DOI: 10.3303/CET2290064 Paper Received: 9 December 2021; Revised: 22 March 2022; Accepted: 5 May 2022 Please cite this article as: Gao J., Yang X., Hu S., Hong Z., Li R., 2022, Study on the synergistic effect of multicomponent gas mixture on the dynamic characteristics of gas explosion, Chemical Engineering Transactions, 90, 379-384 DOI:10.3303/CET2290064 CHEMICAL ENGINEERING TRANSACTIONS VOL. 90, 2022 A publication of The Italian Association of Chemical Engineering Online at www.cetjournal.it Guest Editors: Aleš Bernatík, Bruno Fabiano Copyright © 2022, AIDIC Servizi S.r.l. ISBN 978-88-95608-88-4; ISSN 2283-9216 Study on the Synergistic Effect of Multicomponent Gas Mixture on the Dynamic Characteristics of Gas Explosion School of Safety Engineering, Beijing Institute of Petrochemical Technology, Beijing, China hushoutao@bipt.edu.cn With the development of industry and technology, multi-element gases coexist in many places. The study of the influence of appropriate concentration of flammable gas on the chemical kinetic characteristics of methane-air explosion is great significance for preventing and controlling gas explosions. An experimental system was set up to carry out different concentrations of C3H8/H2/CH4/air premixed gas explosion. The effects of multiple gases on the methane explosion characteristic parameters were studied. It is shown that the pressure peak firstly increases and then decreases with the increase of propane concentration when the C3H8/CH4/air mixture gas explosion experiment is carried out. The explosion of propane/methane/air mixture is most significant when the propane concentration is 0.4%. The experiment of H2/CH4/air mixed gas explosion was carried out. With the increase of H2 concentration, the pressure peak increased gradually. In the experiment of C3H8/H2/CH4/air mixed gas explosion, the peak pressure firstly increases and then decreases with the increase of propane concentration. C3H8/H2/CH4/air mixture gas explosion is most significant when the concentration of C3H8 is 0.2% and the concentration of H2 is 1%. The elementary reactions process were numerical simulated by CHEMKIN-PRO software. The micro-mechanism of multi-element gas explosions based on key radicals, sensitivity and reactions paths. Reaction step R38: H+O2<=>O+OH and R53: H+CH4<=>CH3+H2 to affect the explosion process. 0.1%C3H8+1%H2 and 0.2%C3H8+1%H2 will accelerate the CH4/air premixed gas explosion reaction rate, 0.3%C3H8+1%H2 will inhibit the methane/air premixed gas explosion reaction rate. It is mainly because R312 elementary reaction at this concentration: CH3+C2H5(+M)<=>C3H8(+M) dominates the explosion, inhibiting R38 elementary reaction: H+O2<=>O+OH, reducing OH the amount of production, thereby inhibiting the explosion process. The research results have important practical value for preventing and controlling multi-element gas explosion accidents and reducing accident losses. 1. Introduction With the rapid development of science and technology, complex multi-element gases are widely present in industries such as coal mines, petrochemicals, metallurgy and pharmaceuticals, underground spaces and laboratories. The multi-element gas in coal mines and underground spaces is mainly methane, and contains other elements. Studying the influence of the appropriate concentration of combustible gas on the chemical kinetic characteristics of methane-air explosion and analyzing the laws of multi-element gas explosion are of great significance to the prevention and control of gas explosions. Scholars' research on multi-systems is mainly divided into three aspects: the mixture of methane and dust, methane and combustible gas, and methane and inert gas. (Pinaeva et al., 2020) proved that in the hybrid systems studied, coal combustion competes with methane combustion, but methane is chemically more active than coal. Methane, rather than coal carbon has a decisive influence on the parameters of combustion and detonation waves. (Li et al., 2012) found with appropriate hydrogen and methane ratio, the lower explosion limits of the mixtures are even smaller than that of each component gases. (Wang et al., 2021) reported montmorillonite powders inhibitors generated NH4, ∙NCO, and ∙OH which can interrupt explosion chain reactions to suppress methane explosion. (Wang et al., 2020) studied CO may increase the collision frequency and make the chain initiation reaction of CH4/CO/C2H6/H2/air mixtures easier than CH4/air mixtures. (Liang et al., 2019) analysed the nonlinear effect shows that HO2 recombination is important at high H2 conditions, while the interaction of HO2 and CH3 379 Jiancun Gao, Xigang Yang, Shoutao Hu*, Zijin Hong, Ruxia Li mailto:hushoutao@bipt.edu.cn dominates when the H2 concentration in the fuel mixture is relatively low. (Luo et al., 2019) proposed the key radicals OH and CH2O show a high degree of correlation, with CH2O being more susceptible to oxygen content than OH during the reaction process. (Tan et al., 2020) the addition of CH4/CO2/O2 significantly decreased the minimum ignition temperature of dust, and the minimum ignition temperature of hybrid mixture was inversely proportional to the increase of gas mole fraction. (Chang et al., 2020) measured the effect of CO2 dilution dominating the explosion behavior becomes more apparent than N2 dilution. (Zhao et al., 2020) pointed out the inhibition effect of CO2 was found to be stronger than N2 due to its higher specific heat, but the addition of 1.14% CH4 can offset the inhibition effect of CO2 somehow. (Wang et al., 2020) discovered the extrema of these explosion parameters are found to be at⩽ φ1.0. 2. Experimental apparatus, methods and materials The experimental system is composed of experimental pipeline, transient pressure acquisition devices, gas distribution systems, and ignition devices. A schematic of this system is shown in Figure 1. Figure 1: Schematic of gas explosion experiment device As shown in the schematic in Figure 1, the cylindrical experimental pipeline of length 1000mm, inner diameter of 100mm and thickness of 6mm is pressure-resistant pipeline and equipped with a bursting disc. Three pressure sensors are installed in the pipeline to measure the pressure at different positions. The No. 1 pressure sensor was set to 30 cm from the ignition end, and the No. 2 pressure sensor was set to be 30 cm away from sensor No. 1 in a horizontal direction. Pressure sensor No. 3 was set to 30 cm in a horizontal direction to sensor No. 2. The transient pressure system consists of Kistler-211B3 sensors and a data collector. The software was set to a collection frequency of 80 kHz, that is, 80 times/ms of data collection. The process was operated using measurement software. The gas distribution system includes vacuum pump, circulating pump and two valves. The ignition system consists of a high-energy igniter instrument and an ignition head. The ignition head is located at left of pipeline. The experimental gas materials include CH4, C3H8, H2 and synthetic air with a purity of 99.9999 %. Chapter 2 All experiments were carried out at room temperature and normal pressure. The experimental steps are as follows: The gas seal of the experimental system was checked. A vacuum of <667 Pa (according to GB/T 12474–2008) was established in the experimental pipeline by the vacuum pump, and the pressure remained unchanged within 5 min as observed through a pressure gauge, which indicated that the experimental instruments were appropriate for the experiment. The combustible gas of calculated volume was injected into the pipe in the vacuum environment, and then synthetic air was injected into the pipe until atmospheric pressure. The gas in the pipe was mixed for 2 min by the circulation pump and standing for 5 min to ensure uniformity mixing gas according to the law of Dalton partial pressure method with an accuracy of 0.1%. The combustible gas is ignited by the ignition system, and the pressure data are collected. The residual gas in the pipeline was treated harmlessly by physical (adsorption) and chemical (catalytic combustion) methods to avoid polluting the atmosphere. 3. Results analysis The explosion pressure of CH4/C3H8/H2/air premixed multicomponent gas was shown in Figure. 2. 380 0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 80 90 100 110 120 130 140 150 O v e rp re ss u re /k P a C3H8 concentration% 122 138 139 141 142 137 135 123 122 87 82 0 1 2 3 4 120 130 140 150 160 170 O v e rp re ss u re /k P a H2 concentration% 122 151 158 161 164 0.00 0.05 0.10 0.15 0.20 0.25 0.30 120 125 130 135 140 145 O v e rp re ss u re /k P a C3H8 concentration 122 140 143 133 2a 9.5%CH4+C3H8 2b 9.5%CH4+H2 2c 9.5%CH4+1%H2+ C3H8 Figure 2: multicomponent gas explosion pressure under different working conditions It can be seen from Figure. 2a that with the increase of C3H8 concentration, the explosion pressure of CH4 shows a trend of first promoting and then inhibiting. The explosion pressure of C3H8/CH4/ air mixture was the largest and increased 16.369% when the C3H8 concentration was 0.4%. When the C3H8 concentration was 0.8 %, the explosion pressure was the same as the blank group. When the C3H8 concentration exceeds 0.8 %, the explosion pressure decreases greatly. It can be seen from Figure. 2b that the H2 concentration was positively correlated with the explosion pressure of the multicomponent gas. The greater the H2 concentration was, the greater the explosion pressure was. When the H2 concentration was 1%, the explosion pressure increased the fastest, rising by 23.77%. With the increase of H2 concentration, the rise was indeed gentle. When the H2 concentration reached 4%, the explosion pressure of the mixed gas increased by 34.43% compared with the blank group. It can be seen from Figure 2c that in the C3H8/H2/CH4/air mixture, the concentration of C3H8 was changing, the concentration of H2 was 1%, and the concentration of CH4 was 9.5%. With the increase of C3H8 concentration, the peak explosion pressure first increased and then decreased. Compared with the blank group, the addition of C3H8 and H2 still promoted the explosion pressure. When the propane concentration was 0.2%, the peak explosion pressure increased by 17.21%. 4. Simulation analysis The simulation software was Chemkin-pro, and the mechanism file was GRI Mech 3.0 of Hai Wang team. (Wang et al., 2007) The closed homogeneous Batch Reactor model was used to simulate the transient gas reaction. The blank group and the three conditions of adding 0.4%C3H8, 4%H2 and0.2%C3H8 +1%H2 were simulated. Because these three conditions had the greatest promotion effect on CH4 explosion pressure. Table 1: simulated conditions Serial CH4/vol.% C3H8/vol.% H2/vol.% 1 9.5 0 0 2 9.5 0.4 0 3 9.5 0 4 4 9.5 0.2 1 0.00 0.01 0.02 0.03 0.04 0.05 0.00 0.05 0.10 0.15 0.20 V o lu m e f ra c ti o n Time/s CH4 O2 C3H8 H2 0.000 0.005 0.010 0.015 0.020 0.00 0.05 0.10 0.15 0.20 V o lu m e f ra c ti o n Time/s CH4 O2 C3H8 H2 3a 9.5%CH4 3b 9.5%CH4+0.4%C3H8 381 0.00 0.01 0.02 0.03 0.04 0.05 0.00 0.02 0.04 0.06 0.08 0.10 0.12 0.14 0.16 0.18 0.20 V o lu m e f ra c ti o n Time/s CH4 O2 C3H8 H2 0.0 0.1 0.2 0.3 0.4 0.5 0.00 0.05 0.10 0.15 0.20 V o lu m e f ra c ti o n Time/s CH4 O2 C3H8 H2 3c 9.5% CH4+4% H2 3d 9.5%CH4+0.2%C3H8+1%H2 Figure 3: volume fraction of reactants under different working conditions It can be seen from Figure 3 that the residual amount of CH4 in the blank group was the least. After the addition of 0.4% C3H8, the residual amount of CH4 increased, indicating that in C3H8/CH4/air multivariate gases, C3H8 would be preferentially consumed, and then CH4 was consumed. The addition of H2 also increased the CH4 residue, proving that H2 reacted earlier than CH4 in the H2/CH4/air multicomponent system. When C3H8 and H2 were homochromous added, the remaining amount of CH4 increased, and the remaining amount of C3H8 also increased, indicating that in the multi-system of C3H8/H2/CH4/air, H2 reacted preferentially than C3H8. 0.03821 0.03822 0.03823 0.03824 0.03825 0.03826 0.03827 -0.030 -0.025 -0.020 -0.015 -0.010 -0.005 0.000 0.005 R125 CH4+·OH=·CH3+H2O R123 CH4+·O=·CH3+·OH R123 CH4+·H=·CH3+H2 R101 ·CH3+·CH2O=CH4+·HCO C H 4 R O P m o le /c m 3 -s e c Time/s R88 ·CH3+·H=CH4 0.014 0.016 0.018 0.020 0.022 0.024 -0.00010 -0.00008 -0.00006 -0.00004 -0.00002 0.00000 0.00002 R123 CH4+·O=·CH3+·OH R125 CH4+·OH=·CH3+H2O R123 CH4+·H=·CH3+H2 R101 ·CH3+·CH2O=CH4+·HCO R88 ·CH3+·H=CH4 C H 4 R O P /m o le /c m 3 -s Time/s 4a 9.5%CH4 4b 9.5%CH4+0.4%C3H8 0.0046 0.0047 0.0048 0.0049 -0.010 -0.008 -0.006 -0.004 -0.002 0.000 0.002 C H 4 R O P /m o le /c m 3 -s e c Time/s R88 ·CH3+·H=CH4 R101 ·CH3+·CH2O=CH4+·HCO R123 CH4+·O=·CH3+·OH R125 CH4+·OH=·CH3+H2O R123 CH4+·H=·CH3+H2 0.01510 0.01515 0.01520 0.01525 0.01530 0.01535 0.01540 -0.006 -0.004 -0.002 0.000 C H 4 R O P /m o le /c m 3 -s e c Time/s R125 CH4+·OH=·CH3+H2O R123 CH4+·O=·CH3+·OH R101 ·CH3+·CH2O=CH4+·HCO R88 ·CH3+·H=CH4 R123 CH4+·H=·CH3+H2 4c 9.5% CH4+4% H2 4d 9.5%CH4+0.2%C3H8+1%H2 Figure 4: CH4 ROP under different working conditions 382 Positive represented the elementary reaction to produce CH4, negative represented the elementary reaction to consume CH4. It can be seen from Figure 4 that the first five elementary reactions of CH4 explosion reaction were the same, but the reaction rates were different. R88·CH3+·H= CH4 and R101·CH3+·CH2O=CH4+·HCO generated CH4. R123CH4+·O=·CH3+·OH, R124CH4+·H=·CH3+H2 and R125CH4+·OH=·CH3+H2O were the main reaction of CH4 consumption. CH4 collided with massive ·H, ·O, ·OH to generated ·CH3 and other products. The addition of C3H8 reduced the reaction rate of R88 and increased the reaction rate of R101. The addition of C3H8 and H2 decreased the reaction rates of R123, R124 and R125, indicating that the addition of C3H8 and H2 inhibits the CH4 consumption reaction. It is considered that H2 and C3H8 preferentially reacted with O2, resulting in an increase in CH4 residue. 0.03822 0.03823 0.03824 0.03825 0.03826 0.03827 0.03828 -30000 -20000 -10000 0 10000 20000 ·O S e n s Time/s R1 ·H+O2=·O+·OH R96 ·CH3+HO2=·OH+·CH3O R93 ·CH3+O2=·O+·CH3O R123 CH4+·H=·CH3+H2 R104 ·CH3+·CH3=C2H6 0.00410 0.00411 0.00412 0.00413 0.00414 0.00415 -3000 -2000 -1000 0 1000 2000 3000 R104 ·CH3+·CH3=C2H6 R123 CH4+·H=·CH3+H2 R96 ·CH3+HO2=·OH+·CH3O R93 ·CH3+O2=·O+·CH3O ·O S e n s Time/s R1 ·H+O2=·O+·OH 5a 9.5%CH4 5b 0.4%C3H8+9.5%CH4 0.00460 0.00465 0.00470 0.00475 0.00480 0.00485 0.00490 -2000 -1000 0 1000 2000 3000 ·O S e n s Time/s R1 ·H+O2=·O+·OH R96 ·CH3+HO2=·OH+·CH3O R3 ·OH+H2=·H+H2O R125 CH4+·OH=·CH3+H2O R104 ·CH3+·CH3=C2H6 0.01520 0.01525 0.01530 0.01535 0.01540 -4000 -2000 0 2000 4000 Time/s ·O S e n s R1 ·H+O2=·O+·OH R96 ·CH3+HO2=·OH+·CH3O R94 ·CH3+O2=·OH+·CH2O R125 CH4+·OH=·CH3+H2O R104 ·CH3+·CH3=C2H6 5c 4%H2+9.5%CH4 5d 0.2%C3H8+1% H2+9.5%CH4 Figure 5: O sensitivities analysis under different working conditions The addition of C3H8 and H2 increased O2 consumption, and the ·O sensitivity was analysed. The sensitivity coefficient was positive to promote O generation, that was, to promote explosion, while the negative was the opposite. It can be seen from Figure 5a that R1, R93, R96, R104 and R123 had great influence on ·O sensitivity. R93·CH3+O2=·O+·CH3O had the greatest positive effect on ·O sensitivity and R96·CH3+·HO2=·OH+·CH3O also has a greater positive impact on O, indicating that ·CH3O promoted ·O and in turn promoted explosion. R104·CH3+·CH3=C2H6 was the chain termination reaction and produced larger molecular weight alkanes, which had the greatest negative impact on ·O sensitivity, indicating that R104 inhibits explosion. It can be seen from Figure 5b that the elementary reaction with the greatest positive impact on ·O sensitivity changed from R93 CH3+O2=·O+·CH3O to R1·H+O2=·O+·OH after the addition of C3H8. C3H8 reacted with O2 preferentially than CH4. C3H8 decomposed into ·C3H7 and ·H, and O2 decomposed into ·O. The addition of C3H8 increased the amount of CH4 residue. This indicated that the reaction rate of ·CH3 decreased, and the sensitivity of R93 and R96 to O decreased. ·CH3O still had the positive impact on ·O sensitivity. It can be seen from Figure 5c that compared with blank group, the elementary reaction with the greatest positive impact on ·O sensitivity changed from R93 to R1 after the addition of H2. The sensitivity coefficient of R3·OH+H2=·H+H2O and R125CH4+·OH=·CH3+H2O also increased. The number of ·H,·O and ·OH increased. 383 R96 still had positive impact on ·O sensitivity. R125 was the chain transfer reaction, from simple ·OH into ·CH3. R125 had the negative impact on ·O sensitivity, indicating that R125 inhibits explosion. It can be seen from Figure 5d that the elementary reaction with the greatest positive impact on ·O sensitivity changed from R93 to R1 when C3H8 and H2 were added simultaneously. R104 still had the greatest negative impact. This indicated that R1 promoted explosion and R104 inhibited explosion. R96 still had positive impact on ·O, sensitivity indicating that ·CH3O still had the positive impact on ·O sensitivity. The addition of H2 and C3H8 or the addition of H2 both increased the sensitivity coefficient of R125, and the priority of H2 reaction was higher than that of C3H8, indicating that the main reason for the increase of R125 sensitivity coefficient was the addition of H2. 5. Conclusions The addition of appropriate amount of C3H8 and H2 in CH4/air promoted CH4 explosion, and 0.4% C3H8 had the largest promotion effect on CH4 explosion. The higher the H2 concentration, the more obvious the promotion effect of CH4 explosion. The addition of 0.2% C3H8 and 1% H2 had the greatest promotion effect on CH4 explosion. In the C3H8/H2/CH4/ air premixed multivariate gas, the reaction priority of H2 was higher than C3H8, and that of C3H8 was higher than CH4. Elementary reaction ·H+O2<=>·O+·OH promoted explosion and ·CH3+·CH3=C2H6 inhibited explosion. 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