A類粒子於流體化床中之流力行為探討

Abstract

中文摘要 本實驗使用內徑0.1m、高1.8m的透明壓克力管之流體化床，以平均粒徑80 FCC粒子與60 玻璃砂等A類粒子為研究對象，在不同靜床高與不同軸向壓力探針量測位置下，探討壓力擾動偏差值與通入氣體流速之關係，再更進一步利用壓力擾動變異數求得Umb。由結果顯示壓力探針在單點位置分散板上方20cm或30cm處與雙點位置(10cm-20cm或20cm-30cm)所求出的Umb值較其它量測位置準確。本實驗中如要求得較為準確之Umb值，分散板上方單點位置20cm或30cm處與雙點位置(10cm-20cm或20cm-30cm)為最佳的測量方式。 利用交互相關函數(cross-correlation function)求出氣泡延遲時間，進ㄧ步再求得氣泡上升速度。由結果發現FCC粒子流化床在相同壓力探針量測位置下，Ub隨著靜床高的高度增加而增加；而對於玻璃砂粒子而言，靜床高對Ub並無影響。並發現探針量測位置在管中心且靠近床表面所得Ub值會大於在管壁所得到的結果。 由主頻分析的結果可知，單點、雙點量測位置的主頻隨著氣速與靜床高增加而下降，而單點位置的主頻不隨壓力探針軸向高度增加而改變。但是雙點量測位置(plenum-10cm, plenum-20cm…)的主頻在低氣速時隨著測量位置高度增加而下降，高氣速時主頻則不隨測量位置高度增加而有任何改變。

Abstract In order to understand the effect of bed heights and probe locations on standard deviation of pressure fluctuations have been measured by a absolute pressure and differential pressure method in a bubbling fluidized bed of 0.1m i.d. and height of 1.8 m and, with respect to variations in gas velocity. Air was used as fluidizing gas and fluid catalytic cracking (FCC) catalyst particles and glass bead particles (Geldart’s group A particles) as bed material. The result showed that the variance of pressure fluctuations for Geldart’s group A particles was a practically linear function of the gas velocity. Thus, more consistent value of Umb was determined by using absolute pressure probes (20cm,30cm) and differential pressure probes (10cm-20cm,20cm-30cm) in this study. The cross-correlation function was used to process the signal from probes each separated by a gap are suitable for calculation of the bubble residence time and bubble rising velocity in this study. The value of Ub was found to be nearly independent of bed heights for glass bead particles but to increase with increasing static bed height for FCC particles. In this study, Bubbles near the surface of the bubbling fluidized bed rose faster in the centre than the wall. The dominant frequency was found to be nearly independent of probe locations with absolute pressure probes but to decrease with increasing air velocity and static bed height at absolute, differential pressure probes (plenum-10cm, plenum-20cm…). The dominant frequency decreased with increasing heights of probe locations at differential pressure probes (plenum-10cm, plenum-20cm…) for low gas velocity, but it did not change at high gas velocity.