| Combustible gas/dust/air mixture explosion occurred occasionally in the production,storage and transportation links of coal mining,paint spraying,plastic masterbatch granulation and crushing industries during recent years.However,the existing researches are not able to systematically reveal the explosibility of combustible gas/dust/air mixture,and mainly focus on the change rule of gas/coal dust explosion characteristic parameters,but pay less attention to the change law of other combustible gas/dust explosion systems and flame propagation process.In this paper,experiments are performed to study the explosibility of combustible gas/dust/air mixture in a rectangular pipe with internal dimensions of 800mm x 80mm x 80mm and a standard 20 L spherical dust explosion vessel under the same initial conditions(ignition energy,injection pressure,injection time and ignition delay time).Premixed gas-air mixtures were ejected to explosion chamber along with the dust.The hybrid mixtures were ignited under high turbulence conditions.The main conclusions are listed as follows:(1)The explosion characteristics and flame propagation of a pure dust were studied in a 20L blast vessel and a square pipe,respectively.The most dangerous concentrations of PA,PMMA and TPU dust measured in the experiment were 800g/m~3,700g/m~3 and 700g/m~3,respectively.The maximum explosion pressure was 0.76MPa,0.72MPa and 0.49MPa,respectively.The lower limit of explosion was 70g/m~3,60g/m~3 and 150g/m~3,respectively.(2)The effect of methane volume fraction on explosive propagation of methane/plastic dust/air mixture was studied.The results showed that the explosive process of PA and TPU dust was greatly affected by methane gas,and the flame propagation process was accelerated with the increase of methane volume fraction,while the methane gas had no significant influence on the transmission process of PMMA dust.In addition,methane gas with low volume fraction had little influence on the peak velocity of flame propagation during the explosion of PA and PMMA dust.However,when the methane volume fraction increased to 4%,the peak velocity of PA and PMMA dust increased significantly.However,the peak velocity of TPU dust during explosion is greatly affected by methane volume fraction,and the peak velocity increases with the increase of methane volume fraction.(3)It is found that the addition of methane gas can significantly improve the explosive sensitivity of dust,and the lower explosive limit of dust decreases with the increase of methane volume fraction.The addition of methane gas can also enhance the explosive strength of plastic dust at low concentration of dust,and PA and PMMA dust have a particularly significant enhancement effect with the increase of methane gas volume fraction.However,under the respective concentration of the most dangerous dust,the addition of methane has little influence on the maximum pressure of the three kinds of dust,but the maximum pressure rising rate of PA and PMMA dust increases significantly with the increase of methane volume fraction,and the TPU dust still has little change.(4)The explosion characteristic parameters of combustible gas/dust/air mixture were studied experimentally.The results showed that the flame propagation process of PMMA dust was the fastest with the highest peak speed,followed by PA dust and TPU dust.However,according to the maximum pressure and the maximum pressure rise rate in the explosion process,the explosion effects of the three kinds of dust satisfy the following relationship:PA>PMMA>TPU.In addition,the change of dust particle size can change the flame propagation process and explosion characteristic parameters of the mixture explosion,and with the increase of particle size,the flame propagation process gradually slows down,and the peak velocity keeps decreasing,and the explosion intensity keeps decreasing. |
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