ABSTRACT
To characterize the inerting effect of N2/CO2 mixtures containing various proportions on methane-air explosions, a series of experiments were conducted in a 20 L spherical vessel under the normal temperature (25 °C) and normal pressure (101 kPa). Six concentrations (10, 12, 14, 16, 18, and 20%) of N2/CO2 mixtures were selected to analyze the suppression of methane explosion by N2/CO2 mixtures. The results indicated that the maximum explosion pressure (p max) of methane explosions was 0.501 MPa (17% N2 + 3% CO2), 0.487 MPa (14% N2 + 6% CO2), 0.477 MPa (10% N2 + 10% CO2), 0.461 MPa (6% N2 + 14% CO2), and 0.442 MPa (3% N2 + 17% CO2) in the presence of the same N2/CO2 concentration, and similar decreases in the rate of pressure rise, flame propagation velocity, and production of free radicals were observed. Therefore, with the increase of CO2 concentration in the gas mixture, the inerting effect of N2/CO2 was enhanced. Meanwhile, the whole process of the methane combustion reaction was affected by N2/CO2 inerting, which was mainly attributed to heat absorption and dilution of the N2/CO2 mixture. N2/CO2 with a greater inerting effect leads to lower production of free radicals under the same explosion energy and a lower combustion reaction rate at the same flame propagation velocity. The findings of the current research provide references for the design of safe and reliable industrial processes and the mitigation of methane explosions.
ABSTRACT
To characterize the inhibiting effects of sodium bicarbonate (NaHCO3) on aluminum dust, the inhibiting capacities of NaHCO3 and its solid product sodium carbonate (Na2CO3) on the explosions of 10 and 20 µm aluminum dusts were studied using a standard 20 L spherical chamber. Explosion parameters were analyzed based on the induction period and explosion stage to evaluate the inhibiting effects. The results show that the induction period of 10 µm aluminum dust explosion is 18.2 ms, which is shorter than that of 20 µm aluminum dust. Two aluminum dust explosions can be completely inhibited during the induction period when inert ratios of NaHCO3 are 350 and 150%, respectively, but that is not observed after adding the corresponding amount of Na2CO3. When the inert ratio ranges from 0 to 150%, the physical effect of NaHCO3 on 10 µm aluminum is poor and the chemical effect is the essential process. But as the inert ratio increased from 200% to 350%, the physical effect of NaHCO3 is higher than the chemical effect, suggesting that the physical effect is the key factor. With the increase of NaHCO3, the physical effect increases gradually. However, the chemical effect changes little. The physical effects of NaHCO3 including heat absorption and isolation play an essential role in the inhibiting process, which has a significant impact on the pyrolysis process and explosion parameters. The results of the present work provide guidance for the prevention and control of aluminum dust explosions.
