| As an important energy to support the development of China's modernization,coal is a powerful guarantee to promote the sound and rapid development of China's urbanization.With the increase of coal demand,high-intensity coal mining leads to increasing dust production.Mine safety,employee health,and ecological environment are facing serious threats from dust.Spray is one of the most important technical measures for mine dust control.However,quantitative analysis of atomization characteristics and dust reduction performance of representative single/double fluid nozzles are still lacking,which restricts the development of theory and technology of spray dust reduction.Therefore,the atomization characteristics and dust reduction performance of pressure swirl nozzle and internal mixing gas-liquid nozzle were studied.The main work and results are as followsAnalyze basic atomization mechanism of spray and the basic principle of dust reduction.Spray dust reduction consists of three parts: one is the fluid flow state inside the nozzle;the other is the fragmentation atomization characteristic of the spray medium in the air;and the three is the action mechanism of the droplet and the dust.Generally speaking,for fixed structure single/dual fluid nozzle,the water / gas-liquid pressure is the most important factor to determine the flow field inside the nozzle.The higher the pressure is,the greater the fluid pulsation inside the nozzle is,and the faster the jet velocity at the nozzle outlet is.The faster the jet,the higher the relative velocity between the fluid and the ambient air,or between the fluid and the compressed air,the stronger the two-phase interaction,the more thorough the primary and secondary atomization,and the smaller the droplet size.In addition to the breakup of droplets,it also includes the collision and condensation between droplets.The result of collision depends on the relative velocity and diameter of droplets.The dust reduction efficiency is closely related to the properties of droplets and dust.The smaller the droplet,the quicker the speed and the larger the dust,the higher the dust reduction efficiency.Study the atomization characteristics of single fluid nozzles under low/medium/high pressure.For the 1.2mm pressure swirl nozzle,the water flow rate increases exponentially(0.5281)with the increase of water pressure.The spray interval of 25-60 cm is the droplet condensation zone,and the droplet size increases with the increase of spray distance.With the increase of water pressure,the droplet size of near spray field first decreases and then increases,and the atomization effect is better in the medium pressure group(3,4,5MPa).The larger the water pressure is,the slower the growth rate of droplet size is and the stronger the stability is.The droplet velocity decreases with the increase of spray distance,and increases with water pressure.Low pressure(1,2 MPa)has a great change in velocity,and the droplet almost reaches the maximum velocity of the nozzle under medium and high pressure(6,7 MPa).When the water pressure is higher,the speed decreases more slowly,which indicates that the speed stability is higher.Compared with the relative number of droplets under ideal conditions,the medium pressure group performs best and 5MPa is the best spray pressure.Droplet size distribution showed that when the spray distance is above 40 cm,the droplets above 150?m appear and the proportion increase gradually.Through the analysis of the relationship between droplet size and velocity,there is an approximate linear relationship between them,especially when the water pressure is low.In other words,the size and velocity of axis droplets have the same trend with the spray distance.Reveal the atomization characteristics of double fluid nozzles under different working conditions.The air and water flow rates of the internal mixing gas-liquid nozzle are respectively assisted and restrained by the air pressure,while the water pressure is on the contrary.The atomization angle increases(decreases)with the increase of water pressure(air pressure),which is due to the smaller mixing gas velocity,which leads to more sufficient expansion in the expansion section of gas-liquid mixing chamber.The droplet size increases gradually from the 25-60 cm spray zone.As the air pressure increases,the droplet size decreases,and the growth rate of the droplet size decreases with the spray distance,while the water pressure acts on the contrary.This shows that high gas-liquid ratio plays an important role in ensuring the atomization degree and stability.When air and water pressure increase the pressure of the mixing chamber,the droplet velocity is increased.According to the viscosity law,the gas in the mixing chamber should have a velocity gradient of "big in the center and small in the periphery",and the droplet velocity decreases rapidly from the center to the periphery.Therefore,the droplet size is "small in center and large in the periphery ".However,with the increase of spray distance,the amplitude of droplet size change decreases,and the size of 60 cm plane is basically unchanged.Study dust reduction performance of single/double fluid nozzle for fine dust(<15?m).The self-built tunnel is used to simulate the spray dust reduction experiment,and 1/3 coking coal is used as the dust source of experiment.With the increase of water pressure,the dust reduction efficiency of the pressure swirl nozzle increases.After comprehensive consideration,5MPa is the best spray pressure,and the fine dust reduction efficiency is 50.67%.When the internal mixing gas-liquid nozzle is at0.1MPa water pressure,the dust reduction efficiency decreases significantly with the increase of air pressure,which indicates that the spray dust reduction requires a certain amount of water flow rate.When the water pressure is 0.15 and 0.2 MPa,the dust reduction efficiency increases first and then decreases with the increase of air pressure.When the air pressure is 0.3 MPa,the dust reduction efficiency achieves 50.82% and50.48% respectively.Through comparison and analysis,the best pressure of internal mixing gas-liquid nozzle is 0.15 Mpa water pressure and 0.3MPa air pressure.The required water flow and air flow can be obtained from the underground water supply and air supply pipeline,and the water consumption is only 8% of the pressure swirl nozzle,which can reduce the mine construction cost,reduce the waste of water resources,optimize the working environment,and achieve efficient dust reduction. |
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