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.

Hazard evaluation of ignition sensitivity and explosion severity for three typical MH_(2) (M=Mg,Ti,Zr)of energetic materials

MgH_(2),TiH_(2),and ZrH_(2) are three typical metal hydrides that have been gradually applied to composite explosives and propellants as additives in recent years.To evaluate ignition sensitivity and explosion severity,the Hartmann device and spherical pressure vessel were used to test ignition energy and explosion pressure,respectively.The results showed that the ignition sensitivity of ZrH_(2),TiH_(2) and MgH_(2) gradually increased.When the concentration of MgH_(2) is 83.0 g/m^(3) in Hartmann device,the ignition energy attained a minimum of 10.0 mJ.The explosion pressure of MgH_(2) were 1.44 times and 1.76 times that of TiH_(2) and ZrH_(2),respectively,and the explosion pressure rising rate were 3.97 times and 9.96 times that of TiH_(2) and ZrH_(2),respectively,through the spherical pressure vessel.It indicated that the reaction reactivity and reaction rate of MgH_(2) were higher than that of TiH_(2) and ZrH_(2).In addition,to conduct in edepth theoretical analysis of ignition sensitivity and explosion severity,gas production and combustion heat per unit mass of ZrH_(2),TiH_(2) and MgH_(2) were tested by mercury manometer and oxygen bomb calorimetry.The experimental results revealed that MgH_(2) had a relatively high gas production per unit mass(5.15 mL/g),while TiH_(2) and ZrH_(2) both had a gas production of less than 2.0 mL/g.Their thermal stability gradually increased,leading to a gradual increase in ignition energy.Furthermore,compared with theoretical combustion heat,the combustion ratio of MgH_(2),TiH_(2) and ZrH_(2) was more than 96.0%,with combustion heat value of 29.96,20.94 and 12.22 MJ/kg,respectively,which was consistent with the explosion pressure and explosion severity test results.

Research on the explosion characteristics of chlorine dioxide gas

The explosion characteristics of chlorine dioxide gas have been studied for the first time in a cylindrical exploder with a shell capacity of 201. The experimental results have indicated that the lower concentration limit for the explosive decomposition of chlorine dioxide gas is 9.5% （[ClO2]/[air]）, whereas there is no corresponding upper concentration limit. The maximum pressure of explosion relative to the initial pressure was measured as 0.024 MPa at 10% ClO2 and 0.641 MPa at 90% ClO2. The induction time （the time from the moment of sparking to explosion） at 10% ClO2 was 2195 ms, but at 90% ClO2 the induction time was just 8 ms. The explosion reaction mechanism of ClO2 is of a degenerate chain-branching type involving the formation of a stable intermediate （Cl2O3）, from which the chain branching occurs.

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.

Computational fluid dynamics simulation on the longwall gob breathing

In longwall mines, atmospheric pressure fluctuations can disturb the pressure balance between the gob and the ventilated working area, resulting in a phenomenon known as ‘‘gob breathing". Gob breathing triggers gas flows across the gob and the working areas and may result in a condition where an oxygen deficient mixture or a methane accumulation in the gob flows into the face area. Computational Fluid Dynamics(CFDs) modeling was carried out to analyze this phenomenon and its impact on the development of an explosive mixture in a bleeder-ventilated panel scheme. Simulation results indicate that the outgassing and ingassing across the gob and the formation of Explosive Gas Zones(EGZs) are directly affected by atmospheric pressure changes. In the location where methane zones interface with mine air, EGZ fringes may form along the face and in the bleeder entries. These findings help assess the methane ignition and explosion risks associated with fluctuating atmospheric pressures.

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 experimental of methane-air flame propagation in the tube with quadrate cross section

The flame propagation of methane-air mixture with various methane concen-trations was experimentally investigated at venting flame acceleration tube with quad-rate cross section under different obstacles presented. The flame shape and propaga-tion speed was observed by high-speed color video camera. The explosion pressure was determined by piezoelectricity pressure transducers. The results are: The flame propagates in the shape of a hemisphere before the flame reaches the first baffle and flame propagation speed is not more than 15 m/s. When the flame propagates across the baffle, the flame begins to accelerate due to turbulence induced by obstacle. Blockage ratio has relatively greater effect on the flame propagation speed than re-peated baffle number does. The flame propagation speed and the pressure at different location along the tube are maximum when methane-air mixture is near the chemical stoichoimetric ratio. The pressure increases with the distance from ignition end at first and the maximum pressure was obtained at the middle of tube, but the pressure de-creases and again increases at venting end.

In-situ TiC_P/Al Composites Prepared by TE/QP Method

An in-situ TiCp/Al composite was prepared by a thermal explosion/quick pressure method （TE/QP）. The effect of Al content on the reaction temperature as well as the reaction rate has been studied. Phase constituents and the microstructure of the composites and the particle size of the reinforcement were analysed using X-ray diffraction （XRD） and scanning electron microscopy （SEM）. The results have shown that TiCp/Al composite with 40～70 vol. pct TiC particle reinforcement and high relative density can be directly obtained by TE/QP. TiC is the only reaction product when Al content in Al-Ti-C system is no more than 60 vol. pct, but Al3Ti phase will also form when Al content is more than 60 vol. pct. Increasing Al content prolongs the initial reaction time, reduces the highest reaction temperature and the reaction rate, and decreases the size of TiC particles. In addition, the microstructure of TiCp/Al composite and the structure of interface between TiCp and Al are studied using SEM and transmission electron microscopy （TEM）. The results show that the in-situ synthesized TiC particle has fcc cubic structure. The orientation between TiC particles and Al matrix can be described as （220）Al//（022）TiC and [112]Al//[011]TiC. Results of the mechanical property tests reveal that the ultimate strength （σ） and modulus （E） are 687 MPa and 142 GPa respectively when the Al content is 40 vol. pct. On contrary, 6 elongation increases by 3.2% with increasing Al content.

Experimental study and theoretical analysis on the effect of electric field on gas explosion and its propagation

The effect of the electric field with different intensity on explosion wave pressure and flame propagation velocity of gas explosion was experimentally studied, and the effect of electric field on gas explosion and its propagation was theoretically analyzed from heat transportation, mass transportation, and reaction process of gas explosion. The results show that the electric field can affect gas explosion by enhancing explosion intensity and explosion pressure, thus increasing flame velocity. The electric field can offer energy to the gas explosion reaction; the effect of the electric field on gas explosion increases with the increase of electric field intensity. The electric field can increase mass transfer action, heat transfer action, convection effects, diffusion coefficient, and the reaction system entropy, which make the turbulence of gas explosion in electric field increase; therefore, the electric field can improve flame combustion velocity and flame propagation velocity, release more energy, increase shock wave energy, and then promote the gas explosion and its propagation.

Inhibiting effect of Al(OH)_3 and Mg(OH)_2 dust on the explosions of methane-air mixtures in closed vessel

The inhibiting effect of AI（OH）3 and Mg（OH）2 dust on explosion of methane-air mixtures was investigated by means of explosion parameter tests in a 20-liter closed vessel. The influences of varying methane concentration and dust concentration on explosion parameters were characterized based on the experimental data to determine the maximum explosion pressure, maximum rate of pressure rise, lower explosion limits and upper explosion limits. The inhibiting mechanisms of these kinds of dust were analyzed as well. The investigations indicate that AI（OH）3 and Mg（OH）2 dust can be used as inhibitors to prevent meth- ane explosion, however, their inhibiting effects are less than those of inert gas such as N2 and CO2 in that their dust can weaken the methane explosion but cannot totally eliminate it. The tests show that all of the explosion parameters with dust additives are strongly dependent on methane/air ratio and dust concentration, and AI（OH）3 dust has better performance than Mg（OH）2 dust in inhibiting methane explosion. The average percentage decreases of maximum explosion pressure and maximum rate of pressure rise with AI（OH）3 dust are 11.08% and 66.15%, respectively. Experiments also showed that there is a special phe- nomenon when methane explosion is inhibited by AI（OH）3 and Mg（OH）2 dust, in which is that during the process of explosion the maximum explosion pressure value first decreases then increases as dust concentration increases. The best dust concentrations to inhibit the explosion are 250 g/m3 with methane/air ratio at 9.5%, and 200 g/m3 with methane/air ratio at 7%. It is suggested that water vapor produced by the thermal decomposition of metal hydroxides makes the particles of descending dust combine, resulting in a decrease of the real dust concentration in the vessel. Water vapor also is the major cause of another phenomenon that the LEL curve and the UEL curve never meet with the increase of gas concentration.

Simulation of blast induced crater in jointed rock mass by discontinuous deformation analysis method

Rock blasting is a dynamic process accom panied with the propagations of shock waves and the dispersion of the explosion gas.This paper adopts the discontinuous deformation analysis(DDA)method to simulate the rock blasting process.A dynamic parameter adjustment and the non-reflecting boundary condition are implemented in the DDA method.The sub-block DDA method to simulate fracture problems is used.The blasting process in jointed rock mass is simulated by application of the explosion gas pressure on the expanding borehole walls and induced connected fracture surfaces around the boreholes.The blast craters with different overburdens are derived.The whole process including the explosion gas dispersion,borehole expansion,rock mass failure and cast,and the formation of the final blasting piles in rock blasting are well reproduced numerically.Parametric study for different overburdens is carried out,and the results are analyzed and discussed.

Experimental investigation of flame propagation characteristics in the in-line crimped-ribbon flame arrester

An experimental system that consisted of gas mixing equipment, a sensor detection system, a data acquisition device, and an electric spark ignition device was set up to investigate fuel/air deflagration flame propagation and quenching processes through a crimped-ribbon flame arrester in an enclosed horizontal pipe. Deflagration suppression experiments showed that when the concentration of flammable gas was close to the stoichiometric ratio, the evolution processes of explosion pressure for the propane-air and ethylene-air premixed gases in the pipe diameter （DN32-DN400） were similar and could be divided into four stages： isobaric combustion, slow pressure rise, quick pressure rise, and pressure oscillation. However, the explosion duration of the hydrogen-air premixed gas was relatively short, and the peak explosion pressure was high. The pressure rose quickly after the isobaric combustion stage. Therefore, the process can be divided into three stages in the pipe diameter （DN15-DN150）. Deflagration speed results indicated that the propane-air flame speed initially increased and eventually decreased along with increases in the pipe diameter （DN32-DN400）; however, the ethylene-air flame speed gradually increased with the increase of the pipe diameter （DNS0-DN400）. No notable pattern of change in the hydrogen-air flame speed was observed in the pipe diameter （DN15-DN150）. The maximum propane-air flame speed occurred at 5% concentration. The maximum flame speed for ethylene-air and hydrogen-air happened when the mixture was close to stoichiometric ratio. Under the conditions of the same size of experimental tube configuration and the same ignition distance but different pipe lengths, or the same pipe length but different ignition distances, experimental results showed that the flame arrester successfully stopped the flames at high flame speed and low explosion pressure, but failed at low flame speed and high explosion pressure.