稻稈於流體化床燃燒中聚結之研究

Study of Agglomeration during Fluidized Bed Combustion of Rice Straw

殷祥峰(Siang-Fong Yin)

指導教授 ： 錢建嵩

中原大學/工學院/化學工程研究所/碩士(2014年)

https://doi.org/10.6840/cycu201400596

摘要

稻米為亞洲重要的糧食作物之一，稻稈係稻米種植過程中的主要副產物，全球每年約產720億噸的稻稈，尋找一有效處理稻稈的方法迫在眉睫，流體化床技術是處理農業廢棄物的最佳工具之一，但稻稈於燃燒過程中將面臨聚結與去流體化之問題。本研究係以矽砂為床質、稻稈為燃料，於實驗室規模之渦旋式流體化床燃燒爐進行實驗，探討不同床溫、二次風流量及空床氣速對去流體化時間、床內鹼金屬濃度、粒子的形態與組成、飛灰、汙染物排放量及燃燒效率之影響。
結果顯示去流體化時間隨著床溫增加而縮短，由於熔融現象隨著溫度上升而更為顯著，粒子間的黏滯力因而增強，易形成聚結粒子而去流體化；去流體化時間隨著二次風流量增加而縮短，底灰量的累積因二次風流量的上升而快速地累積，短時間內達到去流體化的臨界值以產生聚結粒子；去流體化時間隨著空床氣速增加而延長，床溫因空床氣速上升而更為均勻，降低熱點的生成機會，亦減少熔融現象的產生。實驗後之砂床可分為三個區域，分別為上氣泡區、下氣泡區與柵格區，其中下氣泡區與柵格區的鉀濃度不受參數改變而有顯著變化，上氣泡區的鉀濃度則受床溫影響甚鉅。

關鍵字

流體化床 ； 稻稈 ； 聚結 ； 去流體化

並列摘要

Rice is one of the important crops in Asia, and rice straw is a major byproduct from rice cultivation. The global rice straw production is approximately 720 million tonnes per year. Finding an effective way to deal with rice straw is urgent. Fluidized bed technology is an effective combustion method of biomass products, but agglomeration and defluidization are a persistent issue during rice straw combustion. The experiments are conducted in bench scale vortexing fluidized bed combustor (VFBC) using silica sand as bed material and rice straw as fuel. The effects of bed temperature, secondary gas flow rate and superficial gas velocity on the defluidization time, alkali concentration within the bed, the compositions and morphology of particles, fly ash, pollutant emissions, and combustion efficiency are investigated.
The results reveal that the defluidization accelerates with bed temperature. This is due to melting increases with temperature, which increases viscous force among particles. Particles agglomerate which causes defluidization. Defluidization accelerates and the amount of bottom ash increases with secondary gas flow rate. The amount of bottom ash reaches the critical point for agglomeration in a short time. Defluidization decelerates with superficial gas velocity, due to the uniform bed temperature at high superficial gas velocity, which reduces the melting phenomena and the hot spot forming probability in the bed. The bed can be divided into three sections which are upper-bubbling zone, lower-bubbling zone and grid zone. The potassium concentration in lower-bubbling zone and grid zone do not change significantly with operating parameters. In upper-bubbling zone, bed temperature has a strong influence on potassium concentration.

並列關鍵字

defluidization ； rice straw ； fluidized bed ； agglomeration

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