矩形氣泡式流體化床中橫向氣體分散之研究

The Study of Lateral Gas Dispersion in a Rectangular Bubbling Fluidized Bed

侯心詠(Hsin-Yung Hou)

指導教授 ： 錢建嵩

中原大學/工學院/化學工程研究所/碩士(2015年)

https://doi.org/10.6840/cycu201500854

摘要

於流體化床燃燒爐中，氣固間之接觸速率及混合將決定其流體化品質。本研究係於0.4 "×" 0.2 "×" 1.5 m3之矩形冷模流體化床中，使用分佈器為穿孔板，以玻璃珠為床質，將追蹤氣體二氧化碳由床底一點源連續注入床中，於同一採樣高度之各點追蹤氣體濃度將以非分散式紅外線光譜儀分析。
於本研究，由統御方程式可得數學模型，而使用殼莫耳平衡可推導出方程式。由OriginPro 8軟體，將實驗數據使用非線性曲面擬合可得橫向氣體分散係數；而橫向氣體分散係數於笛卡爾座標中可分為x軸氣體分散係數 (Dx) 及y軸氣體分散係數 (Dy)。為研究不同操作條件對氣體混合及分散之效應，將改變空床氣速、靜床高、追蹤氣體注入位置、採樣高度及追蹤氣體注入之體積流率等參數。
本實驗及曲面擬合之結果顯示，僅於兩種操作條件下，調整後判定係數將低於0.99，分別為追蹤氣體注入之體積流率為流體化氣體體積流率之0.10% 倍，以及追蹤氣體於側邊注入時；其代表本研究使用之模型可適切描述床內之橫向氣體混合行為。在本研究條件下，由於床壁效應，x軸及y軸之氣體分散係數將不相等；採樣高度若低於10 cm (距分佈器上方) 將受到噴流效應之影響；橫向氣體分散係數隨著空床氣速增加而上升；靜床高效應對橫向氣體分散係數之影響不顯著。

關鍵字

氣體分散係數 ； 橫向混合 ； 曲面擬合 ； 追蹤氣體

並列摘要

In a fluidized bed combustor (FBC), fluidizing quality can be decided by gas-solid contacting and mixing. The experiments are conducted in a cold model of rectangular bubbling fluidized bed of 0.4 "×" 0.2 "×" 1.5 m3. The distributor plate is perforated plate. The bed material is glass beads. The tracer gas is carbon dioxide, and it is injected continuously from a point source from the bottom of the bed. The concentrations of the tracer gas at the same sampling height are analyzed by using a nondispersive infrared gas analyzer.
In this study, the mathematical model is developed by using a governing equation. The governing equation is derived by using shell mole balance. The lateral gas dispersion coefficients are obtained by the nonlinear surface fitting method on the experimental data using “OriginPro 8” software. In Cartesian coordinate, the lateral dispersion coefficients are divided into x-axis and y-axis gas dispersion coefficients, i.e. Dx and Dy, respectively. To investigate the effect of operating conditions on the gas mixing and dispersion coefficients, the superficial gas velocity, static bed height, location of tracer gas injection point, sampling height, and tracer gas injection flow rate are varied.
The experimental and surface fitting results show that only in two conditions, when tracer gas injection rate is 0.10% of the fluidizing air flow rate and tracer gas is injected at the side of the bed, the adjusted “R squared” are less than 0.99. This indicates that the lateral mixing behavior in the bed can be well described by the model which is based on derived equation. In the experimental conditions, because of the wall effect, the gas dispersion coefficients of x and y-axis, i.e. Dx and Dy, are not the same. In this study, the sampling height is maintained above 10 cm to avoid the jet effect of the tracer gas from a point source. The results show lateral dispersion coefficients are increased with increasing superficial gas velocity. The effect of static bed height on the lateral dispersion coefficients is minimal.

並列關鍵字

Gas dispersion coefficient ； Horizontal mixing ； Surface fitting ； Tracer gas

參考文獻

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