以鹼性固體廢棄物碳酸化法封存二氧化碳

Abstract

以鹼性固體廢棄物碳酸化法封存二氧化碳對於減少二氧化碳排放至大氣中是為可行的方法。三種以鈣成份為主的鹼性固體廢棄物即高細度水淬爐石，飛灰爐石，高強牌高爐水泥被選為二氧化碳封存的材料。這三種材料的優點是便宜，離二氧化碳排放源較近且有較好的反應性。三種材料皆在濕式(泥漿)的條件下與二氧化碳進行碳酸化反應，並探討其反應機制。 操作因子有反應時間、泥漿的液固比、反應溫度、二氧化碳分壓和溶液的初始pH值，改變這些因子來探討其對轉換率的影響。結果顯示高強牌高爐水泥在反應時間達到12小時，溫度控制在160 oC，二氧化碳壓力控制在700psig，且粒徑小於44μm時有最大的轉換率約86%。最主要影響轉換率的因子為反應時間(5分鐘到12小時)與反應溫度(40到160 oC)，而此反應動力可用表面覆蓋模式來描述。 另外一種碳酸化方式叫做pH震盪，藉由此方法來提高碳酸化的轉換率。在這系統中，控制pH值來分出三種產物即碳酸鈣、高二氧化矽含量固體和金屬混合物固體。pH 震盪的優點在於其消耗較少的能源並且產生的產物碳酸鈣具有經濟價值可用來補償封存二氧化碳所消耗的成本。最後，應用LCA方法來計算整個實驗過程中二化碳的淨排放量，結果顯示，高強牌高爐水泥和pH震盪程序的二氧化碳淨排放量為-0.028和-0.05 kg/kg (負號代表封存)，表示其為可行的二氧化碳減量技術。

CO2 sequestration by carbonation of alkaline solid wastes is a potential technology to reduce carbon dioxide emissions to the atmosphere. In this study, three kinds of alkaline Ca-rich solid wastes, i.e., ultra-fine slag; fly ash slag; blended hydraulic cement slag, are selected as possible materials for CO2 sequestration. These materials were carbonated in aqueous condition (slurry) and operated under various conditions of reaction time, liquid to solid ratio, temperature, CO2 partial pressure and initial pH to determine their influence on the carbonation conversion. The results indicate that the blended hydraulic cement slag has the highest carbonation conversion about 86% in 12 hr at 700 psig and 160 oC. The major factors effecting the conversion are reaction time (5 min to 12 hr) and temperature (40 oC to 160 oC), furthermore, the reaction kinetics can be expressed by surface coverage model. Another route of carbonation, so called pH swing process, was also employed to enhance the conversion of ultra-fine slag. By controlling the pH in this process, three solid products, i.e., CaCO3, SiO2¬-rich solids and metal mixture solids were formed. The advantages of pH swing process include lower energy consumption and the high purity product of CaCO3 which could reduce the operation and maintenance cost of this sequestration technology. Finally, LCA method was applied to compute the net CO2 emission which indicates that both the blended hydraulic cement slag and pH swing process exhibit a negative sign of CO2 emission, i.e., -0.028 and -0.05 kg/kg, respectively, therefore, they are feasible techniques to reduce CO2.