Investigation Of Pickup Velocity Of Particles Mixtures In Horizontal Pneumatic Transport

Biomass resources,as the most widely distributed and renewable clean energy,have a wide range of sources in our country.At present,Co-firing power generation technology,as ap new-type technology of utilizing straw resources,is being widely applied in the field of electric powder,using mixtures of straw pellets and pulverized coal as fuel.It is crucial for prompting co-firing technique widely that how to pneumatically convey the pulverized coal and straw pellets.Pickup velocity is one of the important parameters affecting the operation of pneumatic transport,but research achievements about pickup velocity of particles mixtures are still inadequate.Thus,pickup velocity of mixtures with pulverized coal and straw pellets in horizontal pneumatic transport was studied in this paper,in order to provide certain reference to design pneumatic transports system of mixtures in engineering practice.Adopting the mechanic of rolling,the stress analysis for additional mass force and equivalent diameter for particles mixtures was carried out to obtain critical theory model of pickup velocity according to method of mechanics and geometry.This model revealed the relationships between pickup velocity and particles size,particle shape,mass ratio and relative exposure degree in particle mixtures.Then,based on the existing pickup theory model of mono-dispersed particles,the ideal model of pickup velocity of mixtures was obtained by taking the particles mixtures as mono-dispersed particles with the same particle size.Through the comparison of the critical and ideal model,the main difference can be found that the critical model had the relevant correction coefficient,which characterized the influence of relative exposure degree,the composition of particles mixtures and the characteristics of each component of the particles on pickup velocity.Also,taking the experimental method to determine the relevant correction coefficient was drafted.Experimental facility of the pickup velocity of the polydisperse particles was established,the characteristics of experimental materials were measured and we also took the glass beads as the research object instead of pulverized coal.And then,tests of the effects of glass beads size,mean particles size,mass ratio and aspect ratio of straw pellets on the pickup velocity of mixtures were carried out in self-built test facility.Results indicated that the measured value of pickup velocity increased with the increase of the size of glass bead,decrease with the increase of particles size,mass ratio and mean aspect ratio of straw pellets.However,the ratio of the measured and the theoretical value would decrease gradually.The relative exposure degree increased with the increase of glass bead size and the decrease of straw pellets size,decreased with the increase of mass ratio of straw pellets.In addition,we also found that pickup velocity of particles mixtures would decrease significantly after adding straw particles into the mono-dispersed particles.Finally,the differences between the measured and the theoretical value of pickup velocity were being analyzed and modified by dimensional analysis.So that,the critical pickup velocity model of particles mixtures was modified and established.Then,the calculation results using the modified formula were accordance with the previous experience and the experimental results on different conditions.