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.

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.

Experimental research on flame propagation characteristics of coal dust combustion

The presence of coal dust explosions in coal mining are significant safety hazards.This study mainly explores the flame propagation of coal dust combustion so as to provide a theoretical basis for the prevention and control of coal dust explosions.In the experiment,a dust cloud ignition device was used to experimentally explore the influence of the coal dust concentration on the flame propagation of the coal dust,and high-speed photography was used to record the coal dust flame propagation process.The results show that the flame propagates vertically along the wall of the vertical glass tube,emits a bright yellow light during the propagation process,and forms a mushroom cloud-shaped flame at the upper end of the vertical glass tube.When the concentration of coal dust is 250 g/m^(3),its burning time is much less than those of 500 g/m^(3)and 750 g/m^(3).When the concentrations are 250 g/m^(3),500 g/m^(3)and 750 g/m^(3),respectively,the corresponding maximum propagation velocities of the flame front reach 1.51 m/s,2.00 m/s and 1.61 m/s at 100 ms,353 ms and 310 ms,respectively.The time for the flame front velocity to reach the maximum and the maximum velocity of flame propagation first increase and then decrease with the rising of concentration.

Chemistry and particle size distribution of respirable coal dust in underground mines in Central Eastern Europe

Despite international efforts to limit worker exposure to coal dust,it continues to impact the health of thousands of miners across Europe.Airborne coal dust has been studied to improve risk models and its control to protect workers.Particle size distribution analyses shows that using spraying systems to suppress airborne dusts can reduce particulate matter concentrations and that coals with higher ash yields produce finer dust.There are marked chemical differences between parent coals and relatively coarse deposited dusts(up to _(500)μm,DD_(500)).Enrichments in Ca,K,Ba,Se,Pb,Cr,Mo,Ni and especially As,Sn,Cu,Zn and Sb in the finest respirable dust fractions could originate from:(i)mechanical machinery wear;(ii)variations in coal mineralogy;(iii)coal fly ash used in shotcrete,and carbonates used to reduce the risk of explosions.Unusual enrichments in Ca in mine dusts are attributed to the use of such concrete,and elevated K to raised levels of phyllosilicate mineral matter.Sulphur concentrations are higher in the parent coal than in the DD_(500),probably due to relatively lower levels of organic matter.Mass concentrations of all elements observed in this study remained below occupational exposure limits.

Mechanism research of gas and coal dust explosion

Combined with the experimental results from the large tunnel of the ChongqingResearch Institute,the mechanism of gas and coal dust explosion was studied.Someconcepts about gas and coal dust explosion were introduced such as the form conditionand influential factors.Gas and coal dust explosion propagation was researched and thelifting process of coal dust was simulated.When an explosion occurred due to great mixtureof gas and air,the maximum explosion pressure appeared in the neighborhood of theexplosion source point.Before it propagated to the tunnel of the deposited coal dust,themaximum explosion pressure appeared to be in declining trend.Part of the energy waslost in the process of raising the deposited coal dust through a shock wave,so the maximumexplosion pressure was smallest on the foreside of the deposited coal dust sector.On the deposited coal dust sector,the explosion pressure rapidly increased and droppedoff after achieving the largest peak value.Because of coal dust participation in the explosion,the flame velocity rose rapidly on the deposited coal dust and achieved a basic stablevalue;coal dust was ignited to explode by initial laminar flame,and the laminar flametransformed into turbulent flame.The turbulence transformed the flame fold into a funnelshape and the shock wave interacted with the flame,so the combustion rate rose and thepressure wave was further enhanced.The regeneration mechanism between the flamecombustion rate and the aerodynamic flowing structure achieved the final critical state forforming the detonation.

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.

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.

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.

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.

Research on numerical emulator of mine methane and coal dust explosion

The mathematical physics model of mine methane and coal dust explosion propagation was established in the research,by using continuous phase,combustion,par- ticulate equations of mathematical physics.Based upon the data from mine methane drainage roadway explosion,and mine methane and coal dust explosion propagation ex- perimental studies,the numerical emulator system of mine methane and coal dust explo- sion software was developed by using prevalent flow simulation platform,which can be used to simulate the explosion accidents process effectively.In addition,the system can also be used to determine whether coal dust involved in the explosion,and to simulate accurately the transition from deflagration to detonation in methane explosion,propagation velocity of explosion shock,attenuation pattern,and affected area of explosion.

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.

Exploration on molecular dynamics simulation methods of microscopic wetting process for coal dust

Wet dust removal is one of the main technical measures in coal dust control,and coal dust wetting is the key factor to determine the effect of wet dust removal.In order to explore the micro-wetting process of coal dust,this paper uses molecular dynamics simulation to study the micro-wetting process of coal dust in different simulation conditions.The molecular dynamics simulation was carried out under different ensemble,thermodynamic states as well as relaxation pretreatment methods,then the H_(2)O molecular layer and coal dust molecular layer in each simulation were quantitatively analyzed by relative concentration.The research results show that a method for establishing molecular model of lignite is proposed and the 2D periodic surface structure is more reasonable.The surface system of coal-H_(2)O molecule is established by NVT aeration method,where the simulation result is close to the actual coal dust wetting process.The simulation effect of medium and large coal dust-H_(2)O molecular system is better than that of small coal dust-H_(2)O molecular system.This study provides a new solution for changing the empirical method of molecular dynamics simulation of coal system wetting and oversimplification of coal system.

Experiment study on the propagation laws of gas and coal dust explosion in coal mine

The experiment of gas and coal dust explosion propagation in a single lanewaywas carried out in a large experimental roadway that is nearly the same with actual environmentand geometry conditions.In the experiment,the time when the gas and coal dustexplosion flame reaches test points has a logarithmic function relation with the test pointdistances.The explosion flame propagation velocity rises rapidly in the foreside of the coaldust segment and comes down after that.The length of the flame area is about 2 timesthat of the original coal dust accumulation area.Shock wave pressure comes down to therock bottom in the coal dust segment,then reaches the maximum peak rapidly and comesdown.The theoretical basis of the research and assemble of across or explosion is suppliedby the experiment conclusion.Compared with gas explosion,the force and destructiondegree of gas and coal dust explosion is much larger.

Controlling the coal dust at transshipment point: A study of the foam-sol foaming device

In order to effectively control the dust at the transshipment point with foam-sol, this paper attempted to study the characteristics of dust diffusion at transshipment point and the foam-sol foaming device with diffusion outlet was also designed in this paper. To study the diffusion rules of coal dust, fluent discrete phase model was utilized in the numerical simulation, as the coal dust was thrown down at a horizontal velocity of 2.5 m/s. A foam-sol foaming device was designed, through which foaming agent could be automatically sucked into the Venturi by the negative pressure. The automatic controller was also equipped,which could transform the energy of the compressed air into the constant pressure difference so that the gelling agent could be qualitatively added into the gel container. The diffusion outlet that could spray out foam-sol in a continuous, conical and 3D manner was also designed. Moreover, this paper also carried out the contrast experiments on dust removal efficiency among water, aqueous foam and foam-sol. The results clearly show that the symmetrical whirlpools appeared below the inlet where the largest whirlpool diameter was 0.52 m, and the horizontal distance from swirl range to the inlet was approximately0.69 m. By using the self-designed foaming device, the foaming was multiplied by 30 times and the volume ratio with water and foaming agent reached 95%:5%. In this context, the gas pressure was controlled at 0.3 MPa, with gas flow at 15 m3/h and water flow at 0.5 m3/h, with water pressure controlled between0.34 and 0.36 MPa. The foam-sol has the highest dust removal efficiency than other agents.

Effect of particle size of coal dust on explosion pressure

The effect of the particle size of coal dust on explosion pressure and the rising rate of explosion pressure is studied. Three coal dusts from Lingan Coal Mine in Canada and Datong Coal Mine in China are selected to test. The influence of particle size on the maximum explosion pressure P max and maximum pressure rising rate (d p /d t ) max of each coal dust was tested experimentally. The results indicate that with the decrease of particle size of coal dusts, explosion pressure increases on condition of the same concentration. If the concentration of coal dust is different, the maximum explosion pressure appears at the concentration of 500 g/m^3. The smaller the particle size of coal dusts, the larger the rising rate of explosion pressure of coal dust. When the concentration of coal dust is 500 g/m^3, the rising rate of explosion pressure of each coal dust is the maximum.

Suppression effect of solid inertants on coal dust explosion

The effect of solid inertants like rock dust on explosion suppression was experimentally tested.By adding solid inertants with different concentrations into three kinds of coal dust,the maximum explosion pressure P max and the rate of explosion pressure rise(d p/d t)max were acquired.Based on this,the suppression effect of rock dust on coal dust explosion was analyzed.The experimental and analytical results show that there are two major factors that play an important role in explosion suppression:composition of solid inertant and particle size of solid inertant.The higher the concentration of solid inertant and the smaller the particle size of solid inertant,the better the suppression effect.In addition,the smaller the particle size of coal dust,the larger the amount of rock dust.

Study on coal dust wettability measurement using cold briquetting technique

Quantitatively-measuring of coal dust wettability is essential for the R/D of chemical coal dust suppressants in the field of dust control with wetting-agent-added water. Analysed the causes which in present lab testing of coal dust wettability cause out-comes＇ low repeat rate and poor consistency with coal dust suppression practices in fields, and investigated the influence of different briquetting pressure （from 0 to 6.5×10^8 Pa） on the wet behavior of coal dust as a new way to evaluate quantitatively coal dust wettability. The study shows that there is a fairly high coincidence between the coal dust wettability data measured by briquetting technique and the results gained from the lab dust suppression tests using an apparatus MCYZ.

Improved Algorithm of Pattern Classification and Recognition Applied in a Coal Dust Sensor

To resolve the conflicting requirements of measurement precision and real-time performance speed,an im-proved algorithm for pattern classification and recognition was developed. The angular distribution of diffracted light varies with particle size. These patterns could be classified into groups with an innovative classification based upon ref-erence dust samples. After such classification patterns could be recognized easily and rapidly by minimizing the vari-ance between the reference pattern and dust sample eigenvectors. Simulation showed that the maximum recognition speed improves 20 fold. This enables the use of a single-chip,real-time inversion algorithm. An increased number of reference patterns reduced the errors in total and respiring coal dust measurements. Experiments in coal mine testify that the accuracy of sensor achieves 95%. Results indicate the improved algorithm enhances the precision and real-time ca-pability of the coal dust sensor effectively.

Coal Dust Explosions in a Large Scale Experimental Tube

Coal dust explosion conducted in a 200 mm diameter, 29.6 m long tube is presented in this paper. 40 dust dispersion system sets were used to disperse coal dust into the tube. A constant temperature hot wire anemometer was used to measure the gas velocity during the dispersion process. Kistler piezoelectric pressure sensors were used to measure the propagation of the pressure wave during the explosion process. The overpres- sure of coal dust explosion in the tube was 70 kPa and the velocity of pressure wave propagating along the tube was 370 m/s approximately. The minimum concentration for dust explosion propagating along the tube was 100 g/m3. The effects of two kinds of suppressing agents used to suppress the coal dust explosion were studled.