| In the shield project,the excavated muck and stone are often transported by conveyor belts.It is a complex device where is easy to mix with stones in the conveyor belt,and also uneven material distribution.During the process of slurry shield boring,the mud plays the role of stabilizing the excavation surface and transporting shield slag.At the same time,a large amount of muck and block are carried by the mud and can be transferred out of the construction site in the form of pneumatic transport.Studying on the pressure loss in the pneumatic conveying process is of great engineering guidance significance for designing pneumatic conveying devices that meet the actual construction conditions,improving the transportation efficiency of pneumatic conveying systems,reducing unnecessary energy consumption in the conveying process,and reducing the failure of pneumatic conveying systems.Moreover,the conveying fluid is slurry,and the pressure drop of the flow process will be affected by the rheological properties of the slurry and the effect of fluid solid-phase turbulence.The system pressure often fluctuates violently to cause failure,so it is necessary to reasonably overhaul or maintain the system.At the same time,repair and maintenance should be arranged in combination with the actual construction plan of the system to reduce unnecessary downtime of the system,to increase the operating life of the system,and to improve work efficiency.In this study,two sets of mud were prepared and the flow characteristics of pneumatic conveying were studied experimentally.Based on the characteristics of the pneumatic conveying flow process,the differential equation of multiphase flow of mud is derived and simplified,and the flow form and flow pressure drop of mud in the pipeline are theoretically calculated and analyzed.Based on the opportunity algorithm,the maintenance arrangement strategy of pneumatic conveying equipment is studied,and maintenance operations are arranged as the downtime of pneumatic conveying equipment according to the time when the episodic machine stops boring.In view of the above content,this paper adopts a combination of experimental research,numerical simplified calculation,and opportunity algorithm theoretical analysis.The following conclusions are mainly obtained.（a）Based on the N-S equation of single-phase fluid,the momentum differential equation of gas-liquid-solid three-phase flow containing solid particles is established based on the pneumatic transport process of slurry,which is gradually converted from the single-phase model to the multiphase model,and considering the role of gas phase and solid particles.Based on the identified flow pattern,the pressure drop was predicted for two sets of experiments using the test bench.（b）Based on the measured data,the pressure drop model of the test platform is verified,and the flow pressure drop when the ratio k of the gas phase wet circumference of the plug unit in the middle section of the pipeline is different values is predicted,and it is found that when the k value is between 0.4 and 0.6,the prediction error of the model is within 40%.（c）Taking the pneumatic conveying system as an example,the maintenance schedule for four cases is given based on the opportunity algorithm.The following conclusions are drawn.a)If the system runs for a long time,compared with the system that has just been put into use,the maintenance schedule will be advanced,which is also in line with the experience of the system.b)If the downtime is small,the impact of the maintainability function on the odds value is greater than the reliability function.And if the downtime is large,the reliability function has a greater impact on the odds value than the maintainability function.c)The greater the average repair time of the equipment,the earlier the downtime for scheduling its maintenance. |
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