Un-ignited and ignited high pressure hydrogen releases: Concentration – turbulence mapping and overpressure effects

Safety studies for production and use of hydrogen reveal the importance of accurate prediction of the overpressure effects generated by delayed explosions of accidental high pressure hydrogen releases. Analysis of previous experimental work demonstrates the lack of measurements of turbulent intensities and lengthscales in the flammable envelope as well as the scarceness of accurate experimental data for explosion overpressures and flame speeds. AIR LIQUIDE, AREVA STOCKAGE ENERGIE and INERIS join in a collaborative project to study un-ignited and ignited high pressure releases of hydrogen.The purpose of this work is to map hydrogen flammable envelopes in terms of concentration, velocity and turbulence, and to characterize the flame behaviour and the associated overpressure. These experimental results (dispersion and explosion) are also compared with blind FLACS modelling.     

Effect of scale on freely propagating flames in aluminum dust clouds

The majority of experimental tests done on combustible dusts are performed in constant volume vessels that have limited or no optical access. Over the years, McGill University has been developing alternative experimental techniques based on direct observation of dust flames, yielding reliable fundamental parameters such as flame burning velocity, temperature and structure. The present work describes two new experimental set-ups allowing direct observation of isobaric and freely propagating dust flames at two sufficiently different scales to test the influence of scale on dust flame phenomena. In the laboratory-scale experiments, a few grams of aluminum powder are dispersed in transparent, 30 cm diameter latex balloons that allow for full visualization of the spherical flame propagation. In the field experiments, about 1 kg of aluminum powder is dispersed by a short pulse of air, forming a conical dust cloud with a total volume of about 5 m³. High-speed digital imaging is used to record the particle dispersal and flame propagation in both configurations. In the small-scale laboratory tests, the measured flame speed is found to be about 2.0 ± 0.2 m/s in fuel-rich aluminium clouds. The burning velocity, calculated by dividing the measured flame speed by the expansion factor deduced from thermodynamic equilibrium calculations, correlates well with the previously measured burning velocity of about 22–24 cm/s from Bunsen dust flames. Flame speeds observed in field experiments with large-scale clouds, however, are found to be much higher, in the range of 12 ± 2 m/s. Estimations are presented that show that the presumably greater role of radiative heat transfer in larger-scale aluminium flames is insufficient to explain the six-fold increase in flame speed. The role of residual large-eddy turbulence, as well as the frozen-turbulence effect leading to large-scale dust concentration fluctuations that cause flame folding, are discussed as two possible sources for the greater flame speed.     

高性能聚醚醚酮紫外光加速老化行为研究

目的 研究特种工程塑料聚醚醚酮(PEEK)在紫外光照射实验室加速条件下的老化行为。方法 对PEEK塑料采取紫外线光老化方式进行试验,对老化前后的样品进行外观变化、力学性能、热性能、微观结构表征与分析,明确紫外环境因素对材料的性能影响,进而确定PEEK塑料在紫外光条件下的老化行为。结果 随着紫外光老化时间的增加,PEEK样品表面变黄,颜色加深,出现鼓包与裂纹等宏观与微观损伤。样品内部力学性能、热性能、红外特征吸收峰、元素含量与价态没有明显变化,样品表面热性能下降,傅里叶变换衰减全反射红外光谱(ATR-FTIR)特征吸收峰变化明显。结论 PEEK塑料表面对紫外光比较敏感,在紫外光的照射下容易发生表层的分解,短时间内不会引起材料整体热性能及力学性能的明显变化。     

Closed loop recycling of plastics containing Flame Retardants

Annually 2.7 million tonnes of plastics containing Flame Retardants (FRs) are globally discarded in Waste Electrical and Electronic Equipment (WEEE). Little is known on the feasibility of closing material loops for FR plastics. Therefore, series of experiments were set up to analyze the feasibility of separating plastics containing FRs from one specific product category, namely End-of-Life (EoL) Liquid Crystal Display (LCD) TVs. The characterization of the housings of this waste stream indicated a concentration of 18 wt% Bromine based (Br) FRs and 31 wt% Phosphor based (P) FRs, the remainder not containing FRs. With practical tests it was demonstrated that, after disassembly and plastic identification, the co-polymer poly-carbonate (PC)/acrylonitrile-butadiene-styrene (ABS) containing PFR can be recycled in a closed loop system. Based on the determined plastic density distributions and separation efficiencies of optical sorters, a purity of 82% was calculated for PFR PC/ABS separated from EoL LCD TVs after size-reduction (shredding). Performed miscibility tests indicated that for this fraction at least a factor 10 dilution with virgin material is required. In addition, higher waste volumes are required for a size-reduction based treatment to become economically viable and technical challenges still need to be faced, whereas closed loop recycling of PFR PC/ABS from the current waste stream of EoL LCD TVs of different brands in a disassembly based treatment is found to be technically feasible and economically viable under European boundary conditions.     

Rate of hexabromocyclododecane decomposition and production of brominated polycyclic aromatic hydrocarbons during combustion in a pilot-scale incinerator

Here, we examined the incineration of extruded polystyrene containing hexabromocyclododecane(HBCD) in a pilot-scale incinerator under various combustion temperatures(800–950℃) and flue gas residence times(2–8 sec). Rates of HBCD decomposition ranged from 99.996%(800℃, 2 sec) to 99.9999%(950℃, 8 sec); the decomposition of HBCD, except during the initial stage of combustion(flue gas residence time 2 sec), followed a pseudo-first-order kinetics model. An Arrhenius plot revealed that the activation energy and frequency factor of the decomposition of HBCD by combustion were 14.2 kJ/mol and 1.69 sec~(-1),respectively. During combustion, 11 brominated polycyclic aromatic hydrocarbons(BrPAHs)were detected as unintentional by-products. Of the 11 BrPAHs detected, 2-bromoanthracene and 1-bromopyrene were detected at the highest concentrations. The mutagenic and carcinogenic BrPAHs 1,5-dibromoanthracene and 1-bromopyrene were most frequently detected in the flue gases analyzed. The total concentration of BrPAHs exponentially increased(range,87.8–2,040,000 ng/m~3) with increasing flue gas residence time. Results from a qualitative analysis using gas chromatography/high-resolution mass spectrometry suggest that bromofluorene and bromopyrene(or fluoranthene) congeners were also produced during the combustion.     

An evaluation approach using a HARA and FMEDA for the hardware SIL

Safety instrumented systems (SIS) are becoming increasingly complex, and form a growing proportion of programmable electronic parts. The IEC 61508 global standard was established to ensure the functional safety of SIS; however, it was expressed in highly macroscopic terms. The safety integrity level (SIL) is a criterion describing whether a component meets the safety requirements of a SIS. The safety requirements give a target SIL for the expected risks using hazard analysis and risk assessment (HARA). The SIL must correspond to the safety requirements. This study introduces an evaluation process for determining the hardware SIL through failure modes, effects, and diagnostic analysis (FMEDA). First, the components of the SIS subsystem are defined in terms of failure modes and effects, and then the failure rate and failure mechanism distribution are assigned to each component. The safety mode and detectability of each failure mode are determined for each component and, finally, the hardware SIL is evaluated. We perform a case study to evaluate the hardware SIL of the flame scanner system using HARA and FMEDA, where the safety requirement of the flame scanner was determined using the risk graph method. We verified that the hardware SIL of the flame scanner corresponded to the safety requirement.     

The characterization of heat transfer fluid P-NF aerosol combustion: Ignitable region and flame development

Heat transfer fluids tend to form aerosols due to the operating conditions at high pressure when accidental leaking occurs in pipelines or storage vessels, which may cause serious fires and explosions. Due to the physical property complexity of aerosols, it is difficult to define a standard term of “flammability limits” as is possible for gases. The study discussed in this paper primarily focuses on the characterization of ignition conditions and flame development of heat transfer fluid aerosols. The flammable region of a widely-used commercial heat transfer fluid, Paratherm NF (P-NF), was analyzed by electro-spray generation with a laser diffraction particle analysis method. The aerosol ignition behavior depends on the droplet size and concentration of the aerosol. From the adjustment of differently applied electro-spray voltages (7–10 kV) and various liquid feeding rates, a flammable condition distribution was obtained by comparison of droplet size and concentration. An appropriate amount (0.3–1.2 ppm) of smaller droplets (80–110 μm) existing in a given space could result in successful flame formation, while larger droplets (up to 190 μm) have a relatively narrowed range of flammable conditions (0.7–0.9 ppm). It is possible to generate a more useful reference for industry and lab scale consideration when handling liquids. This paper provides initial flammability criteria for analyzing P-NF aerosol fire hazards in terms of droplet size and volumetric concentration, discusses the observation of aerosol combustion processes, and summarizes an ignition delay phenomenon. All of the fundamental study results are to be applied to practical cases with fire hazards analysis, pressurized liquid handling, and mitigation system design once there is a better understanding of aerosols formed by high-flash point materials.     

Flame acceleration in unconfined hydrogen/air deflagrations using infrared photography

Flame behavior and blast waves generated during unconfined hydrogen deflagrations were experimentally studied using infrared photography. Infrared photography enables expanding spherical flame behaviors to be measured and flame acceleration exponents to be evaluated. In the present experiments, hydrogen/air mixtures of various concentrations were filled in a plastic tent of thin vinyl sheet of 1 m³ and ignited by an electric spark. The onset of accelerative dynamics on the flame propagation was analyzed by the time histories of the flame radius and the stretched flame speed. The results demonstrated that the self-acceleration of the flame, which was caused by diffusional-thermal and hydrodynamic instabilities of the blast wave, was influenced by hydrogen deflagrations in unconfined areas. In particular, it was demonstrated that the overpressure rapidly increased with time. The burning velocity acceleration was greatly enhanced with spontaneous-turbulization.     

新型膨胀型阻燃剂的合成及其在聚丙烯(PP)中的应用

以氨基三甲叉磷酸（ATMP）、尿素为原料采用热缩合法合成新型膨胀型阻燃剂一ATU。用傅里叶红外光谱及元素分析表征ATU的结构及组成。将ATU与常见碳源季戊四醇进行复配,应用于PP材料的阻燃。研究发现ATU集气源酸源于一身,对于PP阻燃效果明显,甚至好于同比例的APP。极限氧指数仪和垂直燃烧仪测试材料燃烧等级;微型燃烧量热仪（MCC）研究了材料燃烧过程中热释放情况;热重分析（TGA）和扫描电镜（SEM）分别从材料的热降解及成炭原理方面上对ATU的阻燃机理进行了研究。     

阻燃纯棉织物的研究与发展

对阻燃纯棉织物的国内外研究现状、生产和应用中存在的问题，进行了论述，并提出了今后的发展方向