as the initial turbulence, temperature or ignition energy, but obviously also on the materials composition. In the peculiar case of a mixture of two combustible powders, the physical and chemical properties of both dusts have an impact on the cloud flammability and on its explosivity. Nevertheless, no satisfactory ‘mixing laws’ predicting the mixture behavior are currently available and the composition variable to be considered for such models greatly depend on the safety parameters which have to be determined: from volume ratios for some thermal exchanges and ignition phenomena, to surface proportions for some heterogeneous reactions and molar contents for chemical reactions. This study is mainly focused on graphite/magnesium mixtures as they are encountered during the decommissioning activities of UNGG reactors (Natural Uranium Graphite Gas). Due to the different nature and reactivity of both powders, these mixtures offer a wide range of interests. Firstly, the rate-limiting steps for the combustion of graphite are distinct from those of metals (oxygen diffusion or metal vaporization). Secondly, the flame can be thickened by the presence of radiation during metal combustion, whereas this phenomenon is negligible for pure graphite. Finally, the turbulence of the initial dust cloud is modified by the addition of a second powder. In order to assess the explosivity of graphite/magnesium clouds, a parametric study of the effects of storage humidity, particle size distribution, ignition energy, and initial turbulence has been carried out. In particular, it was clearly demonstrated that the turbulence significantly influences the explosion severity by speeding up the rate of heat release on the one hand and the oxygen diffusion through the boundary layer surrounding particles on the other hand. Moreover, it modifies the mean particle size and the spatial dust distribution in the test vessel, impacting the uniformity of the dust cloud. Thus, the present work demonstrates that the procedures developed for standard tests are not sufficient to assess the dust explosivity in industrial conditions and that an extensive parametric study is relevant to figure out the explosive behavior of solid/solid mixtures subjected to variations of operating conditions.     

基于本质安全的化工工艺物质危险指数研究

建立了基于本质安全的化工工艺物质危险性的评价体系,包括火灾危险性、爆炸危险性以及毒性等3个评价指数.基于风险的思想,各个评价指数均包括概率指标与后果指标.为了全面反映化工工艺的实际情况,在各个评价指数中均对所有物质的相应指数值加和.参数的取值以以往的指数法为基础,为了消除边界波动效应,取值采用内插法.由于各个指数的量纲...     

管道燃气火灾爆炸事故树分析

在调查与研究的基础上,采用安全系统工程的方法,对城市管道燃气火灾爆炸事故进行了事故树分析。文中给出的由201个基本原因事件和81个逻辑门所构成的管道燃气火灾爆炸事故树分析图,直观地表现了各可能导致顶上事件发生的初始因素及其逻辑关系,经对FT的求解,得出了243个最小径集,指明了预防事故发生的可能途径;在对采用各可能预防途径的可行性,经济性,可操作性进行充分的考虑与比较后,确定出了城市管道燃气火灾爆炸事故预防措施,并做出安全检查表,以供现场实施使用;最后提出了提高燃气安全运行水平的建议。     

灰关联分析在故障树诊断中的应用

介绍一种灰色诊断法.在故障诊断模式识别中,运用灰关联分析,依据故障树的底事件重要度,通过关联度计算及排序,对故障树分析中,各种故障模式发生的可能性大小作出了准确的判断,从而为处理事故的先后、缓急提供了依据.