The Effect of Distributor on Gas Mixing in a Bubbling Fluidized Bed

• Main Authors: Yann-Lih Liu, 劉燕莉
• Other Authors: Chien-Song Chyang
• Format: Others
• Language: zh-TW
• Published: 2006
• Online Access: http://ndltd.ncl.edu.tw/handle/04545805287760107682

碩士 === 中原大學 === 化學工程研究所 === 94 === Abstract In a bubbling fluidized bed, bubbles pass through the bed from bottom to the top. The inherent radial momentum deficiency of the fluidizing gas usually generates the vertical mixing many times greater than the lateral mixing. This study was performed in a 40 cm x 20 cm x 150 cm and a 48 cm x 16 cm x 150 cm rectangular bubbling fluidized beds. Tuyere and horizontal-nozzle gas distributors were used. Carbon dioxide was injected into the bed as the tracer gas at 5 cm above the distributor. The concentration of CO2 were detected at different positions in the bed. A gas chromatograph (MTI M200) was used to analyze the concentration of CO2. The effects of static bed height, superficial gas velocity, and open-area ratio of the distributor were investigated on the gas mixing. The overall standard deviation of the tracer gas concentration was used to represent the extent of mixing. The experimental results showed that a higher static bed resulted a worse mixing performance. A lower open-area ratio of distributor gave more significant gas mixing than a higher one. The effect of superficial gas velocities on the gas mixing was also concluded to be dependent on the type of the distributor. The best superficial gas velocity for gas mixing was 5 times of minimum fluidization velocity which operated at a high open-area ratio multi-orifices distributor. A horizontal-nozzle distributor with a high open area ratio also obtained a good result at a low superficial gas velocity. A single orifice tuyere distributor with dead zone eliminated design which generated a better gas mixing as the superficial gas velocity increased. For the four types of gas distributor in this research, a single orifice tuyere distributor with dead zone eliminated design which got a lower CO2 concentration gradient and gained a better gas mixing performance as the superficial gas velocity increased. This was more suitable for a rectangular bubbling fluidized bed than other types of gas distributor.