Advancing respirable coal mine dust source apportionment:a preliminary laboratory exploration of optical microscopy as a novel monitoring tool

Exposure to respirable coal mine dust(RCMD)can cause chronic and debilitating lung diseases.Real-time monitoring capabilities are sought which can enable a better understanding of dust components and sources.In many underground mines,RCMD includes three primary components which can be loosely associated with three major dust sources:coal dust from the coal seam itself,silicates from the surrounding rock strata,and carbonates from the inert‘rock dust’products that are applied to mitigate explosion hazards.A monitor which can reliably partition RCMD between these three components could thus allow source apportionment.And tracking silicates,specifically,could be valuable since the most serious health risks are typically associated with this component-particularly if abundant in crystalline silica.Envisioning a monitoring concept based on field microscopy,and following up on prior research using polarized light,the aim of the current study was to build and test a model to classify respirable-sized particles as either coal,silicates,or carbonates.For model development,composite dust samples were generated in the laboratory by successively depositing dust from high-purity materials onto a sticky transparent substrate,and imaging after each deposition event such that the identity of each particle was known a priori.Model testing followed a similar approach,except that real geologic materials were used as the source for each dust component.Results showed that the model had an overall accuracy of 86.5%,indicating that a field-microscopy based moni-tor could support RCMD source apportionment and silicates tracking in some coal mines.

Mechanism of micro-wetting of highly hydrophobic coal dust in underground mining and new wetting agent development

The internal mechanism of the high hydrophobicity of the coal samples from the Pingdingshan mining area was studied through industrial,element,and surface functional group analysis.Laboratory testing and molecular dynamics simulations were employed to study the impact of three types of surfactants on the surface adsorption properties and wettability of highly hydrophobic bituminous coal.The results show that the surface of highly hydrophobic bituminous coal is compact,rich in inorganic minerals,and poorly wettable and that coal molecules are dominated by hydrophobic functional groups of aromatic rings and aliphatic structures.The wetting performance of surfactants as the intermediate carrier to connect coal and water molecules is largely determined by the interaction force between surfactants and coal(Fs-c)and the interaction force between surfactants and water(Fs-w),which effectively improve the wettability of modified coal dust via modifying its surface electrical properties and surface energy.A new type of wetting agent with a dust removal rate of 89%has been developed through discovery of a compound wetting agent solution with optimal wetting and settling performance.This paper provides theoretical and technical support for removing highly hydrophobic bituminous coal dust in underground mining.

Online coal dust suppression system for opencast coal mines

Coal is the major source of power in India and world over.Coal mining is an essential industry which has a major role in the economic development of the country.Most major mining activities contribute directly or indirectly to air pollution.Coal dust is a major air pollutant which affects the personal working in the mines and also people residing in villages near the mines.Air pollution due to coal particulates can affect human health and cause damages to the environment.Hence effective pollution control mechanisms are needed to keep the pollution levels within permissible levels.The easiest and most common method employed for dust suppression worldwide is sprinkling of water.In majority of mines,water sprinklers are operated manually and can lead to wastage of water due to over sprinkling.It can also prove to be ineffective in dust suppression if sprinkling is not done properly.The paper proposes a system which can be deployed to automate the dust suppressions sprinklers.The system will monitor the concentration of PM_(10) and PM_(2.5) in the air and initiate sprinkling operation when the particulate matter content exceeds preconfigured limits.

A systematic review of occupational exposure to respirable coal mine dust(RCMD)in the U.S.mining industry

Cumulative inhalation of respirable coal mine dust(RCMD)can lead to severe lung diseases,including coal worker's pneu-moconiosis(CWP),silicosis,mixed dust pneumoconiosis,dust-related diffuse fibrosis(DDF),and progressive massive fibrosis(PMF).Statistics from the number of reported cases showed a significant decrease in the progression of respiratory diseases in the 1990s.However,an unexpected increase in the number of CWP cases was reported in the late 1990s.To date,there has been no comprehensive systematic review to assess all contributing factors to the resurgence of CWP cases.This study aims to investigate the effects of various mining parameters on the prevalence of CWP in coal mines.A systematic review using the preferred reporting items for systematic reviews and meta-analysis(PRISMA)method was conducted to investigate the health effects of RCMD exposure and identify the factors that may contribute to the recent resurgence of CWP cases.The systematic review yielded a total of 401 papers,which were added to the database.The total number of 148 and 208 papers were excluded from the database in the process of screening and eligibility,respectively.Then,18 papers were considered for data selection and full-text assessment.The review revealed that factors including geographic location,mine size,mining operation type,coal-seam thickness,coal rank,changes in mining practices,technology advancement,and engi-neering dust control practices are contributing to the recent resurgence of CWP among coal workers.However,the evidence for root causes is limited owing to the methodological constraints of the studies;therefore,further detailed studies are needed.

Assessment of gas and dust explosion in coal mines by means of fuzzy fault tree analysis

During the past decade, coal dust and gas explosions have been the most two serious types of disasters in China, threatening the lives of miners and causing significant losses in terms of national property. In this paper, an evaluation model of coal dust and gas explosions was constructed based on a fuzzy fault tree by taking the Xingli Coal Mine as a research site to identify the risk factors of coal dust and gas explosions.Furthermore, the hazards associated with such explosions were evaluated for this particular coal mine.After completing an on-site investigation, the fuzzy probabilities of basic events were obtained through expert scoring, and these expert opinions were then aggregated as trapezoidal fuzzy numbers to calculate the degrees of importance of all basic events. Finally, these degrees of importance were sorted. According to the resulting order, the basic events with higher probabilities were determined to identify key hazards in the daily safety management of this particular coal mine. Moreover, effective measures for preventing gas and coal dust explosions were derived. The fuzzy fault tree analysis method is of high significance in the analysis of accidental coal mine explosions and provides theoretical guidance for improving the efficiency of coal mine safety management in a scientific and feasible manner.

Surface characteristics and wetting mechanism of respirable coal dust

In this study,FTIR and XPS spectroscopy,specific surface area and pore size analyses,wetting and other experimental means have been applied to investigate respirable coal dust surface properties and wetting mechanism.The research shows that coal dust surface structures,chemical and element compositions are changed in the refining process of coal dust.Compared with large particle coal dust,respirable coal dust is a weak hydrophilic and strong hydrophobic substance.The reason:the smaller the particle size of coal dust,the more unsaturated its surface.The absorption of air is strong and it is easy to form an air film on coal dust surfaces. Coal dust contact with water is actually a compound contact of liquid in contact with a solid and gas in contact with a solid. The smaller the particle size,the larger the pore volume and the higher the degree of surface roughness,the larger the area of gas in contact with a solid and the worse the coal dust wettability.Another reason is that the changes in the composition of atoms on the dust surface and structures affect coal dust wettability.The results of this study establish a theoretical basis for the invention of effective reduced-dust technology.

Performance of N95 elastomeric respirators in high humidity and high coal dust concentration environment

High humidity and high dust concentration in deep coal mines may severely challenge the performance of respirators worn by coal miners.This paper aims at quantitatively evaluating the respirators used in deep coal mines and providing scientific guidance for the respiratory protection of miners.Based on the self-designed in-situ PM2.5 collector,controllable PM2.5 generator,human breathing simulator,and respirator simulation testing system,under the simulated deep mine working condition,this study investigated the effects of dust loading,wearing time,and dust concentration on the filtration efficiency,breathing resistance,and quality factor of N95 elastomeric respirators.With the increase of dust loading,the respirator filtration efficiency firstly decreased,then increased(minimum value 97.5%).The breathing resistance increased exponentially from 120 to 180 to 1020-1530 Pa,and the quality factor decreased logarithmically from 0.051 to 0.076 to 0.0058-0.0085 Pa^(-1).As the PM2.5 coal dust concentration increased from 5 to 50 mg/m^(3),the wearing time for the respirator breathing resistance to exceed 300 Pa reduced from 7 h to less than 1 h.One N95 elastomeric respirator is not able to perform an 8-h work shift.To avoid the excessive breathing resistance caused by dust loading,more filter cartridges are needed for coal miners.

Design of a water curtain to reduce accumulations of float coal dust in longwall returns

Accumulation of float coal dust(FCD)in underground mines is an explosion hazard that affects all underground coal mine workers.While this hazard is addressed by the application of rock dust,inadequate rock dusting practices can leave miners exposed to an explosion risk.Researchers at the National Institute for Occupational Safety and Health(NIOSH)have focused on developing a water curtain that removes FCD from the airstream,thereby reducing the buildup of FCD in mine airways.In this study,the number and spacing of the active sprays in the water curtain were varied to determine the optimal configuration to obtain peak knockdown efficiency(KE)while minimizing water consumption.

Floor dust erosion during early stages of coal dust explosion development

An ignition of methane and air can generate enough air flow to raise mixtures of combustible coal and rock dust.The expanding high temperature combustion products ignite the suspended dust mixture and will continue to propagate following the available combustible fuel supply.If the concentration of the dispersed rock dust is sufficient,the flame will stop propagating.Large-scale explosion tests were conducted within the National Institute for Occupational Safety and Health(NIOSH)Lake Lynn Experimental Mine(LLEM)to measure the dynamic pressure history and the post-explosion dust scour depth.The aim of this effort is to provide quantitative data on depth of dust removal during the early stages of explosion development and its relationship to the depth of floor dust collected for assessing the incombustible content most likely to participate in the combustion process.This experimental work on dust removal on is not only important for coal mine safety but also for industrial dust explosions.

Comparative study of the explosion pressure characteristics of micro- and nano-sized coal dust and methane–coal dust mixtures in a pipe

Coal dust explosion accidents often cause substantial property damage and casualties and frequently involve nano-sized coal dust.In order to study the impact of nano-sized coal on coal dust and methane–coal dust explosions,a pipe test apparatus was used to analyze the explosion pressure characteristics of five types of micro-nano particle dusts(800 nm,1200 nm,45μm,60μm,and 75μm)at five concentrations(100 g/m3,250 g/m3,500 g/m3,750 g/m3,and 1000 g/m3).The explosion pressure characteristics were closely related to the coal dust particle size and concentration.The maximum explosion pressure,maximum rate of pressure rise,and deflagration index for nano-sized coal dust were larger than for its micro-sized counterpart,indicating that a nano-sized coal dust explosion is more dangerous.The highest deflagration index Kst for coal dust was 13.97 MPa/(m·s),indicating weak explosibility.When 7%methane was added to the air,the maximum deflagration index Kst for methane–coal dust was 42.62 MPa/(m·s),indicating very strong explosibility.This indicates that adding methane to the coal dust mixture substantially increased the hazard grade.

Laboratory results of a 3rd generation roof bolter canopy air curtain for respirable coal mine dust control

Testing was completed on an earlier roof bolter CAC that used slots to provide a perimeter airflow. NIOSH tested it due to its unique design that differed from canopies that provided uniform airflow. Based upon NIOSH recommendations from the earlier testing, a 3rd generation roof bolter CAC has been developed by J.H. Fletcher & Co. The changes to this CAC involve design modifications to the plenum outlets, using a single row of outlets on the perimeter and a different material for the plenum. This laboratory testing was a continuation of the original perimeter slotted CAC design. Using gravimetric and instantaneous sampling of respirable dust concentrations underneath and outside of the CAC. the laboratory testing was completed using three different blower fans that delivered differing airflows. The maximum plenum airflow velocities ranged from 2.34 to 3.64 m/s (460-716 fpm). Results showed plenum respirable dust concentrations ranging from 34.6% to 49.3% lower than respirable dust concentrations outside the plenum protection zone, thus showing an improvement in protection for the roof bolter operators.

Theoretical and numerical analysis of coal dust separated by centrifugal force for working and heading faces

In order to meet engineering needs of Chinese underground coal mines,a new dust-collecting fan,a device of dust separated by centrifugal force in driven cyclone passageway(DCCP)was designed.In centrifugal dust removal section(CDRS)of DCCP,a general equation is derived from the principle of force equilibrium.According to CDRS structure parameters and fan running parameters,the general equation is simplified,and the simplest equation is calculated numerically by MATLAB.The calculation results illustrate that increasing quantity of air current is against dust removal,but it is beneficial to dust removal by increasing the radius of driven spiral blade and increasing the particle diameter of coal dust.The conclusions show that the dust-collecting structure parameters coupled with the fan running parameters is a novel optimization approach to dust-collection fan for working and heading faces,which is especially suitable for Chinese underground mines.

Field study results of a 3rd generation roof bolter canopy air curtain for respirable coal mine dust control

A 3rd generation roof bolter canopy air curtain(CAC)has been developed and constructed by J.H.Fletcher&Co.,Inc.As with the previous generation of the CAC,this design uses the principle of providing uniform airflow across the canopy area as recommended by the National Institute for Occupational Safety and Health.The new modifications include a plenum that is constructed of a single flat aluminum plate,smaller-diameter airflow openings,and a single row of perimeter nozzles designed to prevent mine air contaminated by respirable dust from entering the CAC protection zone.Field testing was conducted on this new 3rd generation design showing reductions in coal mine respirable dust exposure for roof bolter operators.Dust control efficiencies for the CAC for the left bolter operator(intake side)ranged from approximately 26%–60%,while the efficiencies for the CAC for the right bolter operator(return side)ranged from 3%to 47%.

Water-retaining properties of NCZ composite dust suppressant and its wetting ability to hydrophobic coal dust

Coal dust is a primary threat to underground coal miners.The most common approach to control coal dust is hydraulic methods,such as water spray and coal seam water injection.To improve the dust suppressant efficiency of hydraulic methods,a novel chemical composite dust suppressant,called NCZ,was prepared in this study using calcium chloride(CaCl_(2)),magnesium chloride(MgCl_(2)),and nonionic surfactants using a thermal synthesis method.The water-retaining properties of NCZ powder and its solutions were characterized using the water absorption rate(WAR)and evaporation rate(ER),respectively,and the wetting abilities of the NCZ solutions on coal dust were tested using the initial contact angle(ICA)and sink rate(SR).The results indicate that the NCZ solutions have anti-evaporation effects,and the ER of the solution with a 20.0 wt%NCZ is reduced by 11.7%compared with that of clean water.Furthermore,NCZ solutions have remarkable enhancement effects on the wettability of coal dust.The ICA and SR of clean water and the NCZ solution at 20.0 wt%are 141.9°and 0 mg/s,and 29.3°and 1.46 mg/s,respectively.Finally,quantitative relationships between the solution surface tension and the ICA and IR were established using the least squares method.This study provides a new product for dust suppression in underground mines,which is significant for the optimum applied con-centration of dust suppressant in mining operations.

Application of foam technology for dust control in underground coal mine

In order to effectively control the dust in the underground coal mine,this study proposes and develops a new technology for dust control by foam,and briefly demonstrates the advantage of the foam technology for dust control,such as the good isolation performance,large contact area,high wetting ability,strong adhesion and so on.Besides,the details of the technology are introduced,including the foam agent,foam generator,and foam production process.Then the paper studies the relationship between the foaming agent concentration and liquid surface tension,and explains the principle of the foam generator.The technology is applied in heading face.The application results show that the foam has a remarkable effect on dust control in underground coal mines.

Using self-determination theory to identify organizational interventions to support coal mineworkers’ dust-reducing practices

Advancing the application of safety and health(S&H)technologies is likely to remain a value in the mining industry.However,any information that technologies generate must be translated from the organization to the workforce in a targeted way to result in sustainable change.Using a case study approach with continuous personal dust monitors(CPDMs),this paper argues for an organizational focus on technology integration.Although CPDMs provide mineworkers with near real-time feedback about their respirable coal dust exposure,they do not ensure that workers or the organization will continuously use the information to learn about and reduce exposure sources.This study used self-determination theory(SDT)to help three mines manage and communicate about information learned from the CPDM technology.Specifically,35 mineworkers participated in two mixed-method data collection efforts to discuss why they do or do not use CPDMs to engage in dust-reducing practices.Subsequently,the data was analyzed to better understand how organizations can improve the integration of technology through their management systems.Results indicate that using the CPDM to reduce sources of dust exposure is consistent with mineworkers’self-values to protect their health and not necessarily because of compliance to a manager or mine.

Study on the Evaporation Kinetics of Zinc and Lead in Zn-Pb-Bearing Dust Pellets Mixed with Coal Powder

The study on the evaporation kinetics of zinc and lead in the pellets made of ZnPbbearing dust mixed with carbon ,in nitrogen atmosphere at the temperature range between 1 100 and 1 300 , shows that the reduction temperature has a significant effect on the evaporation rates of zinc and lead and that both the particle size of coal powder and the extra carbon content have no effect on the evaporation rates . The obtained activation energies for the evaporation of zinc and lead are 7942 kJ/mol and 8874kJ/mol respectively. The evaporation rate of zinc is controlled by the reaction between zinc oxide and CO while that of lead is controlled by lead volatilization and the diffusion of gaseous lead through gas boundary layer covering the surface of liquid lead.

Preparation and performance analysis of a coking coal dust suppressant spray

Coking coal dust is extremely hydrophobic;therefore,combination with droplets in the air is difficult and dust suppression is challenging.Here,a dust suppressant spray for coking coal dust was studied in order to improve of the combination of droplets and coking coal dust.Based on monomer optimization and compounding analysis,two surfactant monomers,fatty alcohol ether sodium sulfate(AES)and sodium dodecyl benzene sulfonate(SDBS)were selected as the surfactant components of the dust suppressant.The surfactant monomers were combined with four inorganic salts and the reverse osmosis moisture absorption of each solution was determined.By combining the reverse osmosis moisture absorption values with the water retention experimental results,CaCl_(2)was identified as the optimal inorganic salt additive for the dust suppressant.Finally,the optimal concentration of each component was obtained using orthogonal experimental design i.e.,AES(0.03%),SDBS(0.05%),and CaCl_(2)(0.4%).The dust suppressant solution formulated using this method had a high moisture absorption capacity and excellent performance.

A comparative study of dust control practices in Chinese and Australian longwall coal mines

Mine dust is one of the main hazards in underground longwall mines worldwide.In order to solve the mine dust problem,a significant number of studies have been carried out regarding longwall mine dust control,both in China and Australia.This paper presents a comparative study of dust control practices in Chinese and Australian longwall mines,with particular references to statutory limits,dust monitoring methods and dust management practices,followed by a brief discussion on the research status of longwall mine dust control in both countries.The study shows that water infusion,face ventilation controls,water sprays,and deep and wet cutting in longwall shearer operations are commonly practiced in almost all underground longwall mines and that both Chinese and Australian longwall mine dust control practices have their own advantages and disadvantages.It is concluded that there is a need for further development and innovative design of more effective dust mitigation products or systems despite the development of various dust control technologies.Based on the examinations and discussions,the authors have made some recommendations for further research and development in dust control in longwall mines.It is hoped that this comparative study will provide beneficial guidance for scholars and engineers who are engaging in longwall mine dust control research and practice.

A field study of a roof bolter canopy air curtain(2nd generation)for respirable coal mine dust control

A 2nd generation roof bolter canopy air curtain(CAC)design was tested by National Institute for Occupational Safety and Health(NIOSH)at a Midwestern underground coal mine.During the study,the roof bolter never operated downwind of the continuous miner.Using a combination of personal Data Rams(pDR)and gravimetric samplers,the dust control efficiency of the roof bolter CAC was ascertained.Performance evaluation was determined using three methods:(1)comparing roof bolter operator concentrations underneath the CAC to roof bolter concentrations outside the CAC,(2)comparing roof bolter operator concentrations underneath the CAC to the concentrations at the rear of the bolter,and finally,(3)using the gravimetric data directly underneath the CAC to correct roof bolter operator concentrations underneath the CAC and comparing them to the concentrations at the rear of the bolter.Method 1 dust control efficiencies ranged from 53.9%to 60.4%.Method 2 efficiencies ranged from 150.5%to 52.2%,and Method 3 efficiencies ranged from 40.7%to 91%.Reasons for negative and low dust control efficiencies are provided in this paper and include:incorrect sampling locations,large distance between CAC and operator,and contamination of intake air from line curtain.Low dust concentrations encountered during the testing made it difficult to discern whether differences in concentrations were due to the CAC or due to variances inherent in experimental dust measurement.However,the analyses,especially the Method 3 analysis,show that the CAC can be an effective dust control device.