Dynamics of dust explosions suppression by means of extinguishing powder in various industrial conditions

In industrial conditions, there are different kinds of installations endangered by an explosion of dust–gas mixtures. In order to prevent them from any consequences of potential explosions, active protection systems which use extinguishing powders, as the suppressing material, are more and more widely applied. It often happens that the industrial installations are additionally endangered by an action of mechanical vibrations. In the above-mentioned conditions, the extinguishing powder tends to aggregate, making the process of dispersing it in the protected areas more difficult.

The results of research into optimization of the shape, number of igniters and miniaturization of the explosive charge mass are presented. In case of occurrence of the mechanical vibrations in the installations that cause aggregation of the suppressing powder, the best solution was modification of the perforated combustion chamber located inside the extinguisher. As a result of that, a certain amount of gases generated in the course of combustion of the main charge is directed over the membrane, where the gases crash a layer of aggregated powder. Thus, the process of pushing the powder out from a container towards the dispersing head improves considerably and consequently increases the efficiency of the explosion-suppressing process.     

火电行业环境空气预测评价的研究

以2003年～2011年辽宁省境内新、扩改建火力发电厂和供热机组建设为研究对象,采用案例分析,结合国家有关大气环境影响预测评价的有关规定,就环境影响预测评价中存在的问题进行讨论,提出只有在SO2、NOx、PM10环境现状监测值为标准值的90%、30%、5%以上情况下才进行预测,否则,环境空气预测可以减免。     

An Investigation of Thermal Decomposition Behavior of Hazelnut Shells

Turkey has a drastic potential in terms of biomass energy and it would be of utmost importance for our energy mix if this huge amount of energy is to be utilized. Thermochemical conversion is the most dominant one among the energy conversion processes. The carbonization process is the key point in determining the kinetic parameters of the fuels utilized. Thereafter, the kinetic parameters obtained from carbonization would be utilized in designing the thermochemical conversion equipments. In this study, the thermal decomposition behavior of hazelnut shells was investigated via dynamical thermogravimetry (TG) under N₂ atmosphere. In order to determine the effects of heating rate and gas flow rate, the experiments were performed in four different heating rates of 5, 20, 50, and 100 K/min and two different nitrogen flow rates of 50 and 100 cm³/min. As the heating rate was increased, peak temperature was increased, maximum temperature shifted to the right (higher T zones) and the maximum rate of weight loss was increased. In addition, lignin decomposition temperature interval was decreased whereas; cellulose decomposition temperature interval was increased. Increasing the heating rate from 5 to 20 K/min, hemicellulose decomposition temperature interval was increased. Total weight loss was slightly increased by the increase of gas flow rate. Kinetic parameters were calculated according to Coats Redfern method. It was found that activation energies of thermal decomposition reactions of hazelnut shell varied between 1.30 and 32.19 kJ/mol.     

The System Dynamics of Nuclear Energy in Singapore

In this article, a system dynamics model is developed to study the complex issues involving nuclear energy in Singapore by assessing four essential aspects, namely (1) Economic, (2) Environment, (3) Social, and (4) Political in various scenarios. The first factor juxtaposes the monetary benefit from deploying nuclear energy with the current situation. The second deals with carbon dioxide emission, nuclear waste, and thermal pollution from nuclear power plant. The third part discusses the safety and social acceptance toward nuclear project, and the last section analyzes the political stability in provision of nuclear energy advent. The proposed system dynamic model incorporates all four components that allow us to run sensitivity analysis based on various scenarios and enables us to gain insight in how each domain evolves with time. Based on the model, we present advantages and disadvantages of possessing nuclear power plants in Singapore and suggest remedies to rectify the drawbacks.     

炮烟中毒事故致因机理研究及预防技术

炮烟中毒事故属于矿山事故类型之一。炮烟中的有毒气体是导致井下作业人员中毒的根源。通过理论分析得出,炸药的爆炸反应偏离零氧平衡、炸药组分混合不均匀导致爆炸反应不完全、炸药爆炸时周围岩石成分及环境因素是有毒气体生成量增多的主要原因。利用轨迹交叉事故理论模型探究了炮烟中毒事故发展过程,揭示事故发生为人的不安全行为和物的不安全状态在同一时间空间的交叉,消除人的不安全行为或物的不安全状态是避免事故发生的途径。针对防治炮烟中毒,提出了预防炮烟中有毒气体超标和炮烟中毒的实用技术,对矿山炮烟中毒预防工作具有指导意义。     

生产工艺条件对菌粉爆炸特征参数的影响

利用扫描电镜及激光粒度分析仪,探究了不同生产工艺条件下医药中间体菌粉A和菌粉B的表面形状及粒径分布,并进行了热解分析,证实上述特征参数存在一定差别。在此基础上进行了爆炸特性参数研究。研究结果表明,上述两种菌粉爆炸下限处于70~90 g/m3,最大爆炸压力峰值0.4~0.5 MPa之间,爆炸性相对较弱,但也必须引起足够的重视。与菌粉B相比,菌粉A相对安全,因此条件许可时优先采用菌粉A生产工艺流程。     

Effect of shock strength on dust entrainment behind a moving shock wave

Secondary dust explosion is a serious industrial issue because it occurs under conditions corresponding to an increased quantity and concentration of dispersed, combustible dust when compared with the primary explosion. The problems of lifting and dispersion of a dust layer behind a propagating shock wave must therefore be understood to ensure safety regarding secondary dust explosion hazards. Using a new shock-tube facility for studying shock propagation over dust layers, limestone dust was subjected to Mach numbers ranging from 1.10 to 1.60. A shadowgraph technique was applied by using a high-speed camera (15,000 fps) for visualization of the dust-layer height change behind the moving shock wave. Also, the effect of dust-layer thickness on the entrainment process was observed by performing tests with two different layer depths, namely 3.2- and 12.7-mm thicknesses. New correlations were developed between the shock strength and the dust entrainment height as a function of time for each layer depth. In general, the results herein are in agreement with trends found in previous work, where there is a linear relationship between dust growth rate and shock Mach number at early times after shock passage. Also, new data were collected for image analyses over longer periods, where the longer observation time and higher camera framing rates led to the discovery of trends not previously observed by earlier studies, namely a clear transition time between the early, linear growth regime and a much-slower average growth regime. This second regime is however accompanied by surface instabilities that can lead to a much larger variation in the edge of the dust layer than seen in the early growth regime. In addition, for the linear growth regime, there was no significant difference in the dust-layer height growth between the two layer thicknesses; however, the larger thickness led to higher growth rates and much larger surface instabilities at later times.     

Validation of a new formula for predicting the lower flammability limit of hybrid mixtures

A correlation of the lower flammability limit for hybrid mixtures was recently proposed by us. The experimental conditions including ignition energy and turbulence which play a primary role in a gas or dust explosion were at fixed values. The sensitivity of such experimental conditions to the accuracy of the proposed formula was not thoroughly discussed in the previous work. Therefore, this work studied the effect of varying the ignition energy and turbulence intensity to the formula proposed in our previous paper. For ignition energy effect, results from methane/niacin mixture demonstrated that the MEC and LFL will not be affected by changing ignition energy. There is no distinguishable difference among gas explosion index (K_G) and dust explosion index (K_St) derived from tests with every ignition energy (2.5 kJ, 5 kJ and 10 kJ) in a 36 L vessel. The proposed formula is independent of ignition energy. For turbulence effect, the proposed formula can have a good prediction of the explosion and non-explosion zone if the ignition delay time is within a certain range. The formula prediction is good as the ignition delay time increases up to 100 ms in this work. Propane/niacin and propane/cornstarch mixtures are also tested to validate the proposed formula. It has been confirmed that the proposed formula predicts the explosion and non-explosion zone boundary of such mixtures.     

储罐爆炸抛射碎片对目标储罐的破坏概率研究

化工储罐爆炸产生的抛射碎片击中并破坏相邻罐体后,将引发多米诺效应。N guyen破坏概率模型认为,当罐壳受撞击后,残余壁厚小于某个临界值时就会被破坏,并假设该临界残余壁厚为定值,存在不合理之处。本文基于储罐壳体损失面积安全评价方法AP I 579,把撞击形成的复杂凹坑简化为圆锥形,分别针对圆柱储罐、球罐推导出圆锥形凹坑剩余强度系数的求解方法,并根据塑性失效理论确定了罐壳的临界剩余强度系数,由此建立了新的破坏准则。在此基础上,采用蒙特卡罗法进行模拟,建立了新的爆炸碎片对目标储罐的破坏概率模型,与N guyen模型相比,得出的破坏概率偏大,结果更为安全保守。通过对剩余强度系数与无量纲撞击深度和凹坑锥角的变化关系进行分析,证明N guyen模型中临界残余壁厚为定值的假设并不合理,而新的基于剩余强度系数计算的破坏概率更为准确合理。     

Upward movement of plutonium to surface sediments during an 11-year field study

An 11-year lysimeter study was established to monitor the movement of Pu through vadose zone sediments. Sediment Pu concentrations as a function of depth indicated that some Pu moved upward from the buried source material. Subsequent numerical modeling suggested that the upward movement was largely the result of invading grasses taking up the Pu and translocating it upward. The objective of this study was to determine if the Pu of surface sediments originated from atmosphere fallout or from the buried lysimeter source material (weapons-grade Pu), providing additional evidence that plants were involved in the upward migration of Pu. The ²⁴⁰Pu/²³⁹Pu and ²⁴²Pu/²³⁹Pu atomic fraction ratios of the lysimeter surface sediments, as determined by Thermal Ionization Mass Spectroscopy (TIMS), were 0.063 and 0.00045, respectively; consistent with the signatures of the weapons-grade Pu. Our numerical simulations indicate that because plants create a large water flux, small concentrations over multiple years may result in a measurable accumulation of Pu on the ground surface. These results may have implications on the conceptual model for calculating risk associated with long-term stewardship and monitored natural attenuation management of Pu contaminated subsurface and surface sediments.