以多層次解析度在循環式流體化床內鑑識B類粒子之絮狀物特性

Abstract

在循環式流體化床(Circulating fluidized bed, CFB)系統內，因為氣-固相之間的交互作用產生複雜之氣-固流動型態，導致床內固體粒子聚集而形成絮狀物(clusters)，因此氣-固流經常表現出多尺度之流力行為。以往學者使用固體粒子含率擾動訊號之平均值與標準偏差等參數來探討流體化床內之絮狀物流力行為，但是卻容易遺漏在訊號中的某些時變(time-varient)特徵，而無法準確地分析在循環式流體化床內之絮狀物流力特性。 本研究在裝置為一內徑0.108 m、高5.75 m之循環式流體化床內，使用平均粒徑115 μm、密度2462 kg/m3之玻璃珠(Geldart B類粒子)作為床質粒子，以光纖探針在CFB的底部濃相區及飛濺區中量測其固體粒子含率(solids hold-up)擾動訊號。由於原始訊號具有多尺度與時變特性，因此利用多層次解析度(multi-resolution analysis, MRA)之方式，得到一個較適當的粗波門檻尺度作為絮狀物鑑識之準則。以此準則，可確定在循環式流化床內底部濃相區與飛濺區中之絮狀物流力特性(絮狀物顯現時間分率、絮狀物顯現頻率、平均絮狀物顯現時間 以及絮狀物之平均固體粒子含率 )，並且比較A類粒子與B類粒子在床壁區域附近之流力行為之異同。

Because solid particles accumulated clusters by the chaotic interactions between the void and the solid phases, the gas-solid flow in a circulating fluidized bed (CFB) displayed multi-scales dynamic behaviors. The time-variant features would be neglected by the analytic method using some parameters, eg. the mean and the standard deviation of the solids hold-up signals measured in CFB. The solids hold-up fluctuation signals of Geldart group B particles (glass bead: particle size=115 μm, density=2462 kg/m3) in the bottom dense region and the splash zone of CFB (0.108 m i.d. and 5.75 m height) were measured by a fiber optic probe in this study. Because the solids hold-up signals displayed multi-scales and time-variant dynamic behaviors, an appropriate level of the approximation subsignal was determined by wavelet analysis based on multi-resolution analysis. By this criterion, the dynamic properties of clusters in the bottom dense region and the splash zone of a circulating fluidized bed were determined. The dynamic properties of clusters of Geldert group A and B particles near the wall in CFB were identified and compared.