Wang Hui, Li Zhenshan, Cai Ningsheng
Key Laboratory for Thermal Science and Power Engineering of Ministry of Education, Department of Energy and Power Engineering, Tsinghua University, Beijing 100084, China.
Tsinghua University-University of Waterloo Joint Research Center for Micro/Nano Energy & Environment Technology, Tsinghua University, Beijing 100084, China.
Materials (Basel). 2019 Apr 10;12(7):1170. doi: 10.3390/ma12071170.
Copper oxide is one of the promising oxygen carrier materials in chemical looping with oxygen uncoupling (CLOU) technology, cycling between Cu₂O and CuO. In this study, a multiscale model was developed to describe the oxidation kinetics of the Cu-based oxygen carrier particle with oxygen, including surface, grain, and particle scale. It was considered that the solid product grows with the morphology of disperse islands on the grain surface, and O₂ contacts with two different kinds of grain surfaces in the grain scale model, that is, Cu₂O surface (solid reactant surface) and CuO surface (solid product surface). The two-stage behavior of the oxidation reaction of the Cu-based oxygen carrier was predicted successfully using the developed model, and the model results showed good agreement with experimental data in the literature. The effects of oxygen partial pressure, temperature, and particle structure on the oxidation performance were analyzed. The modeling results indicated that the transition of the conversion curve occurs when product islands cover most part of the grain surface. The oxygen partial pressure and particle structure have an obvious influence on the duration time of the fast reaction stage. Furthermore, the influence of the external mass transfer and the change of effectiveness factor during the oxidation reaction process were discussed to investigate the controlling step of the reaction. It was concluded that the external mass transfer step hardly affects the reaction performance under the particle sizes normally used in CLOU. The value of the effectiveness factor increases as the reaction goes by, which means the chemical reaction resistance at grain scale increases resulting from the growing number of product islands on the grain surface.
氧化铜是化学链氧解耦（CLOU）技术中一种很有前景的氧载体材料，可在Cu₂O和CuO之间循环。在本研究中，开发了一个多尺度模型来描述铜基氧载体颗粒与氧气的氧化动力学，包括表面、晶粒和颗粒尺度。认为固体产物以晶粒表面分散岛的形态生长，并且在晶粒尺度模型中O₂与两种不同的晶粒表面接触，即Cu₂O表面（固体反应物表面）和CuO表面（固体产物表面）。利用所开发的模型成功预测了铜基氧载体氧化反应的两阶段行为，模型结果与文献中的实验数据吻合良好。分析了氧分压、温度和颗粒结构对氧化性能的影响。模拟结果表明，当产物岛覆盖大部分晶粒表面时，转化率曲线发生转变。氧分压和颗粒结构对快速反应阶段的持续时间有明显影响。此外，还讨论了氧化反应过程中外部传质的影响和有效因子的变化，以研究反应的控制步骤。得出的结论是，在CLOU通常使用的颗粒尺寸下，外部传质步骤几乎不影响反应性能。有效因子的值随着反应的进行而增加，这意味着由于晶粒表面产物岛数量的增加，晶粒尺度上的化学反应阻力增大。
