流體化床中水平噴嘴分佈器對氣體混合之效應

Gas Mixing in a Fluidized Bed Equipped with a Multi-Horizontal-Nozzles Distributor

林美秀(Mei-Shiou Lin)

指導教授 ： 錢建嵩

中原大學/工學院/化學工程研究所/碩士(2004年)

https://doi.org/10.6840/cycu200400335

摘要

中文摘要

流體化床操作之主要優點，即氣固接觸良好，在眾多之應用實例中，無一不在強調其流體與固體之良好混合效果。在改良或創新研究方面，多亦在強調其混合效果之提昇，或質傳係數、熱傳係數之提高。

就傳統氣泡式流體化床而言，氣泡由下而上通過床體，致使床內垂直方向的混合相當明顯，通常數倍於水平方向的混合速率。就實際應用而言，如何加強水平方向的混合速率，致使床內達到均一性質的目標，常是工程設計人員的重要課題。內循環式流體化床係一種改良型的氣泡式流體化床，藉由床內不均勻氣體分佈達到粒子內循環的效果，如此之設計應可加速氣體或粒子於水平方向的混合。

本研究中所使用的內循環床為長寬比2:1的長方形設計，分配板採水平噴嘴，噴嘴方向均朝同一方向，與長軸平行，可調整分配板上部份噴嘴的孔徑，改變氣流的分佈造成粒子內循環。可預期氣體在長軸方向有較高之擴散速率，在側向的擴散速率則較低。

在本研究中，我們將以氣速、靜床高、分配板為主要變數，以二氧化碳為追蹤氣體，偵測床中不同位置之二氧化碳濃度，以濃度分佈之標準偏差為混合指標，探討此三個操作變數對混合指標的效應。

由實驗結果顯示，空床氣速與開孔比對氣體混合之影響較明顯於靜床高。並且比較兩種不同之分佈器；水平噴嘴分佈器與穿孔板分佈器，由實驗結果可判斷水平噴嘴分佈器分散效果較佳。

關鍵字

流體化床

並列摘要

Abstract

One of the most important advantages of the fluidized bed is the well mixed between gas and solid. For commercial applications, the high efficient of fluid-solid contact is usually emphasized. For improvement or innovation, how to enhance the efficiency of gas solid mixing, mass transfer coefficient and heat coefficient are focused.

In a conventional fluidized bed, bubbles pass through the bed from bottom to the top. The inherent radial momentum deficiency of the fluidizing gas leads to vertical mixing many times faster than lateral mixing. For commercial application, how to improve the efficiency of mixing in the lateral direction becomes an important topic to the engineers. The internal circulating fluidized bed, an bubbling fluidized bed innovated by employing un-uniformly gas distribution within the bed to achieve internal particle circulation, should increase the particle moment and mixing efficient in the horizontal direction.

In this study, an internal circulating fluidized bed with a dimension of 40 x 20cm equipped with horizontal nozzles type distributor was used. All the gas jets from nozzles are towards the same direction, parallel with the long side. The circulation of particles will be enhanced by adjusting the distribution of gas flow within the bed. It can be said that the gas diffusion rate is higher in the direction parallel to the long axis and lower in the direction perpendicular to that.

In this study, the superficial gas velocity, static bed height and gas distributor type are used as the main parameter. Carbon dioxide is use as
the tracer gas. The analysis of standard deviation of the tracer concentration profile will be used as the mixing index. The relationship between the mixing index between the operation parameter will be discussed.

The experimental results indicate that the effect of superficial and open-area ratio are more significant on gas mixing than static bed height.

To compare the gas mixing performances of different distributor, two types of distributor were compared, horizontal nozzles distributor and perforate. The result indicates that the gas mixing performance of horizontal nozzles is better than perforated plate.

並列關鍵字

fluidized bed

參考文獻

林延金，【流體化床中壓力擾動及徑向氣體混合之研究】，中原大學化工所博士論文，(2003)

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