Please use this identifier to cite or link to this item: http://hdl.handle.net/11455/5498
標題: 流力行為對廢棄物焚化影響之研究
The study of the effects of hydrodynamic behaviors on waste incineration
作者: 林秋良
Lin, Chiou-Liang
關鍵字: Fluidized bed
流體化床
Incineration
Pollutant
Defluidization
焚化
污染物
去流體化
出版社: 環境工程學系
摘要: 本研究主要針對高溫流體化的行為與污染物生成間關係作一系列探討,首先探討高溫下的流體化行為,了解在焚化的高溫下(700~850℃)對最小流體化速度、爐床膨脹率、床質磨損等流體化行為的影響,第二部份則著重於流體化品質對污染物生成的影響。而在第三部份研究中,主要探討焚化過程中結塊、去流體化的產生,並藉此了解結塊與有機物及重金屬等污染物生成的相關性,並以一半經驗式模擬不同條件下結塊去流體化的時間。 對高溫環境下的流體化特性來說,系統最小流體化速度起初是隨溫度的提高而逐漸下降,但達到某一溫度後最小流體化速度開始反轉上升,而燃燒過程中床質磨損速率較無燃燒時為大,因燃燒廢棄物時所產生燃燒熱與熱衝擊增加床質的崩解與磨損。另外由壓力擾動指標顯示燃燒過程中爐床流體化行為的週期性改變,壓力擾動源增加,導致流體化行為較為紊亂,但有機物產生濃度反而降低,顯示因燃燒而產生的氣爆與熱效應對爐床中原本氣泡規律的行為產生影響,將原本已合併的大氣泡再度打散成為較小的氣泡,增加了氧氣傳輸效率,使燃燒效率增加。對四種不同的床質粒徑分布來說可區分為兩群,高斯與單一分布為一群,而二元與平坦則為另一群。而高斯與單一分布所造成的燃燒效率優於二元與平坦分布,因此若操作中保持床質傾向於單一或高斯分布可維持較佳的焚化效率。 鹼金族元素Na對於結塊有相當大的影響,隨著Na濃度增加,結塊去流體化的時間大幅降低,而Mg與Ca對於結塊有抑制的效果可延長爐床操作時間,其可能產生部份高熔點的產物,如Mg2SiO4、MgO、CaO與Ca(OH)2等。而對污染物的影響方面,有機污染物PAHs與BTEXs的排放濃度隨著結塊的逐漸產生而增加,顯示結塊的產生將導致燃燒效率下降,當爐床去流體化後,由於爐床表面溫度升高反而降低有機物濃度,但仍比無結塊產生時為高。對重金屬污染物來說,去流體化之前,不論有無添加Na,其重金屬排放濃度差異不大,但去流體化後,重金屬的排放大幅提高,可能是去流體化後爐床屬於固定床的形式使重金屬無法被石英砂吸附加上爐床表面溫度的增加,使得重金屬排放量大幅增加。而以爐床中力平衡配合實驗數據作迴歸分析所推導之去流體化時間預估式,若廢棄物燃燒後Na留存於床質的比例 值為0.8~1的範圍時,所預估之去流體化時間與實驗值差異不大其誤差範圍約在±20%之間,顯示預估式對焚化過程中去流體化時間有良好的適用性。
The primary object of investigation elucidates the relationship between the fluidized characteristics and pollutants during incineration. The work firstly emphasizes the effects of high temperature on minimum fluidized velocity, expanded bed rate, and attrition. Then, the effects of the mixing of multi substances on the fluidized behavior and generation of pollutants are also performed. Finally, the study focuses on the mechanism of formation of agglomeration and defluidization during incineration process and a simple model has been developed to simulate the defluidization time at various conditions. At high temperature, the minimum fluidization velocity gradually reduces as temperature is increased, but above 800℃, the minimum fluidization velocity reverses with rising temperature. Comparing the result for combustion with those for non-combustion reveals that total weight of attrition during combustion is significantly higher than under the non-combustion condition, because the combustion heat and thermal shock increase attrition. According to index of pressure fluctuations, the concentration of organic pollutants does not increase with uniformity of fluidization decreasing. It may be that the explosion of the volatiles causes the pressure in the chamber to change suddenly and destroy the coalescent bubbles to form small bubbles again. The gas explosion possibly increases the efficiency of conversion of oxygen between bubbles and wastes, increasing the combustion efficiency and reducing the concentration of organic pollutants. The four particle size distributions could be divided into two groups by statistical analysis. The organic concentration of the Gaussian and narrow distributions are lower than that of the other distributions. Consequently, the bed materials should maintain narrow or Gaussian distributions to maintain a good combustion efficiency during incineration. Alkali metals (Na) significantly affected the agglomeration of bed materials. Increasing the concentration of sodium caused a decrease of time to reach defluidization. However, the earth alkali metals (Mg, Ca) apparently inhibited the agglomeration generation, some species with high melting points, such as Mg2SiO4, MgO, CaO and Ca(OH)2 were generated, inhibiting agglomeration. For pollutants, the emission of organics (BTEXs and PAHs) increased with the operating time, as according to the generation of agglomerate, indicating that the size of the agglomerate gradually increased, reducing the efficiency of combustion. However, the concentrations of volatile metals (Cd, Pb and Cr) exhibited similar tendencies with operating time. However, the emission concentrations increased after defluidization, because the silica sand can not capture the heavy metals released from combusted waste in the fixed bed state. The increase in the temperature of the surface of the sand bed is important in promoting the emission level of heavy metal. Accordingly, the emissions of organics and heavy metals pollutants differed during agglomeration and defluidization. A simple model has been developed to describe the defluidization time at various conditions. When the exist ratio of Na in bed material is between 0.8 to 1, the prediction is agreed with experimental data and the error range is between -20% ~ +20%.
URI: http://hdl.handle.net/11455/5498
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