Abstract: A model for the heat of absorption of CO₂ using ammonia was established in the Aspen Plus software based on the e-NRTL model.The vapor liquid equilibrium and speciation of the NH₃-CO₂-H₂O system were validated with the experimental data in literature.The heat of CO₂ absorption was predicted and compared with the experimental data,combined with the analysis of liquid composition in the CO₂ loaded aqueous ammonia.The results show that the model built in this paper can accurately calculate the vapor liquid equilibrium,speciation,as well as the heat of CO₂ absorption in the ammonia based CO₂ capture process.The heat of CO₂ absorption is mainly affected by the dissociation of H₂O and NH₃,formation and hydrolysis of NH₂COO^- and dissolution of CO₂ in the aqueous ammonia.The heat of H₂O dissociation has the largest proportion in the overall heat of CO₂ absorption,which is in restraint of the dissociation of NH₃.The reaction related to NH₂COO^- is exothermic first and then endothermic with the increase of CO₂ loading.As the temperature increases,the heat of CO₂ absorption decreases.The average heat of CO₂ absorption is 70.5 kJ·(mol CO₂)^-1,when the CO₂ loading is between 0.2—0.5 mol CO₂·(mol NH₃)^-1 and temperature is 80℃.

Key words: aqueous ammonia, carbon dioxide, modelling, heat of regeneration, heat of absorption

摘要： 基于e-NRTL模型,利用Aspen Plus软件建立了氨水吸收CO₂的吸收热预测模型,验证了NH₃-CO₂-H₂O体系的汽液平衡、液相组成形态并与前人的实验数据做了对比,进而结合负载CO₂的氨水溶液中各离子及分子的变化特征,对CO₂吸收过程的反应热随着CO₂负载量的变化规律进行了预测并与已发表的数据进行了比较。结果表明,该吸收热模型能够准确地实现氨水吸收CO₂过程中汽液平衡、液相反应以及吸收热的计算。氨水吸收CO₂的反应热主要受H₂O的电离、NH₃的电离、NH₂COO^-的生成与水解、CO₂的溶解等反应过程的影响,H₂O的电离过程受NH₃的电离过程的抑制,对于总吸收热的贡献最大, NH₂COO^-的反应则随着CO₂负载量的增加先放热再吸热。随着温度的升高,总吸收热有所降低,当温度为80℃时,在较低的CO₂负载区间[0.2～0.5 mol CO₂·(mol NH₃)^-1],总吸收热约为70.5 kJ·(mol CO₂)^-1。

关键词: 氨法脱碳, 二氧化碳, 模型, 再生能耗, 吸收热