氣泡式流體化床中分佈器對氣體混合效應之研究

中文摘要氣泡式流體化床中，氣體由下而上通過床體，垂直方向的氣體混合速率通常大於水平方向的氣體混合速率。如何加強水平方向的氣體混合速率，以避免顯著之濃度分佈或溫度梯度，藉以提升床內熱傳與質傳係數則是當前重要的課題。本研究係於40 cm x 20 cm x 150 cm及48 cm x 16 cm x 150 cm的流體化床中進行，分佈器採用鼓風口式及水平噴嘴式，可調整氣體出口孔徑以達到不同之開孔比。在短軸壁邊中心距分配板5 cm處注入二氧化碳作為追蹤氣體，並於床內各點取樣，取樣的氣體濃度以氣相層析儀分析。實驗同時改變靜床高、空床氣速、分佈器之開孔比，比較不同變數對於氣體混合的影響，並以標準偏差百分比值作為評斷追蹤氣體於床內混合的程度。實驗結果顯示，靜床高增加，床內氣體混合較不理想；低開孔比分佈器比高開孔比分佈器具有較顯著之氣體混合；空床氣速對於氣體混合與分佈器型態有關。高開孔比之多孔口鼓風口式分佈器，五倍的最小流體化速度為最佳氣體混合氣速；水平噴嘴分佈器於低氣速下操作可得較佳之氣體混合；消除靜滯區設計之單孔口鼓風口式分佈器，氣體混合會隨空床氣速增加而得到良好的氣體混合。對實驗之四種型態分佈器，因消除靜滯區後之單孔口鼓風口式分佈器有較小的濃度梯度，且隨空床氣速增加能得到更好的氣體混合，較其餘三者分佈器，更適用於方形流體化床。

關鍵字

鼓風口式分佈器；氣泡式流體化床；水平噴嘴分佈器

並列摘要

Abstract In a bubbling fluidized bed, bubbles pass through the bed from bottom to the top. The inherent radial momentum deficiency of the fluidizing gas usually generates the vertical mixing many times greater than the lateral mixing. This study was performed in a 40 cm x 20 cm x 150 cm and a 48 cm x 16 cm x 150 cm rectangular bubbling fluidized beds. Tuyere and horizontal-nozzle gas distributors were used. Carbon dioxide was injected into the bed as the tracer gas at 5 cm above the distributor. The concentration of CO2 were detected at different positions in the bed. A gas chromatograph (MTI M200) was used to analyze the concentration of CO2. The effects of static bed height, superficial gas velocity, and open-area ratio of the distributor were investigated on the gas mixing. The overall standard deviation of the tracer gas concentration was used to represent the extent of mixing. The experimental results showed that a higher static bed resulted a worse mixing performance. A lower open-area ratio of distributor gave more significant gas mixing than a higher one. The effect of superficial gas velocities on the gas mixing was also concluded to be dependent on the type of the distributor. The best superficial gas velocity for gas mixing was 5 times of minimum fluidization velocity which operated at a high open-area ratio multi-orifices distributor. A horizontal-nozzle distributor with a high open area ratio also obtained a good result at a low superficial gas velocity. A single orifice tuyere distributor with dead zone eliminated design which generated a better gas mixing as the superficial gas velocity increased. For the four types of gas distributor in this research, a single orifice tuyere distributor with dead zone eliminated design which got a lower CO2 concentration gradient and gained a better gas mixing performance as the superficial gas velocity increased. This was more suitable for a rectangular bubbling fluidized bed than other types of gas distributor.

並列關鍵字

tuyere distributor ； horizontal-nozzle distributor ； bubbling fluidized bed

參考文獻

Google Scholar

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Google Scholar

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