Prediction of minimum ignition energy of aerosols using flame kernel modeling combined with flame front propagation theory

Flammable aerosols have created many fire and explosion hazards in the process industry, but the flammability of aerosols has not been fully understood. The minimum ignition energy has been widely used as an indicator for flammability of combustible mixtures, but the amount of experimental data on the minimum ignition energy of aerosols is very limited. In this work, the minimum ignition energy of tetralin aerosols is predicted using an integrated model. The model applies the flame front propagation theory in aerosol systems to the growth of the flame kernel, which was created during the spark discharge in the ignition process. The aerosol minimum ignition energy was defined as the minimum level of energy in the initial flame kernel to maintain the kernel temperature above the minimum ignition temperature of 1073 K specific for tetralin aerosols during the kernel growth. The minimum ignition energy obtained in the model is influenced by the fuel-air equivalence ratio and the size of the aerosol droplets. For tetralin aerosols of 40 μm diameter, E_min decreases significantly from 0.32 mJ to 4.3 × 10 e⁻³ mJ when the equivalence ratio rises from 0.57 to 1.0. For tetralin aerosols of 0.57 equivalence ratio, E_min increases from as 0.09 mJ to 0.32 mJ when the droplet diameter rises from 10 μm to 60 μm. The trends are in agreement with previous experimental observations. The method used in current work has the potential to prediction of the minimum ignition energy of aerosol.     

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.     

焊接作业厂房烟尘扩散规律研究与响应面分析

为研究焊接烟尘在多因素耦合作用下的扩散规律，通过在某小型焊接车间进行实验，将不同温度、湿度、风速3种影响因素进行耦合分析，测定不同环境条件下焊接车间内的烟尘浓度。采用Design Expert软件进行Box Behnken实验设计，构建电焊焊接烟尘浓度在3因素3水平条件下的二次回归响应曲面模型，通过研究二次模型实验因素间交互作用，了解二次项对烟尘浓度影响因素的排序，并简要分析电焊烟尘的治理措施。研究结果表明:温度、湿度、风速3个因素均为显著影响；二次项显示因素影响RhV（相对湿度与风速）>TRh（环境温度与相对湿度）>TV（环境温度与风速）。     

基于单颗粒质谱技术的石家庄冬春季气溶胶成分特征及混合状态研究

利用位于石家庄市大气梯度监测站(20 m)的单颗粒气溶胶质谱仪分析了冬、春季大气环境中气溶胶的化学组成及混合状态,并采用ART-2a分类法对气溶胶分类。结果表明,石家庄市大气中主要存在8类颗粒物,即元素碳(EC)、有机碳(OC,相对分子质量小于150)、高分子有机碳(HOC,相对分子质量大于150)、混合碳(元素-有机碳混合,ECOC)、重金属、左旋葡聚糖碎片(LEV)、矿物质和富钾颗粒。8类颗粒中绝大部分包含SO_4~-、NO_2~-和NO_3~-等二次离子组分,表明采集到的颗粒物大都经历了不同的老化,或与二次组分进行了不同程度的混合。冬季气溶胶的主要成分是OC(数浓度36.1%),谱图含有C2H+3、C_2H_3O~+、C_5H_3~+、C_6H_5~+等离子,主要来自化石燃料、生物质等燃烧产生的一次排放颗粒,以及由挥发性有机物光化学氧化而成的二次有机颗粒;春季气溶胶的主要成分是EC(数浓度43.6%)和矿物质(数浓度15.4%)。EC中含有一系列单质碳峰,来自化石燃料或木材等生物质不完全燃烧的一次排放;矿物质颗粒中含有Mg~+、Al~+、Ca~+、Fe~+及SiO_3~-,主要来自扬尘。发生灰霾时,冬季OC和ECOC颗粒占比增大,EC颗粒占比减小;春季矿物质和ECOC颗粒占比变大,OC颗粒占比变小。随着灰霾天气发生,冬、春季碳气溶胶与二次无机气溶胶颗粒的混合加剧,而NH_4~+与碳气溶胶的混合加剧最为明显。冬季气溶胶的数浓度与气象因素的相关性高于春季,而低风速、高湿度和低气压易导致灰霾出现。石家庄市春季和冬季气溶胶污染应分别从机动车尾气、扬尘及燃煤、制药企业加以管控。     

Explosive properties of selected aerosols determined in a spherical 5-L test chamber

Combustible liquids in the form of aerosols are important for many industrial processes. Therefore the problem of explosion hazards posed by the aerosols becomes increasingly more prominent. To correctly assess the explosion risk and fulfil the requirements of the ATEX directive, it is necessary to obtain information regarding the flammable and explosive properties of the aerosols. Unlike in the case of gases and dusts, no standard procedures aimed at obtaining quantitative information of this type exist. Factors that influence the explosion dynamics of aerosols include: concentration, droplet size, temperature etc. Some of these factors are strongly dependent on the aerosol generation methods. A prototype apparatus was designed and constructed to address that dependence. The apparatus was used in an attempt to determine the basic explosion parameters of liquid flammable aerosols. The device consisted of a 5-L spherical vessel equipped with a pump-injection system that generated aerosols as well as a spark ignition source. A wide variety of injection settings were tested to select the most suitable conditions over a broad range of concentrations and fluid properties. A measurement procedure was developed for operating the device. Prototype tests were carried out with fluids commonly used in industry: isopropanol and kerosene. The tests demonstrated the significant influence of the vessel wall temperature on the result accuracy. Correct temperature control made it possible to obtain relationships between the aerosol concentration and the following explosion parameters: maximum explosion pressure and maximum rate of pressure rise.     

郑州环境空气中粉尘浓度的统计分析及预测

对郑州市2005年1月—2009年12月份的可吸入颗粒物(PM10)指数数据进行统计分析,并利用Matlab软件建立了利用气象要素预测PM10的BP神经网络模型。结果表明:2005—2009年郑州市PM10指数的年均值和空气质量超标天数逐步下降,且趋于稳定;年内各月的PM10指数浓度差异很大,冬季PM10指数显著高于夏季,8月最低,而12月最高;采暖期PM10指数显著高于非采暖期,而节假日对于PM10指数的影响不明显;通过平均风速、平均气温、平均气压和平均相对湿度预测PM10浓度可以达到最高精度86.85%。     

Configuration predictions of large liquefied petroleum gas (LPG) pool fires using CFD method

Liquefied petroleum gas (LPG) has potential pool fire risks due to its flammability. The configuration of pool fires plays a significant role when applying the solid flame model or point source model to assess the risks from heat radiation. However, no existing correlations can precisely predict the configuration of large LPG (100% propane) pool fires. To enhance the fundamental understanding on how pool diameter and wind velocity can influence the configuration of large LPG pool fires, an experimentally validated Computational Fluid Dynamics (CFD) model is employed to simulate fires using different burning rate models. Fire temperature profiles, flame heights, and flame tilts predicted by the CFD model were compared with empirical models and experimental data. Accordingly, new correlations for flame height and flame tilt as functions of pool diameter D and wind velocity u_w have been developed. The comparisons demonstrate that the new correlations have the best overall accuracy in the prediction of flame height and tilt for large LPG pool fires under different conditions (10 m ≤ D ≤ 20 m, 0 ≤ u_w ≤ 3 m·s⁻¹).     

浮顶油罐密封圈油气分布数值模拟

浮顶油罐一二次密封空间内的油气在雷击作用下可导致起火事故。为研究浮顶油罐一二次密封空间内的油气浓度影响因素,利用CFD方法进行了数值模拟,并建立了浮顶油罐实验模型,检测一二次密封空间内不同位置处的油气体积分数,两者表征的油气浓度情况较吻合;借助该模拟方法进一步分析温度、风速和二次密封泄漏面积对浮顶油罐一二次密封空间内的油气浓度的影响,研究结果表明:①二次密封泄漏面积增加,密封空间内的油气浓度降低。②温度上升,一二次密封空间的油气浓度升高;当风速较高时,温度对油气浓度变化趋势的影响也更大。③风速增加时,空间内的油气分布差异变大,油气浓度最大值变大。     

氨排放对华北典型地区冬季二次无机盐生成的影响

为研究氨排放对冬季PM_(2.5)中二次无机盐的影响,设置不同排放情景,应用CMAQ模式对华北地区典型城市——保定冬季无机盐进行了模拟研究。结果表明:将氨气在模式中排放置零的情景下,无机盐质量浓度降低了67.08%;氨排放削减与二次无机盐生成呈非线性关系,大气呈"氨限制"状态;氨排放削减能够有效抑制二次无机盐的生成,当削减幅度为50%时无机盐总体降幅达29.89%,其中硝酸盐、铵盐和硫酸盐降幅分别为53.78%、27.87%和5.64%;氨排放对重污染时段二次无机盐的生成贡献较高,当氨削减幅度为50%时无机盐总体降低40.58%;在当前大气环境下,氨排放削减是保定市冬季控制二次无机盐污染的重要途径。     

双波长气溶胶粒径传感方法及其火灾烟雾探测器

提出了双波长光散射气溶胶粒径传感方法,设计实现了采用该方法的双波长火灾烟雾探测器。使用短波长和长波长的双波长光源,通过计算其光功率比值,利用其与中值粒径的关系函数获得气溶胶粒径,并根据不同粒径下的气溶胶浓度分别给出大小不同粒径的火灾烟雾或干扰气溶胶提示。因而,不仅可以有效区分大小不同粒径的火灾烟雾气溶胶,以正确探测火灾,而且能够识别微米级的大粒径干扰粒子,降低火灾误报率,可以应用于飞机等航空器空中密闭的特殊环境。     

气田井喷硫化氢风洞模拟试验研究

为研究高含硫气田发生井喷事故后硫化氢的扩散运动规律,以重庆开县"12·23"井喷事故为研究对象,利用北京大学的2号环境风洞,制作了1∶2000的比例模型,利用乙烯和丙烯的混合气为示踪气体,采用长采样管方法测量浓度,首次在国内进行了井喷事故后硫化氢扩散的风洞试验,获得了低风速下(源处10m高风速为0.5m/s)N,NE,E,SE,S,SW,W,NW8个风向情况下的硫化氢浓度分布随时间的演化动画,定量地给出了各风向情况下硫化氢的最大浓度分布和各点的浓度时间序列,认为在低风速下,最大硫化氢浓度区域在撞山爬坡时出现,而爬过山坡后在背风区的硫化氢浓度会迅速降低。研究成果将为气田的井喷风险分级以及井喷事故后的应急处理提供参考。     

煤层干式钻进粉尘扩散规律的研究

针对煤层干式钻进过程中粉尘污染严重的问题,分别对新庄孜矿c13煤层及10煤层干式钻进粉尘的分散度和煤的硬度进行测定,分析对比2煤层钻进时粉尘在3 m/s风速下的浓度分布情况;并针对C13煤层,在1.5 m/s,2.3 m/s和3 m/s的风速下测定粉尘浓度分布情况.根据粉尘浓度的实测数据,分析煤层干式钻进粉尘扩散规律....     

负压隔离器内病毒空气传播影响因素的研究

病毒活性及病毒气溶胶粒径是病毒空气传播实验中的重要影响因素。病毒活性主要与环境温湿度有关。为了研究负压隔离器内颗粒粒径的影响因素,测量了实际运行工况下的两种粒径的颗粒浓度,并对不同换气次数、送风温度下颗粒浓度和粒径分布进行数值模拟。结果表明,不同粒径颗粒分布规律趋于一致;增加换气次数会导致气流旋涡区域颗粒浓度升高;随着换气次数的增加和送风温度的增大,颗粒平均粒径增大;减小换气次数能显著提高颗粒中0~0.01 mm粒径范围颗粒的占比。     

污水处理厂微生物气溶胶的暴露风险评价

为了给污水处理厂微生物气溶胶的健康风险评价提供定量依据,于2011年6—7月利用Andersen 6级撞击式空气微生物采样仪对西安市第三污水处理厂氧化沟单元内不同距离处的细菌气溶胶进行现场采样,利用平皿培养和菌落计数对细菌进行分析。选用适于我国国情的暴露因子参数,建立暴露风险评价模型,对污水处理厂的工人及周围居民的健康风险进行评价。评价点的细菌气溶胶浓度采用修正的高斯模型计算。结果表明,呼吸吸入是人体(儿童和成人)摄入微生物气溶胶的主要途径,暴露非致癌风险商随距离的增加而逐渐降低。同种途径在同样位置,儿童的风险商是成年男性或成年女性的2~3倍。经呼吸途径的风险商从大到小为儿童、成年男性、成年女性,经皮肤接触途径的风险商从大到小为儿童、成年女性、成年男性。     

南京市大气PM_(10)浓度的估算模型研究

以南京市为例,利用空气污染指数API、气象数据和TERRA/AQUA卫星气溶胶光学厚度(AOD)产品,分析了南京市PM_(10)浓度的变化规律,在PM_(10)浓度与气象要素进行相关分析的基础上,初步建立了基于气象要素和AOD的PM_(10)浓度估算模型。结果表明,南京市PM_(10)浓度在每年11,12月或1月最高,7,8月最低,季节性变化表现为冬春季浓度最高,秋季其次,夏季最低,PM_(10)浓度有逐年下降的趋势,但年均值仍高于国家II级标准;除了大气混合层高度外,PM_(10)浓度与大气压、风速、气温、相对湿度、水汽压、能见度、气溶胶光学厚度都有较好的相关性;基于气象要素的PM_(10)浓度估算模型的绝对系数R~2为0.510、平均相对误差为26.04%,基于AOD的PM_(10)浓度估算模型以TERRA和AQUA卫星AOD平均值构建的最佳,绝对系数R~2为0.482、平均相对误差26.11%,两种模型对PM_(10)的预测预报具有一定的指示意义。     

自然通风消除热源厂房热害的数值模拟与实践

在有余热余湿的厂房 ,大多采用自然通风。笔者采用k ε紊流模型 ,对某钢铁公司二高线厂房自然通风消除热害进行了数值模拟。将生产线上的散热量作为能量方程的附加源项 ,计算厂房内的速度场和温度场 ,优选出了该热源厂房的通风改造方案 :进风口的标高降低 2m ,在操作平台上设置开孔率为 30 %的通风栅栏板。通过对通风改造前、后厂房内温度实测值的对比 ,厂房工作区平均温度下降 5℃ ,风速由原来的平均 0 .2m/s增加到 1.6m/s,厂房内作业区的热环境有明显改善 ,防止了因热环境问题造成的安全事故 ,提高了工人的生产效率。     

On the non-monotonic wind influence on flammable gas cloud from CFD simulations for hazardous area classification

Hazardous areas are defined as a result of a variety of variables as storage temperature, pressure, leak orifice size, physical properties of flammable substance, and wind characteristics. The potential formation of an explosive atmosphere must be accurately assessed to ensure process safety. Therefore, computational fluid dynamics (CFD) arises as an important tool for accurate predictions as recommended by the international standard IEC 60079-10-1 (2015). This study aims to analyze the influence of wind velocity magnitude and direction on the hazardous area classification. The authors evaluated the extent and volume for methane, propane, and hydrogen leakages from a CFD model. For each flammable gas, the wind velocity magnitude and direction were regularly varied. The outcomes show that the behavior of the plume size as the wind varies mainly depends on the gas concentration. Counter-flow wind directions lead to zero relative velocity closer to the release point, which concentrates the gas, and wind in the release direction promotes a higher dilution of the gas cloud increasing the hazardous extent while decreases the volume. As a consequence, the wind also influences the zone type, which was accurately predicted from CFD simulations and significant differences were found when compared to the standard analyses. These differences are, to some extent, related to the consideration of wind velocity effects on the gas jet release.     

北京市城市街区PM10浓度日变化特征及其影响因子

为了解北京城市街区PM10浓度日变化特征及其影响因素,利用2003年10月BECAPEX(Beijing City Air Pollution Experiment)街道、街区及周边小区4个测点PM10浓度的对比观测试验资料和同期街道机动车流量、采样点附近自动气象站风速及探空资料进行了综合对比分析.通过天气诊断和统计学分析相结合,初步分析了北京市城区街道大气污染物PM10浓度日变化特征及机动车排放污染、气象条件对PM10浓度日变化的影响.结果表明,试验期间北京市城区街道PM10浓度日变化特征存在明显差异,交通源污染物PM10浓度日变化具有单峰与双峰型差异的特殊性.工作日PM10浓度日变化出现双峰,周末PM10浓度日变化仅有单峰出现; 交通污染源和气象条件对城市街区PM10浓度日变化特征的影响程度存在空间差异.离交通污染源较近的街区PM10浓度日变化受机动车排放污染的影响程度较大,而离交通源较远的小区PM10浓度受机动车排放污染的影响相对较小; 不稳定天气条件下交通污染源影响范围较小,在特定天气条件下,气象条件的影响强度可显著超过交通污染源的影响.     

Effects of humidity on minimum ignition energy of gaseous epoxypropane/air mixtures

The minimum ignition energy (MIE) is an important property for designing safety standards and understanding the ignition process of combustible mixtures. The minimum ignition energy (MIE) of gaseous epoxypropane/air mixtures is measured using capacitive spark discharge. The effect of humidity on MIE is studied. It is shown that the MIE is not constant when the relative humidity increases from 40% to 88% at room temperature. The relative humidity has no significant influence on the MIE of gaseous epoxypropane/air mixtures at the lower volume fraction of gaseous epoxypropane in air. But, it has significant influence on that at the higher volume fraction. The MIEs of gaseous epoxypropane/air mixtures vary with the fraction of gaseous epoxypropane in air and the humidity. The lowest value of MIE (0.12 mJ) of gaseous epoxypropane/air mixtures is reached at around 10% in the examined ranges of the concentrations for the humidity 40%. The lowest values of MIE (0.1 mJ) of the mixtures are reached also at around 10% in the examined ranges of the concentrations for the humidity 66% and 88% respectively.     

Aerosol concentration and particle size distributions in underground excavations of a hard coal mine

Deposition of aerosols in the respiratory system depends inter alia on their size and the respiratory tract deposition is appreciable for nanometer-sized particles. This article presents the results of measurements of size distributions of aerosols in the range of several nanometers up to about 20?μm in the underground mine excavations of an active hard coal mine. The study included practically all particles of a respirable fraction. The results showed that a high concentration of fine and ultrafine aerosols occurs in key underground workplaces especially during mining machine operations, although their contribution to total mass concentration is usually negligible.