Characterization of Fast Fluidization Regime of Geldart Group B Particles by Pressure Fluctuation Signals

• Main Authors: CHI HU, 胡琦
• Other Authors: 呂理平
• Format: Others
• Language: zh-TW
• Published: 2005
• Online Access: http://ndltd.ncl.edu.tw/handle/23172863707884460882

碩士 === 國立臺灣大學 === 化學工程學研究所 === 93 === The flow characteristics of Geldart group B powder (sand; =155 μm) in fast fluidization bed were investigated by instantaneous pressure signals in a circulating fluidized bed (0.108 m i.d. and 7m height) by using non-mechanical valve (L-vale) to control the flow rate of solid particles. It was found that for the transition from dilute phase convey to fast fluidization, the transition point was determined by plotting pressure gradients measured both at the top and the bottom of the riser. As the gas velocity is gradually reduced at the fixed solid flux, a critical gas velocity （Uc2）would be reached at which two distinct regions in the riser appear. Further reduction of the gas velocity below Uc2 at the same constant solid flux, a point （Uc1）will eventually be reached when steady operation at the given solid flux becomes impossible. The transition between fast fluidization and turbulent occurred at transition velocity Uc1. For Geldart group B particles, the axial bed average voidage distribution in the solid riser changes with superficial gas velocity and solid circulation rates. Dilute phase convey appears for low solid circulation rates or high superficial gas velocity, fast fluidization appears for high solid circulation rates or low superficial velocities. At fast fluidization, the power spectrum density function of differential pressure fluctuation signals in the bottom region of dense phase was well defined. So the region transition from turbulent to dilute phase convey was determined by the power spectrum density function of differential pressure fluctuation signals.