Minimum Explosible Concentration Research Articles

Study on the variation regularities of minimum explosion concentration of moist magnesium dust/derived hydrogen hybrids under multiple working conditions

Magnesium is widely used but often accompanied by frequent magnesium powder explosion accidents. If the variation regularity and mechanism of the minimum explosion concentration (cm) of magnesium powder under the multi-factor coupling effect can be understood, the occurrence of magnesium powder explosion accidents can be fundamentally avoided, and intrinsic safety can be achieved. In this paper, experiments were conducted using a self-made 20 L explosion device to explore the effects of particle size, initial temperature, and equilibrium relative humidity (ERH) coupling on the cm of magnesium powder. The study found that an increase in ERH of moist magnesium powder would lead to easier agglomeration of the dust, making it less prone to activation. Additionally, excessive moisture also absorbed more heat, reducing the ignition sensitivity of the dust cloud and resulting in a continuous increase in cm. However, increasing the initial temperature and decreasing the dust particle size both decreased the cm of moist magnesium powder, weakening the effect of ERH on cm. Furthermore, using the analysis methods of orthogonal experimental range and AHP model, it was determined that the influence weights of the factors coupling effects on the cm of magnesium powder, from highest to lowest weight, were: particle size > ERH > initial temperature.Furthermore, in order to deeper understand the mechanism of the action process that affect the cm of moist magnesium powder, additional experiments were conducted to further confirm that the addition of hydrogen derived from the erosion reaction of moist magnesium powder to the explosion system can reduce the cm of magnesium dust clouds. Moreover, a quantitative mathematical model for predicting the cm of magnesium powder/hydrogen two-phase system was also established.

Study on flame propagation characteristic and mechanism of polypropylene dust explosion

Polypropylene dust explosion poses a significant threat to the safe production of synthetic resin. To elucidate the flame propagation mechanism of polypropylene dust explosions, the flame propagation characteristics of polypropylene dust were experimentally studied. The minimum explosible concentration (MEC) for polypropylene particles with diameter < 75 μm, 75–100 μm, and 100–212 μm was 50 g/m3,100 g/m3,150 g/m3, respectively. Obvious fluctuations were observed in the flame propagation velocity of small particles, with smaller particles exhibiting more pronounced fluctuations, primarily caused by thermal feedback between the particles in the preheating zone and the reaction zone. While for large particles, the flame temperature exhibited multiple peaks, resulted from the discrete flame floating in front of the flame. The combustion process of polypropylene dust comprised the diffusion combustion of large particles and the gas-phase combustion of combustible gases pyrolyzed by small particles.

Use of a two-parameter Weibull distribution for the description of the particle size effect on dust minimum explosible concentration

Combustible dust explosion properties, like Minimum Explosible Concentration (MEC) and Minimum Ignition Energy (or Temperature), have a strong dependency on the particle surface area to mass ratio which varies with the particle size distribution. Unfortunately, the comparison of the dust explosion properties reported in the literature for a given dust material is often difficult because of the lack of description of the particle size distribution which is usually limited only to scattered information about the median (d50), mean, or one, two, or maximum three percentiles (e.g., d10,d50,andd90). This approach often gives conflicted conclusions or observations of no trend with measured independent parameters. It seems that a different approach is necessary to comprehensively describe the dependency of dust explosion properties on the particle size distribution. Such improvement could be achieved using a continuous probability distribution of which an example is a two-parameter normal distribution. However, the normal probability density function can only represent a symmetrical bell-shaped distribution which does not apply to the dust particle size analysis that often results in a skewed bell-shaped histogram. This study explored the use of a two-parameter (shape and scale) Weibull probability density function to describe a particle size distribution. A series of experimental data on the Minimum Explosible Concentration (MEC) of sulfur and polyethylene dust samples for which the particle distribution is measured were used to estimate the Weibull's scale and shape parameters. Two- and three-dimensional plots were generated to demonstrate the correlations of these parameters with MEC. The results show that as the scale and shape parameters increase, the MEC increases with higher dependence on the scale parameter (b). This is consistent with the initial conclusion where the MEC increases with increasing particle size. The paper discusses the advantages of using such an approach to describe the effect of particle size distribution on dust explosion properties but also shows that using only a median or mean of a particle size distribution to describe MEC may be misleading, especially if a sample represented by d50 as a coarse distribution contains a long tail of fine particles.

High-performance palladium nanotube network as fast, high-resolution, and wide range hydrogen detector in atmosphere

Due to its high energy density, cleanliness, and renewable properties, hydrogen (H2) has found wide applications in aerospace, fuel cells, biomedicine, and chemical production. However, ensuring its safety is crucial, and a quick response time for H2 leakage detection is urgently needed for subsequent explosion-proof measures, requiring a limit of less than 5 s. So far, there is no reported device with both high-resolution and wide range capabilities. In this study, we propose a novel solution by designing and fabricating a hollow palladium nanotube network (HPNN) as a rapid leaking-sensing H2 detector. The HPNN sensor demonstrates excellent performance with a low detection limit of 10 parts per million (ppm) and a fast response time of less than 0.6 s in atmospheric environment. These impressive safety characteristics are attributed to the unique structure of the Pd nanotube network, where both the lattice volume expansion effect and electron accumulation under mechanical deformation affect the electrical resistance. The device is capable of effectively detecting a wide range from 4 % to 0.001 % of H2 concentrations. Compared to previous results, the response speed is improved by over 8 times at the minimum explosion concentration (4 %) and two orders of magnitude at low limit concentration. Such simple and cost-effective manufacturing method offers potential for the development of high-performance hydrogen leakage detectors.

Analysis and prediction model of the minimum explosion concentration of plastic dust in gaseous fuel environments

Polyethylene dust and polypropene dust were selected to measure the minimum explosion concentration in three kinds of gaseous fuel environments. The results show that the MEC of polyethylene dust with higher apparent activation energy decreased more significantly, and the plastic dust showed higher explosion sensitivity for the gaseous fuel with high combustion heat. The explosion mechanism for plastic dust in gaseous fuel environments was proposed with the global reaction kinetics of plastic pyrolysis, and it suggests that the gaseous fuels reduce the apparent activation energy of plastic dust and provide additional heat for the plastic dust explosion. A corresponding prediction model for the minimum explosion concentration of plastic dust was established. The new model has good applicability for the data obtained in this work and the data in the previous reference.

Effects of dust concentration, particle size, and crude oil concentration on the explosion characteristics of oil-immersed coal dust

To investigate the explosion hazards of oil-immersed coal dust in co-existing mine areas, the explosion characteristic parameters of coal dust under different particle dimensions, coal dust concentration, and oil-immersed concentration were studied in a 20-L explosion chamber. The maximum explosion pressure of oil-immersed coal dust first decreases and then increases as coal dust particle size increases. For oil-immersed concentration samples between 2 and10 wt.%, the Kst value, and maximum explosion pressure of the oil-immersed samples were higher than those of the raw coal counterpart. The maximum explosion pressure of oil-immersed samples was 7.49%, 4.10%, 5.7%, 7.13%, and 4.10% higher than the raw samples. Moreover, when the oil-immersed concentration was 6 wt%, the minimum explosion concentration (MEC) of finer particles was the lowest, while the MEC for large particles was the highest. The impact mechanism of coal dust concentration on maximum explosion pressure is that the number of coal dust particles affects the distance between particles and heat transfer efficiency. The influence mechanism of particle size on the explosion of oil-immersed coal is that the particle size can reflect the specific surface area size, which affects the diffusion of oxygen in particles and the rate of combustible volatiles released by particles. Hydrocarbons released from the crude oil via heating and the complex organic molecules generated during high-temperature pyrolysis produced simpler hydrocarbons, generating hydrogen and higher temperatures that accelerated the onset of explosions and increased coal dust explosion intensity. These experimental results were of use to process safety working and can help prevent coal dust explosion accidents in underground coal mines.

The study of coal dust minimum explosion concentration of subbituminous coal

The coal dust explosion tests have been conducted using an explosion chamber 20-L with coal dust sizes of 53–44 µm (average particle size is 48.5 µm) for subbituminous coal from Indonesia. The coal dust explosion has been tested with various energies of the ignitor, i.e., 4.2 kJ, 6.3 kJ, and 8.4 kJ, to obtain the effect of ignitor energy on the coal dust’s Minimum Explosion Concentration (MEC). The results show that the MEC for the 4.2 kJ, 6.3 kJ, and 8.4 kJ ignitor energy are 120 g/m3, 100 g/m3, and 70 g/m3, respectively. The present study in subbituminous coal resulted in a relatively higher MEC compared to previous studies conducted in bituminous coal.

Gravity Effects on the Minimum Explosive Concentrations in 1-D Dust Explosion

ABSTRACT Theoretical predictions of dust-explosion characteristics, such as the minimum explosive concentration (MEC), can help improve the accuracy of quantitative risk assessment. This paper presents a continuum model to simulate one-dimensional dust-cloud combustion. It is found that the dilution of dust by thermal expansion reduces the propagation speed of a combustion wave through a dust cloud. At the same time, the delay in the increase of particle velocity due to relaxation time counteracts the dilution effect. Therefore, neglecting the relaxation time results in the underestimation of propagation speed. In the absence of heat loss, extinction occurs when the adiabatic combustion temperature decreases to the ignition temperature; MEC is independent of particle size in such cases. With the presence of heat loss, on the other hand, extinction occurs at a higher dust concentration; MEC increases with particle size. Accurate evaluation of ignition temperature is key to the quantitative prediction of MEC. A particular focus is given to gravity effects, reflecting recent experimental efforts to obtain fundamental insights into propagation mechanisms without being affected by gravity. In upward propagation, particles fall toward the reaction front, enhancing combustion and increasing the propagation speed. The situation in downward propagation is the opposite, and extinction occurs when the gravity level is beyond a critical value. In upward propagation, MEC can decrease with an increase in particle size, owing to the influence of gravity.

Study of dust cloud behaviour in the modified Hartmann tube using the image subtraction method (ISM)

A dispersion of fine particles in the air is needed for a dust explosion to occur since an explosion is the fast combustion of particles in the air. When particles are poorly dispersed, agglomerated, or their concentration is low, the combustion velocity decreases, and deflagration would not occur. The combustion rate is strictly related to dust concentration. Therefore, the maximum explosion pressure rise occurs at dust concentration close to stoichiometric. Conversely, Minimum Explosion Concentration (MEC) is the lower limit at which self-sustained combustion and a pressure rise are possible. Dust explosion tests are designed to reproduce the dispersion and generation of dust clouds in industrial ambiences by using dispersion devices activated by pressurised air pulses. The resulting dust cloud, which has a marked transient character, is considered representative of real clouds by current standards. Over time, several studies have been carried out to optimise these devices (e.g. to reduce the inhomogeneity of the cloud in the 20 L sphere). The Minimum Ignition Energy (MIE) of dust is measured using the Mike3 modified Hartmann tube, where the ignition attempt is made 60–180 ms after dust dispersion regardless of dust characteristics.This work investigates the dust clouds’ actual behaviour inside the modified Hartmann tube before ignition using high-velocity video movies and a new image post-treatment method called Image Subtraction Method (ISM). Movies are recorded with high-speed cameras at a framerate of 2000 fps and elaborated with an on-purpose developed LabVIEW® code. Concentration (mass per volume) and dispersion pressure are varied to evaluate their effect on dust clouds. Maise starch, iron powder and silica powder are chosen to investigate the effect of particle density and size on the cloud structure and turbulence. This approach will help to investigate the structure of the dust cloud, the shape and size of the particle lumps and the change in dust concentration over time. In addition, information on the actual concentration and cloud turbulence at the ignition location and delay time were obtained, which may help identify the local turbulence scale and widen the characterisation of the cloud generated in the Hartmann tube.

Experimental research on flammability characteristics and ignition conditions of hybrid mixture emissions venting from a large format thermal failure lithium-ion battery

When the concentration of gas is below its lower flammable limit and the content of the particles is below its minimum explosible concentration, it can be explosible. Thermal abuse tests for 50 Ah lithium-ion batteries were conducted under an inert atmosphere. The battery failure venting emissions were collected and their composition was identified previously. It still needs further research for the flammability characteristics and ignition conditions for hybrid mixture emissions venting from a large format lithium-ion battery thermal failure. In this study, the likelihood, severity, and kinetics of the batteries' hybrid mixture emissions flammability have been researched. To analyze battery emission flammability characteristics, five indexes have been investigated; they are ignition temperature (Tig), ignition time (τig), maximum explosion pressure (Pmax), pressure rise maximum rate ((dP/dτ)max), and size-normalized maximum rate pressure rise (KSt). Based on quantitative analysis for the hybrid mixture flammability characteristics, it indicates that particle size and gas content can impact hybrid mixture emission flammability characteristics. As for the mixture with finer particles, the optimum combustion condition of the particle and gas concentration pairs were 0.3 and 0.7. The ignition temperature for the optimum combustion conditions was 495 °C. The pressure rising velocity was 23 Mpa/s during ignition. High solvent content and low particle concentration are the conditions for optimum combustion. This indicates that the gas admixture solvent plays a major role in the combustion kinetics of the mixture emission. This research offers a fundamental perspective and provides preventive and protective thermal safety designs that are more suitable for large format commercial battery thermal systems.

Redefining of potential dust explosion risk parameters for additives in the petrochemical manufacturing process

Petrochemicals are an indispensable part of our everyday life, necessitating large-scale production facilities. Additive aids play a pivotal role in the petrochemical production process, which are required for the final product to have certain desired properties. The additives used are prone to ignition and combustion, but are frequently overlooked as a source of potential hazard. This study examines the hazard profile of five common powder additives in the petrochemical manufacturing process. The inherent combustion and explosion characteristics were investigated in detail. Each sample’s potential to produce a dust explosion was evaluated based upon the parameter test results, e.g., minimum ignition energy (MIE), minimum ignition temperature (MIT), and minimum explosible concentration (MEC). MIT of all five samples was between 350 and 390 °C, and MEC was less than 45 g/m3. Two of the powders had a KSt explosion rating of “extremely strong” (St-3). After a comprehensive evaluation of dust explosion sensitivity and dust explosion severity, all five additive samples were categorised as high-level potential dust explosion risks. Process safety staff and engineers working with petrochemical production should be aware of the risks posed by dust additives and be prepared to implement more stringent loss prevention measures to curtail the likelihood of dust explosions.

Characterization of the explosiveness of wood dust

Factors that influence the explosiveness of wood dust, like particle size distribution, moisture content and microscopic structure, have been characterised. Sawdust flammability has been tested in a Hartmann tube. The Minimum Explosive Concentration and Minimum Ignition Temperature of dust clouds and layers have also been measured. Dust granulometry linked to the regularity of its structure and moisture are the essential parameters to generate or not an explosive atmosphere. Smaller particle size dust with a lower moisture content is much more likely to create an ignition and/or explosion risk. The samples have been classified into two groups, those collected from cutting processes and those found in the ventilation ducts or deposited in the facilities. The most dangerous samples are those from Group 2. In some cases, dust samples up to 35 % moisture or with particle size greater than 500 µm at maximum dryness are able to produce an explosion.

Development of a model for the prediction of the ignition properties of combustible dusts undergoing homogeneous combustion: Application to sulfur dust

The determination of ignition properties such as the minimum explosible concentration (MEC) is critical for the control of the risks associated with handling combustible dust. This work describes a novel approach for the determination of the MEC of combustible dusts undergoing homogeneous combustion, using sulfur dust as a case study. The proposed model is developed based on the heat and mass transfer occurring when a sulfur dust particle in a control volume is exposed to a hot planar surface acting as an ignition source. The model includes radiative and convective heat transfer from the ignition source to the particle and predicts the dust particle’s fusion and vaporization. Ignition criteria of sulfur vapor accumulation in the control volume are based on the material’s lower flammability limit (LFL) and the comparison of accumulated energy in the control volume to the activation energy of the vapor-air combustion initiation reaction. The model also includes a correlation describing a time to ignition which accounts for necessary dynamic changes like the exposure time of the dust to the ignition source. The model is capable of predicting the influence of the dust particle diameter on the MEC of sulfur dust and was validated with experimental data.

An alternative explosion criterion of combustible dusts based on combustion duration time: Applications for minimum explosion concentration and limiting oxygen concentration

A novel method based on combustion duration time was newly proposed as an explosion criterion to determine minimum explosion concentration (MEC) and limiting oxygen concentration (LOC) in our recent works. This work further studies the reasonability and reliability of the alternative method experimentally and theoretically. Six different dust samples were tested via a 20-L spherical explosion chamber. The experimental results showed that the data of MEC and LOC determined by using the alternative and the standardized methods are in good agreement. The minimum flame propagation velocity ( S f ) and the corresponding maximum combustion duration time ( t c ) were found at its MEC and LOC, suggesting that the theoretical analysis can well explain all the experimental data. It is the first time to study the theoretical basis of the explosion criterion, thus helping to improve our understandings of dust explosion characteristics, and to amend the explosion criterion in future test standards. • An alternative method based on t c was proposed to determine MEC and LOC. • The alternative method was found to be reliable and feasible. • A theoretical analysis on flame propagation velocity was performed to explain the proposed method. • The alternative method compensates the deficiency of the current standardized explosion criterion.

Experimental study on the minimum ignition energy of cornstarch particle-air flows in a horizontal pipeline

Pipelines and process equipment are commonly interconnected in a network of dust extraction or pneumatic conveying in lines industry. History has shown that the severity of a dust deflagration could be much accentuated if the initial fireball is allowed to propagate further through pipelines. However, less is known about the hazard of a primary ignition in a pipeline conveying system with combustible dust and high airflow velocity. This paper presents an experimental study on the ignitability of cornstarch particle-air flow in a lab-scale piping system. The results show that minimum ignition energy (MIE) of dried cornstarch flow at 12–28 m/s was less than 300 mJ, and the minimum explosible concentration (MEC) was less than 100 g/m3. An increase in airflow velocity increased both MIE and MEC, as well as stretching the spark plasma. Moisture in the dust significantly decreased its ignitability, with this being a more marked factor than airflow velocity in influencing the ignition hazard in a pipeline.

Iron dust explosion characteristics with small amount of nano-sized Fe2O3 and Fe3O4 particles

Iron powder, as one of the most abundant metal fuels that can be used as recyclable carriers of clean energy, is a promising alternative to fossil fuels in a future low-carbon economy. It may pose a potential explosion hazard during the process of processing, storage, transport, and reduction/oxidation (redox). The explosion characteristics of iron dust in air were undertaken via a 20 L spherical explosion chamber with an emphasis on minimum explosion concentration (MEC) of iron dust. The alternative method of combustion duration time (tc) was used to determine MEC and compared with the standardized over pressure method. Two kinds of nano-sized iron oxides (Fe2O3 and Fe3O4) were used as inertants to determine the inhibition effect of different oxidation products. The iron dust explosion products with various shapes and sizes were found to be able to grow up 4–6 times of the iron dust for the first time. Adding small amount of Fe2O3 or Fe3O4 could reduce the explosion severity and sensitivity of iron dust. The MEC data determined by both methods were comparable. The addition of 5 % oxide has obvious inhibition effect under 1500 g/m3 concentration. With the increase of oxide concentration to 10 %, the inerting effect increases, and the MEC of iron dust increases more than 3 times. The increase of dust concentration will weaken the inerting effect. When the concentration increases from 500 g/m3 to 3000 g/m3, the weakening effect of 10 % Fe2O3 on the explosion pressure decreases from 38.45 % to 2.24 %, and 10 % Fe3O4 decreases from 46.21 % to 10.63 %. Unlike coal, biomass or aluminum dusts, the iron dust explosion was found to have a unique secondary acceleration of pressure rise rate for the first time. These results provide a fundamental basis to mitigate the iron dust explosion via solid inerting method without adding extra elements.

Effect of CaCl2, Al(OH)3 and NH4H2PO4 on the explosion sensitivity of pulverized coal

ABSTRACT In this paper, the effects of 30 wt%, 50 wt% aluminum hydroxide, calcium chloride and ammonium dihydrogen phosphate three explosion inhibitors on the two sensitivity parameters of the minimum explosion concentration and the minimum ignition energy of pulverized coal were investigated. It was found that for the same explosion inhibitor, the higher the content of explosion inhibitor, the higher the increase of MEC and MIE of pulverized coal-explosion inhibitor. At the same time, dust reduction measures should be taken in time when the coal dust concentration will be close to 70 g/m3. It was found that for the same explosion inhibitor, the higher the content of explosion inhibitor, the higher the increase of MEC and MIE of pulverized coal-explosion inhibitor. In the meantime, dust reduction measures should be taken in time when the coal dust concentration will be close to 70 g/m3. Furthermore, 150 g/m3 was the critical concentration of the ignition energy of pulverized coal. In order to prevent the occurrence of coal dust explosion accidents, it was necessary to resolutely prevent the concentration of pulverized coal from approaching this value on site. In addition, when the pulverized coal-explosion inhibitor concentration was 100 g/m3-250 g/m3, whether it was 30 wt% NH4H2PO4 or 50 wt% NH4H2PO4, the ignition energy required for mixing with pulverized coal was greatly increased. Overall, in the concentration range of 30–50 wt%, 50 wt% NH4H2PO4 was more advantageous in the suppression of coal dust explosion.

Explosion characteristics and mechanism of aluminum-reduced graphene oxide composite powder

Aluminum-based fuel in energetic formulations has favorable ignition and combustion characteristics, but it is also prone to an explosion. To ensure safe production and prevent accident, explosion characteristics and the mechanism of aluminum-reduced graphene oxide (Al-RGO) composite were investigated. Thermal analysis showed that after adding RGO, the activation energy of Al dust in the initial oxidation stage decreased from 241.5 kJ/mol to 90.0 kJ/mol. With the addition of 5 wt% RGO, PTFE, and Ni inclusions, the minimum explosible concentration increased by 40%, 10%, and 25%, the maximum explosion pressure increased by 20.8%, 13.8%, and 7.5%, respectively. Moreover, the addition of RGO could significantly improve the flame propagation speed and oxidation efficiency of aluminum but with a slight effect on the burning time of single Al particles. XPS results revealed that the major explosion product of Al-RGO is Al2O3. Based on these results, the explosion mechanism of Al-RGO was discussed in-depth.

Effect of stearic acid coating on the explosion characteristics of aluminum dust

To explore the effect of stearic acid coating on the explosion characteristics of aluminum dust, the flame propagation characteristics, minimum explosion concentration and explosion overpressure characteristics of aluminum (Al) and stearic acid coated aluminum dust (SA-Al) were studied by using the synchronous thermal analyzer, the improved Hartmann tube explosion test device, and 20 L explosion test device. Then micro morphology and composition of the explosion products were determined by scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS), and a physical model of stearic acid coated aluminum dust explosion was established. The results showed that the combustion intensity and flame propagation velocity of SA-Al dust cloud in the semi-closed pipe were lower than that of Al dust cloud, and the flame propagation was weak in the initial stage of explosion. The minimum explosion concentration (MEC), the optimal explosion concentration, the maximum explosion pressure (Pmax) and the maximum explosion pressure rise rate ((dP/dt)max) of SA-Al dust cloud were greater than that of Al dust cloud, and its products contained the incomplete combustion products AlO2, indicating that the stearic acid coating could abate the explosion sensitivity of Al dust cloud, and weaken the degree of oxidation of Al dust. In case of explosion, stearic acid coating could significantly enhance the explosion hazard of Al dust, resulting in a higher explosion risk.

Pt/WO3 Nanoparticle-Dispersed Polydimethylsiloxane Membranes for Transparent and Flexible Hydrogen Gas Leakage Sensors.

Hydrogen gas is a promising, clean, and highly efficient energy source. However, to use combustible H2 gas safety, high-performance and safe gas leakage sensors are required. In this study, transparent and flexible platinum-catalyst-loaded tungsten trioxide (Pt/WO3) nanoparticle-dispersed membranes were prepared as H2 gas leakage sensors. The nanoparticle-dispersed membrane with a Pt:W compositional ratio of 1:13 was transparent and exhibited a sufficient color change in response to H2 gas. The membrane containing 0.75 wt.% of Pt/WO3 nanoparticles exhibited high transparency over a wide wavelength range and the largest transmittance change in response to H2 gas among the others. The heat treatment of the particles at 573 K provided sufficient crystallinity and an accessible area for a gasochromic reaction, resulting in a rapid and sensitive response to the presence of H2 gas. The lower limit of detection of the optimized Pt/WO3 nanoparticle-dispersed membrane by naked eye was 0.4%, which was one-tenth of the minimum explosive concentration. This novel membrane was transparent as well as flexible and exhibited a clear and rapid color response to H2. Therefore, it is an ideal candidate sensor for the safe and easy detection of H2 gas leakage.