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Experimental Study On Particle Agglomeration Characteristics Of Circulating Fluidized Bed Riser

Posted on:2018-02-02Degree:MasterType:Thesis
Country:ChinaCandidate:J J HuFull Text:PDF
GTID:2352330518492615Subject:Architecture and civil engineering
Abstract/Summary:PDF Full Text Request
The circular fluidized bed combustion technology as a kind of high efficiency low pollution energy utilization technology, having the important significance to the coal pollution control. At present the study of circulating fluidized bed gas-solid two phase flow are mainly concentrated in the macroscopic characteristics, and on mesoscopic scale gas-solid two phase suspension flow in the process of cluster formation, development and dispersal is less, the research on characteristics of clusters in the riser is not enough and needs to be studied further and systematically.Experiments were carried out in a cold circulating fluidized bed riser with 100 x 25 mm square cross-section and 3.2 m height, with an average diameter of 234?m glass beads as the object, adopting the technology of the high-speed video capture the process of cluster formation, development and dispersal; Research shows that, due to the complex air distribution and the uneven distribution of particle concentration makes the clusters exhibit different shapes, different sizes and common clusters with U, inverted U shape, comet, strip,adherent stick and binuclear forms. The central region of the riser is mostly upward inverted U and comet shaped clusters, as well as downward movement of U shaped clusters and the wall region is mostly adherent stick. Different types of clusters will be transformed, and there will be radial migration.At the same time, non-intrusive optical fiber is used to measure the characteristics of Geldart B class particles in the ascending pipe and with the operating parameters and the change of riser space position relations. Research shows that, due to the particle velocity on the radial shows a characteristic of the uneven distribution: the velocity of particle movement in the central region is large and wall region is small. The particle time mean concentration in the central region is small and the wall region is large. In the axial direction, the particle velocity increases rapidly in the central region of the bed and the growth at the side wall is slow. Therefore, with the increase of axial height, the particle concentration at the cross-section decreases gradually.The radial distribution of the time fraction of clusters also exhibits the characteristics of clusters, which is low in the central region of the bed and high in the wall region. But in the axial direction,the time fraction of the clusters in the lower part of the bed is not obviously affected by the operating conditions. Unlike the distribution of the time fraction of clusters,the frequency of the clusters appears to be the largest in the center and gradually decreases in the direction of the border wall. With the increase of the axial height of the riser, the frequency of the clusters increases gradually. The concentration of clusters has a similar distribution with the time mean particle concentration, and the concentration of clusters is about 5?6 times of the time mean particle concentration at the same location in the test range.
Keywords/Search Tags:circulating fluidized bed, riser, optical fiber probe, high-speed CCD camera, clusters
PDF Full Text Request
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