Flame characteristics of premixed H2-air mixtures explosion venting in a spherical container through a duct

The explosion venting duct can effectively reduce the hazard degree of a gas explosion and conduct the venting energy to the safe area. To investigate the flame quantitative propagation law of explosion venting with a duct, the effects of hydrogen fraction and explosion venting duct length on jet flame propagation characteristics of premixed H₂-air mixtures were analyzed through experiment and simulation. The experiment results under initial conditions of room temperature and 1 atm show that when hydrogen fraction was high enough, part of the unburned hydrogen was mixed with air again to reach an ignitable concentration, resulting in the secondary combustion was easier produced and the duration of the secondary flame increased. With the increase of venting duct length, the flame front distance and propagation velocity increased. Meanwhile, the spatial distribution of pressure field and temperature field, and the propagation process and mechanism of the flame venting with a duct were analyzed using FLUENT software. The variation of the pressure wave and the pressure reflection oscillation law in the explosion venting duct was captured. Therefore, in the industrial explosion venting design with a duct, the hazard caused by the coupling of venting pressure and venting flame under different fractions should be considered comprehensively.     

芳烃原料罐区有机气体回收装置运行问题初探与分析

本文介绍了四川石化65万t·a-1对二甲苯芳烃联合装置配套芳烃原料罐区有机气体回收装置工艺流程简述,主要控制指标、运行状态以及运行过程中出现的问题分析及应对措施。装置运行半年来,操作稳定,外排气体烃含量小于35×10-6,远低于国家设计标准,达到安全环保要求。     

Experimentelle und numerische Untersuchungen von Brandszenarien vor Fassaden unter Berücksichtigung verschiedener Abstände

Experimental and numerical investigations of fire scenarios in front of façades considering various distances Constructional boundary conditions, e. g. walls or façades, close to ignition sources affect the fire formation and the plume. It is already known, that boundaries (e. g. walls) constrain the entrainment of air and oxygen into the plume and the combustion of gas or flammable products is completed at larger heights. How far the location of the fire sources, the building geometry and the heat release rate affect the characteristics of a flame is investigated at the Institut für Baustoffe, Massivbau und Brandschutz (iBMB) of TU Braunschweig in line with a series of experiments with a square gas burner. For the implementation of the fire tests the test rig in Braunschweig is provided with extensive measurement techniques to determine heat flux, wall‐bounded temperatures, temperatures for plume measurements and upward velocity. In this paper the data of the fire tests are discussed and compared with the results of a CFD‐Model and selected empirical calculation approaches.     

环形走廊机械排烟口水平布置对机械排烟效果的影响

以1幢高层建筑环形走廊为例,利用火灾动力学模拟软件FDS研究了环形走廊不同的排烟口水平布置方式对走廊机械排烟效果的影响。定义了排烟效率和排热效率2个定量评价机械排烟效果的指标,计算了各种工况的排烟效率和排热效率,通过与走廊上温度等参数的对比分析证明了这种方法的可行性。研究表明:对于环形走廊,排烟口的开启数量和设置位置对排烟效果具有很大影响,在排烟量一定的情况下,并非开启排烟口数量越多越好。针对本文火灾场景,排烟口设置在走廊的转角处比设置在走廊中间位置排烟效果更好;当排烟口设置在4条走廊的转角处时,火灾时开启适当位置的2个排烟口排烟效果远好于4个全开。     

Visualized measurement of extremely high-speed droplets in Venturi scrubber

Venturi scrubbers for filtered venting have been installed in nuclear power plants worldwide. Venturi scrubbers can eliminate fission products from a polluted gas by interaction through gas–liquid interfaces. Therefore, droplet diameter is important from the viewpoint of decontamination. When Venturi scrubbers are used in severe accidents, the gas flow velocity might be extremely high. In these studies, the authors did not measure droplet diameter under extremely high gas velocity conditions. In the scenarios, experimental data pertaining to droplet diameter, under the extremely high gas flow velocity, are required. Therefore, this objective is to evaluate the diameter of extremely high-speed droplets. A visualization experiment was conducted using a Venturi scrubber. The droplet diameter distribution and the Sauter mean diameter (SMD) were determined. By comparing between the experimental value of SMDs and the one evaluated using Nukiyama–Tanasawa equation, it was confirmed that the Nukiyama–Tanasawa equation can be used to evaluate SMD with good accuracy in the gas velocity range of 82–250 m/s, except the highest gas velocity conditions. Furthermore, the droplet generation mechanism in the Venturi scrubber was considered to clarify the main reason why the Nukiyama–Tanasawa equation can be used to evaluate SMD droplet diameter.     

Pressure release characteristics of premixed hydrogen-air mixtures in an explosion venting device with a duct

The technology of explosion venting with a duct can effectively reduce the destructive effect generated from gas accidental explosion in the place of intensive industrial production, while it is not applicable to the production site designed for the technology without ducts. Since it is not clear how to quantitatively evaluate the regularity of energy release in explosion venting especially under high cracking pressure, it is still challenging on the safe application of the technology. This paper aimed to explore the basic characteristics of explosion pressure in a 20 L sphere vessel and venting duct during hydrogen explosion venting for safety design. The effects of the cracking pressure and duct length on explosion pressure at different positions were systematically analyzed according to the test of the hydrogen with different concentrations in an explosion venting device with a duct. Comparing the results of explosion pressure characteristics with experiments conducted in a device without a duct, and quantitatively analyzing the pressure release rule, manifested that the presence of the duct reduced the explosion venting efficiency to a certain extent. In the meantime, by comparing the standard NFPA 68 (P_cra ≤ 0.075 MPa, 0.1 m³ ≤ V ≤ 10,000 m³) for safety design of explosion venting devices, the extended implementation scheme with a venting duct was assessed, implying that the calculation results from NFPA 68 were relatively stable in over-scope (P_cra > 0.075 MPa, V < 0.1 m³) measurement. In future industrial productions, the design of high-pressure hydrogen venting is suggested, leaving sufficient safety margin when referring to the result.     

Advantages and challenges with using hypoxic air venting as fire protection

The use of hypoxic air venting system as fire protection is increasing and is sometimes used to replace traditional extinguishing systems. An oxygen level of 15% is generally used because a lower concentration could pose serious health risks. On the request of the Swedish Radiation Safety Authority, a literature review was conducted to determine advantages and challenges with the system and further research needs. The main advantages with a reduced oxygen environment are the reduced probability of ignition and lowered heat release rate. However, at 15% oxygen level, risk for fire still exists, and the system cannot be seen as an alternative to extinguishing systems. Reduced oxygen environment also results in higher production rates of soot and smoke, and there is limited knowledge regarding the effect of fuel configuration and fire behavior of products. In addition, a first evaluation of the test method specified in the hypoxic air venting standards was carried out through testing. The testing showed that the particleboard passed the test criteria at normal atmosphere even though it is commonly known that a particleboard burns in normal air. It is concluded that the test method has deficiencies, and there is clearly a need for development of the test method to guarantee safety levels. © 2013 The Authors. Fire and Materials published by John Wiley & Sons, Ltd.     

The roles of altitude and fear in the perception of height.

Previous research on perceiving spatial layout has found that people often exhibit normative biases in their perception of the environment. For instance, slant is typically overestimated and distance is usually underestimated. Surprisingly, however, the perception of height has rarely been studied. The present experiments examined the perception of height when viewed from the top (e.g., looking down) or from the bottom (e.g., looking up). Multiple measures were adapted from previous studies of horizontal extents to assess the perception of height. Across all of the measures, a large, consistent bias was found: Vertical distances were greatly overestimated, especially from the top. Secondary findings suggest that the overestimation of distance and size that occurs when looking down from a high place correlates with reports of trait- and state-level fear of heights, suggesting that height overestimation may be due, in part, to fear. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

高层住宅落地窗、低窗台防护措施研究

近年高层住宅中因大量使用落地窗、低窗台所带来的安全问题被广泛关注,本文在梳理与落地窗、低窗台防护高度、强度、防火间距及材料做法相关规范的基础上对高层住宅的防护措施进行了研究,并提出了适宜的解决方案.