Moderation of dust explosions

Inherent safety is a proactive approach to process safety in which hazards are removed or minimized so as to reduce risk without engineered (add-on) or procedural intervention. Four basic principles are available to attain an inherently safer design—minimization, substitution, moderation, and simplification. The subject of the current paper is the principle of moderation as it applies to the prevention and mitigation of dust explosions.

Moderation can be achieved by processing a material under less severe operating conditions or by processing the material in a less hazardous form. With respect to the latter approach, it may be possible to alter the composition of a dust by admixture of solid inertants, or to increase the dust particle size so as to decrease its reactivity. Additionally, avoidance of the formation of hybrid mixtures of explosible dusts and flammable gases is an application of moderation of the material hazard.

Several examples are given for each of the above three forms of moderation. The discussion on admixture of solid inertants includes examples from the following industrial applications: (i) refractory materials manufacturing, (ii) food processing, (iii) power generation, (iv) industrial recycling, and (v) foundry shell mold fabrication. The importance of particle size consideration is explained first from the perspective of engineering tools such as the Dow Fire & Explosion Index, and professional guidance on the definition of a dust and suitable particle sizes for explosibility testing. Industrial examples are then drawn from the following areas: (i) rubber recycling and textile manufacturing, (ii) industrial recycling, (iii) wood processing, (iv) dry additive handling (polyethylene facility), (v) polyethylene production, (vi) carbon block recycling, and (vii) coal mining. The concluding discussion on hybrid mixtures includes brief cases from the process safety literature.     

试论蒸汽采暖系统的安全管理

通过对蒸汽采暖系统的热煤压力选择、工程验收以及减压阀的调整管理等几方面的分析 ,阐述了如何确保蒸汽采暖系统安全运行的有关系统保障措施     

Hybrid H2/Al dust explosions in Siwek sphere

Explosion indices and explosion behaviour of Al dust/H₂/air mixtures were studied using standard 20 l sphere. The study was motivated by an explosion hazard occurring at some accidental scenarios considered now in ITER design (International Thermonuclear Experimental Reactor). During Loss-of-Vacuum or Loss-of-Coolant Accidents (LOCA/LOVA) it is possible to form inside the ITER vacuum vessel an explosible atmosphere containing fine Be or W dusts and hydrogen. To approach the Be/H₂ explosion problem, Be dust is substituted in this study by aluminium, because of high toxicity of Be dusts. The tested dust concentrations were 100, 200, 400, 800, and 1200 g/m3; hydrogen concentrations varied from 8 to 20 vol. % with 2% step. The mixtures were ignited by a weak electric spark. Pressure evolutions were recorded during the mixture explosions. In addition, the gaseous compositions of the combustion products were measured by a quadruple mass-spectrometer. The dust was involved in the explosion process at all hydrogen and dust concentrations even at the combination ‘8%/100 g/m3’. In all the other tests the explosion overpressures and the pressure rise rates were noticeably higher than those relevant to pure H₂/air mixtures and pure Al dust/air mixtures. At lower hybrid fuel concentrations the mixture exploded in two steps: first hydrogen explosion followed by a clearly separated Al dust explosion. With rising concentrations, the two-phase explosion regime transits to a single-phase regime where the two fuel components exploded together as a single fuel. In this regime both the hybrid explosion pressures and pressure rise rates are higher than either H₂ or Al ones. The two fuels compete for the oxygen; the higher the dust concentration, the more part of O2 it consumes (and the more H₂ remains in the combustion products). The test results are used to support DUST3D CFD code developed at KIT to model LOCA or LOVA scenarios in ITER.     

Effects of ignitors and turbulence on dust explosions

The aim of this work is in an attempt to increase the understanding of the acting behaviour of pyrotechnic ignitors and their effects on confined dust explosions. Flame visualization has shown that pyrotechnic ignitors can initiate an explosion by instantaneous jet-like volumetric and/or multipoint ignition. Hence, the rate of pressure rise and also the apparent burning velocity will be increased to some extent, depending on the ignitor energy and the reactivity of the mixtures. The ignitor effect is more important for the early stages of flame propagation and would be more significant in small explosion chambers. Thus, for dust explosion tests with various purposes, use of pyrotechnic ignitors should be made carefully, and the ignitor effect must be accounted for in the data interpretation. Turbulence induced by dust dispersion is a dominant factor in affecting dust explosions. At different ignition delays, however, the turbulence influence will be coupled with that of ignitors. This complicates further the interpretation of explosion data measured under turbulent conditions.     

蒸汽系统安全阀泄漏原因分析及改进措施

从技术及管理两方面分析了蒸汽系统安全阀泄漏的原因,提出了预防措施。     

氢气爆炸特性研究

本文研究、总结了氢气与空气(氢气与氧气)的混合物的爆炸特性.即氢气在空气中,在比较低燃烧界限的情况下,只有向上的传播和非常少的超压可以观测得到.正因为氢气的这种特性,将氢应用于科技将极大地推进社会进步,氢燃料将成为一种主要的能源.然而,氢技术应用的成功与否主要取决于氢使用的安全性.所以,必须掌握实际使用时氢气燃烧的性能.本文在日本过去十年实验数据的基础上,通过实验研究了氢气与空气混合物的燃点.研究了氢气、氧气混合物经氮气稀释后,按化学当量比例将不同浓度的氢气与空气进行混合,并得出了低温下的爆炸压力特性.随后,分别讨论了在初始压力下一致的情况下,试管直径相同的状况下,氢气与空气混合浓度相同的情况下,这三种爆轰传播限制之间的关系.得出了在空气中直接点燃的发生爆轰的最小试管直径,最小的装药量之间的关系,进行了爆轰危险性分级.最后,文章概括比较了氢与其他燃料的燃烧特性,评估了氢气燃烧过程中的危险与安全因素.     

基于STAMP模型的核动力蒸汽发生器水位控制系统安全性分析

核电厂蒸汽发生器(SG)水位控制系统的安全可靠运行是保证核电厂安全性和经济性的关键因素,其控制对象具有高度复杂、非线性的特点。由于复杂系统的安全性是特定环境下由系统相关要素交互作用所产生的一种涌现特性,运用系统理论,以STAMP模型为基础对SG水位控制系统进行安全性分析,以利于在设计早期阶段发现影响该系统安全运行的潜在风险因素,预防危险事故。该方法将系统理论用于核电厂关键系统和设备安全性分析,为核电厂安全运行提供了新的技术手段支持。     

The effect of vent ducts on the reduced explosion pressures of vented dust explosions

An investigation into the effects of vent ducts on reduced explosion pressures is described. Experiments were made using an 18.5m³ explosion vessel and a modified 20 1 sphere, with dusts having K_st values ranging from 144 bar ms⁻¹ to 630 bar ms⁻¹. The vent area/vessel volume ratio bursting pressure of the vent cover, and the length to diameter ratio of the vent duct have been varied. Straight vent ducts, and ducts containing sharp 45° and 90° bends have been used.A simple model to describe the effect of vent ducts on the reduced explosion pressure has been derived and compared with the experimental results. Agreement is shown to be satisfactory in nearly all cases. A comparison between the experimental results and guidance on the effect of vent ducts already available in the literature is discussed.     

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.     

浅谈蒸气锅炉的水位事故

通过分析锅炉缺水、满水和汽水共腾三种锅炉水位事故的原因 ,有针对性地提出了预防措施及发生锅炉水位事故的处理方法     

蒸汽锅炉改热水锅炉应注意的问题

系统地分析了蒸汽锅炉在改装为热水锅炉时存在的问题,提出改进方法及今后的注意事项。     

Dust explosion incidents and regulations in the United States

The U.S. Chemical Safety and Hazard Investigation Board (CSB) investigated three fatal dust explosions that all occurred in 2003. These explosions caused the deaths of 14 people and injured hundreds more. Two of the facilities were damaged beyond repair, and several hundred employees lost their jobs.

CSB's investigations revealed that the explosions had common causes, despite their geographic and industrial diversity. Consequently, CSB commissioned a study of combustible dust fire and explosion hazards. This paper presents a summary of CSB's findings and recommendations developed during that study.     

我国钢铁企业安全管理发展状况的分析与研究

企业安全管理是企业正常运营不可或缺的部分,认清企业安全管理发展脉络,找准企业安全管理发展方向,对促进企业的持续发展有着重要作用.追溯了我国安全管理的发展过程,总结出我国企业安全管理发展的3个阶段,并以石家庄钢铁有限责任公司为例,结合该企业事故规律对其安全管理发展状况进行了分析研究,进一步印证了我国钢铁企业安全管理发展状况.     

Review of the DESC project

Dust Explosion Simulation Code (DESC) was a project supported by the European Commission under the Fifth Framework Programme. The main purpose of the project was to develop a simulation tool based on computational fluid dynamics (CFD) that could predict the potential consequences of industrial dust explosions in complex geometries. Partners in the DESC consortium performed experimental work on a wide range of topics related to dust explosions, including dust lifting by flow or shock waves, flame propagation in vertical pipes, dispersion-induced turbulence and flame propagation in closed vessels, dust explosions in closed and vented interconnected vessel systems, and measurements in real process plants. The new CFD code DESC is based on the existing CFD code FLame ACceleration Simulator (FLACS) for gas explosions. The modelling approach adopted in the first version entails the extraction of combustion parameters from pressure–time histories measured in standardized 20-l explosion vessels. The present paper summarizes the main experimental results obtained during the DESC project, with a view to their relevance regarding dust explosion modelling, and describes the modelling of flow and combustion in the first version of the DESC code. Capabilities and limitations of the code are discussed, both in light of its ability to reproduce experimental results, and as a practical tool in the field of dust explosion safety.     

建设江西省本质安全型工业园区研究

在调查研究江西省工业园区发展现状和分析工业园区事故特点的基础上,结合江西省工业园区建设的实际情况及安全生产中存在的主要问题,运用人机原理和系统安全分析方法,提出江西省本质安全型工业园区建设的框架.     

在役工业厂房建筑维护管理分析评价

在调研了全国各区域各行业工业厂房结构安全的基础上,提出工业厂房后期运营阶段的结构安全性和可靠性需要通过科学的维修制度来保证。分析了引起工业厂房结构失检、误判的因素,建立了相应的评价指标体系,以评价企业厂房结构安全的维护管理水平。理论分析和实例评价表明,通过提高维护管理水平可以减少厂房结构失检、误判事件的发生,加强厂房的检测、维护,可以有效预防工业厂房结构渐发性事故发生,在有限成本内实现对工业厂房结构安全管理的效益最大化。     

我国劳动安全卫生管理系统及其近期的发展

劳动安全卫生管理系统是指以降低工作岗位上的工伤事故和职业病为目的系统，即包括：立法、监察、企业安全管理在内的管理系统。我国当前正处在从计划经济向市场经济转轨的过程中，国家的劳动安全卫生管理系统也发生着重要变化，笔者从目前的劳动安全卫生管理系统现状分析入手，找出存在的问题，并指出其面临的选择和近期发展     

The effect of moisture content within multilayer protective clothing on protection from radiation and steam

The moisture from skin sweat and atmospheric water affects the thermal protective performance provided by multilayer protective clothing. Four levels of moisture content were selected to evaluate the impact of moisture on thermal protection under dry (thermal radiation) and wet (thermal radiation and low-pressure steam) heat exposure. Also, the role of moisture and its relationship with exposure time were analyzed based on skin heat flux and Henriques integral value. The addition of moisture to a fabric system was found to result in differences in second-degree and third-degree skin burn times. When moisture is added to a fabric system, it both acts as a thermal conductor to present a negative effect and provides a positive effect owing to thermal storage of water and evaporative heat loss. The positive or negative effects of moisture are mainly dependent on the thermal exposure time, the moisture content and the presence of hot steam.     

An application of 3D gasdynamic modeling for the prediction of overpressures in vented enclosures

A three-dimensional gasdynamic model with constant burning rate is applied for the prediction of the maximum pressure rise from gaseous combustion in vented enclosures. A series of calculations for an enclosure with aspect ratio close to unity are presented. Both cases with and without obstacles in the enclosure are considered. Results of calculations are compared with a simple 0D solution for spherical vessels. It is shown that, in cases without obstacles, the 0D solution for the maximum reduced overpressures is close to the predictions of the detailed modeling. In cases with obstacles, the detailed simulation gives significantly higher overpressures than those from the 0D model. However, in all the cases the reduced pressures are correlated well with the maximum flame surface area.