Abstract: In order to effectively reduce negative influence of non-condensable gas on falling film evaporation and optimize the geometrical parameters of evaporators,a model for chemical desorption of CO₂ in the multi-effect distillation(MED)system is presented.The desorption rate of CO₂ and its influencing factors are obtained by simulating an actual MED setup.Compared with previous study and practical operation data of an MED desalination plant,the present model is proved to be reliable and has a higher accuracy.The results indicate that the evaporation temperature is the key factor influencing the chemical reaction rate,which increases as the evaporation temperature increases.The salinity and pH value play an important role in determining chemical reaction rate before the seawater temperature is saturated.The increase in the concentrations of the carbonate systems due to seawater evaporation contributes to the chemical desorption of CO₂.The desorption rate of CO₂ decreases stage by stage mainly due to the reduction of mass transfer coefficients as the evaporation temperatures in evaporators decrease.

Key words: CO₂ chemical desorption, multi-effect falling film evaporation, mass transfer coefficient, chemical reaction rate

摘要： 为有效降低不凝气对降膜蒸发过程的影响和优化蒸发器结构参数,建立了多效蒸发(MED)海水淡化系统中CO₂化学解吸的数学模型,通过对实际海水淡化装置的模拟,得到了系统CO₂的解吸速率及其影响因素,并通过与前人研究成果和MED海水淡化厂实际运行数据对比分析,验证了模型的正确性并且证明具有更高的精度。结果表明,蒸发温度是决定化学反应速率的关键因素,蒸发温度越高,反应速率越快,在海水加热到饱和温度阶段,海水盐度和pH值也显著影响化学反应速率;碳酸盐离子浓度因海水蒸发而增大,有助于CO₂的化学解吸;随着各效蒸发器内蒸发温度的降低,液膜中传质系数降低,CO₂解吸速率逐效降低。

关键词: CO₂化学解吸, 多效降膜蒸发, 传质系数, 化学反应速率