以氨水组分分离为特征的“制冷-碳捕集”耦合循环构建理论及性能分析

Taking aim at the current problems of ammonia-based carbon capture and ammonia absorption refrigeration. A novel ammonia absorption refrigeration cycle coupled with carbon capture is proposed, which is based on ammonia-water separation. By integrating absorption refrigeration process with carbon capture process, the cooling process combines with CO2 separation process is realized, the system performance is improved efficiently and hence the energy penalty is reduced. The new absorption refrigeration coupled with carbon capture cycle is going to be researched in the following. First, by using theoretical analysis, the component, composition and molecular groups on ammonia-water mixtures in absorption and desorption processes are studied quantitatively, the thermodynamic model and the correlation equations will be confirmed. Then, by experimental researching and numerical modeling, the mechanism of component separation of ammonia-CO2 mixture through T-junction under the conditions of incomplete condensation is investigated. The effects of thermos-physical parameters and flow parameters of ammonia-CO2 mixture as well as the geometrical parameters of T-junction on the component separation will be determined. Meantime, based on the established cycle of ammonia absorption refrigeration coupled with carbon capture, the thermodynamic cycle will be characterized. Through thermodynamic calculation, the optimal working fluids for different working conditions will be determined, the synergic relationship between the entropy production of individual thermodynamic process and the total entropy production of the cycle is investigated, and the collaborative relationships of operation parameters for each component is conducted to search the optimal parameters.

针对氨法碳捕集氨逃逸、氨水吸收式制冷部件多、COP偏低的现状，本项目以氨水工质对为基础，将吸收式制冷与碳捕集结合，提出了以氨水组分分离为特征的“制冷-碳捕集”耦合循环的实现形式与分析方法，以求实现制冷与分离CO2一体化、提升系统循环性能及降低捕集能耗的目标。首先，理论分析吸收与发生（解吸）过程氨水工质组元构成与组分浓度变化规律，建立描述循环工质热力特性的模型及其关联式；然后通过实验与数值模拟，对解吸气非完全冷凝条件下氨-CO2气液两相流在T型管内的流动与分离过程进行深入研究，明确混合物热物性参数、流动参数及流道几何参数等对混合物两相分离特性的影响；随后展开氨水吸收式制冷耦合吸收法碳捕集循环的构建与热力循环表征，并通过热力学计算，针对不同工况，研究各热力过程不可逆损失与循环整体熵增的协同关系，明确系统各部件协同运行的特征参数以及最优匹配关系。

氨法脱碳具有良好的CO2吸收效率和较低的再生能耗，且不存在设备腐蚀、氧化降解等问题，成为缓解当前二氧化碳排放的有效途径之一。然而，由于氨的饱和蒸气压高，具有高的挥发速度，氨法捕集过程氨逃逸仍是氨法工艺中的一大技术壁垒。针对氨法碳捕集氨逃逸的特性，本项目以氨水工质对为基础，将吸收式制冷与碳捕集结合，提出了以氨水组分分离为特征的“制冷-碳捕集”耦合循环的实现形式与分析方法，以求实现制冷与分离CO2一体化、提升系统循环性能及降低捕集能耗的目标。通过对NH3-CO2-H2O体系的研究，建立了描述三元体系的热力学与化学反应模型，实现了组分分压及浓度的预测；结合吸收与解吸实验，确定了高浓度氨水吸收过程氨逃逸的变化情况以及解吸气中氨与二氧化碳的占比情况，并对解吸气非完全冷凝条件下氨-CO2气液两相流在T型管内的流动与分离过程进行深入研究，明确了混合物热物性参数、流动参数及流道几何参数等对混合物两相分离特性的影响。随后开展了氨水吸收式制冷耦合吸收法碳捕集循环的构建与热力循环表征，并通过热力学计算，针对不同工况，明确了系统各部件协同运行的特征参数以及最优匹配关系。