化學迴圈是二氧化碳捕捉與封存的其中一種技術,其特點為低耗能， 並可產生熱能以供發電使用， 同時不需要額外的耗能的單位就可得到接近100% 的二氧化碳。 根據不同的燃料和氧化氣體， 可得到不同的合成氣及反應氣體, 載氧體主要是以提供氧氣予燃料並經在兩反應器間循環。其反應器主要分為燃料反應器或還原反應器及氧化反應器， 反應器主要是以流動床和移動床兩種。由於化學迴圈的基本概念為氣化還原反應， 故熱力學分析可助於實際操作時作為參考。
本研究主要以赤鐵礦 (Fe2O3)作為載氧體, 以熱力學平衡的角度探討化學迴圈在900 °C 下甲烷作為燃料時的表現。 還原反應器中， 控制甲烷與赤鐵礦(碳/鐵)的比值為一重要參數, 而在氧化反應器中， 氧氣與赤鐵礦(氧/鐵)的比值作為另一控制參數,本研究以五種不同的碳/鐵比值(1/15， 1/12， 1/10， 1/8 和 1/5) 及五種不同的氧/鐵比值(1.5，0.3， 0.2， 0.18 和 0.15) 作為基準， 根據這些操作參數所得到的反應器的氧化還原程度， 找出最佳的操作條件。
結果表現較高的碳/鐵比值會需要較多的循環才能夠達到平衡, 在碳/鐵比值< 1/5的情況下, 其只需要5個循環左右就可以達到平衡狀態。而不同的氧/鐵的比值也是明顯的影響循環次數，在五種的碳鐵比值中，其甲烷的轉化率幾乎都能達到接近100%的程度，其中最多的二氧化碳和水蒸氣產生主要落到碳/鐵比值為1/15 的時候，隨着碳/鐵比值的增加，此兩種氣體的產生呈現減少的趨勢。在較低碳/鐵比值的時候，其主要產物為Fe3O4，在高的碳/鐵比值中，更高還原態的鐵產物更容易產生。碳/鐵比值的增加同時也伴隨着更多的一氧化碳以及氫氣的生成同時其耗氧程度會變高。 積碳現象在高碳/鐵比值下會更容易產生。
在不同的氧/鐵比值中，其最高的產生為二氧化碳與水蒸氣，其產生會隨着氧/鐵比值的減少而減少。其積碳在較少氧氣的情況下更容易產生。根據能量的分析， 其焓在還原以及氧化的反應器中皆為吸熱反應 (除了碳/鐵比值為1/15時)，表示在化學迴圈的過程中，系統維持吸熱的狀態，根據氧化還原度的結果，最佳的操作條件為碳/鐵比值為1/12，而氧/鐵比值為0.18以及溫度在900度，在此條件下，反應器皆呈現放熱行為。

Chemical looping is a promise technology in carbon dioxide capture and storage, which is an almost less energy and provide heat during the process. This technology can get pure carbon dioxide by condense the water vapor of the outlet gas, depend on what fuel and oxygen carriers (OCs) used, there will be different syngas and outlet gas release. OCs is an import role in chemical looping because it can transfer oxygen to the fuel and recycle between reduction and oxidation two reactors. Generally, the reactor is fluidized bed or move bed two kind, since the basic concept of the chemical looping is redox reaction in the reactor, so that thermodynamic analysis is helpful reference to operator reactor.
This study use hematite as oxygen carrier (OC) with chemical looping process, methane as reduction gas and air as oxidation gas at 900 °C. Five different M/H ratio (1/15, 1/12, 1/10, 1/8 and 1/5) and O/H ratio (1.5, 0.3, 0.2, 0.18 and 0.15) on iron oxide redox reaction were examined. In addition, a redox degree of the reactors was defined.
The results showed that higher M/H ratio needed more cycles to achieve equilibrium state and O/H ratio also show that it is significantly relate to cycle number. The maximum CO2 and H2O yield was located at M/H=1/15, but the yield of these two compounds decreased with an increase of M/H ratio. The demonstrate species would be Fe3O4 at lower M/H ratio, the further reduced stage iron oxides will show with higher M/H ratio, but accompany CO and H2 generated. The O2 consumption in the air reactor was decreased with increasing M/H ratio. The overall CH4 conversion of the five M/H ratio almost remained at 100%, revealing that the conversion did not relate to M/H ratio and O/H ratio. Carbon formation is also presented in this study, the yield of carbon deposition is direct proportion to M/H ratio. Under five O/H ratios with M/H=1/12, the maximum CO2 and H2O yield are achieved in O/H≥0.8, similar with M/H ratio result, the gas yield is decrease when O/H is reduced. Our results showed that the less oxygen input to the reactor, the more carbon formation. The enthalpy of the reactors reveals that the behavior of reactors was endothermic (expect M/H=1/5). To find the optimal parameters, the redox degree was introduced in this study and the results showed that reactor should be controlled at M/H=1/12 and O/H=0.18 where temperature is 900 °C, the enthalpy of this condition showed endothermic behavior at both reactor.

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