Explosion Severity Parameters Research Articles

Evaluation of dust and gas explosion potential in chemical looping processes

The explosibility of metals typically used as oxygen carriers in chemical looping processes are reviewed. Chemical looping processes use intensified process conditions such as elevated temperatures and pressures to accelerate reduction and oxidation reactions of metals. A review of literature on metals indicates they are generally non-explosible under standard test conditions, however, at conditions used in chemical looping processes the opportunity to remove kinetic limitations exists resulting in reclassification of these dusts as marginally explosible under these circumstances. Potential locations and scenarios for explosions involving oxygen carriers in chemical looping processes are described. Operating conditions (temperature, pressure) and oxygen carrier qualities (base metal, support/loading) are reviewed for their effect on explosion severity parameters. These studies show explosions are unlikely to be severe in chemical looping reactors, but severity can increase while likelihood decreases in windboxes and in downstream process units following cooling. The potential for explosions where a metal oxide dust acts as the oxidizing agent for gaseous fuels through heterogeneous (chemical looping combustion – CLC) and homogenous (chemical looping oxygen uncoupling – CLOU) pathways as may be found in chemical looping processes is introduced, which we term a metal oxide reducing environment (MORE) explosion. Methane was shown to have the potential for the most serious consequences when reacting with copper- and manganese-oxides due to their reduction both being exothermic and increasing the quantity of gas present. Hematite and nickel oxide do not demonstrate this behaviour with common gaseous fuels. Potential prevention and mitigation strategies for explosions in chemical looping processes are briefly introduced. Particulate management strategies, venting, and downstream concerns are discussed.

Computational assessment of biomass dust explosions in the 20L sphere

Determination of the explosion severity parameters of biomass is crucial for the safety management and dust explosion risk assessment of biomass-processing industries. These are commonly determined following experimental tests in the 20L sphere according to the international standards. Recently, CFD simulations have emerged as a reliable alternative to predict the explosion behavior with good accuracy and reduced labor and capital. In this work, numerical simulations of biomass dust explosions are conducted with the open-source CFD code OpenFOAM. The multi-phase (gas-solid) flow is treated in an Eulerian-Lagrangian framework, using a two-way coupling regime and considering the reactions of biomass conversion (moisture evaporation, devolatilization, and char oxidation), the combustion of volatile gases, and convective and radiative heat transfer. The model is validated with pressure-time and concentration-dependent experimental measurements of two biomass samples. Results suggest that the characteristics of the cold-flow (ı.e., turbulence levels, actual dust concentration, spatial distribution of the dust cloud, and turbophoresis effect) govern the course of the explosion process, and depend strongly on particle size, dust concentration, and ignition delay time effects. These findings may be relevant in the design of better dust explosion testing devices and to the reexamination of the guidelines for the operation of the experiment. Finally, a thorough discussion on the explosion pressures, degree of biomass conversion, flame temperature, flame propagation patterns, and the dust agglomeration effect is presented.

Explosion severity behavior of micro/nano-sized aluminum dust in the 20L sphere: Influence of the particle size distribution (PSD) and nozzle geometry

Due to its industrial applications, the assessment of the explosibility parameters of aluminum powder is essential. However, they strongly depend on the Particle Size Distribution (PSD), which impacts both the rate-limiting step of the combustion mechanism and the radiative transfer. This article describes the influence of the test procedure on the explosion severity of six aluminum samples, having primary particle diameters ranging between 0.04 and 125 μm. The PSD measured in situ after dispersion in a 20 L sphere differs from those obtained before dispersion, particularly for nanoparticles for which the presence of agglomerates is evidenced. The explosion severity parameters were measured at different turbulence levels by changing the nozzle geometry and ignition delay time. The impact of the injection procedure varies from micron-sized aluminum dust to nanoparticles due to their low inertia. Moreover, if an alternative nozzle could be more appropriate at a lower turbulence level, the rebound nozzle is always the most conservative option for standard test conditions. Finally, the mean particle surface area was identified as an appropriate indicator of the micro/nano scale's explosivity performance. Results suggest that below 3 m2/g, the combustion would be diffusion-limited and kinetic-limited otherwise.

Suppression effect of inert gases on aluminum dust explosion

The suppression mechanism of inert gases for 5 μm aluminum dust explosion was investigated in a confined cuboid chamber. The characteristic parameters of flame propagation and explosion severity parameters that were affected by the inert gases were systematically studied. The results indicated that the minimum inerting volume fraction of carbon dioxide was lower than that of nitrogen, thereby indicating that the suppression effect of carbon dioxide on aluminum dust explosion was superior to that of nitrogen. To reveal the suppression mechanism on a micro level, a kinetic model that considered the surface kinetic mechanism was proposed. The results revealed that as the inerting volume fraction of the inert gas increased, the heterogeneous reactions that promoted the generation of intermediate species were mostly suppressed, while the heterogeneous reactions that consumed intermediate species were facilitated. Thus, carbon dioxide and nitrogen exerted certain suppression effects on surface reactions in their characteristic ways.

Inhibition evaluation of gas inhibitors in micron-sized aluminum dust explosion

The inhibition effects of gas inhibitors (nitrogen, carbon dioxide, and heptafluoropropane) on aluminum dust explosion were investigated experimentally and numerically. The results showed that as the inhibition volume fraction increased, the flame propagation characteristics parameters and explosion severity parameters were inhibited by inert gases accordingly. The inhibition performance of carbon dioxide was superior to that of nitrogen, and the minimum inhibition volume fractions of nitrogen and carbon dioxide were determined. XRD results indicated that the crystal form of major condensed product of aluminum dust explosion using two kinds of inert gas as inhibitors was different due to the distinct inhibition effect. Moreover, the XPS analysis revealed that the nitrogen oxide of aluminum adsorbed on the surface of aluminum particles blocked gasification process of aluminum particles. To explore the inhibition mechanism microscopically, a kinetic model concerning gas phase combustion was established. The above discussion indicated that the inhibition effect was the combination of multiple factors. In addition, due to the strong reactions between aluminum particles and heptafluoropropane, it cannot be regarded as gas inhibitor in aluminum dust explosion.

Study on the effect of simulated nuclear industry working conditions on the explosion severity parameters of zirconium powder and the explosion mechanism

Explosion caused by zirconium powder was revealed as one of main reasons in accidents happened in reprocessing of spent fuel in nuclear industry. It is urgent to study the explosion severity characteristic of zirconium dust cloud due to the great harm of its explosion. According to the equipment used in the actual post-treatment process in nuclear industry, the 20L cylindrical explosion equipment as a scale model was manufactured as the experimental device. The experimental results showed that Pmax and (dp/dt)max increased at first and then decreased with the increase of concentration. Small zirconium particles produced larger value of explosion severity parameters. Interestingly, initial temperature had no significant effect on Pmax of zirconium powder. However, the value of (dp/dt)max was strongly dependent on the initial temperature. Additionally, the oxidation degree of zirconium dust and temperature generated during explosion were studied by means of oxygen content and crystal form of explosion products. The study found that the particles develop toward spheroidization and its size became smaller, indicating that zirconium particles combustion is a heterogeneous shrinking core process. Under the condition of constant mass, increased number of ZrO2 particles leads to enlarged particle total surface area, increasing the amount of radioactive material released.

Experimental investigations of the ignition delay time, initial ignition energy and lower explosion limit of zirconium powder clouds in a 20 L cylindrical vessel

Zirconium powder, a main potential dangerous source in nuclear industry, has been focused on its explosion characteristics in this paper. Experiments were performed in a 20 L cylindrical explosion vessel with the influences of initial ignition energy, ignition delay time and zirconium concentration. Results showed that the maximum explosion pressure of zirconium-air mixture rose with the increase of the initial ignition energy, and a peak value was obtained with the variation of the ignition delay time. Lower explosion limit with the initial ignition energy of 10 kJ is 10 g/m³. Furthermore, explosion severity parameters, including maximum explosion pressure, maximum rate of pressure rise and maximum explosion index of zirconium-air mixture, were also obtained with the coupling variation between initial ignition energy and dust concentration. Research results and data obtained are a supplement to the utilization and safety operation of zirconium powders.

Effects of a carbon monoxide-dominant gas mixture on the explosion and flame propagation behaviors of methane in air

This work aimed to experimentally evaluate the effects of a carbon monoxide-dominant gas mixture on the explosion characteristics of methane in air and report the results of an experimental study on explosion pressure measurement in closed vessel deflagration for a carbon monoxide-dominant gas mixture over its entire flammable range. Experiments were performed in a 20-L spherical explosion tank with a quartz glass window 110 mm in diameter using an electric spark (1 J) as the ignition source. All experiments were conducted at room temperature and at ambient pressure, with a relative humidity ranging from 52 to 73%. The peak explosion pressure (Pmax), maximum pressure rise rate ((dp/dt)max), and gas deflagration index (KG) were observed and analyzed. The flame propagation behavior in the initial stage was recorded using a high-speed camera. The spherical outward flame front was determined on the basis of a canny method, from which the maximum flame propagation speed (Sn) was calculated. The results indicated that the existence of the mixture had a significant effect on the flame propagation of CH4-air and increased its explosion risk. As the volume fraction of the mixed gas increases, the Pmax, (dp/dt)max, KG and Sn of the fuel-lean CH4-air mixture (7% CH4-air mixture) increase nonlinearly. In contrast, addition of the mixed gas negatively affected the fuel-rich mixture (11% CH4-air mixture), exhibiting a decreasing trend. Under stoichiometric conditions (9.5% CH4-air mixture), the mixed gas slightly lowered Pmax, (dp/dt)max, KG, and Sn. The Pmax of CH4-air mixtures at volume fractions of 7%, 9.5%, and 11% were 5.4, 6.9, and 6.8 bar, respectively. The Sn of CH4-air mixtures at volume fractions of 7%, 9.5%, and 11% were 1.2 m/s, 2.0 m/s, and 1.8 m/s, respectively. The outcome of the study is comprehensive data that quantify the dependency of explosion severity parameters on the gas concentration. In the storage and transportation of flammable gases, the information is required to quantify the potential severity of an explosion, design vessels able to withstand an explosion and design explosion safety measures for installations handling this gas.

EXPERIMENTAL STUDY OF THE EFFECTS OF COAL DUST PARTICLE SIZE ON LAMINAR BURNING VELOCITY IN A MIXTURE OF COAL DUST AND METHAN

This study investigates the effect of variations of coal dust particles size on the rate of burning of coal dust particles in a 2-liter closed chamber. Coal dust was selected from three different mines with different sizes (149μm, 125μm, 105μm, 74μm, 63μm, 53μm, 44μm, 37μm) for explosion testing in a closed chamber of 2-liters. In this analysis, the concentration of coal dust was considered constant (10000 g/m3), all tests were carried out at a pressure of 1.5 bar and the initial tem- perature was 25 °C. To calculate the burning rate, the explosion severity parameters of each sample, such as the maxi- mum explosion pressure, the maximum rate of increase in pressure, and the explosion index must be determined during various tests. The results of the experiments show that by variating the size of the coal dust particles, the burning rate of the particles also changes and there is an inverse relationship between them. Coal dust particles with dimensions of 44μm and 37 μm have a higher burning velocity than other dimensions. Thus, with a reduction in the size of coal dust particles, the burning velocity of coal dust increases. The outcomes acquired in this examination are not just valuable in developing information on coal dust explosion processes, but also improve the measures needed to prevent coal dust explosions in coal mines.

Effect of the ignition delay time on explosion severity parameters of coal dust/air mixtures

Explosion pressure and pressure rise rate are two important indicators of the severity parameters of coal dust explosion. Ignition delay time has a significant effect on the explosion severity parameters of coal dust/air mixtures. In this work, this effect was studied through a combination of experiment and numerical simulation. The 20-L spherical vessel explosion test system was used to study the severity parameters of coal dust/air mixtures at the concentration of 250 g/m3 under different ignition delay times. The results showed that both of the maximum explosion pressure and the maximum rate of pressure rise appear a trend of first increase and then decrease with the increase of ignition delay time, reaching its maximum at 60 ms. Besides, the numerical simulation was conducted to investigate the distribution and variation of gas flow, coal dust particles, and turbulence kinetic energy before ignition in detail. The simulation results were in good agreement with the previous research data, and the effect of ignition delay time on the explosion severity parameters of coal dust/air mixtures was analyzed from the aspect of mechanism.

Characterization of the Products of Explosions of Varying Concentrations of Coal Dust

ABSTRACTCoal dust explosions using various concentrations of dust were performed and the gaseous and solid explosion products were analyzed. The explosion severity parameters Pm and (dP/dt)m were found to initially increase and then decrease with increasing dust concentration, while combustion time, tc, exhibited the opposite trend. The value of tc was also found to exhibit a linear correlation with both Pm and (dP/dt)m. Volatile matter and fixed carbon were the major components of each explosion and were significantly reduced in residues. CO, CO2 and CH4 were the major gas components and were present at different levels depending on the dust concentration. Micropores and mesopores played an important role in the explosion process. The data show that an explosion involving a low dust concentration is dominated by heterogeneous combustion, while homogeneous combustion is the primary process when employing worst-case and high concentrations.

Investigation on the structure evolution of pre and post explosion of coal dust using X-ray diffraction

To reveal the effects of coal dust explosion on its crystal structures evolution, the micro structure of six different rank of coal dust and its explosion solid products had been studied using 20 L explosion sphere vessel and X-ray diffraction (XRD) analyzer. The correlations between structural parameters and explosion severity had been analyzed detailed. Results show that coal dusts with higher volatile matter contents (Vdaf), lower vitrinite reflectance (Ro,max) and less ash contents (Aad) show stronger explosion severity. The effects of vitrinite reflectance (Ro,max) on the explosion severity parameters present the same role as the influence of volatile matter contents (Vdaf). Coal dusts with developed porous structure (SBET and VBJH) also present higher explosion reactivity. Interestingly, six selected coal samples present the strongest explosion severity at the same optimum explosion concentration (250 g/m3). For the different rank raw coal, the difference of the shape and intensity of 002 peak varies greatly. With the decreasing of coal ranks, the 002 band tends to be blunt and the peak intensity is relatively short. Quantitative analysis show that the lattice parameters (La, Lc, and Navg) of six coal samples are found to relatively increase with increasing vitrinite reflectance (Ro,max), whereas the d002 slightly decreases. The explosion treatments have significant effects on the ordering of coal aggregate structure. Compared with raw coal sample, the relative intensity of 002 bands at about 26° is reduced by the explosion treatments, which would increase the degree of graphitization of the explosion solid products. With the increasing of explosion pressure, the relative intensity of 002 peak would be gradually decreased. However, the shape of 002 peak for the explosion solid products tend to be more asymmetric and blunter than that at lower explosion conditions. Compared with the parent coals, the inter-layer spacing d002, Lc and Navg of all explosion products would be slightly reduced correspondingly. However, there is no clear rule for the evolution of La parameter. Moreover, calculated aromaticity (fa) of the coals ranges from 0.2208 to 0.6883, which is linear positively increased with the coal maturity by vitrinite reflectance.

Effects of metal foam meshes on premixed methane-air flame propagation in the closed duct

In many practical applications, the comprehensive measures are needed to suppress the gas explosions, and lining the channel walls with porous materials before a special installation for flame résistance is an effective choice. The aim of the present work is to investigate the effect of porous materials on the premixed flame propagation process in a closed combustion tube. Experiments are carried out to examine the flame dynamics for the stoichiometric methane/air mixtures both in the empty tube and in the presence of porous materials. The results demonstrate that the flame propagation can be divided into five typical stages, and a tri-tulip flame is observed during the development of the classic tulip flame. The inversion distance L of the flame front is selected to characterize the tulip flame evolution. It is worth to notice that the flame tip fronts travel faster with smaller porous densities PPI(pores per inch) from the finger shape stages to flat shape stages. The explosion severity parameters, including peak pressure and maximum pressure growth rates, are compared for all configurations, and the porous density plays an important role on the explosion severity. The maximum rate of pressure rise decreases linearly with the porous densities. It is deduced that the metal foam meshes with the larger porous densities PPI have more significant impacts on suppressing the tulip formation. The coupling of the flame front with the pressure wave plays a significant role in the onset and evolution of the tulip flame. As a whole, the metal foam meshes can reduce the overpressures can reduce the overpressures by33.3%–46.6%, while they have little effect on the flame tip speeds and shapes.

Explosion pressure measurement of methane-air mixtures in different sizes of confinement

This article reports the results of an experimental study on explosion pressure measurement in closed vessel deflagration for methane-air mixtures over its entire flammable range at standard pressure and temperature in vessels with variable geometry and size- 20-L spherical, 27-L cubical, 0.8 m3 rectangular and 25.6 m3 spherical-under quiescent conditions using electric spark (3 J) as ignition source. The outcome of the study is comprehensive data that quantify the dependency of explosion severity parameters on gas concentration and vessel volume. The information is required to quantify the potential severity of an explosion, design the vessels able to withstand an explosion and to design explosion safety measures for installations handling this gas. The data presented include maximum explosion pressure, explosion time and rate of explosion pressure rise in terms of deflagration index over a range of methane-air equivalence ratio (φ: 0.53–1.52). The maximum explosion pressures are: 8.6, 8.4, 8.2 and 8.0 bar in 20-L sphere, 27-L cubical vessel, 0.8 m3 rectangular vessel and 25.6 m3 sphere, respectively, at φ=1.05. Time to reach the maximum explosion pressure varies from 80 ms in 20-L sphere to 680 ms in 25.6 m3 sphere. The deflagration index values are: 82, 84, 86 and 106 bar m/s in 20-L sphere, 27-L cubical vessel, 0.8 m3 rectangular vessel and 25.6 m3 sphere, respectively, at φ=1.05. The deflagration index increases with increase in size of the test vessel.

Experimental and numerical studies on the explosion severities of coal dust/air mixtures in a 20-L spherical vessel

Severity parameters are critical for safety management and risk assessment of coal dust explosions. We evaluated explosion severity parameters using a 20-L spherical vessel and numerical simulation by the program FLUENT to reveal the explosion mechanism of coal dusts. The explosion pressure and the rate of explosion pressure increased with coal dust concentration and the ignition delay up to a concentration of 250g/m3 coal dust and an ignition delay of 60ms for a maximum explosion pressure of 0.67MPa and a rate of explosion pressure rise of 68.89MPa/s. Comparison of the numerical and experimental explosion pressure profiles showed reasonable quantitative and qualitative agreement. Additionally, the numerical simulation was used to address the technical difficulties of understanding the mechanisms of dust explosion, it suggested that the airflow of the dust explosion played a more important role in the secondary explosion of dusts in a closed chamber than in a half-closed one.

Methods for more accurate determination of explosion severity parameters

Accurate determination of explosion severity parameters (pmax, (dp/dt)max, and KSt) is essential for dust explosion assessment, identification of mitigation strategy, and design of mitigation measure of proper capacity. The explosion severity parameters are determined according to standard methodology however variety of dust handled and operation circumstances may create practical challenge on the optimal test method and subsequent data interpretation. Two methods are presented: a statistical method, which considers all test results in determination of explosion severity parameters and a method that corrects the results for differences of turbulence intensity. The statistical method also calculates experimental error (uncertainty) that characterises the experimental spread, allows comparison to other dust samples and may define quality determination threshold. The correction method allows to reduce discrepancies between results from 1 m3 vessel and 20-l sphere caused by difference in the turbulence intensity level. Additionally new experimental test method for difficult to inject samples together with its analysis is described. Such method is a versatile tool for explosion interpretation in test cases where different dispersion nozzle is used (various turbulence level in the test chamber) because of either specific test requirements or being “difficult dust sample”.

Explosive decomposition of ethylene oxide at elevated condition: effect of ignition energy, nitrogen dilution, and turbulence

Experimental and theoretical investigation of explosive decomposition of ethylene oxide (EO) at fixed initial experimental parameters ( T = 100 °C, P = 4 bar) in a 20-l sphere was conducted. Safety-related parameters, namely the maximum explosion pressure, the maximum rate of pressure rise, and the K d values, were experimentally determined for pure ethylene oxide and ethylene oxide diluted with nitrogen. The influence of the ignition energy on the explosion parameters was also studied. All these dependencies are quantified in empirical formulas. Additionally, the effect of turbulence on explosive decomposition of ethylene oxide was investigated. In contrast to previous studies, it is found that turbulence significantly influences the explosion severity parameters, mostly the rate of pressure rise. Thermodynamic models are used to calculate the maximum explosion pressure of pure and of nitrogen-diluted ethylene oxide, at different initial temperatures. Soot formation was experimentally observed. Relation between the amounts of soot formed and the explosion pressure was experimentally observed and was calculated.