Study On The Key Technology Of Removing Static Electricity In High Speed Packaging Of Food Powder

Electrostatic phenomenon has attracted people’s attention for a long time.It has both advantages and disadvantages.Electrostatic phenomenon has been actively used in electronic photography,electrostatic spraying,electrostatic classification and other aspects.However,in the field of powder production,particle charging still brings harm and safety problems.The edible powder is easy to produce and accumulate static electricity because of its small particle size,high resistivity and good insulation.At the same time,because the edible powder needs to meet the requirements of safety and health,the electrostatic elimination method used by other industrial powders is difficult to apply.In order to effectively eliminate the charge of food powder,wheat flour was selected as experimental material.The main work and achievements are as follows:(1)The static electricity characteristics of wheat flour were obtained through the experiment of static electricity chute.The experimental results show that: when the chute materials are different,the sample’s starting power is different.When the chute materials are glass,stainless steel and aluminum alloy,the sample will generate positive charge and the static electricity will increase in turn;the static electricity generated by the sample is linearly related to the sliding distance,in which the chute materials are aluminum alloy and the sliding distance is more than 70 cm.When the water content of the powder increases from 11.2 % to 16.7 %,the starting power decreases from 13.88 nC/g to 8.41 nC/g,and the starting power decreases by 39.41 %.The half-life of the static electricity of the wheat powder is 781.3 min in the Faraday cylinder.(2)In order to reduce the electrostatic generation of powder,a method to change the induced potential of metal surface is proposed based on the existing contact electrification theory.Through the way of charging on the metal surface,the induced potential on the surface of the chute is changed,and the total potential difference between the two substances in contact friction is reduced.The experimental results show that the static electricity generated by the sample decreases exponentially with the charge of the chute in the first order.When the applied voltage is 3000 V,the starting power of the powder changes from 13.88 nC/g to 8.36 nC/g,and the starting power decreases by 39.77 %.When the water content of the sample is increased from 11 % to 16.7 %,and the external voltage of the chute is 1500 V,the electrostatic charge of the sample is 0,and the voltage continues to increase,and the reverse charging phenomenon occurs.(3)In order to reduce the static electricity generated by the powder in the conveying process,combining with the previous experimental results and the structure and working characteristics of the screw conveyor,the structure of the screw conveyor is improved,and two structural schemes of the screw shaft charging are proposed.(4)Based on the mechanism of gas-solid coupling,using FLUENT software,using turbulence model and discrete phase model(DPM)to simulate the dust bag dropping process of powder packaging under the condition of external wind field,the influence of ion wind speed on the dust particle capture rate of different particle size was analyzed.The simulation results show that when the wind speed is less than 0.4 m/s,the impact of the wind field on the capture rate of dust particles is small.When the wind speed is between 0.4 m/s and 0.6 m/s,the capture rate of dust particles with a diameter of 1 μm to 30 μm,can be significantly improved.It can be concluded that when the ion fan is added to the filling station,combined with the particle size of the packing powder and the appropriate wind speed,the static electricity of the powder can be eliminated and the efficiency of dust falling into the bag can be improved at the same time.In addition,the wind field will not aggravate the dust during the powder filling process.