多元混合气体爆炸特性及惰化防爆研究

为了完善常见多元混合气体爆炸特性参数数据库,为安全工程师开展城镇燃气防爆管理、安全操作规程的制定及对废弃管道进行改造、拆除提供依据,采用理论和试验方法对CO2与N2两种惰性气体对液化石油气(LPG)爆炸特性参数的影响规律进行了研究,对比分析了两种惰化剂对LPG的抑爆效果。结果表明:LPG体积分数为4.0%、CO2体积分数为22%时,LPG可燃气退出爆炸区间,此时极限氧体积分数为15.54%;LPG体积分数为3.5%、N2体积分数为32%时,LPG可燃气退出爆炸区间,此时极限氧体积分数为13.545%;两种惰化剂对LPG爆炸特性的抑制规律基本相似,但CO2的抑制效果明显优于N2。当CO2和N2充入的体积分数均为20%时,最大爆炸压力到达时间分别由166 ms延长到1 222 ms和826.30 ms;两种惰化剂用量在体积分数大于10%之前,对最大爆炸压力到达时间的影响均较小,因此在工程应用中采用惰化方式抑爆,惰化剂充入的体积分数需高于10%。     

惰化系统极限氧浓度变化规律及监测预警研究

为解决高龄油气管罐事故多发且事故后果严重的问题,通过研究惰性气体保护封存技术,提出惰化系统氧浓度等级分级、氧浓度安全裕量设定原则以及极限氧浓度(LOC)测试方法;通过理论与试验相结合的方法,分析CO_2、N_2等2种惰化剂对液化石油气(LPG)爆炸极限与LOC的影响以及抑制机制,并基于此设定预警阈值。结果表明:随着CO_2、N_2量的增加,最大爆炸压力到达时间延时可达7倍,抑爆效果明显,2种惰化剂抑爆机制的不同主要体现在三元碰撞反应;当CO2充入量达到22%或N2充入量达到32%时,LPG处于完全惰化状态;根据试验结果,可设定LPG惰化系统在线和间断氧浓度监测时预警阀值。     

N2/CO2混合气体对丙烯爆炸特性的影响

为了研究N₂、CO₂及其混合气体对丙烯爆炸特性的影响，使用可燃气体爆炸极限试验装置，将气体按一定比例进行混合，从爆炸极限与危险度、临界氧体积分数和惰化效果3个方面研究了N₂/CO₂混合气体对丙烯爆炸的影响。结果表明：1)N₂和体积比分别为2∶1、1∶1、1∶2的N₂/CO₂混合气体，以及CO₂的添加对丙烯的爆炸均有抑制作用，且使丙烯的爆炸范围缩小，爆炸危险度减小，变化趋势近似为线性；2)随着惰性气体体积分数的增加，爆炸极限对应的氧体积分数呈下降趋势，CO₂惰化丙烯比N₂惰化丙烯时的临界氧体积分数提高了约1.87个百分点；3)结合爆炸三角形图，对比发现，在5种不同的比例下，CO₂惰化丙烯时的爆炸区域面积最小，表明CO₂对丙烯的抑爆效果更好。     

丙烯氨氧化制丙烯腈反应器开车过程尾气燃爆危险性研究

丙烯直接氨氧化制丙烯腈工艺由于反应温度高,且反应器内的气相空间存在丙烯、丙烷、丙烯腈、乙腈、氧气、氮气等可燃性气体混合物,极易发生燃爆危险。为研究和评估该工艺装置反应器尾气的燃爆特性,采用11 L爆轰管测试在400℃、40 k Pa (G)工艺条件下,装置开车进料及反应过程中不同进料配比时反应器尾气组成的爆炸极限,并以此绘制爆炸极限三元相图,最终得到爆炸极限和极限氧体积分数。结果表明:反应器内可燃尾气的爆炸上限随氧气体积分数增加而升高,爆炸下限没有明显变化;在开车进料及反应过程中,反应器可燃尾气的极限氧体积分数LOC范围在8. 0%～8. 5%。因此,为避免反应器气相空间在开车过程中发生燃爆危险,需监测反应器内氧气体积分数,并设置氧体积分数报警值小于8. 0%。     

不同可燃气体影响氮气惰化甲烷爆炸的试验

为了探究矿井瓦斯中不同可燃气体对CH_4惰化防爆的影响,通过测定加入少量C_2H_4和CO时混合气体中CH_4的爆炸极限、临界体积分数等参数,归纳了C_2H_4和CO对N_2惰化CH_4爆炸的作用规律。结果表明:少量C_2H_4或CO均会降低CH_4在空气中的爆炸上下限,2. 0%C_2H_4和2. 0%CO分别可以使CH_4爆炸上限下降0. 9%、0. 2%,使爆炸下限下降3. 6%、0. 6%;且少量C_2H_4或CO均会使CH_4爆炸危险度上升,而爆炸下限相对爆炸上限下降的程度更大; C_2H_4或CO存在时将CH_4-空气体系完全惰化所需的N_2量相应加大,2. 0%C_2H_4和2. 0%CO分别使N_2量增大4. 7%、3. 7%;随C_2H_4或CO体积分数由0增加至2. 0%,CH_4的爆炸上下限在达到重合点时的体积分数逐渐下降,分别下降了2. 0%、0. 8%;含有2. 0%C_2H_4时CH_4的爆炸极限范围为13. 5%,比含有2. 0%CO时大3. 4%,重合点低1. 2%; C_2H_4和CO均会使CH_4爆炸三角形向左下方移动并延伸,爆炸区域扩大,窒息比明显增大。不同可燃气体对N_2惰化CH_4爆炸的影响程度差异明显,C_2H_4存在时带来的防爆难度明显比CO更大。     

叔丁醇燃爆危险性研究

为预防叔丁醇氧化制甲基丙烯酸甲酯工艺过程中燃爆危险的发生,利用11L爆轰管测定不同工况温度、压力条件下,叔丁醇在不同氧含量的氧氮混合气中的爆炸极限,得到不同工况条〖JP2〗件下“叔丁醇-氧气-氮气”混合体系的燃爆区域;针对工艺过程中存在水蒸汽的条件,研究了水蒸汽含量对叔丁醇燃爆的影响。结果表明:叔丁醇在80℃、015MPa,170℃、015MPa,280℃、01MPa条件下的极限氧含量分别为159%、153%和135%;随着水蒸汽含量的升高,叔丁醇爆炸极限范围变小,在80℃、015MPa,170℃、015MPa条件下当水蒸汽含量增加到27%和34%时无燃爆现象发生。     

丙烯燃爆危险性分析

为预防丙烯氧化制环氧丙烷工艺流程中丙烯燃爆危险的发生,利用5 L爆炸极限测试仪测定丙烯在空气中常压不同温度条件下的爆炸极限,得到丙烯在常压下爆炸极限随温度的变化情况;针对丙烯工艺中的典型工况,采用11 L爆轰管测定不同工况温度、压力条件下,丙烯在空气中不同氧含量下的爆炸极限,并以此绘制爆炸极限三元图,得到不同工况条件下"丙烯-氧气-氮气"混合体系的燃爆区域。结果表明:随着温度、压力及氧气含量的升高,丙烯爆炸上限明显提高,但爆炸下限变化不明显;丙烯在80℃、0.24 MPa,130℃、0.96 MPa,40℃、1.90 MPa条件下的极限氧含量(LOC)分别为11.0%,10.2%和10.8%。降低体系中氧气含量有助于预防丙烯燃爆危险的发生。     

空气泡沫驱伴生气燃爆特性及临界氧体积分数变化规律研究

为了探究高初始压力条件下空气泡沫驱井筒伴生气的燃爆特性，设计并搭建了高温高压可燃气体燃爆特性测试系统，对井筒伴生气的爆炸上限、下限以及临界氧体积分数等燃爆特性进行了测试。测量结果表明，随着初始温度和压力的升高，爆炸下限和临界氧体积分数降低，爆炸上限增加，伴生气的危险性增加。在0.5 MPa和10℃条件下伴生气的爆炸极限为2.01%～19.97%,而在15 MPa和80℃时爆炸极限迅速扩大至1.14%～56.67%。临界氧体积分数的测试结果从11.85%(0.5 MPa, 10℃)下降到8.91%(15 MPa, 80℃),最大差值为2.94%。根据试验结果拟合了临界氧体积分数的经验式，可快速评定不同初始条件下伴生气的安全氧含量。     

载流雾化水惰化甲烷空气预混气体特性实验研究

设计了预混气体载流雾化水惰化和抑制燃烧管实验台,对层流火焰的燃烧速度、稳定性及拉伸变形规律进行实验研究,分析了雾化水抑制和熄灭层流预混火焰的过程和机理,获得了雾化水惰化爆炸极限内甲烷和空气预混气体的特性。研究结果表明:浓度为7%的甲烷和空气预混气体,最小惰化雾化水通量为20.8ml/(m2.min);对于浓度为9%的甲烷和空气预混气体,最小惰化雾化水通量为32.9ml/(m2.min);对于浓度为11%的甲烷和空气的预混气体,最小惰化雾化水通量为44.6ml/(m2.min)。研究成果为雾化水熄灭甲烷火焰和抑制甲烷爆炸具有一定的指导意义。     

多元混合气爆炸极限的非线性预测研究

根据混合气的爆炸极限与混合气各成分的体积浓度之间具有非线性关系的特点,笔者提出采用神经网络非线性方法来计算含有H2,CH4和CO的多元混合气体的爆炸极限。在模型中,H2,CH4和CO的体积浓度作为输入,爆炸上限和下限作为输出。计算结果表明,该非线性模型预测混合气爆炸下限和上限的最大相对误差为3.90%,3.57%,而模型预测值与计算值的相关系数分别为0.971,0.981;非线性模型的预测结果要好于偏最小二乘回归的预测结果。当H2,CO,CH4在混合气中的体积浓度给定时,非线性模型能够准确预测混合气的爆炸极限。     

Effects of initial temperature and pressure on explosion characteristics of propane–diluent–air mixtures

The explosion characteristics of propane–diluent–air mixtures under various temperatures and pressures were investigated using a 20-L apparatus. The explosion limits of propane diluted with nitrogen or carbon dioxide were measured at high temperatures from 25 to 120 °C. The results showed that the upper explosion limit (UEL) increased, and the lower explosion limit (LEL) decreased with the rising temperature. The explosion limits of propane diluted with nitrogen or carbon dioxide were also measured at high pressures from 0.10 to 0.16 MPa. The results showed that the UEL increased, and the LEL almost remainedunchanged along with increased pressure. Under the same initial operating conditions, the concentration of nitrogen required to reach the minimum inerting concentration (MIC) point was higher than the concentration of carbon dioxide. Finally, the study investigated the limiting oxygen concentration (LOC) of propane under various initial temperatures, initial pressures, and inert gases. The LOC of propane decreased approximately linearly with increased temperature or pressure, and the LOC of propane dilution with carbon dioxide was greater than dilution with nitrogen from 25 to 120 °C or from 0.10 to 0.16 MPa, which indicated that the dilution effect of carbon dioxide was better than that of nitrogen.     

Law of variation for low density polyethylene dust explosion with different inert gases

To reveal the effects of different inert gases on explosion characteristics during low density polyethylene (LDPE) dust explosion and optimize the explosion-proof process, eight N₂ (CO₂)/air mixed inerting conditions were experimentally studied. Typical inerting conditions with 12 L cylindrical explosive tank were used to study the characteristics on the flame propagation. The thermogravimetric analysis with related theories were used to further explain the mechanism and quantities in low density polyethylene (LDPE) dust explosion with different inert gases. The results showed that the reduction of O₂ concentration could effectively delay the progress of flame growth process and weaken the effect of dust combustion reaction. The flame growth process of condition (N₂/air (18% O₂)) was 2.05 times slower than that of the non-inert condition. The explosion strength was obviously reduced, and the characteristic parameters such as explosion pressure and flame propagation speed were also affected by the decrease of O₂ concentration. For LDPE powder, the smaller the median diameter, the greater the explosion intensity and the lower the limiting oxygen content (LOC). The LOC with CO₂ was usually higher than that with N₂ and the effect of CO₂ was significantly better than N₂ in inerting.     

Effect of initial pressure on explosion characteristics of 2, 3, 3, 3–tetrafluoropropene

With the popularity of refrigerants in the process industries, the potential safety problems caused by the use of refrigerants have attracted worldwide attention as people have realized their inherent explosion characteristics of refrigerants. This paper studied the explosion characteristics of refrigerant 2, 3, 3, 3–tetrafluoropropene (R1234yf) at different concentrations and initial pressures based on a 20 L experimental apparatus. The experimental results illustrated the peak overpressure of R1234yf increased with the rise of initial pressure. At a constant ambient temperature of 25 °C, the maximum rate of pressure rise and deflagration index showed an N-shaped trend with the increase of the refrigerant concentration from 6.8% to 10%. The maximum rate of pressure rise and deflagration index increased first and then decreased with the increase of the refrigerant concentration at atmospheric pressure, while they presented an M-shaped trend at pressurization condition. The peak overpressure, the maximum rate of pressure rise, and deflagration index reached 0.742 MPa, 4.04 MPa s⁻¹, and 1.1 MPa.m.s⁻¹ with a refrigerant concentration of 7.6%, respectively, which were less than those of refrigerant propane and difluoromethane (R32) at the optimal concentration. Furthermore, R1234yf exhibited better safety performance compared with refrigerant R32 in the same flammability classification.     

Effect of initial temperature on explosion characteristics of 2, 3, 3, 3–Tetrafluoropropene

The flammability of refrigerants is a major cause of refrigerant explosion incidents. Studying the explosion characteristics of refrigerants at different initial temperatures can provide significant benefits for solving the safety problems of refrigerants under actual working conditions. This paper studied the effects of the initial temperature and refrigerant concentration on the explosion characteristics of refrigerant 2, 3, 3, 3-tetrafluoropropene (R1234yf) at 0.1 MPa. The curves of explosion characteristics with different initial temperature revealed the same variation trend ranged from 25 °C to 115 °C. Specifically, as the refrigerant concentration was raised, the peak overpressure, the maximum rate of pressure rise, and laminar burning velocity increased initially and decreased afterwards, along with maximum values at the refrigerant concentration of 7.6%. When the refrigerant concentration was 7.6%, the peak overpressure declined exponentially with the initial temperature rise, while the maximum rate of pressure rise increased linearly. The laminar burning velocity calculated from the spherical expansion method indicated that the flame propagation was gradually accelerated by the increase of initial temperature, which coincided with the change of the maximum rate of pressure rise. Meanwhile, experiments and CHEMKIN simulation results demonstrated the effects of elevated temperature from 20 °C to 50 °C on the explosion limits of R1234yf. The lower explosion limit reduced and the upper explosion limit increased with rising initial temperature. In general, R1234yf exhibited moderate combustion and lower explosion risk, compared with traditional refrigerants.     

Inerting effect of N2 on explosion of LDPE dust/ethylene hybrid mixtures

Explosion flame propagation characteristics and overpressure distribution of low density polyethylene (LDPE) dust and ethylene hybrid mixture were investigated under N₂ inerting conditions using a custom-designed 12 L cylindrical explosion tank. The results showed that a small amount of ethylene could promote the explosion characteristics of LDPE dust. N₂ inerting had different inhibitory effects on the explosion flame of LDPE dust and its mixture with ethylene. The explosion overpressure strength of the LDPE dust/ethylene hybrid mixture decreased with increasing N₂ concentration. The overall suppression effect of N₂ on the explosion overpressure of the LDPE dust was better than that of the LDPE dust/ethylene hybrid mixture explosion. As the ethylene concentration increased from 0% to 2.5%, the limiting oxygen concentration decreased by 13% oxygen. This small amount of ethylene restricted the traditional inerting process. The study conclusions can provide further scientific basis for the inerting and explosion proofing design of production process equipment involving LDPE dust.     

Inerting characteristics of ultrafine Mg(OH)2 on starch dust explosion flame propagation

Experiments on the flame propagation of starch dust explosion with the participation of ultrafine Mg(OH)₂ in a vertical duct were conducted to reveal the inerting evolution of explosion processes. Combining the dynamic behaviors of flame propagation, the formation law of gaseous combustion products, and the heat dissipation features of solid inert particles, the inerting mechanism of explosion flame propagation is discussed. Results indicate that the ultrafine of Mg(OH)₂ powders can cause the agglomeration of suspended dust clouds, which makes the flame combustion reaction zone fragmented and forms multiple small flame regions. The flame reaction zone presents non-homogeneous insufficient combustion, which leads to the obstruction of the explosion flame propagation process and the obvious pulsation propagation phenomenon. As the proportion of ultrafine Mg(OH)₂ increases, flame speed, flame luminescence intensity, flame temperature and deflagration pressure all show different degrees of inerting behavior. The addition of ultrafine Mg(OH)₂ not only causes partial inerting on the explosion flame, but also the heat dissipation of solid inert particles affects the acceleration of its propagation. The explosion flame propagation is inhibited by the synergistic effect of inert gas-solid phase, which attenuates the risk of starch explosion. The gas-solid synergistic inerting mechanism of starch explosion flame propagation by ultrafine Mg(OH)₂ is further revealed.     

小苏打对红色彩跑粉粉尘云爆炸极限氧浓度的影响*

为研究彩跑粉的爆炸强度和爆炸敏感性,采用20 L球形爆炸实验系统和热重-差热分析仪开展实验,在分析红色彩跑粉爆炸压力和爆炸极限氧浓度(LOC)的基础上,进一步揭示小苏打对红色彩跑粉爆炸极限氧浓度的影响规律。研究结果表明:在玉米粉中添加红色食用色素后形成的彩跑粉会增加爆炸风险,爆炸猛烈度属于St1级;在50~400 g/m3粉尘浓度范围内,红色彩跑粉的LOC值先减小后增大,在200 g/m3时LOC值达到最低9%;当添加不同比例小苏打对红色彩跑粉爆炸风险进行抑制时,发现LOC值随着红色彩跑粉与小苏打混合性粉尘掺混比的增大而增大,在掺混比为50%时,红色彩跑粉与小苏打混合性粉尘的LOC值为21%。研究结果可为彩跑粉加工厂的抑爆和惰化防爆技术提供基础数据参考。     

Effects of N2 and CO2 on the flammability of 2,3,3,3-tetrafluoropropene at elevated temperatures

The flammability characteristics of refrigerants are affected by environmental factors, making them prone to flammability and explosion accidents in cooling systems. In this paper, the flammability characteristics of R1234yf–air mixtures with N₂ and CO₂ were investigated comparatively at temperatures between 20 and 50 °C at 80% relative humidity. The lower and upper flammability limits of R1234yf were measured. The limiting oxygen concentration (LOC), critical flammable ratio (CFR), and critical flammable concentration (CFC) of the R1234yf–air mixtures with inert gases were investigated. The paper developed a linear formula between the flammability limit of R1234yf and the temperature. The changes in CFC with different temperatures were negligible for R1234yf. Furthermore, the mixed refrigerant had both non-flammability and the lowest vapor pressure when the CFR of the R1234yf/CO₂ mixture was 2.9. The experimental results were used to propose a new prediction model to estimate the flammability limits of R1234yf. Finally, molecular simulation explained the effect of inert gases on the flammability of R1234yf from a microscopic point of view. The research aimed to provide valid evidence and data for preventing flammable and explosive refrigerant incidents.     

Theoretical and experimental study of the inhibition and inert effect of HFC125, HFC227ea and HFC13I1 on the flammability of HFC32

HFC32 is a potential alternative refrigerant with excellent thermal performance, but the flammability is a main obstacle for its applications. The group contribution method is utilized to analyze the inhibition efficiency of nonflammable refrigerants in binary mixtures. Furthermore, a novel equation of predicting the minimum inerting concentration of nonflammable refrigerants has been proposed by analyzing the variation of the flame propagation velocity and the flammable refrigerant concentration. Experimental studies of the explosion limits of HFC125/HFC32, HFC227ea/HFC32 and HFC13I1/HFC32 were carried out and the ranges of explosion limits were obtained. At the same time, the relationship between the maximum charge of the flammable refrigerants and lower flammability limit (LFL) was analyzed. The result demonstrates that the proposed novel theoretical equation can effectively predict the minimum inerting concentration of nonflammable refrigerants to flammable refrigerants, and the theoretical results have significance on the security application of the binary mixtures.     

Experimental investigation of limiting oxygen concentration of hybrid mixtures

An investigation into the limiting oxygen concentration (LOC) of fifteen combustible dusts and methane, ethanol and isopropanol hybrid mixtures in the standard 20 L explosion chamber was performed. Three ignition energies (10 J, 2 kJ and 10 kJ) were used. The results show that a 10 J electrical spark ignition leads to significantly higher limiting oxygen concentration values than either 2 kJ or 10 kJ pyrotechnic igniters. This could be due to the “overdriving” effect of the chemical igniters, which produce a hot flame that virtually covers the entire explosion chamber during combustion. With respect to hybrid mixture investigation, the 20 L sphere was modified to allow the input of methane gas and flammable solvents. The limiting oxygen concentrations of the hybrid mixtures were found to be considerably lower than those of dust air mixtures when the relatively weaker spark igniter was used. There was no significant change in limiting oxygen concentration when the higher energy chemical igniters were used.