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

Research on Explosion Pressure Characteristics of Long Flame Coal Dust and the Inhibition Effect of Different Explosion Suppressants

To discuss the inhibition of long flame coal dust explosion pressure, NaHCO3, KHCO3, and NH4H2PO4 are selected as explosion suppression dust for explosion pressure tests under different conditions. The results show that when 25-38 and 38-45 μm coal dust are mixed in 1:1 ratio, the maximum explosion pressure is the largest, the maximum pressure is 0.79 MPa, and the maximum pressure rise rate is 74.89 MPa·s-1. The suppression dusts have good inhibition effect on explosion, the order of inhibition is NaHCO3, KHCO3, and NH4H2PO4 from the smallest to the largest. With the reduction of particle size of NH4H2PO4, its inhibition effect on explosion pressure is increasing, because more NH4H2PO4 particles move around coal dust particles, blocking the heat transfer and kinetic energy exchange. The above three suppression dust and their suppression methods can provide important data for dust prevention and control and have certain reference significance for carrying out explosion suppression work.

Ignition temperature and explosion pressure of suspended coal dust cloud under different conditions and suppression characteristics

The ignition and explosion processes of suspended coal dust clouds and their suppression characteristics are important aspects of dust prevention and control. To understand the ignition temperature and explosion pressure of coal dust clouds, as well as the inhibitory effect of explosion suppressants, experimental tests are conducted. The study found that during the ignition process of coal dust clouds, the optimal dust spray pressure is 20 kPa, because coal dust clouds are more likely to ignite under this condition. When the mass concentration of coal dust cloud is 500 g m-3, the maximum pressure and maximum pressure rise rate are both the highest. When Al(OH)3 is mixed with coal dust and the mass percentage is 60%, the coal dust cloud can still be ignited. When KH2PO4 is mixed with coal dust, the upper limit of the test temperature is reached when the percentage of mixture is 55%. When NH4H2PO4 is mixed with coal dust and the mass percentage is greater than 40%, the coal dust cloud can't be ignited anymore. The suppression effect of mixing Al(OH)3 and NH4H2PO4 is not as good as that of mixing KH2PO4 and NH4H2PO4.

Influence of initial gas concentration on methane-air mixtures explosion characteristics and implications for safety management

Gas explosions, particularly those involving methane-air mixtures, present considerable hazards in confined spaces, such as coal mines. Comprehending the explosion characteristics and their correlations with initial gas concentrations is vital for devising effective safety measures. This study examines the influence of initial gas concentration on explosion temperature, overpressure, and flame evolution in methane-air premixed gas explosions, utilizing a custom-built 20-L spherical explosion experimental apparatus. The explosion temperatures display an oscillatory pattern, reaching maximum values at 6.5%, 9.5%, and 12% initial gas concentrations, with corresponding temperatures of 995 K, 932 K, and 1153 K. The maximum overpressure exhibits an initial rise and fall trend, modeled by an exponential function. Notably, in proximity to the 9.5% concentration, the pressure wave fosters the reverse propagation of the flame wave, leading to a secondary temperature increase. Flame sensors were employed to investigate the presence, absence, and duration of flames, demonstrating that elevated initial gas concentrations resulted in more prolonged flame durations and increased harm. At an initial gas concentration of 9.5%, a persistent flame is generated instantaneously during the explosion. Furthermore, the study analyzes the interplay between temperature and overpressure, underscoring the significance of mitigating high-temperature burns near tunnel walls and enclosed spaces. These findings advance the understanding of gas explosion dynamics and hold substantial implications for safety measures in coal mines.

Global evolutional trend of safety in coal mining industry: a bibliometric analysis

Mining safety is recognized as one of the factors influencing the mining industry's long-term viability. Therefore, we did a bibliometric analysis to take stock of safety management in the coal mining industry. This study suggests a three-step strategy, comprising literature extraction and screening, bibliometric analysis, and discussion, to provide an in-depth understanding of the present state and development trend of mine safety research. The findings raise additional concerns which include the following: (i) Coal dust pollution has a direct and indirect impact on the environment. (ii) Most research projects have prioritized technology innovation and development over safety norms. (iii) Most works have come from advanced countries such as China, the USA, the UK, and Australia to the neglect of developing nations, leaving a significant vacuum in the literature. (iv) There are more major safety principles in the food business than in the mining industry, indicating a weak safety culture in the mining industry. Additionally, future research goals are provided, such as creating safer policy guidelines to support technological advancements, constructing effective safety mines, and creating solutions to dust pollution and human errors.

Explosion Flame and Pressure Characteristics of Nonstick Coal Dust and the Inhibition of Explosion Suppressants

Nonstick coal is widely distributed in the world and is an important resource for human beings. The explosion characteristics and explosion suppression of nonstick coal dust are increasingly concerning. In this paper, the flame and pressure characteristics of a nonstick coal dust explosion are studied, and the suppression effect of SiO2, KCl, and NH4H2PO4 on the explosion is analyzed. It is concluded that the maximum propagation distance of a nonstick coal dust explosion flame is 0.59 m, the maximum pressure is 0.63 MPa, and the maximum pressure rise rate is 40.79 MPa/s. The explosion suppression effect of SiO2 is worse than that of KCl, but the inhibition effect of NH4H2PO4 is the best among the three kinds of explosion suppressants. When the mass percentage of NH4H2PO4 dust mixed with coal dust is 70%, the coal dust explosion is completely suppressed. It absorbs a certain amount of heat to promote the chemical reaction, which plays a certain role in controlling the explosion process, and its explosion suppression mechanism includes both physical and chemical explosion suppression.

Revealing Impact Characteristics of the Cassava Dust Explosion Process: Experimental and Numerical Research

The combustion and explosion characteristics of cassava starch and the dispersive physical motion law of dust were systematically studied using a 20 L (=0.02 m3) spherical explosive test device and the numerical simulation method. The experimental results show that the explosion pressure first increases and then decreases with increasing ignition delay time, dust concentration, and spray pressure in the dust storage tank. The maximum explosion pressure was obtained with a dust concentration of 750 g/m3, while the maximum rate of pressure increase was obtained when the concentration was 250 g/m3. The calculated maximum explosion index was 22.3 MPa∙m∙s−1. The simulation results show that the physical movement law of the dust was as follows: high initial velocity → gradual decrease in diffusion velocity → upward linear movement of dust → outward diffusion motion → continuous disorder motion → free settlement → gradual reduction and disorder state → finally, complete settlement. With a powder diffusion time of 120 ms, the dust distribution in the round sphere was the most uniform, which was consistent with the experimental results. After dust ignition, the temperature first gradually increased and then decreased due to heat dissipation. The maximum pressure in the vessel was 46.7 MPa, and the turbulence was the most intense close to the ignition point.

Experimental Research on the Suppression Effect of Different Types of Inert Dust on Micron-Sized Lignite Dust Explosion Pressure in a Confined Space

Coal is an important strategic resource in the world; coal production safety has always been widely concerned. In coal mine production, inert dust can effectively reduce coal dust explosion accidents in mine tunnels. To reveal the suppression effect of inert dust on lignite dust explosion, CaCO₃, SiO₂, and NH₄H₂PO₄ are selected for suppression experiments. It is found that the lignite dust explosion pressure decreases continuously as the mass percentages of inert dust mixed into lignite dust increase. By calculating the molar mass, the suppression effects of CaCO₃ and SiO₂ on lignite dust explosion are compared. The lignite dust no longer explodes when the mass percentage of NH₄H₂PO₄ dust mixed into lignite dust is 70%, indicating that NH₄H₂PO₄ is more effective than that of CaCO₃ and SiO₂. The smaller the particle size of NH₄H₂PO₄, the better the suppression effect on explosion. The lignite dust does not explode when the mass percentage of NH₄H₂PO₄ is 60% and the particle size of NH₄H₂PO₄ is 25-38 μm, which proves that decreasing the particle size of NH₄H₂PO₄ is important to suppress explosion. The research results are of great significance for grasping the explosion suppression effect of inert dust on lignite dust.

Explosion Performance of Al Powder-Liquid Fuel Mixtures under Different Ambient Conditions

The explosion performance of Al powder-diethyl ether (A-D) and Al powder-diethyl ether-nitromethane (A-D-N) mixtures under low-temperature and low-pressure as well as high-temperature and high-humidity conditions were investigated in a 20 L explosion vessel. The explosion pressure, maximum pressure rise rates, and lower flammability limit (LFL) of the mixtures under binary ambient conditions were obtained. The results showed that the A-D-N mixture had a higher explosion pressure and LFL under the same ambient condition due to the addition of nitromethane. The explosion pressure and LFL of the A-D-N mixture had lower sensitivity to the variation of ambient parameters. The result could further help in explosion performance assessment of multi-phase fuel under actual ambient conditions.

Modelling Coal Dust Explosibility of Khyber Pakhtunkhwa Coal Using Random Forest Algorithm

Coal dust explosion constitutes a significant hazard in underground coal mines, coal power plants and other industries utilising coal as fuel. Knowledge of the explosion mechanism and the factors causing coal explosions is essential to investigate for the identification of the controlling factors for preventing coal dust explosions and improving safety conditions. However, the underlying mechanism involved in coal dust explosions is rarely studied under Artificial Intelligence (AI) based modelling. Coal from three different regions of Khyber Pakhtunkhwa, Pakistan, was tested for explosibility in 1.2 L Hartmann apparatus under various particle sizes and dust concentrations. First, a random forest algorithm was used to model the relationship between inputs (coal dust particle size, coal concentration and gross calorific value (GCV)), outputs (maximum pressure (Pmax) and the deflagration index (Kst)). The model reported an R2 value of 0.75 and 0.89 for Pmax and Kst. To further understand the impact of each feature causing explosibility, the random forest AI model was further analysed for sensitivity analysis by SHAP (Shapley Additive exPlanations). The study revealed that the most critical parameter affecting the explosibility of coal dust were particle size > GCV > concentration for Pmax and GCV > Particle size > Concentration for Kst. Mutual interaction SHAP plots of two variables at a time revealed that with <200 gm/L concentration, −73 µm size and a high GCV coal was the most explosive at a high concentration (>400 gm/L), explosibility is relatively lower irrespective of GCV and particle sizes.

Identification and monitoring of coal dust pollution in Wucaiwan mining area, Xinjiang (China) using Landsat derived enhanced coal dust index

Coal dust is the main pollutant in coal mining areas. Such pollutants easily diffuse and are difficult to monitor, which increases the cost of environmental pollution control. Remote sensing technology can be used to dynamically monitor mining areas at a low cost, and thus, this is a common means of mining area management. According to the spectral characteristics of various ground objects in remote sensing images, a variety of remote sensing indexes can be constructed to extract the required information. In this study, the Wucaiwan open-pit coal mine was selected as the study area, and the Enhanced Coal Dust Index (ECDI) was established to extract the coal dust pollution information for the mining area. A new mining area pollution monitoring method was developed, which can provide technical support for environmental treatment and mining planning in Zhundong. The results of this study revealed the following: (1) Compared with the normalized difference coal index, the ECDI can expand the difference between the spectral information about the coal dust and the surrounding features, so it has a significant recognition ability for coal dust information. (2) From 2010 to 2021, the coal dust pollution in the study area initially increased and then decreased. With the continued exploitation of the coal mines in the study area, the coal dust pollution area increased from 14.77 km2 in 2010 to 69.49 km2 in 2014. After 2014, the local government issued various environmental pollution control policies, which had remarkable results. The coal dust pollution area decreased to 36.85 km2 and 17.85 km2 in 2018 and 2021, respectively. (3) There was a great deal of pollution around mines and roads, around which the pollution was more serious. Various factors, such as wind, coal type, and the mining, processing, and transportation modes, affect the distribution of the coal dust pollution.

Evaluation on explosion characteristics and parameters of pulverized coal for low-quality coal: experimental study and analysis

Fully utilizing the energy generated by the explosion of pulverized coal will contribute to realize the clean and efficient exploitation of coal resources. The pulverized coal explosion characteristics will be a far-reaching and important task to explore. In this paper, ten kinds of low-quality coals such as high sulfur, high ash, and low metamorphic degree coals were investigated and the minimum ignition energy (MIE), lower explosion limit (LEL), and explosion intensity (EI) parameters under different particle sizes and coal powder concentration conditions were also analyzed combined with a 1.2-L Hartmann tube and a 20-L explosion sphere experimental system. Finally, the morphological characteristics of the exploded coal powder surface were evaluated by scanning electron microscopy (SEM). The results show that the particle size is positively correlated with MIE. LEL shows an inverted "U"-shaped trend with the increasing degree of coal deterioration. The low-rank coal is more flammable and explosive. The maximum pressure P_Max at the LEL concentration and maximum pressure rise rate (dP/dt)_Max overall value is small. Here, optimum pulverized coal particle size (75μm) for explosive utilization of low-quality coal was determined. Within 50-225 g/m³ of pulverized coal concentration range, the explosion intensity increases with increasing concentration. The smaller the particle size of pulverized coal, the greater the possibility of agglomeration of pulverized coal particles. The surface of the exploded coal particles produces more developed pores. They are irregularly shaped and have more rounded edges than the original coal.

The Thermal Decomposition Behavior of Pyrite-Pyrrhotite Mixtures in Nitrogen Atmosphere

To assess the thermal transformation process of common sulfide minerals in a nitrogen atmosphere, thermogravimetric analysis, X-ray diffraction, scanning electron microscopy, and thermogravimetric mass spectrometry are employed to define the influence of the pyrrhotite content in pyrite-pyrrhotite mixtures (mixed minerals). The results indicate that an increase in pyrrhotite content decreases the temperature of the maximum mass loss rate of mixed minerals and reduces its mass loss. The solid-phase transformation of the thermal decomposition of mixed minerals is accelerated because the apparent activation energy of pyrrhotite is lower than that of pyrite and mixed minerals. However, the pyrrhotite makes the mixed minerals easier to sinter and agglomerate, which reduces the total volatilization amount of the gas product, S2; thus, the rate of mass loss decreases.

Effects of Initial Turbulence on the Explosion Limit and Flame Propagation Behaviors of Premixed Syngas-Air Mixtures

Syngas with important industrial applications has explosive hazards because of its flammability. It is necessary and valuable to study the combustion and explosion characteristics of syngas under actual working conditions. To explore the effects of initial turbulence on the explosion limits and the flame propagation behavior of the syngas-air mixtures, the explosion limits were tested by the explosive limit instrument, and the flame propagation process in the spherical pressure vessel was recorded by a high-speed camera. By adjusting the rotating speed of the stirrer to obtain turbulence of different intensities, the explosion limit and flame propagation behavior of syngas under different turbulent conditions were analyzed. The explosion limit of syngas in the macro-static state was 9.5-76.1%, and its flame front was relatively smooth. However, with the increase in turbulence intensity, both the upper and lower explosion limits of syngas decreased. The disturbance of turbulence made the flame shape change. The flame front was wrinkled, and the flame boundary was blurred, which became more and more obvious with the increase in turbulence intensity. The maximum velocity and duration of flame propagation increased with the increase in turbulence intensity. Under the same turbulence intensity, the flame propagation velocity generally augmented first and then lessened.

SARS-CoV-2 vaccination modelling for safe surgery to save lives: data from an international prospective cohort study

BACKGROUND

Preoperative SARS-CoV-2 vaccination could support safer elective surgery. Vaccine numbers are limited so this study aimed to inform their prioritization by modelling.

METHODS

The primary outcome was the number needed to vaccinate (NNV) to prevent one COVID-19-related death in 1 year. NNVs were based on postoperative SARS-CoV-2 rates and mortality in an international cohort study (surgical patients), and community SARS-CoV-2 incidence and case fatality data (general population). NNV estimates were stratified by age (18-49, 50-69, 70 or more years) and type of surgery. Best- and worst-case scenarios were used to describe uncertainty.

RESULTS

NNVs were more favourable in surgical patients than the general population. The most favourable NNVs were in patients aged 70 years or more needing cancer surgery (351; best case 196, worst case 816) or non-cancer surgery (733; best case 407, worst case 1664). Both exceeded the NNV in the general population (1840; best case 1196, worst case 3066). NNVs for surgical patients remained favourable at a range of SARS-CoV-2 incidence rates in sensitivity analysis modelling. Globally, prioritizing preoperative vaccination of patients needing elective surgery ahead of the general population could prevent an additional 58 687 (best case 115 007, worst case 20 177) COVID-19-related deaths in 1 year.

CONCLUSION

As global roll out of SARS-CoV-2 vaccination proceeds, patients needing elective surgery should be prioritized ahead of the general population.

Explosion behaviors of hybrid C2H2/CaC2 dust in a confined space

In order to investigate the explosion process of calcium carbide (CaC₂) dust in the acetylene (C₂H₂) atmosphere, the explosion characteristics of C₂H₂ gas and C₂H₂/CaC₂ dust gas-solid two-phase mixture were studied using a 20-L spherical vessel, and the chemical composition of solid residues after explosion were also analyzed. Experimental results showed that the P_ex values of C₂H₂ gas explosion rose first and then remained stable with the increasing stoichiometric ratio values (φ) of C₂H₂/air, while the (dP/dt)_ex values tended to increase at early stage and then decrease, the inflection point of (dP/dt)_ex values was φ = 1.78. The explosion severity and risk of C₂H₂ gas were enhanced by adding CaC₂ dust, and the optimum additive concentration of CaC₂ dust was 100 g/m³. In the oxygen atmosphere, the C₂H₂/CaC₂ hybrid explosion was divided into two stages when the concentration of CaC₂ dust was over 300 g/m³. The explosion risk of the first stage (Stage Ⅰ) was much more serious, while the explosion severity of the second stage (Stage Ⅱ) was much more fierce. The solid residues of hybrid explosion only contained CaO in the oxygen atmosphere, however, Ca(OH)₂ and CaO were detected in the solid residues in the air atmosphere, owing to the combustion heat of C₂H₂ gas in oxygen was higher than that in air. The hydrolysis reaction time of CaC₂ particle with large particle size was prolonged, and the diffusion of solid product layer and surface chemical reaction both influenced the hydrolysis process according to the shrinking core model. Based on the explosion and chemical analysis experiments, the explosion mechanism of C₂H₂/CaC₂ dust gas-solid two-phase mixture was analyzed systematically.

Nanometal Dust Explosion in Confined Vessel: Combustion and Kinetic Analysis

Extensive application of metal powder, particularly in nanosize could potentially lead to catastrophic dust explosion, due to their pyrophoric behavior, ignition sensitivity, and explosivity. To assess the appropriate measures preventing accidental metal dust explosions, it is vital to understand the physicochemical properties of the metal dust and their kinetic mechanism. In this work, explosion severity of aluminum and silver powder, which can be encountered in a passivated emitter and rear contact (PERC) solar cell, was explored in a 0.0012 m³ cylindrical vessel, by varying the particle size and powder concentration. The P _max and dP/dt _max values of metal powder were demonstrated to increase with decreasing particle size. Additionally, it was found that the explosion severity of silver powder was lower than that of aluminum powder due to the more apparent agglomeration effect of silver particles. The reduction on the specific surface area attributed to the particles' agglomeration affects the oxidation reaction of the metal powder, as illustrated in the thermogravimetric (TG) curves. A sluggish oxidation reaction was demonstrated in the TG curve of silver powder, which is contradicted with aluminum powder. From the X-ray photoelectron spectroscopy (XPS) analysis, it is inferred that silver powder exhibited two reactions in which the dominant reaction produced Ag and the other reaction formed Ag₂O. Meanwhile, for aluminum powder, explosion products only comprise Al₂O₃.

Transient reaction process and mechanism of cornstarch/air and CH4/cornstarch/air in a closed container: Quantitative research based on experiments and simulations

Both dust/air explosion and flammable gas/dust/air explosion are common forms of energy release. Experiments and simulation models with a multi-step chemical reaction mechanism were used to study the intensity parameters and mechanism of the CH₄/air explosion, cornstarch/air explosion and CH₄/cornstarch/air explosion in a closed container. Results showed that the peak overpressure, maximum flame temperature, and average flame propagation speed of the stoichiometric CH₄/air explosion reach 0.84 MPa, 2614 K and 3.5 m/s, respectively. The optimal concentration of cornstarch explosion is 750 g/m³, and its peak overpressure, maximum flame temperature and average flame propagation speed are 0.76 MPa, 2098 K and 1.77 m/s, respectively. For a three-components system, adding methane can significantly increase the explosive intensity and combustion performance of cornstarch. The explosive intensity parameters (peak overpressure, maximum flame temperature, average flame propagation speed) of a certain concentration of cornstarch first increase and then decrease with the increase of methane concentration. The maximum explosion intensity parameters of a three-components system with a certain concentration of lean-methane/air are higher than that of single-phase, but always lower than that of the stoichiometric methane/air. Moreover, the mutual coordination of dust and combustible gas in energy release and the mutual competition mechanism in oxygen consumption are described.

Phase Change Materials Application in Battery Thermal Management System: A Review

The purpose of a battery thermal management system (BTMS) is to maintain the battery safety and efficient use as well as ensure the battery temperature is within the safe operating range. The traditional air-cooling-based BTMS not only needs extra power, but it could also not meet the demand of new lithium-ion battery (LIB) packs with high energy density, while liquid cooling BTMS requires complex devices to ensure the effect. Therefore, phase change materials (PCMs)-based BTMS is becoming the trend. By using PCMs to absorb heat, the temperature of a battery pack could be kept within the normal operating range for a long time without using any external power. PCMs could greatly improve the heat dissipation efficiency of BTMS by combining with fillers such as expanded graphite (EG) and metal foam for their high thermal conductivity or coordinating with fins. In addition, PCMs could also be applied in construction materials, solar thermal recovery, textiles and other fields. Herein, a comprehensive review of the PCMs applied in thermal storage devices, especially in BTMS, is provided. In this work, the literature concerning current issues have been reviewed and summarized, while the key challenges of PCM application have been pointed out. This review may bring new insights to the PCM application.

Impact of Lithium Salts on the Combustion Characteristics of Electrolyte under Diverse Pressures

The electrolyte is one of the components that releases the most heat during the thermal runaway (TR) and combustion process of lithium-ion batteries (LIBs). Therefore, the thermal hazard of the electrolyte has a significant impact on the safety of LIBs. In this paper, the combustion characteristics of the electrolyte such as parameters of heat release rate (HRR), mass loss rate (MLR) and total heat release (THR) have been investigated and analyzed. In order to meet the current demand of plateau sections with low-pressure and low-oxygen areas on LIBs, an electrolyte with the most commonly used lithium salts, LiPF6, was chosen as the experimental sample. Due to the superior low-temperature performance, an electrolyte containing LiBF4 was also selected to be compared with the LiPF6 sample. Combustion experiments were conducted for electrolyte pool fire under various altitudes. According to the experimental results, both the average and peak values of MLR in the stable combustion stage of the electrolyte pool fire had positive exponential relations with the atmospheric pressure. At the relatively higher altitude, there was less THR, and the average and peak values of HRR decreased significantly, while the combustion duration increased remarkably when compared with that at the lower altitude. The average HRR of the electrolyte with LiBF4 was obviously lower than that of solution containing LiPF6 under low atmospheric pressure, which was slightly higher for LiBF4 electrolyte at standard atmospheric pressure. Because of the low molecular weight (MW) of LiBF4, the THR of the corresponding electrolyte was larger, so the addition of LiBF4 could not effectively improve the safety of the electrolyte. Moreover, the decrease of pressure tended to increase the production of harmful hydrogen fluoride (HF) gas.

Study on thermal expansion characteristics of mixed systems of flaky dust and alkane liquid

To obtain the cubical coefficients of thermal expansion of a mixed system of flaky dust and alkane liquid, the volume and pressure of the mixed system under different temperatures and volume fractions of aluminum powder were measured. On the basis of the experimental results, the cubical coefficients of thermal expansion under the corresponding conditions were calculated and the effect of each influencing factor was obtained. The results show that since the volume of each phase component in the system increases with temperature, the volume of the mixed system also increases with temperature. With increasing temperature, the cubical coefficients of thermal expansion of the mixed system generally increase. Affected by the increase in mass concentration of low-expansion-coefficient substances, an increase in the volume fraction of aluminum powder results in a decrease in the volume thermal expansion coefficient of the mixed system. At the same time, due to the changes in the state of the mixed system, the mass fraction of aluminum powder decreased sharply within a certain range. The low mass fraction of aluminum powder weakens the supporting effect of the metal particle skeleton, the thermal expansion properties of the liquid dominate the mixed system, and the volume thermal expansion coefficient is high. The high aluminum powder mass fraction creates the metal particle skeleton, the metal thermal expansion properties dominate the mixed system, and the volume thermal expansion coefficient is low.

Characteristics of Dust in Coal Mines in Central North China and Its Research Significance

The identification of the dust characteristics in coal mine working faces is essential for preventing coal dust explosion and occupational diseases. In this paper, dust samples from the coal mines in southern Shanxi province and Henan province, central North China, were selected as the research objects. The results show that the dust contains primarily organic matter, as well as considerable amounts of minerals. The chemical composition of dust at the working faces is the most complex. According to the proportion of PM10, the dust composition can be divided into three types: symmetrical, fine-dominated, and coarse-dominated. The wettability of dust increases with the increase of the oxygen-carbon ratio on its surface, increase of ash content, decrease of fixed carbon content, and decrease of particle size. In addition, the great variety of harmful elements in dust, some with a high content, can harm the human body. An explosion index is proposed to evaluate the likeliness tendency of coal dust explosion based on several key affecting factors. The surfactant (0.05% AN solution) adopted in this paper can significantly increase the wettability of coal dust and inhibit the generation of dust greatly, showing good ability in preventing coal dust explosion and occupational diseases.

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 P_max 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 P_max 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.