流體化床中壓力擾動及徑向氣體混合之研究

Researches on Pressure Fluctuations and Radial Gas Mixing in Fluidized Beds

林延金(Yen-Chin Lin)

指導教授 ： 錢建嵩

中原大學/工學院/化學工程研究所/博士(2003年)

https://doi.org/10.6840/cycu200200621

摘要

中文摘要
本研究係從壓力擾動及氣體混合方面探討氣泡/塊泡式流體化床之流體化行為，並可分為三個研究主題，分述於下。
1. 魯式鼓風機特性對流體化床壓力擾動之影響
實驗於一內徑0.29 m之流體化床冷模中進行，流體化空氣由魯式鼓風機所提供。此外，為研究氣源設備對壓力擾動之影響，另於一內徑0.10 m之冷模床中實驗，使用壓縮機為氣源設備。
由魯式鼓風機產生之壓力脈衝頻率已成功於壓力擾動頻譜圖上辨識。該脈衝頻率證實與鼓風機葉輪轉速有關，並具一良好之線性關係。於相同氣體流率下，大規格之鼓風機產生較低之脈衝頻率、較大之脈衝強度及較高之床內壓力擾動變異係數。隨著空床氣速之增加，脈衝強度減弱，影響壓力擾動程度變小。
2. 渦旋流體化模式之研究
於本研究中建立一由水平噴嘴氣體分佈器產生之渦旋流體化模式。分別於內徑0.29 m及0.19 m之流體化床冷模中進行壓力擾動及細粒子淘淅實驗，以研究流體化模式之影響。此外，並比較渦旋流體化模式及由穿孔板氣體分佈器產生之傳統軸向流體化模式之性能。
於一低噴嘴氣體排放速度，床內可達一穩定之細粒子濃度。於渦旋流體化模式之作用下，一階之淘淅速率方程式不適於描述細粒子之淘淅行為，除非於極高之氣體排放速度下。研究結果證明渦旋流體化模式於增進流體化品質及減少淘淅皆有顯著之成果。
3. 以回應曲面法研究流體化床之徑向氣體混合
本研究使用回應曲面法探討流體化床之徑向氣體混合，可以少量之實驗組數進行因子效應分析。實驗係於一內徑0.29 m之流體化床冷模中進行，並使用柱塞流分散模型描述床內之氣體分散程序。氣體追蹤劑為二氧化碳，其下游之徑向濃度分佈由氣相層析儀測定。
徑向氣體分散係數與過量氣速比、床高對床徑比、分佈器開孔比及阿基米德數等操作因子之相關程度良好，其檢定係數R-squared為0.966。因子效應檢定顯示，過量氣速比對徑向氣體混合之影響程度最大；床高對床徑比之影響則較不顯著。過量氣速比與開孔比之交互作用及過量氣速比與阿基米德數之交互作用效應，皆對徑向氣體混合扮演重要角色。於本研究中亦發展一回應曲面演進模型，以描述氣泡/塊泡流體化床之徑向氣體混合。

關鍵字

淘析 ； 壓力擾動 ； 流體化床 ； 氣體混合

並列摘要

Abstract
This research makes investigations into the fluidization behaviors in bubbling/slugging fluidization regimes, from respects of pressure fluctuations and gas mixing. It can be divided into three subjects, as depicted bellow.
1. Influence of the nature of the roots blower on pressure fluctuations in a fluidized bed
Experiments were conducted in a 0.29-m I.D. fluidized-bed cold model with fluidizing air supplied by a Roots blower. To investigate the influence of the air-supply equipment on pressure fluctuations, another experiment was carried out in a 0.10-m I.D. cold model with fluidizing air supplied by a compressor.
The pressure pulsation frequency from the Roots blower was successfully identified on the pressure-fluctuation frequency spectrum. The pulsation frequency was found to be related to the blower impeller rotary speed and exhibited a good linear relationship. At a given air flow rate, a larger-scale blower produced a lower pulsation frequency, higher pulsation intensity and a higher coefficient of variation for pressure fluctuations in the bed. With increasing superficial air velocity, the pulsation intensity abated and became less influential.
2. A study in the swirling fluidizing pattern
An innovative swirling fluidizing pattern produced by a multi-horizontal nozzle distributor was developed. Experiments of pressure fluctuations and fines elutriation in the fluidized-bed system were conducted in 0.29-m I.D. and 0.19-m I.D. fluidized-bed cold models respectively to investigate the influence of the fluidizing pattern. The performances of the “swirling fluidizing pattern” and the conventional “axial fluidizing pattern” caused by a perforated plate were assessed.
At a low nozzle air-discharge velocity, a stable concentration of fines within the bed would be attained. The first-order elutriation rate equation cannot describe the elutriation behavior of fines under a swirling fluidizing pattern, except at an extremely high air-discharging velocity. The swirling fluidizing pattern has proven to produce remarkable improvements of both the fluidization quality and elutriation reduction.
3. Radial gas mixing in a fluidized bed using response surface methodology
Radial gas mixing in a fluidized bed was studied using response surface methodology (RSM), which enables effect examinations of parameters with a moderate number of experiments. All experiments were conducted in a 0.29-m I.D. fluidized-bed cold model. The gas dispersion process within the bed was described using the dispersed plug flow model. Pure carbon dioxide was used as the tracer gas. The downstream radial tracer concentration profile was measured using a gas-chromatograph.
The radial gas dispersion coefficient was well correlated with operating parameters and the particle and gas properties: the characteristic gas velocity, the static bed height to bed diameter ratio, the distributor open-area ratio, and the Archimedes number, with a determination coefficient R-squared of 0.966. The effect test indicates that the dimensionless characteristic velocity possesses the most significant influence on radial gas mixing, while the static bed height to bed diameter ratio is less remarkable. Both the interactions of gas velocity with the open-area ratio and with the Archimedes number play important roles. An evolutive response surface model was proposed to describe the radial gas mixing in bubbling/slugging fluidization regimes.

並列關鍵字

pressure fluctuation ； elutriation ； fluidized bed ； gas mixing

參考文獻

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