A correlation of the lower flammability limit for hybrid mixtures

Hybrid mixtures are widely encountered in industries such as coal mines, paint factories, pharmaceutical industries, or grain elevators. Hybrid mixtures explosions involving dust and gas can cause great loss of lives and properties. The lower flammability limit (LFL) is a critical parameter when conducting a hazard assessment or developing mitigation methods for processes involving hybrid mixtures. Unlike unitary dust or gas explosions, which have been widely studied in past decades, only minimal research focuses on hybrid mixtures, and data concerning hybrid mixtures can rarely be found. Although methods to predict the LFL have been developed by using either Le Chatelier's Law, which was initially proposed for homogeneous gas mixtures, or the Bartknecht curve, which was adopted for only certain hybrid mixtures, significant deviations still remain. A more accurate correlation to predict an LFL for a hybrid mixtures explosion is necessary for risk assessment. This work focuses on the study of hybrid mixtures explosions in a 36 L dust explosion apparatus including mixtures of methane/niacin, methane/cornstarch, ethane/niacin and ethylene/niacin in air. By utilizing basic characteristics of unitary dust or gas explosions, a new formula is proposed to improve the prediction of the LFL of the mixture. The new formula is consistent with Le Chatelier's Law.     

Flame propagation behaviors of nano- and micro-scale PMMA dust explosions

Flame propagation behaviors of nano- and micro-polymethyl methacrylate (PMMA) dust explosions were experimentally studied in the open-space dust explosion apparatus. High-speed photography with normal and microscopic lenses were used to record the particle combustion behaviors and flame microstructures. Simple physical models were developed to explore the flame propagation mechanisms. High-speed photographs showed two distinct flame propagation behaviors of nano- and micro-PMMA dust explosions. For nano-particles, flame was characterized by a regular spherical shape and spatially continuous combustion structure combined with a number of luminous spot flames. The flame propagation mechanism was similar to that of a premixed gas flame coupled with solid surface combustion of the agglomerates. In comparison, for micro-particles, flame was characterized by clusters of flames and the irregular flame front, which was inferred to be composed of the diffusion flame accompanying the local premixed flame. It was indicated that smaller particles maintained the leading part of the propagating flame and governed the combustion process of PMMA dust clouds. Increasing the mass densities from 105 g/m³ to 217 g/m³ for 100 nm PMMA particles, and from 72 g/m³ to 170 g/m³ for 30 μm PMMA particles, the flame luminous intensity, scale and the average propagation velocity were enhanced. Besides, the flame front became more irregular for 30 μm PMMA dust clouds.     

Effects of different pretreatment methods on the enzymatic hydrolysis of oak shell

Sawtooth Oak (Quercus acutissima) shells were used as a renewable and low-cost agricultural residue for bioethanol production for the first time. The efficiency of H₂SO₄, NaOH, steam explosion and the combination of these methods was compared in terms of delignification, saccharification efficiency and yield. The structural features of samples were characterized by SEM, XRD and FTIR. Results show H₂SO₄/steam explosion resulted in the highest hemicellulose reduction (98.5%) and cellulose recovery yield (99.9%). NaOH /steam explosion resulted in the highest delignification level (31.5%). Steam explosion exhibited the highest enzymatic digestibility of 98.8% and total product yield of glucose of 84.8%, an increase of 130.8% and 98.1% than that of untreated oak shell, respectively, which seemed to be the most effective for improving enzymatic saccharification. The results of structural features showed the structure and surface of shells were changed that is in favor of the following enzymatic hydrolysis.     

含NaCl超细水雾抑制甲烷爆炸实验研究

为研究含NaCl添加剂超细水雾对甲烷爆炸的影响,在自制的半封闭透明管道内,进行含NaCl添加剂超细水雾抑制甲烷爆炸试验,通过检测和分析在不同NaCl浓度情况下超细水雾的粒径和甲烷爆炸的平均火焰传播速度、爆炸超压以及平均升压速率,探究NaCl浓度对超细水雾粒径及其对抑制甲烷爆炸有效性的影响。研究结果表明:NaCl浓度对超细水雾粒径影响较小;对于体积分数为9.5%的甲烷,相比于纯甲烷爆炸,其平均火焰传播速率、最大爆炸超压以及平均升压速率分别下降了53.7%,63.4%和60.7%,相比于超细纯水雾,其平均火焰传播速率、最大爆炸超压以及平均升压速率分别下降了38.6%,58%,56%;在通雾量相同的条件下,浓度为2.5%NaCl超细水雾对体积分数为9.5%的甲烷爆炸抑制性能最佳;含NaCl添加剂超细水雾的物理化学共同作用可以有效抑爆甲烷。     

基于木质素磺酸钙的湿式除尘系统氢气爆炸事故控制措施研究

为了减少湿式除尘系统发生氢气爆炸事故的可能性,提出通过抑制湿式除尘系统中铝粉与水反应的方法来从本质上加以控制。选取木质素磺酸钙为抑制剂,利用研发的金属粉与水反应产生氢气测试仪进行氢气抑制实验,得出不同浓度木质素磺酸钙溶液随时间变化的抑氢曲线,表明木质素磺酸钙能较好地抑制铝粉和水反应产生氢气。使用扫描电子显微镜(Scanning Electron Microscope,SEM)和傅里叶变换红外光谱法（Fourier Transform Infrared,FTIR）对铝粉与木质素磺酸钙溶液反应后的产物进行表征,研究木质素磺酸钙的抑制机理。研究结果表明:可以将木质素磺酸钙应用到铝制品抛光打磨场所的湿式除尘系统中,从而降低氢气爆炸事故发生的可能性。     

“头顶库”风险量化分析模型研究及实例应用

为了对天然气长输管道等设施穿越尾矿库下游形成的“头顶库”风险进行量化分析,基于假定和边界条件构建了尾矿库溃坝风险分析模型,并通过引入计算公式构建了尾矿库溃坝风险量化分析模型,提取了冲击波超压和爆破地震烈度法计算公式来量化分析管道爆炸对尾矿库影响效应。以福建龙岩某尾矿库“头顶库”为例,研究了该尾矿库溃坝后冲击力是否会造成管道断裂;模拟了爆炸对人员影响的范围;进而分析了管道完全破裂后爆炸造成的冲击波和爆炸振动对尾矿库的影响。研究结果表明:在500 a一遇的洪水条件下,尾矿库溃坝下泄的泥砂流对该穿越管道造成的冲击力不会造成管道断裂;管道泄漏10 min的爆炸情形产生的爆炸冲击波对尾矿库坝体结构没有影响,产生的等效爆炸地震烈度大于尾矿库的抗震设防烈度6度。可为同类实例提供工程理论方法。     

过氧化苯甲酸叔丁酯热危险性实验研究

为了研究TBPB的热危险性,采用液体自燃点测试仪研究TBPB自燃点随浓度的变化规律,应用快速筛选量热仪研究不同升温速率下TBPB的热分解,同时利用差示扫描量热仪研究TBPB热流-温度变化规律。研究结果表明:当TBPB浓度为0.83 g/L时,自燃温度达到最低值125.1 ℃,浓度是影响其自燃温度的重要指标;随升温速率升高,初始分解温度逐渐升高,可见升温速率越高,TBPB分解的初始温度越高,当环境温度未达到初始分解温度时,相对较安全;TBPB最低起始反应温度为95.4 ℃,平均放热量为893.28 J/g,运用Kissinger,Ozawa 这2种方法得出E1=84 063.2 J/mol,E2=86 442.3 J/mol,指前因子为1.69×109,反应级数为0.92。其放热量较大,起始反应温度较低,热量无法及时移出时,极易发生燃烧爆炸事故。     

内凹型蜂窝结构在冲击载荷作用下的力学行为及响应特性研究

为减少危险化学品爆炸事故造成的大量应急救援人员伤亡,提升应急救援人员防爆服的防爆能力,有效抵御由爆炸产生的冲击波、破片及高温对人体造成的伤害。研究了具有负泊松比效应的内凹蜂窝结构,通过准静态及激波管冲击实验,对比分析了传统蜂窝结构与内凹蜂窝结构在力学特性、吸能效果与冲击波衰减效率等方面的差异;通过改变内凹蜂窝中结构单元的凹角、尺寸以及构成蜂窝结构的原材料实现对蜂窝结构的优化设计,并对优化后的蜂窝结构吸能特性以及冲击波在结构中的衰减规律进行研究和综合分析。结果表明:内凹蜂窝结构单元的最佳尺寸为3.4 mm,最佳凹角为30°,最佳材料为钛合金。研究成果为寻求同时满足轻质高强、抗冲击和吸能效果要求的结构设计方案提供了理论基础。     

障碍物对瓦斯煤尘爆炸火焰传播规律的影响

为了进一步探究瓦斯煤尘耦合爆炸火焰的传播规律,用自行搭建的半封闭垂直管道爆炸试验系统,研究障碍物对瓦斯煤尘耦合爆炸火焰传播规律的影响。研究结果表明:障碍物能显著提高瓦斯煤尘爆炸火焰的传播速度,其加速机理主要是障碍物诱导的湍流区会促进火焰的传播;火焰在传播过程中的加速度不是一直增加,随着火焰速度的增加会出现上下波动;煤尘的加入会使瓦斯爆炸产生的火焰传播速度显著增大及速度的最大值距离点火端较远;通过障碍物时爆炸产生的火焰形状发生较大的改变,出现拉伸和褶皱现象。     

除尘管道内木粉尘爆炸压力传播规律研究

为了探明除尘管道中粉尘爆炸压力的传播规律,利用自制通风除尘管道爆炸特性测试装置进行试验。研究结果表明:整个管道中粉尘爆炸压力波的传播过程可以分为自由传播阶段、管壁反射阶段和一维传播阶段;压力波在传递过程中处于边移动边生长的状态,具有压力累积效应;除尘管道中粉尘爆炸压力波幅及平均升压速率均与粒径呈负相关关系,二者随浓度变化呈现先上升后下降的趋势;利用Matlab分析了浓度、粒径对压力波的交互效应,表明二者交互作用显著。