Differences of premixed methane-air explosion in pipelines suppressed by three ultrafine water mists containing different salts
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摘要: 针对管道输送可燃气体时爆炸引发的连锁安全问题,自行搭建了两节管道预混气爆炸传播及抑爆实验系统,开展了不同种类、不同盐类质量分数和不同雾通量的盐类超细水雾抑制甲烷体积分数为9.5%的甲烷-空气预混气爆炸的系列实验。基于火灾学和爆炸学理论,深入探讨了不同实验工况下爆炸超压振荡曲线、最大超压峰值、爆炸火焰阵面位置、火焰平均传播速度和火焰结构演化的差异性。研究表明:随着盐类添加剂(NaCl、NaHCO3和MgCl2)质量分数和雾通量的增大,最大爆炸超压峰值相对于纯水超细水雾作用时呈不同幅度下降,爆炸超压振荡曲线上升趋势缓慢,火焰平均传播速度下降趋势明显。爆炸火焰锋面在管道B内呈现不同次数的后退现象,到达管道末端的时间较无细水雾和纯水超细水雾下延迟效应明显。通过比较分析,发现含NaCl超细水雾在弱化爆炸超压、延缓火焰锋面推进、降低火焰平均传播速度以及火焰后退次数方面均优于含MgCl2和NaHCO3超细水雾。主要原因在于,阴离子Cl−销毁链式爆炸反应中OH·、H·自由基的能力强于
${\rm{HCO}}_3^- $ ,阳离子Na+销毁爆炸反应中OH·、H·自由基的能力强于Mg2+。Abstract: In order to solve the safety problem caused by flammable gas explosion in pipeline transportation, an experimental system for premixed gas explosion and explosion suppression in multiple pipelines was self-built. And then a series of premixed methane-air explosion and explosion suppression experiments were carried out under the ultrafine water mists without or with three kinds of salts in the different working conditions including the different salt mass fractions and the different mist fluxes. In the experiments, the methane volume fraction in the premixed methane-air mixture was 9.5%, and three salts used as additives were NaCl, NaHCO3 and MgCl2. According to the theories of fire science and explosion science, the different changes in the explosion characteristics were explored involving the oscillation curves and the maximum peak values of explosion overpressure, the front positions and the average propagation velocities of the explosion flame, the evolution images of the flame structure in pipe B. The results show that with the increases of salt mass fractions and ultrafine water mist fluxes with salts (NaCl, NaHCO3 and MgCl2), the maximum peaks of explosion overpressure decreased by different amplitudes compared with those under the action of pure water mist, the oscillation curves of explosion overpressure increased slowly, and the average propagation velocities of explosion flame decreased significantly. The explosion flame fronts receded different times in the pipe B. And the times when the explosion flames reached the terminal end of the pipe B delayed obviously compared with those with or without the pure ultrafine water mist. Comparisons display that the ultrafine water mist containing NaCl is superior to the ones containing MgCl2 and NaHCO3, respectively, in weakening the explosion overpressure, delaying the advance of the flame front position, decreasing the average flame propagation velocity, and reducing the receding times of the explosion flame front. The primary reason is that the ability of the anion Cl−to destroy OH· and H· radicals in chain explosion reactions is stronger than that of the anion${\rm{HCO}}_3^- $ and the ability of the cation Na+ to destroy OH· and H· radicals in explosion reactions is stronger than that of the cation Mg2+. -
表 1 NaCl超细水雾作用下最大爆炸超压的变化
Table 1. Changes of the maximum explosion overpressures under the suppression of ultrafine water mists containing NaCl
w/% V/mL pmax/kPa Δpmax/kPa η/% w/% V/mL pmax/kPa Δpmax/kPa η/% 0 4.2 18.7 0 8.4 15.4 2 17.0 1.7 9.1 2 13.6 1.8 11.7 4 15.2 3.5 18.7 4 12.8 2.6 16.9 6 14.5 4.2 22.5 6 10.8 4.6 29.9 8 13.9 4.8 25.7 8 9.9 5.5 35.7 表 2 含NaHCO3超细水雾作用下最大爆炸超压的变化
Table 2. Changes of the maximum explosion overpressure under the suppression of ultrafine water mists containing NaHCO3
w/% V/mL pmax/kPa Δpmax/kPa η/% w/% VL/mL pmax/kPa Δpmax/kPa η/% 0 4.2 18.7 0 8.4 15.4 2 18.6 0.1 0.5 2 15.0 0.4 2.5 4 18.3 0.4 2.1 4 14.3 1.1 7.1 6 17.7 1.0 5.3 6 13.5 1.9 12.3 8 16.6 2.1 11.2 8 12.8 2.6 16.9 表 3 MgCl2超细水雾作用下最大爆炸超压的变化
Table 3. Changes of the maximum explosion overpressures under the suppression of ultrafine water mists containing MgCl2
w/% V/mL pmax/kPa Δpmax/kPa η/% w/% V/mL pmax/kPa Δpmax/kPa η/% 0 4.2 18.7 0 8.4 15.4 2 17.3 1.4 7.5 2 15.3 0.1 0.6 4 16.1 2.4 13.9 4 14.5 0.9 5.8 6 15.7 3.0 16.0 6 13.0 2.4 15.6 8 14.0 4.7 25.1 8 11.7 3.7 24.0 表 4 不同工况下3种盐类超细水雾作用下火焰峰面到达管道末端的时间
Table 4. Times for the flame front to arrive at the terminal end of pipe B affected by three ultrafine water mists with different salts under different working conditions
工况 tter/ms Δt/ms ξ/% 工况 tter/ms Δt/ms ξ/% 工况 tter/ms Δt/ms ξ/% 无水雾 5.27 无水雾 5.27 无水雾 5.27 0%-NaCl 8.06 2.79 0%-MgCl2 8.06 2.79 0%-NaHCO3 8.06 2.79 2%-NaCl 11.16 5.89 38.5 2%-MgCl2 8.68 3.41 7.7 2%-NaHCO3 8.68 3.41 7.7 4%-NaCl 12.09 6.82 50.0 4%-MgCl2 12.40 7.13 53.8 4%-NaHCO3 9.30 4.03 15.4 6%-NaCl 14.88 9.61 84.6 6%-MgCl2 13.64 8.37 69.2 6%-NaHCO3 10.23 4.96 26.9 8%-NaCl 17.98 12.71 123.0 8%-MgCl2 15.19 9.92 88.5 8%-NaHCO3 12.40 7.13 53.8 -
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