Process And Design And Research Of Key Parts Of Closed Nitrogen Pneumatic Conveying System

In the new energy automobile industry,powder transportation,loading and unloading are often accompanied by a large amount of dust.The closed pneumatic conveying technology is a clean and recyclable powder transportation method,which is safe,environmentally friendly,highly automated,and free of dust.Advantages such as pollution,dry transportation,Reduced the labor intensity of the staff and ensured the personal health and safety of the staff.As the powder material of new energy power batteries,lithium iron phosphate is the most critical for controlling the moisture content of the powder when it is transported to the packaging.It is required that the moisture content does not exceed 600 ppm.This thesis aims at the characteristics of easy absorption of moisture and oxidation during the transportation of lithium iron phosphate.Based on the analysis of powder characteristics,calculation of conveying gas velocity,conveying pressure,conveying pipe diameter and other parameters,the equipment selection of lithium iron phosphate closed nitrogen pneumatic conveying system was carried out.An industrial transportation test was conducted to investigate the changes in water content and output of lithium iron phosphate powder at different return air speeds(10~60m/s).At the same time,in order to solve the problems of material blocking and powder emergence in industrial tests,The air flow field and particle trajectory of the key part of the closed nitrogen pneumatic conveying system,the return air venturi,were studied.Then,in response to the problem that the positive pressure in the return air Venturi in the conveying system affects the powder transportation,In this paper,a new type of negative pressure ejection feeding device,ejector,is designed for optimization.The designed ejector was numerically calculated using CFD,and its internal velocity field,pressure field,and particle trajectory were analyzed and verified.(1)In the process of industrial closed nitrogen pneumatic conveying of lithium iron phosphate powder,due to the influence of return air venturi,the output of powder decreases as the return air speed increases.When the return air speed is 8m/s,due to the lack of air volume,the materials cannot be transported through the star feeder into the conveying pipeline,which eventually causes the system to block materials;When the return air speed is60m/s,the air volume at the inlet position of the star-shaped feeding valve is too large,powdering occurs,and the entire conveying system cannot work normally.When the return air speed is about 28m/s,the system air volume is 12m~3/min,and the conveying output is the highest.At different return air speeds(10~60m/s),the closed nitrogen gas conveying combined with the new process of dehumidification packaging room,the moisture content of the lithium iron phosphate powder delivered is less than 600 ppm,which meets the industrial requirements.(2)CFD simulation results:With the increase of the return air speed(10~60m/s),the pressure at the inlet of Venturi gradually increases and is always in a positive pressure state,the pressure is about 1000Pa,and the inlet vortex becomes more and more obvious as the wind speed increases.As a result,the particle trajectory is chaotic,and the particle escape rate is getting smaller and smaller,which leads to the phenomenon of clogging and powdering of materials with large return air speed in industrial experiments(3)Due to the positive pressure at the feed inlet and the presence of vortices,the output of the industrial conveyor has changed.This problem can be effectively solved by optimizing the ejector feed structure.According to the design requirements of industrial closed pneumatic conveying,the theoretical design calculation method is used to design and calculate the ejector,and the main parameters are given:the nozzle outlet diameter is 32mm,the nozzle contraction angle is 12°,and the mixing chamber length is 380mm.The diameter of the mixing chamber is 62mm,the shrinkage section is 30°,and the nozzle distance is determined to be 142mm.The diffusion angle of the expansion chamber is 10°and the length is 150mm.When designing the ejector,the discharge port can be angled with a horizontal direction.This article is designed as 45°.When the ejector nozzle distance is in the range of 122~142mm,the particle escape rate is 98%,and the particles can be basically delivery.This is due to the existence of a slight negative pressure(-4kPa)at the feeder inlet of the ejector,so that the material can easily enter the ejector and be conveyed at a high transfer rate.