Analysis On Flow Characteristics Of Dense Phase Pneumatic Conveying In Complex Pipeline

FGD gypsum, predicted from thermal power plants, had shortcomings of dustpollution and high energy consumption, which became a bottleneck restricting itsapplication. However, dense phase pneumatic conveying technology with advantagesof device security, high degree of automation, cleaning and environmental protection,became an important means to solve this problem. Simultaneously, complex pipe hadsignificance to the layout of the pipe network and promote.In this paper, the horizontal elbow tube and horizontal gradient tube wereselected as the object, for applications more and study less. Dense phase pneumaticconveying experiment was carried out with FGD gypsum as the transportation ofmaterials, which had two different physical properties. Dense phase pneumaticconveying flow field variation was obtained through experimental study, theoreticalstudy and numerical simulation.The experimental system operating parameters and delivery law were determinedat first. Offer feed tank pressure was controlled between0.26MPa to0.32Mpa; the gassuperficial velocity was from9m/s to17m/s; with the increase of gas superficialvelocity, solid mass flow and solid particles average velocity increased.At the same time, for complex pipeline, the parameters of pipeline geometry,solid-gas mass ratio, gas velocity and other parameters was significant to gas-solidtwo-phase flow pressure drop. When the solid-gas mass ratio, gas superficial velocityand particle size were constant, the pressure drop of the horizontal elbow tube wasincreasing with the increase of the bending angle and the decrease of radius ofcurvature; for gradually expanding tube, the pressure drop decreases as the diameterratio and diffusion angle increases; for gradually shrink tube, The pressure dropincreases as the diameter ratio and diffusion angle increases.When geometric parameters of the pipeline and physical properties of thematerials were constant, the pressure drop of complex pipe increased with the increaseof the solid-gas mass ratio; the pressure drop of two-phase flow increased with the increase of the gas velocity. Particle size of FGD gypsum had a certain impact toresistance properties of complex pipeline. When particle size was42.63μm, thepressure drop was small than particle size was15.75μm.On the basis of experiments, the main factors of the different pipe resistancecharacteristics as well as the correlation between them were got by principalcomponent analysis. To horizontal elbow tube: bending angle> solid-gas ratio>radius of curvature> gas superficial velocity> particle size. And negative correlationwas between bending angle, solid-gas ratio and radius of curvature. To horizontalgradient tube: tube diameter ratio> solid-gas ratio> diffusion angle> gas superficialvelocity> particle size. And negative correlation was between tube diameter ratio,solid-gas ratio, diffusion angle.Based on the above research, combined with the method of dimensional analysis,set up the equivalent mathematical model of predict the level bends, horizontal taperedtube and the level gradually flaring the resistance loss, by compared with theexperimental data to analysis found that the mathematical model has the high accuracy.The paper establish the appropriate geometric model according to the actual sizeof the complex pipe and mesh, then mesh refinement in the near-wall boundary layer.Based on this, the two phases of gas-solid selection the Euler-Euler two-fluid model,using the SIMPLE algorithm and the standard k-ε turbulence model, Using two-waycoupling to two phases, make the numerical simulation to two phases when flowthrough a complex pipeline get hydrostatic, hydrodynamic, two phases’ speed and thetransient variation. At the same time, make the numerical calculation to the resistanceloss, comparison with the experimental data, can find that the simulation results hadhigh accuracy.