旋轉填充床中以氫氧化鈉吸收二氧化碳 -氫氧化鋇再生及碳酸鋇分離程序

Abstract

面對如何減少化石燃料所排放的溫室氣體問題及達成碳中和的目標，如何在火力發電過程中捕捉二氧化碳以及減少其排放量為近年來最重要的課題之一。本研究方向內容為選用氫氧化鈉水溶液作為吸收劑來吸收二氧化碳，結合超重力旋轉填充床之技術，進一步提升質傳以及吸收效果，同時透過連續添加氫氧化鋇於進料桶的方式進行吸收劑再生之程序，並利用碳酸鋇與水密度差大的特性，透過增設整流牆及導流牆於沉降槽中，有效將循環系統中的固體顆粒與吸收劑分離，使得吸收劑再次流入旋轉填充床中不因固體顆粒含量過高而造成吸收程序中斷。

實驗結果顯示，碳酸根濃度為影響吸收及再生之最不利因素，因此可透過縮短添加再生劑時間間隔、降低液體流量來掌控在進料桶的滯留時間、添加過量再生劑及預先溶解再生劑等方式來提升再生效果。

本研究目前得到RPB循環系統的最適化的操作條件分別為: 設定進料桶與沉降槽體積各為2 L、吸收劑濃度為0.7 M情況下，操作時需每隔10分中添加0.064 M (過量24%)預先溶解的Ba(OH)_2於進料桶中即可有效消除碳酸根及延長系統操作時間。而當系統pH值大於13.74時調高液體流量至200 mL/min，可得較好的吸收效果；當系統pH值小於13.74時可調低液體流量至100 mL/min，會有較好的再生效果進而延長吸收時間。

Aiming at the target of carbon neutrality and net zero emission, the process of reducing and capturing carbon dioxide remains a crucial issue in recent years. This research used sodium hydroxide as an absorbent in a rotating packed bed (RPB) of high mass transfer to absorb carbon dioxide; simultaneously, adding barium hydroxide periodically in the feeding tank to regenerate sodium hydroxide by transforming carbonate ion into barium carbonate. With proper baffle design in the sedimentation tank, the precipitate(barium carbonate) could be separated from the process.

According to the results of the experiment, sodium carbonate is considered an adverse effect on both absorption and regeneration. Therefore, this research investigated several possible improvements, such as shorter the regenerant additional time intervals, lower the liquid flow rate to ensure enough residence time for regeneration, an excess amount of regenerant, and adding the regenerant in an aqueous state.

The optimal operating method of this RPB circulating system in this research was found to be a 2 L feeding tank connected with a 2 L sedimentation tank, the initial concentration of the absorber is 0.7 M, adding pre-dissolved 0.064 M of Ba(OH)_2 in the feeding tank per 10 minutes. When the concentration of hydroxide ion was more than 0.55 M, the liquid flow rate was set to 200 mL/min for better absorbance; when the concentration of hydroxide ion was less than 0.55 M, set the liquid flow rate to 100 mL/min for better regeneration.