Coal Dust Concentration Research Articles

Re-explosion hazard potential of solid residues and gaseous products of coal dust explosion

In the present work, solid residues and gaseous products after the initial explosion of coal dust were collected by self-made devices, respectively, and their explosiveness was further studied to assess the re-explosion hazard. The results show that the solid residue can explode again, and its explosion pressure (Pex) and pressure rise rate ((dP/dt)ex) both increase gradually as dust concentration and ignition energy increase, but decrease with the larger particle size. Solid residue is characterized by a lower deflagration index (Kst) than raw lignite dust, but it can produce greater severity than some raw high-rank coal dust in some cases. The gaseous products of coal dust explosion are mainly composed of CO, H2 and CH4, and some trace gases. The volume fraction of CO and H2 in the gaseous products rises in proportion to the concentration of coal dust. For coal dust explosion with a concentration >200 g/m3, the gaseous products collected are flammable and have a wider explosion limit and a lower limited oxygen content. This research provides valuable information and reference for future prevention and control of secondary explosion disasters in coal mines.

Impacts of Fines at Morupule Coal Mine, Botswana

Morupule Coal Mine (MCM) classifies fines as coal particles that are less than 3.35 mm in size. Fines are one of the problems MCM is facing and have occasionally led to penalties from some customers. This paper quantifies the fines generated in MCM from the working face to the run-of-mine stockpile and its economic and environmental impacts. Data about the wash plant's production losses were collected through an examination of missed deadlines, stoppages due to tail-end blockages, and conveyor belt breakdowns using company reports. Data on coal dust concentrations were obtained from the mine. It was found that the overall haulage system generates about 27% of the fines of the coal produced monthly. The total monetary loss per shift from production and the wash plant is BWP 418,285. Coal dust concentration underground is kept within acceptable limits due to strict engineering control measures while it exceeds the required levels on the surface and is difficult to control as it is exposed to the atmosphere. As a result, the vegetation around the mining concession is affected by coal dust.
 
 Fine generation; Dust production; Coal degeneration; Economic impact; environmental impact.

Analysis of dust and noise exposure levels in the mining industry from the national surveillance program in 2019

Objective: To understand the exposure level of dust and noise in the mining industry and provide data support for revising policy for the prevention and control of occupational diseases. Methods: In May 2022, Data was collected through the National Surveillance Program for Occupational Hazards in the Workplace. Descriptive analysis was conducted for dust and noise levels by industry type and enterprise size from 7, 679 enterprises in the mining industry among 29 provincial regions nationwide. Results: The enterprises in the mining industry included in the National Surveillance Program for Occupational Hazards in the Workplace are mainly small and micro, accounting for 47.97% (3684/7679) and 30.00% (230/7679) respectively. The industry is mainly compred of employers in the non-metallic ming and beneficiation industry, accounting for 50.25% (3859/7679). Among the enterprises with silica dust, coal dust, and noise hazards, the proportion of enterprises where total dust concentration and noise intensity exceed the standard is higher than 50%. 30% of the posts are with an exposure level of silica dust, coal dust, and noise that exceeds the standard. The exceedance rate and the median of the time-weighted average concentration of total coal dust among large and medium-sized enterprises are higher than those among small and micro-sized enterprises (P<0.05) . Conclusion: The dust and noise hazards in the mining industry are lower than in the past in China, but more than 25% of workers are still at a high risk of occupational pneumoconiosis and noise deafness. Therefore, intervention and surveillance strategies should be strengthened in the future.

Development of a Coal Dust Concentration Sensor Based on the Electrostatic Induction Method.

In order to solve the problems of easy blockage and difficult maintenance of the current coal dust concentration sensor, a coal dust concentration sensor based on the electrostatic induction method was designed. Based on the analysis of the principle of electrostatic induction dust concentration detection, an electrostatic induction dust concentration sensor composed of a electrostatic detection electrode, a dust extraction fan, an induction signal processing circuit, an insulator, a shield, and other parts was designed. The influence of the length and width of the electrostatic detection electrode and the particle flow rate on the standard deviation of the induction signal was analyzed through experiments to optimize them. The induction signals on the electrostatic detection electrode at different dust concentrations were determined in tests, and the mathematical relationship between the standard deviation of the induction signal and the dust concentration was obtained. According to segment multiple-curve height fitting, the maximum deviation between the detected value and actual dust concentration does not exceed 10%.

Influence of Molasses on the Explosion and Decomposition Properties of the Coal Dust Deposited in Underground Mines

Coal dust endangers the health and safety of workers in underground coal mines. Therefore, developing coal dust suppressants with dust prevention and explosion-proof properties is critical. The influence of molasses on the explosion and decomposition of the coal dust deposited in underground mines was investigated using 20 L explosion experiments and thermogravimetric and differential thermal analysis (TG-DTA). Findings reveal that, first, molasses can weakly promote the explosion of coal dust at low coal dust concentrations (&lt;400 g/m3) but has no significant effect on the explosion at high coal dust concentrations (≥400 g/m3). Second, the decomposition process of the coal dust mixed with molasses has three stages: the moisture evaporation stage (0–150 °C), the molasses decomposition stage (150–300 °C), and the coal dust decomposition stage (300–500 °C). Molasses oxidation consumes oxygen and releases heat; at low coal dust concentrations, the released heat can promote coal dust decomposition to produce combustible gas, enhancing the coal dust explosion; at high coal dust concentrations, under the co-influence of the heat generation and oxygen consumption, molasses has no effect on the coal dust explosion. This is the mechanism of which molasses influences coal dust explosions.

The impact of coal trains on PM2.5 in the San Francisco Bay area

Exposure to fine particulate matter (PM2.5) is associated with adverse health effects, including mortality, even at low concentrations. Rail conveyance of coal, accounting for one-third of American rail freight tonnage, is a source of PM2.5. However, there are limited studies of its contribution to PM2.5, especially in urban settings where residents experience higher exposure and vulnerability to air pollution. We developed a novel artificial intelligence-driven monitoring system to quantify average and maximum PM2.5 concentrations of full and empty (unloaded) coal trains compared to freight and passenger trains. The monitor was close to the train tracks in Richmond, California, a city with a racially diverse population of 115,000 and high rates of asthma and heart disease. We used multiple linear regression models controlling for diurnal patterns and meteorology. The results indicate coal trains add on average 8.32 µg/m3 (95% CI = 6.37, 10.28; p < 0.01) to ambient PM2.5, while sensitivity analysis produced midpoints ranging from 5 to 12 µg/m3. Coal trains contributed 2 to 3 µg/m3 more of PM2.5 than freight trains, and 7 µg/m3 more under calm wind conditions, suggesting our study underestimates emissions and subsequent concentrations of coal train dust. Empty coal cars tended to add 2 µg/m3. Regarding peak concentrations of PM2.5, our models suggest an increase of 17.4 µg/m3 (95% CI = 6.2, 28.5; p < 0.01) from coal trains, about 3 µg/m3 more than freight trains. Given rail shipment of coal occurs globally, including in populous areas, it is likely to have adverse effects on health and environmental justice.

Study on dust reduction characteristics and mechanism of softened mine water

ABSTRACT At present, the intensity of coal mining is increasing gradually, and the concentration of coal dust in roadways under integrated mining is high, making it difficult to control. As a result, the mechanism and technology of dust reduction remain one of the key points of efficient mining research. To study the influence of physical and chemical properties of mine water on dust reduction efficiency, this work used spray dust reduction experiment system to assess dust reduction efficacy of several solutions at 3～6MPa, and the differences in the dedusting characteristics and atomization characteristics of each group of each solution were analyzed. The result demonstrates that softened mine water’s surface tension and contact angle fall significantly, spray droplet size lowers, and fog dispersion becomes more symmetrical. When compared to before softening, the dust reduction efficiency of softened water (SW) is 72.52% for total dust and 69.74% for respiratory dust, considerably improving the working environment of underground coal miners and optimizing mining efficiency.

석탄 저장시설의 석탄비산먼지와 총 휘발성유기화합물의 분포 특성

Coal dust scattering by the wind in the areas around outdoor coal storage facilities of steel mills and coal-fired power plants has been reported. We tried to address this issue by the indoorization of the outdoor coal yard, which will reduce the coal dust scattering. Thus, this study investigated the distribution characteristics of scattering coal dust and total volatile organic compounds, and recommended measures to improve the internal environment. The average concentration of coal dust above the ground by upper dust scattering was measured to be roughly twice as high as that closer to the ground. The highest concentration of dust particles was between 33 and 50 m above ground near the central deck. In addition, the dust concentration was always low in the north entrance area because of external ventilation provided by open door. However, the dust concentration was high in the southwest area, which lacked an entrance door and was further obstructed by mountain terrain. The concentration of total volatile organic compounds was estimated to be higher in the lower part of the coal storage than in the other areas, although there was no significant difference because it was typically extreme low concentration. Therefore, to improve the internal environment, the installation of an air purifier is recommended at the height of central deck in the southwest area of the indoor coal storage.

Study on coupling diffusion of composite dust and cloud-mist dedust technology in fully mechanized driving face of mixed coal-rock roadway

Aiming at addressing the problem of coal dust and rock dust mixed pollution in mixed coal-rock roadways, this study conducted a CFD numerical simulation on the coupling migration and pollution of coal dust and rock dust in the fully mechanized driving face of mixed coal-rock roadway (i.e., roadway section with both coal seam and rock stratum). Research findings: Small coal dust particles mainly migrate backward along the upper space of the roadway, while large coal dust particles mostly diffuse backward along the bottom of the air return side and settle evidently, with the concentration being higher than 1,000 mg/m3. The concentration of rock dust starts to decline significantly to about 350–800 mg/m3 in the middle and rear of the roadway. The concentration of coal dust is relatively high (200–500 mg/m3) in the front of the roadway, and it decreases gradually to around 175 mg/m3 in the middle and rear sections. With the increase of diffusion time T of rock dust and coal dust, the diffusion distance LD shows a linear increasing trend. Both rock dust and coal dust conform to the linear equation LD = 0.82 T + 11. After the application of the cloud-mist dedust technology, all the measuring points in the mixed coal-rock roadway witnessed a dust removal efficiency of above 75 %, which is a mark of effectiveness of the technology in improving the underground working environment.

Review and prospects of mining chemical dust suppressant: classification and mechanisms.

Coal mine pollution is a serious threat to the mine safe production and occupational health of miners. Chemical dust suppression can effectively reduce the concentration of coal dust and suppress the re-entrainment of dust. This paper discusses the research progress of three kinds of traditional dust suppressants: the wetting-type, cohesive type, and condensed type. In order to meet dust suppression and environmental protection requirements, 7 kinds of new type dust suppressants, such as compound, ecological environmental protection, polymer, functional, microbes, and enzymes, have been developed by the predecessors. And all kinds of dust suppressant mechanism and main performance index have been summarized. Through the analysis of the research results from 1985 to 2021, it is found that the compound and environment-friendly dust suppressants have gradually become the research focus in this field, accounting for 17.93% and 26.21% of the total number of achievements. In the recent 5years, new materials, such as microbe suppressant, urease suppressant, and nanomaterials, have gradually emerged. Because of their natural and environmental protection characteristics, it could be predicted that they will become the future development trend in this field. However, there are still some problems to be improved, such as expensive price and complex preparation technology.

Investigation of lag on ignition of coal dust clouds under varied experimental conditions

• Determined LOI of coal dust clouds under varied experimental conditions. • Ignition temperature significantly influenced the LOI of coal dust clouds. • LOI of coal dust clouds showed increasing trend with thermal properties of coal dust. • Optimum dust dispersion pressure that yielded minimum LOI is found at 70 kPa. • Established empirical relations between LOI and all the influencing parameters. Lag on ignition (LOI) of coal dust cloud greatly influences the initiation and propagation of coal dust explosion. This paper investigates the effects of coal dust particle size, dust concentration, ignition temperature, and dust dispersion pressure on LOI of coal dust clouds using Godbert-Greenwald furnace along with a high-speed camera. LOI of coal dust cloud significantly decreased by 1/13 times from 959 to 77 ms with increase in the ignition temperature from 600 to 1000 °C, demonstrating greatest influence of ignition temperature on LOI. LOI increased by 60% with increase in dust concentration from 500 to 4000 g/m 3 . Optimum dust dispersion pressure at which LOI was found minimum is determined 70 kPa. Empirical relations are established between LOI of coal dust cloud and particle size, ignition temperature, dust concentration, and dispersion pressure. The results are analysed in terms of the occurring physical processes, which led to a better understanding of the variation of LOI, ignition behavior, and explosion propagation of coal dust clouds at varied experimental conditions.

Research Progress on Pulverized Coal Concentration Detection Device

Background: Pulverized coal detection is an indispensable detection measure in the coal industry. The current detection devices can be divided into two types: invasive and non-invasive. The coal dust detection methods and devices based on acoustics, optics, and electricity have been extensively studied. In order to achieve a high-efficiency online detection scheme, improving the accuracy and stability of the detection means is the primary goal of the research. Objective: The general problems and characteristics of coal dust detection device design are summarized, as well as recent technological developments and the need for online testing to predict future research trends. Methods: The current typical detection devices are classified according to the detection principle and whether they invade the target, analyzing its advantages and disadvantages according to the device performance and application scenarios. Results: It has a beneficial effect on the design of the pulverized coal concentration detection device. Conclusion: The paper summarizes and analyzes several representative coal concentration detection device patents in recent years. Then it points out advantages and main problems. On this basis, the main development direction of the coal dust concentration detection device in the future is discussed.

A risk of pulmonary diseases in miners while using dust respirators

Purpose. To determine magnitudes of the occupational risks of respiratory disease (pneumoconiosis) occurrence in miners while using filter respirators on the basis of an exposure dust dose with the consideration of work experience. Methodology. To assess occupational risks, a new approach proposed by the Research Institute of Complex Hygiene and Occupational Diseases is used. The approach is based on determining an exposure dose of a hazardous substance entering the workers lungs during their professional contact with it taking into account the volume of pulmonary ventilation, the number of shifts, and work experience. Findings. Use of dust respirators reduces the risk of occupational respiratory diseases but does not eliminate it completely. It has been established that with more than three-year work experience and coal dust concentrations of more than 50 mg/m3, use of dust filter respirators does not ensure a minimal degree of the occupational disease risks. At the same time, it has been identified that if work experience is less than 3 years with the use of filter respirators, the risk of occupational diseases will be minimal. It has been proved that the risk assessment should involve using the minimal value of a protection factor of a respirator, which is fixed in the production environment. It has been shown that working within the areas with dust concentrations higher than 100 mg/m3 is dangerous for miners; over time, with the accumulation of sufficient dust in the lungs it will lead to the development of silicosis. Originality. It consists in scientific substantiation of the magnitude of occupational risk of respiratory diseases in miners, taking into account a real protection factor of respirators, which is determined at the workplace based on the calculation of an exposure dose and time of professional contact with hazardous substances. Practical value. The experience of safe operation in mine workings with and without using filter respirators has been substantiated, basing on a safe value of coal dust concentration, at which a low level of occupational risk of respiratory diseases is recorded. Recommendations for determining the dust load taking into account a protection factor of respirators at the workplace have been developed.

Experimental exploration and mechanism analysis of the deflagration pressure of methane/pulverized coal blenders inhibited by modified kaoline-containing compound inhibitors

In this work, with the assistance of the intercalation modification approach, three kinds of intercalated compounds, dimethyl sulfoxide (DMSO), potassium acetate (KAc), and ammonium sulfamate (AS) were successively employed for modification on kaoline to prepare a modified kaolin inhibitor. Then, the TG/DTG test, SEM observation, XRD characterization, and FTIR analysis were respectively utilized to probe the thermal stability, surface structures, and functional groups of the modified kaoline inhibitor. Moreover, the compound inhibitors fabricated by modified kaoline powder blending with ammonium polyphosphate (APP) of different mass fractions were employed to inhibit the explosions of methane/pulverized coal blenders. In the explosion inhibition experiments, the concentrations of methane and coal dust were respectively selected for 9.5 % and 0.105 g/L, while the compound inhibitors with seven various mass fractions of 0.05, 0.075, 0.1, 0.125, 0.15, 0.175, and 0.20 g/L were severally chosen to explore its inhibiting effect on methane/pulverized coal blenders using the 20-L standard spherical explosion apparatus. Results show that both the modified kaoline inhibitor and its compound inhibitor demonstrate a prominent inhibiting effect on methane/pulverized coal blenders. Besides, the inhibiting effect presents the most outstanding as the mass fraction for APP of the compound inhibitor occupies 35 %. Under such a circumstance, the Pmax of the hybrid mixture decreases from 0.784 to 0.47 MPa and declines by 40.05 % after adding the compound inhibitor, the dP/dtmax declines to 3.03 MPa·s−1 while the tPmax delays to 1.122 s. Finally, we theoretically analyzed the suppression mechanism of the modified kaoline-containing compound inhibitors on the explosions of methane/pulverized coal blenders based upon the physicochemical properties of the raw samples and the solid particles collected from the post-explosion experiments from the macro and molecular-kinetics perspectives. This preliminary study would contribute to the development of high-efficiency inhibitors for preventing methane/pulverized coal-involved explosion disasters.

Influencing factors of coking coal dust explosion pressure and flame and effect of inert dust on its explosion suppression

Coking coal is a precious resource in the world and an important raw material for the production of steel, but it is easy to cause explosion accidents in the process of coking coal mining, which is very detrimental to safe production. In order to reveal the influencing factors of coking coal dust explosion intensity and the suppression effect of inert dust on coking coal dust explosion, an experimental study was carried out in this paper. The results show that the particle size and the mass concentration of coal dust have a great influence on the explosion pressure and flame. By analyzing the suppression effects of NaCl, KCl, and NH4H2PO4 on coking coal dust explosion, it is got that NH4H2PO4 has the best explosion suppression effect. When the mass percentage of NH4H2PO4 mixed into coking coal dust increases to 60%, the maximum explosion pressure decreases by 0.47 MPa, and the maximum flame length decreases by 0.50 m. As the particle size of NH4H2PO4 decreases, the explosion intensity continue to decrease. When the particle size of NH4H2PO4 is 0 ~ 25 μm, and the mass percentage of NH4H2PO4 mixed into coking coal dust is 50%, the explosion doesn’t occur anymore.

Effect of glycerol microemulsion on coal seam wetting and moisturizing performance

In coal mining, coal seam water injection is effective for rock burst prevention and dust suppression, and the microemulsion as a water injection agent can greatly improve the wettability of coal seams. In order to further study the effect of glycerol in microemulsion as a phase substance on the wettability of coal body after water injection in coal seam, and its role in promoting coal seam moisturizing performance, on the basis of changing the phase material, the influence of different microemulsion components on the wettability of coal is explored through the contact angle experiment and Fourier infrared spectroscopy experiment, and the effect of glycerol on the moisturizing performance of coal is analyzed through the wettability control experiment in this paper. The experimental results show that the microemulsion as a wetting agent exhibits good wettability, and the composition of the microemulsion phase material affects the formation and dissociation of the functional groups on the coal surface by the microemulsion to a certain extent. The dissociation of the functional groups on the coal surface by the surfactant components in the microemulsion dominates the wetting mechanism of coal, and the effect of glycerol molecules on the functional groups shows a certain degree of wetting promotion. In addition, glycerol molecules easily react with other molecules such as water and sulfur dioxide molecules. After being injected into the coal seam, the glycerol microemulsion has a good moisturizing effect and a certain effect of coalbed methane purification. Therefore, it has practical significance for reducing coal dust concentration on coal mining face and increasing coal seam permeability.

Experimental research on the inhibition of methane/coal dust hybrid explosions by the ultrafine water mist

This experimental study focused on the inhibition of ultrafine water mist on methane/coal dust hybrid explosions inside the closed vessel. Combined with the change of explosion parameter (including the flame propagation characteristics, explosion pressure, pressure rising rate and flame temperature), the corresponding relationship between the flame propagation and pressure rise of gas/dust hybrid explosions was clarified. And the influence factor and inhibition mechanism on two-phase hybrid explosions were analyzed. Results indicate that flame propagation and pressure rise inside the closed vessel were corresponding. The flame front appeared an obviously thermal diffusion instability and becamean irregular structure after adding mist. Meanwhile, the hybrid explosions could be effectively inhibited by the mist. The explosion intensity, flame propagation velocity and temperature were reduced obviously and the inhibition effect was enhanced with increasing mist concentration. The vmax and △Pmax were decreased by 57.06% and 18.97% respectively. And the (dP/dt)first and (dP/dt)second were reduced by 55.91% and 61.11% respectively. In particular, the flame temperature was also decreased by 50.18%. Besides, the concentration and diameter of coal dust could also obviously affect the inhibition effect of hybrid explosions. Explosion parameter presented a trend of rising firstly and then decreasing as coal dust concentration increased. However, an increasing trend was presented with decreasing coal dust diameter. The inhibition of mist on gas/dust two-phase hybrid explosions was attributed to the combination of physical and chemical effects.

Comparison of static tests and dynamic tests for coal dust surfactants evaluation: A review

Coal workers’ pneumoconiosis is one of the most severe occupational diseases due to long-term exposure to high concentrations of coal dust. Water spray with surfactant addition is an effective and commonly used method to control the coal dust in coal mines. Usually, the surfactant evaluation methods can be divided into two categories, including static and dynamic tests. The performance of surfactants may vary with different evaluation methods, which make the results hard to conclude. By critically reviewing previous studies, this paper highlighted the four surfactants’ evaluating methods for coal dust suppression, including the surface tension test, the sink test, the field test, and the wind tunnel test. Firstly, the basics of four evaluating methods were described, and the general result was concluded and presented. Secondly, static and dynamic tests were compared to reveal the consistency and discrepancy. It was found that the surface tension test takes dominations at lower concentrations of surfactants, while it cannot further take advantage after a critical concentration. The anionic and non-ionic surfactants showed better performance than cationic surfactants mostly in static tests. The field test and the wind tunnel test can directly evaluate the suppression efficiency of surfactants, with consideration of environmental factors such as the particle collision and the contact time. This paper is important for producing comparable results between static and dynamic tests and revealing the consistency and discrepancy. The outcomes of this study could be a guidance for evaluating and selecting the optimum surfactants for coal dust suppression.

Progress in the epidemiological studies on coal mine dust exposure with workers' health damage

Coal is one of the major fuels, which brings huge energy and economic benefits to global industry and daily life. large amounts of coal dust produced in the process of coal mining and transportation, which seriously threatens the health of related workers. Productive coal dust exposure not only directly leads to respiratory diseases, but also may cause health damage to various systems throughout the body. Numerous studies have shown that coal dust exposure is closely associated with decreased lung function, coal worker's pneumoconiosis, chronic obstructive pulmonary disease, lung cancer, and cardiovascular diseases, and the severity of diseases is affected by coal rank, coal dust concentration, cumulative dust exposure, coal dust composition, and individual lifestyle, etc. The article comprehensively summarized the progress of the epidemiological studies on the health hazards of coal miners from coal dust exposure, in order to provide clues for further researches on health damage and protect the health of the occupational population.

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.