Study On Explosion And Venting Characteristics Of Toner

Accidents have shown that toner as an important component of waste selenium drum in printers is widely used and there is a risk of explosion.At present,there are few studies on the safety protection technology of toner production by scholars,and there is a lack of experimental support and verification.Based on it,this paper uses a 20 L sphere as the basic experimental device to carry out the research on the explosion characteristics and the maximum reduced pressure and venting flame characteristics.The specific contents are as follows:(1)The explosion characteristic parameters of toner were studied in a standard 20 L chamber.The results show that with the increase of toner concentration,the maximum explosion pressure and the maximum rate of explosion rise increased first and then decreased.The overpressure and the rate of explosion pressure reached the maximum at the concentration of 700 g/m3,indicating that the maximum explosion overpressure is 0.694 MPa and the maximum rate of explosion overpressure is 87.2 MPa/s,respectively.According to the explosion risk analysis,the explosion intensity of toner is St2 and highly explosive.(2)Explosion reactor is a standard 20 L chamber and the venting port is on the side of the20 L chamber.The vent diameter Dv is same with the diameter of the plate orifice,varying between 40 mm,60 mm and 80 mm.The results show that the maximum explosion pressure of toner in the container can be increased by increasing the static opening pressure of the discharge film under three discharge apertures,and the maximum explosion pressure increases with the increase of the static activation overpressure.When the static activation overpressures of 40 mm,60 mm and 80 mm discharge apertures reach 0.68 MPa,0.64 MPa and 0.58 MPa respectively,the points on the discharge curve are basically consistent with the equilibrium discharge line,and basically reach the equilibrium discharge state.In addition,compared with 40 mm,60 mm,80 mm discharge caliber under the change curve can be found that if the static opening pressure value of the device is the same,the larger the discharge caliber,the smaller the maximum explosion pressure;Secondly,compared with small aperture,increasing the static opening pressure under large discharge aperture will make the device reach the equilibrium discharge state faster.(3)The high-speed photography system is used to record the venting flame propagation process.The results show that reducing the static opening pressure increasing the toner dust concentration and increasing the venting diameter can prolong the duration of the external flame.Two types of venting features under different parameters were founded according to the experimental results: single flame and multiple flame.Under the higher dust concentration,the lower static opening pressure and the larger venting diameter,it is prone to multiple flames.(4)According to the prediction results of the dust discharge design empirical formula given in the current high recognition standard NFPA 68 and standard EN 14491,whether in40 mm discharge aperture,or 60 mm and 80 mm venting diameter,the standard NFPA 68 has higher accuracy and better stability than the prediction results of standard EN 14491.It is suggested that the discharge design method in standard NFPA 68 is used as the basis for the toner dust venting design.(5)In view of the shortcomings of secondary explosion which is easy to cause dust deposits in the process of conventional explosion discharge.The DN 80 cylindrical removable flameless discharge device formed by stainless steel material is designed and manufactured independently.The size is 230 mm × 300 mm,and the opening pressure of the discharge element is 0.02 MPa.The 60 mesh and 80 mesh porous metal wire mesh are selected as the fire extinguishing elements to carry out the flameless discharge experiment.The results show that the designed flameless discharge device can effectively quench the external venting flame.When the layer number of the wire mesh in the flameless discharge device increases,the flame quenching effect will be significantly improved,but the hindrance of the wire mesh in the flameless discharge device to the venting pressure will also be further strengthened,resulting in further improvement of the overpressure inside the chamber.When the flameless discharge effect is achieved,the required 60 mesh and 80 mesh layers are 10 layers and 8layers,respectively.The maximum explosion pressure inside the container is 0.241 MPa and0.191 MPa,respectively.Compared with the conventional discharge,the maximum explosion pressure increases are 0.131 MPa and 0.061 MPa respectively.(6)The fitting of the discharge efficiency formula of the flameless discharge device given in the dust discharge standards of EN 14797-2006,EN 16009-2011,EN 14491-2012 and GB/T 15605-2008 is used as a reference evaluation.The results show that due to the blocking effect of the wire mesh in the flameless discharge device,the discharge efficiency is related to the number of wire mesh layers and mesh.When the layer number increases or mesh decreases,the venting efficiency decreases.Obviously,when the same quenching effect is achieved,there is an optimal value between the layer number and the mesh number,so that the discharge efficiency of the device reaches the highest.