摘要
本研究採用高3 m、內徑0.0529 m之上升床與高0.55 m、內徑0.28 m之氣泡流體化床互相並聯，以空氣為氣相，平均粒徑230 μm的玻璃砂為固相，在冷模情況下探討化學迴圈燃燒各種操作變數之影響。上升床可視為空氣反應器，氣泡流體化床可視為燃料反應器。利用追蹤粒子測量固體迴流量並以迴路壓封閥控制之。上升床之氣體表面速度與固體迴流量為操作變數，由壓力探針量測系統中壓力分佈、壓力擾動、壓力降、壓力標準偏差與粒子軸相空隙度分佈，討論系統流力行為與穩定性。參考文獻中載氧粒子之化學性質，模擬在不同溫度、壓力與粒徑大小下對載氧粒子轉化率的影響，並估計二氧化碳的產量。 本實驗之閉塞現象屬於實驗裝置限制造成的B類型閉塞現象。上升床中氣固流態的操作範圍為由紊流流體化床流態至快速流體化床流態。觀察系統壓力分佈，迴路壓封閥是系統中壓力最大處。對化學迴圈燃燒系統而言，在迴路壓封閥之密封作用下，二氧化碳可避免被氮氣稀釋，燃料反應器中的二氧化碳也沒有流竄至空氣反應器的現象。所以迴路壓封閥是化學迴圈燃燒系統的核心。 就本實驗粒子(玻璃砂)而言，軸向平均空隙度分佈是隨著表面氣體速度與固體迴流量而改變。稀相輸送呈現單一直線分佈；快速流體化輸送呈現近單調指數函數分佈圖形或S型分佈圖形。 以體積不變之收縮模型的氣固反應中，粒子外層之氣體擴散對於NiO/YSZ 與NiO/bentonite粒子皆是可忽略的。NiO/bentonite之轉化率對反應時間關係顯示，隨著反應溫度升高、氣體反應物壓力增加與載氧粒子粒徑之減少其反應速率因而變快。根據二氧化碳產率分析，由於NiO/YSZ具高反應性，故於化學迴圈燃燒系統中，選擇NiO/YSZ (Ishida et al., 1996)粒子為載氧粒子優於NiO/bentonite (Ryu et al., 2001)粒子。
並列摘要
The study adopted interconnecting the riser (0.0529 m i.d. × 3 m height) and the bubbling fluidized bed (0.28 m i.d. × 0.55 m height) and researched the cold modeling of chemical looping combustion (CLC) for Geldard group B powder (glass beads, dp = 230 μm). The riser acted as air reactor and the bubbling fluidized bed as fuel reactor. The solids circulating rate was measured by tracking solids and was controlled by a loop seal valve. The superficial gas velocity of the riser and solids circulating rate were the variables to investigate the pressure profile, pressure fluctuations, pressure drop, standard deviation of pressure and axial voidage distribution measured by the pressure taps and observed the hydrodynamic and stability of the system. Simulated the solid conversion against reaction time at different temperature, pressure and diameter referring to solid oxygen carrier’s parameter and calculated the production of carbon dioxide. It was found that the choking on the experiment was classified as B-type choking induced by blower or standpipe. The riser operated from turbulent fluidized bed to fast fluidized bed. The pressure profile showed that loop seal was the highest pressure of the system. As for CLC, the sealing effect of the loop seal was able to avoid diluting carbon dioxide with nitrogen and leakage of carbon dioxide form fuel reactor into the air reactor. Therefore loop seal is the core of CLC. For the bed material (glass beads), the average axial voidage distribution in the riser changed with superficial gas velocity and solids circulating rate. It appeared a straight line on dilute phase conveying and a simple exponential or S-shape profile on fast fluidization. On the gas-solid reaction for unreacted shrinking core model of unchanging size, the gas film diffusion control on the NiO/YSZ and NiO/bentonite can both be neglected. According to the solid conversion of NiO/bentonite against reaction time figure, the reaction rate increased with the rising of temperature and pressure and the reduction of solid oxygen carrying’s diameter. The productivity of dioxide carbon showed that NiO/YSZ (Ishida et al., 1996) is more suitable than NiO/bentonite (Ryu et al., 2001) as solid oxygen carrier in the chemical looping combustion system due to the high reactivity of NiO/YSZ.
參考文獻
延伸閱讀
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