雙流體化床氣化爐採用快速內循環流體化床 ( Fast Internal Circulating Fluidized Bed, FICFB)的概念來設計，將其分為氣化流體化床區及燃燒流體化床區，在這兩個區域間藉由固體粒子流動來形成一個循環迴路，將流體化床燃燒爐進行燃燒反應後所產生的熱攜帶至流體化床氣化爐，供給生質燃料進行氣化反應所需的能量。在連接兩區域間的連接管中注入水蒸汽以利固體粒子流動，並將燃燒反應及氣化反應後所產出的氣體隔絕開來。如此一來，在氣化區中能得到幾乎沒有氮氣的合成氣。因此，本研究以計算流體力學軟體FLUENT 來進行模擬，針對雙流體化床氣化爐建立以生質燃料為進料之多相反應流模擬分析模式。本研究將對三維雙流體化床之氣化性能進行流場與參數分析，進行了長時間運行下床爐之穩定度及溫度變化、流場等等分析，可以觀測到雙流體化床氣化爐從點火開始之溫昇行為及熱量循環，並且觀察到氣化爐生質燃料進爐後之氣化行為；藉由改變粒子循環率、負載，觀察其對於氣化性能的影響，可以確認到粒子循環率與負載對氣化性能有正面影響；亦進行了放大分析，觀察尺寸對於流體行為及氣化性能之影響，即便將床爐放大後，雙流體化床氣化爐仍能正常運作，其反應區域縮小，出口氣體組成與原尺寸相仿，冷煤氣效率則波動變大。

The dual fluidized bed gasifier used in this work is designed using the FICFB (Fast Internal Circulating Fluidized Bed) concept. It is separated into two parts: the gasification zone and the combustion zone. Two zones are linked together as a circulation loop by flowing solid particles, where the heat produced in the combustion zone can be transferred to the gasification zone, supplying the energy that biomass needs to gasify. In the loop seals, steam is injected for the purpose of fluidizing the solid particles and separating the gases produced from combustion and the gasification reaction. In this way, the syngas in the gasification zone is free of nitrogen. In the present study, an analytical technology used for the simulation of a dual fluidized bed gasifier was developed for the multi-phase reaction of biomass fuel using the commercial CFD software, FLUENT. In this study, a fluid dynamic analysis was conducted for the dual fluidized bed, where the stability, temperature, flow, etc. were analyzed. we focus on the temperature changing, the heat cycle of the combustion zone after the ignition, and the gasification of the gasifier after the biomass fuels are introduced into the gasifier zone. Thus, by adjusting the particle circulation rate and biomass load to observe their influence on gasification efficiency, it can be confirmed that the particle circulation rate and the load have a positive influence on gasification efficiency. A scale-up analysis is also carried out to determine the effect of size on the flow and gasification performance. Even after the bed is scaled-up, the dual-fluidized bed gasifier can still simulate and analyze successfully. Compare to the reference condition case, the reaction zone of the whole gasifier is reduced, the composition of the produced gas is similar, and the efficiency of the cold gas fluctuated.

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