氨水吸收CO_2的吸收热预测模型

Prediction model of absorption heat for CO_2 capture using aqueous ammonia

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[0.2～0.5mol CO2·(mol NH3)-1],总吸收热约为70.5kJ·(mol CO2)-1。

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℃.