Ignition of dust-air atmospheres by ultrasonic waves

This paper shows the results of our investigations on the ignition source ultrasound in dust-air atmospheres. Ultrasound is, on the one hand, considered to be an ignition source according to international safety standards (EN 1127–1 (2011)). On the other hand, though, ultrasound is used for various applications in gases and air, such as level and flow measurement, or in the process industry, but no explosion accidents have yet been reported. Our research now shows that it is indeed possible to ignite dust-air mixtures in ultrasound fields under certain conditions. We conducted our experiments in an ultrasound standing wave field and used maize starch, calcium stearate and sulfur dust. For ignitions, an absorbing target was needed to convert the acoustic energy into heat. From theoretical estimations and experiments critical conditions that provoke ultrasonically triggered explosions are identified.     

Development of a method for predicting the ignition of explosive atmospheres by mechanical friction and impacts (MECHEX)

Mechanical friction and impacts is still today a main cause of ignition of explosive atmospheres (ATEX) in the industry and this trend seems to be stable in time. This situation certainly results from a significant gap of knowledge in the underlying mechanisms so that the parameters to play on are not precisely identified. In this programme of European dimensions, the process of degradation of the mechanical energy into heat during friction and impacts have been studied.

An extensive experimental programme is presented to this end. The mechanisms of dissipation of the mechanical energy into heat during friction has been studied with rubbing machines in which a slider equipped with temperature sensors rubs against a rotating wheel. For impacts, a new device has been developed using a special “air driven cannon” to propel a projectile accurately up to 50 m/s onto an inclined target. A very significant effort has been reserved to the investigation of the ignition mechanisms, not only for ATEX but also for dust accumulations.

Some “simple” modelling is proposed on purpose of practical applications. For frictional situations, a critical rubbing power is calculated without any limitations about any lower boundary concerning the rubbing velocity. For “impacts”, the relevant parameter for ignition is not the kinetic energy of the projectile but its velocity and the nature of the materials.     

Simplified model for the evaluation of the effects of explosions on industrial target

The evaluation of vulnerability of process equipment to explosion is a central issue in the analysis of industrial risks. In this work, we have developed a simplified model, however based on fundamental equations, which includes structural and fluid–dynamic parameters for the target (the industrial equipment) and for the impacting pressure wave (shock waves) or object (fragment, debris) produced by different type of chemical explosions.The validity of methodology has been assessed by case histories. Several insights on the dynamic of structural interaction of the explosion with the target have been obtained, with specific reference to escalation effects.The model derives from the well-known Johnson's number, often adopted in impact engineering.     

Computer-aided modeling of the protective effect of explosion relief vents in tunnel structures

This paper aims at contributing to the efficient design of explosion protection systems against confined explosions. The issue addressed concerns the quantitative estimation of the protective effect of explosion relief vents in the case of confined explosions inside tunnels. A series of virtual experiments performed by computer simulation, revealed how the number of vents, their diameter, as well as the angle between the vents and the tunnel, influences the blast wave attenuation. The computational study was performed considering a complicated large-scale tunnel configuration with branches on its half portion. The purpose was the calculation of the attenuation effect due to the presence of vents by comparing the total explosion-specific impulse developing at antidiametric positions inside the tunnel. Simulations were carried out via a three-dimensional numerical model built in the computational fluid dynamics code CFX 5.7.1, which has been validated in previous papers against experimental overpressure histories data demonstrating reasonable performance. Computer results showed that the use of branch vents provides an effective method for shock wave attenuation following an explosion, whereas their statistical elaboration revealed that the attenuation is mainly affected by the number of vents and their diameter. In contrast, the angle between the side vents and the main tunnel appeared to slightly affect the pressure wave weakening. Eventually, the quantitative influence of the above parameters was effectively illustrated in functional diagrams, so that the total attenuation effect may be promptly estimated, if the design variables are known. In addition, two statistical models with reasonable fitting to the calculated data are proposed, which express the attenuation effect as a dependent variable of the design variables including their interactions.     

基于Fluent的养猪场恶臭风险分析及应用

由规模化养猪场所带来的恶臭问题越来越受到公众的重视,也影响着养猪行业的可持续健康发展.而确定恶臭防护距离是控制恶臭污染和减轻养猪场周边居民健康影响的重要措施之一.采用了典型养猪场中NH3和H2S的联合恶臭强度分级方法,利用Fluent软件对养猪场恶臭源扩散模拟结果进行联合恶臭强度分级,最后从恶臭管理的角度确定了养猪场恶臭防护距离,并与国外推荐的养猪场恶臭防护距离计算公式法的结果进行了比较.结果表明,养猪场内部恶臭强度为5级,为不可接受区,需要加强猪舍的粪便清理及通风条件的改善;生活在恶臭强度为3、4、5级所覆盖区域的居民应该尽量减少户外活动,并有必要向当地的环保部门或政府举报,要求加强恶臭管理.养殖规模为2 000头的实例养猪场的恶臭安全防护距离约为200m.     

Some observations on explosion development in process pipelines and implications for the selection and testing of explosion protection devices

In recent years there has been continuing interest in the potential hazards from detonations in pipelines. The interest has arisen in several instances due to the introduction of vapour recover systems, as part of measures to limit environmental emissions. These environmental pressures initially coincided with the preparation of new European-wide test procedures for explosion arrester devices and, more recently, moves to develop a new international ISO standard for the certification and approval of detonation arrester devices. It is an opportune time therefore to review current understanding of explosion development in pipelines and to consider the implications for plant design and explosion arrester selection and testing.     

大连市水资源安全评价模型的构建及其应用

水资源安全问题是水科学与系统科学交叉研究的热点.以大连市为例构建评价指标体系,通过层次分析法(AHP)与熵值法确定评价指标在满足主客观条件下的综合权重; 采用率定方程确定各指标的安全度;应用指数合成法对大连市水资源的安全状况进行评价.研究结果表明,近几年大连市水资源总体上处于不安全状态且不安全状况主要发生在农村.为保证社会、经济、环境各方面协调发展,必须重点解决农村地区的用水问题.本文同时也就解决水资源安全问题提出了一些建议.     

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.     

多目标优化方法在区域水资源优化配置中的应用——以唐山市为例

水资源供需矛盾日益加剧,如何优化配置区域内有限的水资源已成为水资源规划与管理研究中的热点.本文在考虑不同水质和水源的基础上,研究了决策变量的约束条件,综合考虑不同用水户的用水效益,采用工业、生活、环境和农业多目标优化的方法,按照决策者的不同意愿,给出不同的配置方案,即一系列非劣解集.通过调用Matlab优化工具箱中的函数对其进行求解,给出了5种不同的水资源优化配置方案,能够合理配置唐山市区内有限的水资源,使得该区域内环境、社会与经济协调发展.     

Safety line method for the prediction of deep coal-seam gas pressure and its application in coal mines

Gas pressure is an important index for evaluating the outburst risk and determining the gas content in coal seams. It is recommended to predict coal-seam gas pressure of the workface at deep levels before extending mining activities to deeper levels. According to the prediction results, measurements are taken for gas outburst prevention and control and for workload estimation. At present, regression methods are always used to process the numerous gas pressure data for prediction. Because there are many factors that influence the gas pressure which could lead to a deviation from actual values, the measured data do not possess basic conditions for regression methods; this can cause unexpected dangers if the methods are adopted.Based on a statistical analysis of actual measured results of coal-seam gas pressure in a same geological section in certain coal mine, two symbol measured points are selected to make a line for prediction, i.e. safety line, and the other measured points should be below the line except the abnormal points due to the confined water. It has been successfully applied in numerous coal mines in China. Particularly, this method is analyzed in this paper for the case of the No. 8₂ coal seam in the Taoyuan coal mine in Huaibei coalfield, China. By comparatively analyzing the relationship between gas pressure and depth from surface using regression methods, it is found that the safety line method could lead to a better prediction for deep coal-seam gas pressure, and therefore promote early warning ability and mining safety.     

Methodology for the quantification of toxic dispersions originated in warehouse fires and its application to the QRA in Catalonia (Spain)

A tool for the quantification of the consequences of toxic dispersions coming from fires in warehouses has been developed. This tool is expected to be applied in the framework of the risk assessment in Catalonia, specifically in the Quantitative Risk Assessment. The present study is based on the criteria gathered in the technical guide BEVI 3.2 and the methodology CPR-15 used in the Netherlands. Hence, the approach performed accepts the main body of the foresaid methodology but implements a different and free source dispersion model, a modified Gaussian model that takes into account the warehouse effect. In the work conducted, a historical analysis of accidents involving fire in warehouses has been performed in order to justify the importance of assessing their potential toxic dispersions. Furthermore, the tool has been tested in different case studies providing results that have been compared with other methodologies, observing similar results that can be useful for the stakeholders and decision makers in the framework of the risk assessment.