Experimental Study Of Intensification In Fluidized Bed With Wide Particle Size Distribution

The fluidized chemical vapor deposition(FCVD) will form a relatively wide particle size distribution during the reaction progress, so the intensification of wide particle size distribution in a gas-solid fluidized bed need further research. The heating plates in the reactor will affect the fluidization characteristic of the particle, so the intensification of the internals to the fluidization should also be considered.(1) An experimental device for this work was made, and the heart of the set-up was an organic glass column of 0.215 m in diameter and 1.5 m in height with a conic bed, which could give a better fluidization to the large particles at the bottom. Set 1-3 belonged to single size distribution and Set 4-5 had wide size distribution, respectively. The axial solid concentration distributions were measured by the pressure drop between two points along the bed, and the particle concentration distribution and the particle size distribution were researched through sampling method. We calculated the mean bed voidage through the bed height at different gas velocity, and analyzed bubble size in the fluidized bed through the amplitude of the pressure fluctuations, and the bubble frequency through the major frequency of pressure fluctuations.(2) Compared with the the particles of single size distribution, the bubble behaviors, the axial solids distribution, the particle size distribution, the particle concentration distribution and the bed void fraction of those ones with wide size distribution were considered. The results showed that:(Ⅰ) When superficial gas velocity researched 0.155m/s, the pressure pulsation frequency of Set 2 was 3.667 and Set 4 was 3.533, and like Set 1, Set 5 also had no obvious main peak power spectrum due to the large coalescence and breakage frequency of the bubbles. The particles of wide size distribution could have a better fluidization quality because of the fine particles, which could increase the coalescence and breakage frequency of the bubbles.(Ⅱ) The joining of fine particles made the polydisperse particles can be taken to the upper bed at a low superficial gas velocity and had a uniform axial solid concentration distribution.(Ⅲ) The density decreased with the increase of axial height, and increased gradually from the center to the wall in the dense-phase zone, for Set 4, the average solids volume fraction at 0.2m was from 45% to 60% at 0.155m/s.(IV) Particle size decreased with the increase of axial height, and had no significant change in the radial direction. For Set 4 at 0.294m/s, the average particle diameter in the dense phase was approximately 200μm, while it was more smaller in dilute phase. There was a evident decline during 0.2-0.4m, from 210μm to 165μm. While, the particle size in different radial positions at 0.6m were all about 150μm at 0.232m/s.(V) The joining of fine particles can improve the bed voidage. The bed voidage of Set 4 was from 0.37 to 0.48 and Set 5 was from 0.36 to 0.46, larger than that of Set 3, which was from 0.38 to 0.44.(3) 18 heating plates were located in the fluidized bed. It could affect the fluidization of particles as the internals in the bed. To study the effect of heating plates on fluidization characteristics, the mean voidage and pressure fluctuation under different superficial gas velocity were investigated. The results showed that the fluidized bed with the internals had a little higher pressure drop, with △P less than 400Pa, and a little lower bed voidage,, but a more stable fluidized state. The increase of the coalescence and breakage frequency of the bubbles could explain that the heating plates break the big bubbles well. After installing the plates, the pressure pulsation frequency of Set 4 increased from 3.533 to 6.000, the amplitude decreased from 2.795 to 2.504 at 0.155m/s, and the pressure pulsation frequency increased from 4.567 to 5.700, the amplitude decreased from 6.533 to 4.264 at 0.232m/s.