Deflagration characteristics of freely propagating flames in magnesium hydride dust clouds

The flame propagation processes of MgH_(2)dust clouds with four different particle sizes were recorded by a high-speed camera.The dynamic flame temperature distributions of MgH_(2)dust clouds were reconstructed by the two-color pyrometer technique,and the chemical composition of solid combustion residues were analyzed.The experimental results showed that the average flame propagation velocities of 23μm,40μm,60μm and 103μm MgH_(2)dust clouds in the stable propagation stage were 3.7 m/s,2.8 m/s,2.1 m/s and 0.9 m/s,respectively.The dust clouds with smaller particle sizes had faster flame propagation velocity and stronger oscillation intensity,and their flame temperature distributions were more even and the temperature gradients were smaller.The flame structures of MgH_(2)dust clouds were significantly affected by the particle sinking velocity,and the combustion processes were accompanied by micro-explosion of particles.The falling velocities of 23μm and 40μm MgH_(2)particles were 2.24 cm/s and 6.71 cm/s,respectively.While the falling velocities of 60μm and 103μm MgH_(2)particles were as high as 15.07 cm/s and 44.42 cm/s,respectively,leading to a more rapid downward development and irregular shape of the flame.Furthermore,the dehydrogenation reaction had a significant effect on the combustion performance of MgH_(2)dust.The combustion of H_(2)enhanced the ignition and combustion characteristics of MgH_(2)dust,resulting in a much higher explosion power than the pure Mg dust.The micro-structure characteristics and combustion residues composition analysis of MgH_(2)dust indicated that the combustion control mechanism of MgH_(2)dust flame was mainly the heterogeneous reaction,which was affected by the dehydrogenation reaction.

Active protection of work area against explosion of dust-gas mixture

Potentially explosive atmosphere can occur not only in the production systems of the food,energy,chemical and petrochemical industries but also in the production processes of the mining industry.Gases,vapours,mists and dusts arise can escape in an uncontrolled way during production,processing,transportation and storage of flammable substances.In combination with oxygen,they create explosive atmospheres that,if ignited,lead to an explosion causing catastrophic damage to peopled lives and property.To protect against the results of hazardous dust-gas mixtures explosions in a confined work space,where employees can stay,various control and protection mechanisms are used in the form of an active explosion-proof system.The article presents the results of tests on an active system for limiting the effects of ignition of gas and/or dust based on a highly efficient explosion suppression system-equipped with an ignition detection system,high-pressure fire extinguisher and a power supply and trigger system.Smokeless powder was used as the explosive charge and sodium bicarbonate as the suppressive material.Tests of the effectiveness of the active explosion suppression system were carried out on two devices:a small-size dry dust collector and a zone extinguishing system adapted for direct explosion suppression in closed working spaces.In both cases,the explosion suppression process took place through the action of extinguishing powder blown out of the fire extinguisher after membrane perforation by compressed combustion products.

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.

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.

Inhibition of different types of inert dust on aluminum powder explosion

Aluminum powder explosion accidents occurred frequently,but the mechanism of aluminum powder explosion is unclear.Therefore,the inhibitive effect of aluminum powder explosion plays a key role.To evaluate the inhibition capacity of different kinds of carbonates and phosphates:Na H2PO4,(NH4)2HPO4,NH4H2PO4,KHCO3 and Na HCO3 on aluminum deflagrations,a standard 20-L spherical chamber was used to determine the explosion severity,characterized by the maximum explosion pressure(Pmax).New parameters have been proposed:the minimum significant inert concentration(MSIC)and the minimum complete inert concentration(MCIC),which characterized the effect of inert.Experimental results showed that from the minimum significant inert concentration(MSIC)and the minimum complete inert concentration(MCIC),phosphate can have a significant inhibiting effect.40%Na H2PO4 can totally inert the aluminum explosion,and 50%(NH4)2HPO4or 50%NH4H2PO4 can also suppress the explosion.Through simulation,phosphate mainly acts via a chemical inhibition pathway,which inhibits the reaction of aluminum powder and oxygen by catalyzing the recombination of H atoms and O atoms.Carbonate performs inhibition in chemically,producing CO2,diluting the oxygen around the aluminum powder.Studies indicated that the explosion pressure of the mixture decreases as the concentration of inert dust increases.However,when the concentration of carbonates was low,SEEP(suppressant enhanced explosion parameter)phenomenon was found.This research work has a potential industrial application in high hazard aluminum working condition,which can help decrease the explosion pressure and reduce the accident loss.

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.

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.

The risk evaluation of mine coal-dust explosion based on BP neural network

Introduced the theory of three types of hazardous sources, and it recognized and analysed such three types of hazardous sources as the factor of inherent hazardous source, factor of inducing hazardous source and factor of men, which affect the safety and reliability of coal-dust explosion risk system and then builds up the risk factor indices of coal-dust explosion according to analysis of conditions inducing the coal-dust explosion. It fixes the risk degree of coal-dust explosion risk system by analyzing loss probability and loss scope of risk system and by means of the probabilistic hazard evaluation method and risk matrix method, etc.. According to the feature of strong capability of nonlinear approximation of BP neural network, the paper designed the structure of BP neural network for the risk evaluation of the mine coal-dust explosion with BP neural network. And the weight of the network was finally determined by training the given samples so that the risk degree of samples to be measured could be exactly evaluated and the risk of mine coal-dust explosion could be alarmed in good time.

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.

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.

Review of preventive and constructive measures for coal mine explosions:An Indian perspective

Firedamp and coal dust explosion constitute a lion’s share in mine accidents in a global mining scenario.This paper reports a list of mine explosion disasters since last two decades,a critical review of the different prevention and constructive measures,and its recent development to avoid firedamp and coal dust explosion.Preventive legislation in core coal-producing countries,viz.China,USA,Australia,South Africa,and India related to firedamp and coal dust explosion are critically analysed.Accidents occurred due to explosion after Nationalisation of Coal Mines(1973)in India are listed.Prevention and constructive measures adopted in India are critically analysed with respect to the global mining scenario.Measures like methane credit concept,classification of mines/seams with respect to explosion risk zone,deflagration index;installation of automatic fire warning devices,canopy air curtain technology,explosion-prevention measures,such as fire-retardant materials,inhibitors,extinguishing agent,dust suppressor,and active explosion barrier are discussed in detail to avoid explosion and thereby adhering to zero accident policy due to coal mine explosion.

CFD modeling to study the effect of particle size on dispersion in 20l explosion chamber: An overview

Mine disasters occur predominantly due to methane or coal dust explosion or a combination of both.Among the top ten worst coal mine disasters in India, nine are due to coal dust explosion. The current paper describes a general overview of the parameters causing dispersion leading to coal dust explosion,and computational fluid dynamics(CFD) simulation study to observe the effects of particle size on dispersion in Indian coal mines. Turbulent kinetic energy(TKE) and velocity vector path of dust-air mixture and dust-free air were simulated to understand their effects on coal dust dispersion. The TKE contours and velocity vector paths for dust-free air were uniform and symmetrical due to resistance-free path available. The TKE contours and velocity vector paths for dust-air mixture shows the asymmetrical distribution of contours, due to entrainment of air with dust particles. Vortices were observed in velocity vector paths which gradually diminish on increment of time sequence. These vortices are dead centres where velocity and coal dust particles concentration are both zero.

Deflagration-to-detonation transition process for spherical aluminum dust/epoxypropane mist/air mixtures in a large-scale experimental tube

The deflagration-to-detonation transitions (DDTs) for clouds of spherical aluminum dust (SAD) mixed with air or epoxypropane mist (EPM) and air were investigated in a 29.6-m-long experimental tube of 199 mm in diameter. The clouds formed through the injection of SAD and SAD/liquid epoxypropane samples into the experimental tube. Explosions of the SAD/air mixture were initiated using a 7-m-long EPM/air cloud explosion ignited by a 40-J electric spark. Explosions in SAD/EPM/air clouds were initiated using a 1.2-m EPM/air cloud explosion ignited by a 40-J electric spark initiated using a 40-J electric spark. Self-sustained detonation waves formed in SAD/EPM/air mixtures instead of in SAD/air mixtures. The stages and characteristics of the DDT process in SAD/air and SAD/EPM/air mixtures were studied and analyzed. Self-sustained detonation was evident from the existence of a transverse wave and a cellular structure. Moreover, a retonation wave formed during the DDT process in SAD/EPM/air clouds.