化學迴路為新興的能源技術，由於具高能源效率、低污染排放及捕獲二氧化碳低成本之特性，因此美國能源部評估化學迴路為最前瞻的能源系統與二氧化碳捕獲技術，尤以顆粒移動床式化學迴路可大幅度地降低反應系統內載氧體之負載量及系統相關成本。然而，目前顆粒移動床技術成熟度尚低，在優化系統設計與操控技術上，仍然有相當大的改善空間。本計畫以擬三維實驗與離散元素電腦模擬探討載氧體在化學迴路反應器中之流動行為與流場優化機制，規劃之物理實驗為化學迴路反應器中之儲槽卸載循環實驗 (包含無置入物與數種置入物的情況)，採用的載氧體為三氧化二鐵 (Fe2O3) 球形及非球形顆粒，並進行對應的離散元素電腦模擬。以物理實驗為主，電腦模擬為輔，探討兩者巨觀行為 (顆粒體的流速分佈與質量流率) 差異的原因，用以修正電腦模擬之理論模式。確定採用之離散元素電腦模擬模式的合理性與可靠性後，同時透過數種置入物儲槽實驗與對應電腦模擬結果，尋找載氧體最佳均勻流速分佈，使得載氧體的化學反應更為均勻、更為有效，達到流場優化效果，並進一步探索優化機制。 本計畫發展相關的離散元素電腦模擬技術與驗証實驗探究三維儲槽顆粒體的流動行為與流場優化機制。本計畫首先提出離散元素電腦模擬技術「切片法」與「降低模數法」，此兩種方法不僅大幅度地減少電腦模擬的計算時間，而且不影響結果的精度，將有助於離散元素電腦模擬應用至工業界大尺寸的化學迴路反應器。由於顆粒體在圓柱形反應器中呈現軸對稱流動，因此本計畫建置擬三維實驗，用以重建三維儲槽顆粒體的流速分佈，擬三維反應器為一半的原型反應器，反應器正面為一透明而且非常平滑的玻璃板，並使用粒子影像測速 (Particle Image Velocimetry, PIV) 量測顆粒體在反應器内之速度場分佈，藉以驗證離散元素電腦模擬結果。 本計畫最後透過離散元素計算内部物理量 (中觀與微觀行為) ，中觀行為有滯流時間 (residence time)、內部應力與應變 (stress and strain) 及粒子體積佔有率 (solid fraction)，微觀行為有力量傳遞鏈 (force chain)、配位數 (coordination number) 及顆粒間的組構 (fabric)，進行多尺度 (巨觀、中觀與微觀) 行為之分析，藉以更深入地探究載氧體在化學迴路反應器中之流動行為。 ;According to the assessment of US Department of Energy, chemical looping, especially for a moving bed gasifier, is the most powerful energy system and has the most efficient CO2 capture technology due to its high energy efficiency, low pollutant emission and low cost of CO2 capture. However, the processing technology for this moving bed gasifier is still not maturely developed. For example, the flow behaviour and residence time of the metal oxides in a chemical looping reactor is poorly understood. This project investigates the flow behaviour of metal oxides in a chemical looping reactor by using quasi-3D physical experiment and discrete element modelling (DEM). Cyclic silo discharge test is designed to copy chemical looping system. The metal oxides are spherical and non-spherical Fe2O3 particles. The Particle Image Velocimetry (PIV) is employed to measure the velocity field of Fe2O3 particles. The corresponding DEM simulations will be performed. The macro behaviour, such as velocity distribution and mass flow rate, will be calculated. The comparison between numerical simulation and quasi-3D physical experiment will be made and discussed. The DEM model will be validated and then modified. For more efficient chemical reaction, the placement of inserts will also be designed and the flow field of Fe2O3 particles will further be explored. After careful validation for the proposed DEM models, the meso and micro behaviours (meso properties: residence time, solid fraction, strain and stress; micro properties: force chain, coordination number and fabric) will be evaluated. The effect of insert on macro, meso and micro behaviours of Fe2O3 particles will be systematically explored. This project will provide useful and valuable strategies for DEM applications to realistic engineering problems in energy industries.
