Study On Explosion Characteristics Of Tobacco Dust And Risk Assessments Of Production Environment

In recent years,dust explosion accidents occur frequently in industry and trade,especially in Zhongrong,Kunshan,in 2014,and Guangming New Area,Shenzhen,in2016,resulting in a large number of casualties and economic losses.Dust explosion not only brings disaster,but also sounds an alarm for safe production.Tobacco dust is combustible and explosive organic dust.A large number of tobacco dust will accompany the production process of cigarettes,and there are some potential safety hazards.In this paper,the explosion characteristics of tobacco dust under different particle size and concentration conditions were investigated.The dispersion characteristics of tobacco dust were investigated by using self-designed dust cloud evolution visualization device,and the standard rebound nozzle was optimized.Combining the characteristic parameters of tobacco dust explosion measured by experiments with the actual production environment of the cigarette factory,the dust explosion hazard in tobacco production process was analyzed comprehensively by using the principle and method of system safety evaluation,and the corresponding improvement suggestions were put forward for the occasions with potential hazards.The main conclusions and innovations of this paper are as follows:?1?Explosion intensity of tobacco dustThe maximum explosion pressure of tobacco dust can reach 8.376 bar,and The maximum explosion index K_stt is 90.7 bar·m/s.The degree of explosion is weak or medium.The explosion pressure generally decreases with the increase of the particle size of tobacco dust,but with the increase of the particle size of tobacco dust,the explosion pressure of large particle size dust is larger than that of small particle size dust.This is due to the agglomeration of small-sized tobacco dust,resulting in no obvious difference in particle size between the experimental samples.With the increase of concentration,the explosion pressure of tobacco dust increases first and then decreases.The optimum explosion concentration is 500 g/m³.?2?Dispersion of tobacco dust in 20 L cavityWhen the standard rebound nozzle is used to disperse tobacco dust,the dispersed dust presents symmetrical distribution left and right.With the increase of dust particle size,the time when the dust cloud evolves to the best uniformity in 20 L cavity is ahead of schedule,so the corresponding ignition delay time should also be ahead of schedule.The lower the dust concentration is,the easier it will be to gather on the inner wall of 20 L cavity,resulting in the lower actual dust concentration than the nominal concentration.With the increase of tobacco dust concentration,the amount of dust gathered on the wall will gradually decrease,the evolution speed of dust cloud will accelerates,the time of dust uniformity and settlement will advance,so the ignition delay time should be advanced.Aiming at the non-uniformity of dust in space after dispersed by rebound nozzle,the structure of the rebound nozzle was optimized and a bowl-shaped rebound nozzle was designed.The experimental results of explosion pressure and dust dispersion show that the optimized nozzle has better repeatability of explosion pressure experiment and dust dispersion effect.?3?Explosion sensitivity of tobacco dustThe minimum ignition temperature of tobacco dust cloud decreases first and then increases with the increase of dust concentration.There exists an optimum concentration value.The minimum ignition temperature of tobacco dust cloud is the smallest under this concentration value,and the optimum concentration of tobacco dust with different particle sizes is different.The influence of dispersion pressure on the minimum ignition temperature of tobacco dust cloud is complex.With the increase of dispersion pressure,the minimum ignition temperature of tobacco dust cloud decreased first and then increased.There is a most suitable dispersion pressure to achieve the best dispersion effect of dust clouds.In the experiment,the dispersion pressure of about 20 kPa is the best for 0.1 g tobacco dust sample.The stacking thickness has a great influence on the minimum ignition temperature of the dust layer of tobacco dust.With the increase of stacking thickness,the minimum ignition temperature of tobacco dust layer tends to decrease.However,when the thickness increases to a certain extent,the lowest ignition temperature of the dust layer decreases slowly.The agglomeration of small particle size dust and the small accumulation density of large particle size dust make the minimum ignition temperature of tobacco dust layer change little with the particle size effect.With the increase of particle size,the lower explosion limit concentration of tobacco dust increases gradually,and the minimum explosion limit concentration is 10-20 g/m³.Because the maximum ignition energy of the minimum ignition energy test device for dust cloud is 2000 mJ,the tobacco dust can not be ignited after changing the concentration and particle size several times.Therefore,the minimum ignition energy of tobacco dust is determined to be over 2000 mJ.?4?The explosion risk of tobacco processing sites was assessed.According to the assessment results,the explosion possibility and the severity of the explosion consequences of most workstations belong to the general level,but it is still necessary to keep the environment clean and ventilated to avoid the occurrence of explosive dangerous environment.A small number of jobs with potential safety hazards can be combined with corresponding rectification suggestions to improving the level of safety production.