Explosive Concentration Research Articles

Dust Explosion Characteristics near the Minimum Explosible Concentration

Dust Explosion Characteristics near the Minimum Explosible Concentration

Экспериментальные и расчетные значения температуры вспышки смесей растворителей, применяемых в промышленности

The experimental verification of the calculated flash point temperatures of solvent mixtures used in industry is presented, and the evaluation of the adequacy of the methods for calculating the rate of its evaporation is given. To verify these methods, acetone-benzene and acetone-chloroform mixtures were experimentally studied, for which a deviation from Raoult's law could be assumed. The dependences of the evaporated substance on time at room temperature are obtained. An increase in the saturated vapor pressure and an increase in the evaporation rate are observed in the first mixture, and a decrease in the second. In the first case, the amount of substance that is taking part in the explosion increases and must be taken into account when calculating the room pressure increase during explosion, and the second can be used to reduce the potential explosive hazard of solvent mixtures. The problem of predicting fire and explosion hazard of solvents is associated with the identification of the fact of the formation of explosive concentrations of their vapors and change of flash point temperatures of the mixed liquids. By the example of a number of binary mixtures of flammable liquids, the influence of the interaction of their components on the flash point is shown, the calculated and experimental (reference) data in a closed crucible are compared for the ratio of components in the range from 0 to 100 % in benzene-toluene and benzene-ethanol mixtures. It is noted that for mixtures with a similar molecular structure, the results of calculating the flash point are in good agreement with the experiment, otherwise, the calculation gives overestimated values for liquids of various classes. Therefore, for mixtures of solvents used in industry, the number of components of which is three or more, it is required to check the flash point experimentally in order to more accurately predict their fire and explosion hazard.

The simulate of the stratification of an explosive mixture of hydrogen and air in the RBMK-1000 spent-fuel storage pool

Currently, in Russia, codes with concentrated parameters are used as software tools to justify the hydrogen explosion safety of nuclear power units, which use the concept of “average concentration of hydrogen” in the calculated volume and do not take into account the stratification of hydrogen, due to which local concentrations of hydrogen can significantly exceed the “average”. This paper presents the hydrogen explosion safety analysis results during a beyond-design accident in the RBMK-1000 spent-fuel storage pool taking into account local concentrations of gas components using the gas dynamic code ANSYS FLUENT. The vapor-gas mixture propagation problem in the spent-fuel storage pool was solved in a two-dimensional approximation. The following sources of hydrogen were considered radiolysis hydrogen generation, hydrogen generation by reducing its solubility in water and the vapor-zirconium reaction. As a result of modeling, the possible accumulation areas of an explosive mixture and their sizes were determined. It is shown that under certain combinations of boundary conditions, due to the presence of convective flows, an explosive concentration is not achieved even if the mixture components stratification is taken into account.

DETERMINATION OF OIL AND OIL PRODUCT LOSSES FROM EVAPORATION WHEN LOADING VEHICLES

Background Losses of oil and oil products from evaporation when they are loaded into tankers, automobile and railway tanks at points that are not equipped with steam recovery units are inevitable. This also leads to environmental pollution and may lead to the formation of explosive concentrations in the air of the working area. Therefore, the control of losses of oil and oil products from evaporation at filling points is an urgent task. Aims and Objectives The purpose of this article is to develop a method for calculating losses of oil and petroleum products from evaporation at filling points. Results A formula has been obtained for calculating the loss of oil and oil products from evaporation based on the results of measuring the mass content of hydrocarbons in a vapor-air mixture. It is shown that the previously proposed formulas of P.R. Rivkin for this purpose do not take into account a large number of significant factors.

Explosion characteristics and energy utilisation of coal mine ultra-lean methane

Reasonable recycling low concentration methane, especially the ultra-lean methane (the concentration lower than 5%), is significant to resource saving and environment protection. Nowadays, low concentration gas power generation technology is well developed. Notwithstanding this, ultra-lean methane has not been applied in large scale mainly due to the high utilisation costs. Therefore, to address this issue, we break through the empirical thinking to make ultra-lean methane combustion by blending with combustible substances other than only increasing the methane concentration. Its feasibility was analysed from theoretical analysis, especially the cost analysis. Dimethyl ether (DME) was selected as the additive from a range of combustible substances. Then experimental study on the explosion parameters of coal mine ultra-lean methane blending with DME was carried out in a standard 20-L explosion spherical vessel; the lower explosion limits (LEL) at different initial temperatures (ambient temperature, 40°C, 60°C and 80°C) were tested at methane concentration of 0.5%, 1%, 2%, 3% and 4%, respectively. The experimental results indicate that the addition of DME can significantly reduce the minimum explosion concentration of methane, and both P max and (dP/dt)max increase with an increase of DME content in the total fuel. The overall trend of P max and (dP/dt)max increases first and reaches to the maximum. In addition, both CO and CO2 in explosion tail gases are consistent with the decrease trend with increasing in gas mixture. The explosion solid product contained a large number of aromatic hydrocarbon structures, and the solid particles were mainly two types of spherical and blocky with the diameter between 30 and 50 µm. The explosion phenomenon and data provide a reference for assessing the hazards of practical energy system, and guiding the designs of fuel formula and engine safety.

The effects of thermal pyrolysis and decomposition products on explosive characteristics of flufenacet and sulfentrazone

Thermal pyrolysis and decomposition products of flufenacet and sulfentrazone powders were tested by thermogravimetric analysis (TGA), TGA coupled with Fourier transform infrared spectroscopy and pyrolysis-gas chromatography/mass spectrometry. Besides, the explosion sensitivity (minimum ignition temperature, minimum ignition energy, minimum explosion concentration) and explosion severity (maximum explosion pressure, and the maximum rate of pressure rise) were measured in standard 20-L spherical chamber, Hartmann apparatus and Godbert-Greenwald Furnace apparatus. Moreover, the effect of thermal pyrolysis characteristics on the explosion sensitivity and severity of flufenacet and sulfentrazone dust clouds were analyzed. The results indicated that flufenacet had lower decompose temperature, and smaller activation energy than sulfentrazone. Both flufenacet and sulfentrazone expressed flammable and toxic substance during their decomposition. Greater amount of products with higher flammability were expressed from flufenacet compared with sulfentrazone. The flufenacet had lower explosion sensitivity than sulfentrazone In addition, the flufenacet’s explosion severity was higher than sulfentrazone, which was mainly determined by the larger number of combustible gases from flufenacet. What’s more, both the two herbicide powders can lead to serious dust explosion accidents due to their explosive and toxic characteristics.

Influence of the Permeability of the Longwall Goaf Zones on the Location of an Area With Explosive Methane Concentration Levels

Abstract One of the basic ventilation hazards and, at the same time most dangerous, in hard coal mines is the methane hazard. During the exploitation process using the longwall system with the breaking down of roof rocks, methane is released into mining excavations from both mined coal and the one left in goaves. Significant amounts of methane also flow from the underworked and overworked seams, through cracks and fissures formed in the rock mass. When accumulated at an explosive concentration level in goves and at an appropriate oxygen concentration level and the occurrence of a trigger (e.g. a spark or endogenous fire), methane may either explode or ignite. These are immensely dangerous phenomena. Therefore, the possibility of their occurrence should be limited. The article presents the results of the research aimed at determining the impact of the permeability of goaf zones on the distribution of methane and oxygen concentration levels in these goaves. The study was carried out for the longwall ventilated with the Y system. The model analysis was conducted, the results of which allowed the authors to determine these distributions. On their basis, both the location and size of the areas in which hazardous methane concentrations could occur were designated. The results are of great practical importance as they indicate areas in goaves where preventive measures should be implemented.

Flame propagation through dust clouds of nano and micron scale aluminum particles

Temperature measurement on propagating flame and minimum explosible concentration are investigated. The dust explosion experiments of nano-particle dust clouds exhibit higher temperature gradient in preheat zone and lower MEC than those of micron particle dust clouds. A heterogeneous model is proposed to describe the oxidation process under two extreme conditions: whether the alumina film is involved in the reaction or not. The new methodology allows the estimation of oxidation kinetics of growing alumina. For micron particle, the model clarifies that the activation energy which has been wrongly considered to be for aluminum oxidation should be for lattice diffusion, and the initial reaction rate is proved to be dominated by the diffusion rate of oxygen through alumina shell as diffusion controlled reaction. For nano-particle, the model explained that why the reported activation energy shows significantly lower than that for micron particle, due to initially ignorable alumina film or considered as kinetically controlled reaction. However, as reaction occurs and alumina builds up on the surface, the interference of alumina somewhat increases the activation energy.

Study on the influence of coal dust concentration on flame propagation characteristics of gas explosion in semiclosed tube

ABSTRACT In order to deeply study the influence of the addition of coal dust on the propagation characteristics of gas explosion flame, in this paper, the frontal structure, front position, propagation velocity, propagation form, and duration of explosion flame produced by single-phase gas explosion and different concentration coal dust-gas coupling explosion are studied systematically. The results show that: when coal dust with different concentrations of 25~200 g/m3 is added, the time required for the complete development of the flame front of gas-coal dust coupling explosion is 50%~78.3% of that of single-phase gas explosion. In terms of propagation time, when coal dust with different concentrations of 25~200 g/m3 is added, compared with single-phase gas explosion, the time required for gas-coal dust coupling explosion flame to propagate from the ignition point to the outlet of the propagation tube will be shortened to varying degrees, with a range of 3.3%–28.6%. The addition of coal dust can greatly stimulate the development trend of explosion flame in the propagation tube. When coal dust with different concentrations of 25~200 g/m3 is added, the speed of explosion flame in the propagation tube will be increased in varying degrees, and the range of increase is 188% to 314.3%. After adding a certain amount of coal dust into the single-phase gas system, the overall duration of the explosion flame is greatly prolonged, and the flame oscillation phenomenon appears in the experimental tube.

Effects of the Particle Size and Agglomeration on the Minimum Explosible Concentration and Flame Propagation Velocity in Dust Clouds

The flame propagation behavior and the effect of particle agglomeration are examined by changing the size of PMMA particles in laboratory-scale experiments. PMMA particles having a very narrow size distribution are used. We show that the minimum explosible concentration increases as the particle size decreases. On the other hand, the flame propagation velocity also increases as the particle size decreases. Therefore, the minimum explosible concentration and the flame propagation velocity show the opposite dependences on the particle size. It is considered that the minimum explosible concentration is strongly affected by the interparticle distance; meanwhile, the flame propagation velocity strongly depends on the specific surface area. It has to be emphasized that the severity of the explosion can be serious for very fine particles, although the minimum explosible concentration is fairly high.

Flame propagation and burning characteristics of pulverized biomass for sustainable biofuel

One of the critical energy challenges, which our planet is confronting today, is how to curtail the reliance on fossil fuels for a sustainable environment. Biomass is a promising source of renewable energy for sustainable power generation compared to the conventional coal. However, they are hard to mill to finer size due to their fibrous nature. In this study, the size dependency on the flame propagation and burning characteristics of pulverized biomass is examined compared to coals. Modified Hartmann and 1-m3 explosion vessels were used to perform flame speed and explosion tests. Fine-sized particles propagated the flame with a flame velocity of 2.5 m/s for non-spherical-shaped particles compared to round-shaped lycopodium and corn flour. For coarse size particles, the flame speeds were measured to be around 1 m/s. The minimum explosion concentration was measured to be 0.2–0.4 equivalence ratio for a size range of 40–200 μm and higher for larger particle sizes. Reactivity data showed functional correlations for selected biomass and coal samples. SEM images of post-explosion residues showed incomplete combustion of bigger particles and formation of the cenosphere because of siliceous contents. The study findings concluded that the fine-sized particles of biomass had higher fire/explosion risk due to greater burning characteristics and it could only be replaced with conventional coal after assessing their combustion data by reliable methods.

Influences of coal dust components on the explosibility of hybrid mixtures of methane and coal dust

In order to study the influences of coal dust components on the explosibility of hybrid mixture of methane and coal dust, four kinds of coal dust with different components were selected in this study. Using the standard 20 L sphere, the maximum explosion pressure, explosion index and lower explosion limits of methane/coal dust mixtures were measured. The results show that the addition of methane to different kinds of coal dust can all clearly increase their maximum explosion pressure and explosion index and decrease their minimum explosion concentration. However, the increase in the maximum explosion pressure and explosion index is more significant for coal dust with lower volatile content, while the decrease in the minimum explosion concentration is more significant for coal dust with higher volatile content. It is concluded that the influence of methane on the explosion severity is more pronounced for coal dust with lower volatile content, but on ignition sensitivity it is more pronounced for coal dust with higher volatile content. Bartknecht model for predicting the lower explosion limits of methane/coal dust mixture has better applicability than Le Chatelier model and Jiang model. Especially, it is more suitable for hybrid mixtures of methane and high volatile coal dust.

An Innovative Finite Tube Method for Coupling of Mine Ventilation Network and Gob Flow Field: Methodology and Application in Risk Analysis

Explosions and fires originated from longwall gob due to the formation of methane-air mixture have been a severe threat to coal miner’s lives. Many numerical studies on coal mine fire and explosion hazards have focused on the airflow in roadways and mine gobs. However, most of these studies isolate the gob from its surrounding roadways, and the network analysis and the CFD method are applied independently to model the two classes of airflows. This approach greatly limits the ability of simulating mine ventilation flow, especially unable to consider the effects of gob boundary conditions on air exchange between the gob and the surrounding airways. An innovative finite tube method (FTM) is developed to couple the one-dimensional mine ventilation network (MVN) and the 2D/3D gob flow field (GFF). In FTM, GFF is discretized into a finite number of flow tubes each of which is formed by any two adjacent stream lines. These tubes, representing the gob’s field flow, connect the MVN into a new coupling network. To solve the coupling model between MVN and GFF, an iterative solution technique is developed in which the MVN analysis is used to evaluate the boundary pressures for GFF simulation and in turn the FTM feeds the GFF results back to the coupling network. Based on the FTM approach, a model for gas migration in gob has been established for delineating the hazard zones of explosive methane concentration and spontaneous combustion. A computer program is developed to implement the FTM simulation. An illustrative example with five flow tubes representing the GFF is created to verify the stability and convergence of the FTM solution process. A simulation example also indicates that the accuracy of FTM is improved by 12% compared with previous method. Results of an application case show that the program is capable of quantitatively evaluating the gob’s risk zones prone for spontaneous combustion and gas explosion as well as performing risk analysis for various ventilation scenarios.

Monitoring and Control Model for Coal Mine Gas and Coal Dust

In order to provide production safety and determine the optimal ventilation scheme in coal mining, the mines should be classified by their gas emission and mine security rank. In this paper the three models of mine classification, mine insecurity, and the optimal ventilation required by the mine are established and solved by MatLab and Lingo software. In answer to question 1, firstly, the daily absolute gas emission amount and relative gas are evaluated by average values of absolute and relative gas emission rates. It is shown that average values distribution complies with the normal distribution and fluctuation around the stable value. Finally, according to the standard requirements, the mine is classified as a high gas mine. In answer to question 2, the relationship is established between the gas concentration and the lower limit of coal dust explosion concentration, and a specific function relationship between gas concentration and coal dust explosion concentration is obtained by logarithmic fitting. The fuzzy membership function is derived, and the fuzzy statistical evaluation model is established to evaluate the mine safely. The probability safety value calculated by MatLab software is 4.63 %. In answer to question 3, firstly, according to the relationship between gas concentration, coal dust concentration and ventilation speed, the minimum air volume actually required by the coal mining face under the condition of safe production is established. Through MatLab programming calculation, the minimum air volume of coal mining face 1 and face 2 is 385.10 and 531.08 m3/min, respectively. According to the diversion of the air volume of each working zone and the specific requirements for ventilation speed in each zone, a ventilation optimization model is established and solved by Lingo software. The calculated air volume of the local ventilator and the optimal (total) air volume required by the mine are 150 and 1491.18 m3/min, respectively. Finally, through the solution and analysis of the model, it is shown that the simulation method is reasonable and can produce reliable guidance for management of high-risk coal mining enterprises.

Flammability and flame propagation of propane/L-leucine powder hybrid mixtures

The minimum explosible concentration (MEC) and flame propagation behaviors of propane/L-leucine powder hybrid mixtures were experimentally investigated. The results of the experiment demonstrated that the MEC values decreased as the propane concentration increased. Additionally, the findings of the analysis proved that the flame propagation limitation in dust explosions increased with the increase in propane concentration. The results indicated two things. First, the flame speed of stoichiometric propane-air/L-leucine powder hybrid mixtures in the initial period of propagation was almost constant notwithstanding an increase in the L-leucine concentration. Second, the dimensionless flame speed was close to unity because the speed of the hybrid mixture was strongly affected by the propane–air premixed flame speed, although the flame speed increased with the increase in propane concentration. Further, it was found that the separate propagating flames of dust/gas hybrid mixtures had a considerable difference in flame speeds were observed.

Integrated experimentation and modeling of the formation processes underlying coal combustion-triggered methane explosions in a mined-out area

A methane explosion can take place when a methane concentration is within the explosive concentration range. Therefore, the methane migration around a coal combustion zone is important for assessing the disaster risk and revealing the disaster formation process. The thermal buoyancy effect has seldom been considered before, even though it could influence methane movement in coal mined-out areas. In this study, an integrated investigation using experimentation and modeling was conducted to explore the disaster formation process. For the experiment, a coal mine gob was heated locally to produce the buoyancy effect, and the consequent methane accumulation was observed. To explain this observation, a gas flow model reflecting the buoyancy effect was developed and verified against the experimental observations. Through this analysis, the formation processes for a methane explosion disaster in a coal mined-out area were revealed as follows: (1) coal combustion decreases the gas density to produce the buoyancy effect and create negative pressure in the combustion area; (2) this negative pressure leads to methane inflow, and the buoyancy effect causes upward methane movement; and (3) the local methane inflow and the local upward movement develop methane accumulation in the coal combustion area to form a methane explosion.

Wide Dynamic Range Hydrogen Sensing Device Made of Hexagonal Nanoplates of AgInO2 with Exposed Facets

Wide Dynamic Range Hydrogen Sensing Device Made of Hexagonal Nanoplates of AgInO2 with Exposed Facets

Revealing patterns of the effective mechanical characteristics of cellular sheet polycarbonate for explosion venting panels

Explosive concentrations of various substances can accumulate inside industrial premises. In the presence of a sufficient amount of oxygen and an ignition source, such a situation could lead to explosion that may result in the destruction of building structures and the building in general. Strengthening the stability of supporting structures is aimed at protecting industrial premises against possible destruction by explosion indoors. One of the effective ways to protect construction structures against the excessive pressure of explosion is to use explosion venting panels. In order to solve practical tasks on protecting industrial premises and structures against explosion, one must be able to choose both the area and parameters for explosion venting panels. In addition, in order to reduce the related loads to safe quantities, it is necessary to properly calculate the bearing structures in terms of dynamic stability while maintaining their carrying capacity. The set task to ensure protection against explosion by applying explosion venting panels with flexible elements can be solved through integrated accounting for mechanical properties of cellular polycarbonate sheets. We have performed experimental research into performance of the inertia-free explosion venting panels with flexible enclosing elements exposed to dynamic loads under conditions of explosion. Based on the obtained results, the effective rigidity and critical displacement of cellular polycarbonate sheets of flexible elements have been determined. It has been established that for cellular polycarbonate sheets with a thickness of 4‒8 mm effective rigidity ranges within 301–215 N·m; the critical displacement of edges in this case is 2.9–9.8 mm. A mathematical model has been proposed that takes into consideration the influence of geometric dimensions and the critical value of deflection in a polycarbonate sheet as the flexible element of fencing on the operational conditions for explosion venting panels

Effect of initial pressure on the lower explosion limit of nicotinic acid/acetone mixture

In the work presented in this paper, the effect of initial pressure on the lower explosion limit (LEL) of the hybrid nicotinic acid/acetone mixture was investigated through standard explosion tests carried out in the 20 L sphere. From experimental results, the flammability diagram was built in the plane (concentration/minimum explosive concentration) of nicotinic acid versus (concentration/LEL) of acetone. Interestingly, it has been found that, in going from low pressures (P < 1 atm) to high pressures (P > 1 atm), the extension of the flammability region increases. This behavior has been attributed to the fact that the turbulence kinetic energy (and thus the energy dissipation) decreases with increasing initial pressure. Bartknecht's correlation for LEL of hybrid mixtures was modified to take into account the effect of pressure, and two correlations were obtained able to give satisfactory predictions of experimental data at both low pressures and high pressures.

Effects of Moisture Content on the Minimum Explosible Concentration of Aluminum Powder and the Related Mechanism

Aluminum powder has been widely applied to various industries. However, its high activity and high burn rate can cause serious explosion risks. Many factors affecting the explosion of aluminum powder have been determined, yet moisture content has not been included. In the present work, the minimum explosible concentrations of aluminum powders with different moisture contents were measured with a 20-liter explosion test apparatus using the explosion accident in Kunshan, China, as a study case. The experimental results suggest that the minimum explosible concentration of aluminum powder dramatically increases with the increase of its moisture content first and the increasing trend becomes slower as the moisture content further increased. The oxidation time has no significant effects on the minimum explosible concentration of aluminum power in 8 hours at room temperature. Further investigation suggests that the moisture lowers the explosion risk of aluminum powder by altering its surface oxide film, ignition, and combustion process. The low contents of moisture in the range of 0%-8% increase the minimum explosible concentration of aluminum powder by inhibiting the reaction kinetics and particle agglomeration, while high contents of moistures in the range of 8%-20% affect the minimum explosible concentration by the endothermic effect and oxygen dilution effect.