CO2化学吸收法中再生气的陶瓷膜余热回收特性

在CO₂化学吸收法工艺中，采用富液分流工艺，利用在贫富液换热器前分流的冷富CO₂吸收剂溶液回收再生塔顶排出的热再生气（一般为CO₂和水蒸气混合气）的余热，有助于降低CO₂再生热耗。本文在乙醇胺（MEA）基富液分流化学吸收工艺中，以纳米级多孔亲水陶瓷膜作为分流冷富液和热再生气之间的换热介质，利用水的热质耦合传递强化余热的回收性能。以余热回收通量为指标，探讨了分流的MEA富液流量、温度、质量分数、CO₂负荷和热再生气流量及再生气中水蒸气摩尔分数对陶瓷膜热回收性能的影响，并对比了不同分离层孔径陶瓷膜的余热回收性能。结果显示，陶瓷膜的余热回收性能随MEA富液流量的增加而增加，但却随富液温度的升高而大幅下降。同时，随着气体流量和再生气中水蒸气摩尔分数的增大，热回收通量均会增大。由水传质所引发的对流换热对热回收通量具有促进作用，可占总热回收量的10%左右。由于CMHE-10陶瓷膜的分离层孔径与孔隙率均大于CMHE-4陶瓷膜，因而其水传质通量大于CMHE-4陶瓷膜。但CMHE-10陶瓷膜的有效热导率却低于CMHE-4陶瓷膜，因而热回收过程中其水蒸气的冷凝总量要小，导致其热回收性能低于CMHE-4陶瓷膜。

Waste heat recovery performance from stripping gas in CO2 chemical absorption process by using ceramic membrane

In CO₂ chemical absorption process, the rich-split technology can be used to recover the waste heat from the hot stripping gas (i.e., the mixture of CO₂ and water vapor) for reducing the CO₂ regeneration heat consumption. In monoethanolamine (MEA)-based CO₂ chemical absorption process adopting the rich-split technology, the hydrophilic nanoporous ceramic membrane was selected as the heat exchanging medium between the cold bypassed CO₂-rich MEA solvent and the hot stripping gas for enhancing the waste heat recovery performance through the coupled water and heat transfer. Effects of key operation variables including the flow rate and temperature of bypassed CO₂-rich MEA solvent, CO₂ loading and MEA mass fraction, the stripping gas flow rate and water vapor molar fraction on the waste heat recovery were investigated in terms of the total heat recovery flux. Additionally, the waste heat recovery performance for the ceramic membranes with different mean pore sizes of ceramic membrane separation layer was also compared in this study. Results showed that the increase of rich MEA solvent flow rate in addition to the reduction of rich MEA solvent temperature can improve the waste heat recovery performance greatly. In addition, the waste heat recovery performance also increases with the stripping gas flow rate and the water vapor molar fraction in the stripping gas. Moreover, the convective heat relevant to the water transfer from the stripping gas to rich MEA solvent can contribute to increasing the waste heat recovery performance, in which the ratio of convective heat is about 10%. Furthermore, the CMHE-10 ceramic membrane has a higher mean pore size of separation layer and overall porosity than the CMHE-4 ceramic membrane, resulting in its higher water transfer flux. However, compared to the CMHE-4 ceramic membrane, the effective thermal conductivity of the CMHE-10 ceramic membrane is lower mainly caused by its higher porosity, resulting in the lower water vapor condensation amount in the membrane tube. Thus, the heat recovery performance of the CMHE-10 ceramic membrane is inferior to the CMHE-4 ceramic membrane.