Research On Pneumatic Conveying Characteristics Of Spraying Materials In Long-distance Pipeline

With the acceleration of the construction technology of coal mining rock roadway engineering in China,the combination of excavation smooth blasting technology and bolting and spraying support makes the roadway be formed at one time,and the monthly footage of an inclined shaft well construction can reach more than 100 m continuous ly.However,the domestically used coal mining currently uses a large amount of dust in the spraying process,and the conveying distance of the spraying materials is currently short,and the manual spraying has a large occupational hazard and low work efficie nc y.Therefore,the long-distance conveying of the spraying materials has a high economic value and social benefit.This paper combined theoretical analysis,numer ica l calculation and experimental results through the researches on auto-feeding system of the spraying materials,selection of conveying pipeline,remote transportation of the spraying materials and mixing dust control of the spraying machine.This method explored the "pneumatic conveying characteristics of long-distance pipelines for spraying materials",and the results provided theoretical basis and experimental basis for auto-feeding and long-distance conveying of the spraying materials.At the same time,the conveying mode of the underground spraying materials was broadened,and this technology could also be extended to long-distance conveying of the granular materials such as underground coal and vermiculite.Based on the Newton's law of motion and Euler's law of motion,a discontinuo us force-displacement model between particle and particle was established to obtain the normal force between the particle streams during the collision of particles,directiona l force and viscous force.Based on Newton's law,the equations of motion of spherical particles and non-spherical particles in three-dimensional space were obtained.Based on the CFD-DEM coupling method of non-analytic surface,the drag-force model between airflow and particles was established by Ergun-Wen&Yu theory,and the void fraction was added to the continuity equation of the two-fluid model,and the gas-solid phase A and type B was obtained accordingly.Based on the particle-wall collis io n theory and the erosion wear equation,it was pointed out that the existing main particle flow erosion wear form was cutting wear.Based on the study of the near-wall layer processing method of the fluid mechanics,the wall function method of Fluent near-wall treatment was proposed,and the Non-Equilibrium Wall Function for the near-wall processing of non-analytical surface CFD-DEM coupling method was proposed..According to the airflow pressure involved in the researches and the characterist ics of the conveying materials,a set of pneumatic conveying auto-feeding system for spraying materials was designed.With the orthogonal experimental design method,the airflow speed,particle size and feed mass were studied to pick up the materials of the auto-feeding system in the pneumatic conveying.The results showed that the airflow rate has the greatest influence on the material pick-up masses,however,the particle size and the material feeding mass had little effect.For pebble particles of different particle sizes,the pick-up speed required for the small particles was lower,and the bulk density of the large particles decreased as the particle size increased.As the feeding mass increased,the surface velocity of the particle piles deposited at the bottom of the pipeline was greater,and the pick-up mass of the spraying material was positive ly related to the feed mass.By the range analysis and variance analysis,the influe nce trends of each level of the research factors on the pick-up mass,the horizontal pipeline pressure drop and the pressure were obtained,and the pressure signal and the material pick-up mass of the pressure transmitter 1 were normalized.The results showed that the pressure signal of the flow field was obtained as a function of the picking mass for the pebble particles.In the venturi dense-phase pneumatic conveying system,the effect of airflow velocity and water content on the conveying characteristics and flow stability of the spraying materials were studied,and the critical wind speed was proposed,at which the pressure drop of the conveying system was the lowest.The coefficient of variation of the outlet pressure of the venturi was proposed,and the stability of the flow field was measured by the coefficient of variation and the optimal airflow velocity was obtained.Through the combination of numerical simulations and experiments,the optimal conveying water content of the spraying materials was obtained by the coefficient of variation of the airflow pressure drop and pressure drop as the measurement index.By studying the pressure drop in the venturi and the flow of the airflow in the pipe,the pressure drops in the venturi feeder and the pipe were periodically fluctuated at a fixed gas flow rate greater than the critical wind speed.The coefficient of variation was introduced to describe the stability of the flow field,and the instability of the particle multiphase flow field under the critical wind speed was obtained.The pulsating pressure drop of each component of the pneumatic conveying system was obtained by analyzing the power spectrum density of the flow field pressure signal.By the empirical analysis of the pebble particles pick-up,the pick-up speed of the pebble particles used in this experiment was studied based on the results of several studies.The results showed that the airflow velocity as a function of picking speed could describe all the results well and had a very simple correlation.The experimenta l relationship described the pick-up in the airflow and solid by considering various influence parameters such as particle diameter and fluid velocity.For a horizonta l pneumatic conveying pipe with a diameter of 50 mm,the superficial airflow velocity on the large particles was larger,so there was a possibility that the pick-up speed of the larger particles was lower.By analyzing the horizontal pipe particle pick-up process,it was found that there was an optimum swirling number,and the picking rate of the spraying materials is the largest under the action of the swirling number.Visual observation,mass weighing,coefficient of variation analysis of the flow field pressure drop and flow field pressure drop peak-to-average ratio could be used to measure the pick-up rate of materials.The experimental results showed that the accuracy of particles pick-up speed obtained by visual observation was lower,and the mass loss rate of the particles was the best measurement of the pick-up speed.By prediction of the flow regime of the rotating flow in the vertical pipe,the flow pattern,pressure drop and bed height of the axial flow and the swirling flow gas-solid two-phase flow in the vertical tube were studied experimentally.The results showed that the inertia and secondary flow had a significant effect on the particles at the elbow.The particles in the vertical pipe moved from the inner wall to the outer wall of the elbow in the axial flow,and the swirling number had a significant effect on the particle flow pattern with fixed solid mass flow rate and inlet airflow velocity.When the particle size was larger than the critical particle size,the pressure drop increased with the increase of the particle size,and the particle size had a great influence on the gas permeability and gas storage of the particle cluster for the gas-solid two-phase flow in the vertical pipe.The swirling flow helped to reduce the pressure drop,but a larger swirling number would result in an increase in the pressure drop due to the swirling decay.A quaternary coupling method considering the effects of lifting angle,airflow velocity and solid mass flow was proposed to predict the flow characteristic of the pebble particles in four different lifting elbows.The simulation scheme was designed by orthogonal design method to reduce the simulation number.The results showed that the pressure drop in the lifting elbow was much greater than the pressure drop between the elbow inlet and outlet due to fluid inertia and secondary flow,and the airflow velocity is critical to the pressure drop in the elbow.Through the study of the flow pattern of the lifting elbow,it was found that the secondary flow formed at the elbow had a great influence on the void fractio n and the particle concentration distribution in the pipe,so that the particle moved to the downstream pipe sidewall near the exit of the elbow.In the elbow,the particle concentration differed greatly,but this did not affect the maximum erosion area of the elbow.For the lifting elbow,the particle collision was evenly distributed across the cross-section,significantly changing the other observed el ipse-shaped erosion areas,and colliding at the outer bend of the elbow near the exit,causing severe erosion in both areas.This paper includes 115 pictures,20 tables,and 198 references.