利用小波分析壓力擾動訊號來界定B類粒子紊流流體化流域

Characterization of Turbulent Fluidization Regime with Geldart Group B Particles by Wavelet Analysis of Pressure Fluctuation Signals

余傛斯(Yung-Sz Yu)

指導教授 ： 呂理平

國立臺灣大學/工學院/化學工程學研究所/碩士(2007年)

https://doi.org/10.6342/NTU.2007.01162

摘要

本研究使用高7m，內徑0.108m的循環式流體化床，使用空氣為氣相，平均粒徑204μm及344μm的砂為固相。以氣體速度為操作變數，來界定循環式流體化床中紊流及快速流體化區域。再由壓力探針量測上升床內的相對與絕對壓力擾動訊號，並經小波分析所得到的小波能量分佈圖來探討不同流態下之特徵。
由壓力擾動的分析可知，利用相對壓力擾動和絕對壓力擾動的測量方式，皆可以得到移轉速度Uc及Uk。而且，兩方式所得Uc及Uk皆隨粒子粒徑的增加而增大。與其他文獻比較，吾人以為Uk值會受到上升床頂部的擴大管影響。具有擴大管的設備會影響上升床中的流態，導致在絕對壓力擾動的分析中，無法得到Uk值。然而，沒有擴大管的設備卻有可能量測到Uk值。
另外，以相對和絕對壓力擾動信號做小波分析後，發現於氣泡流體化床及紊流流體化床流域時，主要能量分佈於D6與D7，而且Uc會出現在D6 + D7能量曲線的極大值之對應值。快速流體化床則分為濃相及稀相，其中濃相區主要能量分佈於D8與S8，稀相區主要能量分佈於D4與D5。當氣體流速到達Uk值時，D6 + D7的能量曲線會急速降低，而逐漸被D4 + D5或D8 + S8的能量曲線所取代。

關鍵字

壓力擾動訊號 ； 小波能量分佈圖

並列摘要

The transition velocities Uc and Uk, discriminated the bubbling, turbulent and fast fluidization, were investigated by the traditional and wavelet analysis on instantaneous pressure fluctuation signals in a circulating fluidized bed (0.108m i.d. × 7m height) for Geldart group B powder (sand: Dp = 204μm, Dp = 344μm). The solid mass flow rate was measured by an impact-line solid flow meter and was controlled by a L-valve.
The results showed that Uc and Uk could be obtained by methods of differential and absolute pressure fluctuations. Both Uc and Uk by methods of differential and absolute pressure fluctuations increased with the particle size. Comparing with other literature data, the value of Uk was significantly influenced by the solid recycle type. Besides the solid recycle system from solid downcomer to riser bed, the solid recycle type could be influenced by the expanded top section on the riser bed. If there was an expanded top section on the riser, the value of Uk was not found by analysis of absolute pressure fluctuations. However, If there was not an expanded top section on the riser, the value of Uk could be found.
By means of the multi-resolution analysis of wavelet transform, the wavelet energy distribution profiles of absolute and differential pressure fluctuations in the three flow regimes were calculated. In bubbling and turbulent fluidization, the energy distribution was dominated by detail signals D6 and D7. Moreover, When the superficial gas velocity reached the value of Uc, the wavelet energy distribution at D6 + D7 was the maximum value. In fast fluidization regime, there were two sections, densely lower section and tenuously upper section. In lower section, the energy distribution was dominated by detail signals D8 and S8; in upper section, the energy distribution was dominated by detail signals D4 and D5. When the superficial gas velocity reached the value of Uk, the value of the wavelet energy distribution at D6 + D7 decreased quickly. When the superficial gas velocity exceeded the value of Uk, the energy distribution was dominated by detail signals D6 + D7 or D8 + S8.

並列關鍵字

pressure fluctuation ； wavelet energy distribution profile

參考文獻

陶政隆(Tao Cheng Lung), “紊流流體化床的床-壁間熱傳現象”, 國立台灣大學化學工程研究所碩士論文, 台北, 台灣 (2006)。

Avidan, A. A. and J. Yerushalmi, “Bed Expansion in High Velocity Fluidization”, Powder Technol., 32, 223-232 (1982).

Bi, H. T., N. Ellis, I. A. Abba and J. R. Grace, “A State-of-the-Art Review of Gas-Solid Turbulent Fluidization”, Chem. Eng. Sci., 55, 4789-4825 (2000).

Bi, H. T. and L. S. Fan, “Existence of Turbulent Regime in Gas-Solid Fluidization”, AIChE J., 38, 297-301 (1992).

Bi, H. T. and J. R. Grace, “Effect of Measurement Method on Velocities Used to Demarcate the Onset of Turbulent Fluidization”, Chem. Eng. J., 57, 261-271 (1995).