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The Study On Flow Characteristic Of Gas-Solid Two-Phase In The Bubbling Fluidized Bed With Horizontal Tubes

Posted on:2016-09-15Degree:MasterType:Thesis
Country:ChinaCandidate:W Q LiuFull Text:PDF
GTID:2271330461494770Subject:Chemical Engineering and Technology
Abstract/Summary:PDF Full Text Request
The fluidized beds are widely applied in chemical industry, energy industry and so on. They are characterized by their ability of higher heat transfer and good mixing. On the other hand, the lack of comprehensive understanding of the complex fluid dynamics involved in these systems makes their design and scale-up very difficult. In many applications tubes are generally inserted to enhance the rate of heat transfer, chemical conversion, and solid circulation and distribution. However, these tubes further complicate the fluid dynamics of the fluidized bed. And the particles constantly erosion and wear the horizontal tubes, so it is very important to design and apply the kind of reactors by studying hydrodynamics in fluidized bed with the horizontal tubes.In this research numerical simulations on hydrodynamics of gas-solid two-phase in fluidized bed with horizontal tubes were carried out by hydrodynamics simulation software FLUENT 6.3, and the results from numerical simulations and experimental measurements were compared to verify the reliability of the numerical simulation.Firstly, the average voidage and expansion rate in fluidized beds without and with the horizontal tubes were researched by using the method of combination of experiments and numerical simulation. The results were shown that the distribution of average voidage at the tube row area was more uniform in the fluidized bed with the horizontal tubes, but the average voidage was high near the center but it was low near the wall in the fluidized bed without tubes. The expansion rate of the fluidized bed with tubes was greater than that of the fluidized bed without horizontal tubes at the same superficial gas velocity, but their expansion rates was gradually close to each other with the increasing of superficial gas velocity.Secondly, the influence of the diameter of horizontal tube, the angle of tube row and the number of tube rows on the turbulent kinetic energy, the velocity vector and pressure fluctuation value was researched by the numerical simulation, and the most optimal distribution of horizontal tubes was obtained. The results were shown that the tube of bigger diameter affected backmixing, but that of the smaller diameter easily caused cavitation; the angle could affect the distribution of the solid particles and the bubble size; the number of tube rows could affect the rise frequency of bubble and its size.Finally, the bubble properties of the pressure fluidized bed with tubes were inve-stigated by means of the optical fiber system. The results were shown that in the row area the radial distribution of the bubble size, rise velocity and frequency was more uniform; their axial distribution was fluctuant at the tube rows, but the bubble size increased gradually at the region above the tube bank, the frequency did not change. At the regions of the tube bank and below the tube bank, but it was low at the regions above the tube bank. The bubble size increased and then decreased with the increase of the operating pressure, but it increased with the increase of superficial gas velocity; bubble rise velocity and frequency increased with the increase of superficial gas velo-city, but the effect of high pressure on bubble size and rise velocity was weak.
Keywords/Search Tags:gas-solid fluidized bed, horizontal tube, numerical simulation, hydromechanics, bubble properties
PDF Full Text Request
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