流體化床具有高熱傳率、高效率、低污染物排放、低燃燒溫度以及燃料選擇限制較低等優點，也廣泛應用於工業及發電上。雙流體化床氣化爐是採用快速內循環流體化床(Fast Internally Circulating Fludized-Bed)之概念來設計，其設計是將流體化床分為氣化流體化床區以及燃燒流體化床區。在這兩個區域間藉由固體粒子之流動來形成一循環迴路，此設計能將燃燒反應以及氣化反應分開：在氣化流體化床區只注入水蒸汽進行氣化反應；在燃燒流體化床區只注入空氣進行燃燒反應。因此能在氣化流體化床區中得到近乎沒有氮氣之合成氣。
本研究以計算流體力學軟體ANSYS-FLUENT來進行模擬，針對雙流體化床氣化爐氣化區以及雙流體化床氣化爐建立三維多相反應流模擬分析模型。針對雙流體化床氣化爐氣化區模型之氣化性能進行參數分析：不同蒸汽燃料比及不同床砂循環率之影響。變動蒸汽燃料比，固定燃料量，改變水蒸汽流量，得到不同蒸汽燃料比並進行測試。結果顯示，當蒸汽燃料比較高時，水蒸汽增加，有助於水氣轉化反應，使得合成氣中之氫氣和二氧化碳之含量較高，一氧化碳含量較低。變動床砂循環率並觀察其對氣化性能之影響。結果顯示，當床砂流量增加時會擴展水氣轉化反應速率之範圍。在雙流體化床氣化爐中，已成功建立床砂之循環模式，將內部流場可視化，檢視粒子於兩區之間之流動現象。並加入燃燒及氣化反應，觀察氣體成份分佈、反應區域大小、合成氣出口成份比例等等。與實驗進行比較，發現模擬之二氧化碳以及氫氣含量高於文獻數據；甲烷之含量與文獻相近；一氧化碳之含量低於文獻許多。此一結果推測是因為反應範圍會受到氣固相流場影響，床砂之滾動範圍不夠大導致反應無法發展並堆積在床區底部。為使其在冷流場能達到鼓泡效應，將水蒸汽流量加大，結果與預期相符。

A fluidized-bed gasifier is characterized by high thermal conductivity, high efficiency, low pollutant emissions, and few fuel selection limitations, and is widely used in industries and power plants. For the present research, a dual fluidized-bed gasifier was designed using the FICFB (Fast Internal Circulating Fluidized Bed) model, which is divided into two sections, the gasification zone and the combustion zone, which form a circulation loop through which a stream of solid particles flows. Gasification occurs only in the gasification zone, so the syngas produced is completely free of nitrogen.
In this study, the CFD software, ANSYS-FLUENT, is used to simulate both the dual fluidized-bed gasifier and the gasification zone. The dual fluidized-bed gasifier and the gasification zone are modeled in 3D multiphase flow numerical systems. The SF (steam to fuel ratio) and the bed material circulation rate are tested in the model of the gasification zone. In gasification results, when SF changed, the biomass inlet would be fixed, and the steam inlet would be changed. The results show that when the SF is changed, the biomass inlet becomes fixed and the steam inlet changes. When SF increased, the reaction rate of the water gas shift reaction also increases. Regarding the changing bed materials circulation rate, when the circulation rate increased, the scope of the chemical reaction also increases. When the bed materials circulation in the dual fluidized-bed gasifier model is successfully constructed, the path of bed materials can be predicted, the flow field can be visualized, the syngas composition, and both the gas distribution and reaction zone can be observed. The content of CO2 and H2 in the simulation turned out to be higher than in the actual experiment whereas the content of CO was lower. Only the CH4 level was accurately predicted by the simulation. The differences between the simulation and the reference are due to the chemical reaction range, which is influenced by the flow field. The bed material never reached the bubbling stage, so the reaction was incomplete. In order to achieve the bubbling effect, the steam in let was increased, after which the results fell in line with expectations.

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