於漿體反應器中進行濕式碳酸化反應之績效評估

Abstract

二氧化碳與溫室效應議題於近年來在國際被廣泛討論，據此，本研究以漿體反應器進行轉爐石碳酸化之二氧化碳封存實驗，並探討其動力學行為。實驗所使用之轉爐石原料為中聯公司所提供，於常壓及純二氧化碳流速0.1 L/min下，進行不同溫度、及液固比之濕式碳酸化反應。 本研究熱重分析儀（TGA）決定轉爐石之碳酸化轉換率，結果發現反應進行60分鐘後，反應速率將會趨於平緩；然而，在反應進行120分鐘時，具有最佳碳酸化反應轉化率56.99%（操作條件為：純二氧化碳流速為0.1 L/min、液固比為20 mL/mg、粒徑為44 μm、及操作溫度為50 ℃）；在二氧化碳的氣固相平衡方面，二氧化碳的淨輸入和封存量之相對誤差小於十個百分比，證明漿體反應器在二氧化碳的封存技術應用上極為可行。此外，本研究亦利用反面曲線法進行最佳操作條件的計算，發現最佳化操作條件為實驗進行120分鐘時，操作溫度為50 ℃，純二氧化流速為0.1 L/min、液固比為10 mL/g、粒徑為44 μm時會得到最佳預測轉換率63%。 此外，本研究利用縮核模式（SCM）探討本研究所進行之濕式碳酸化反應之反應機制，估算結果於三個模式中皆相近，但相較之下較適用的為擴散反應機制；在液固比(L/S)為5，不同反應溫度條件下，有效擴散係數(De)可從1.66 x 10-6 到 1.8 x 10-6 (cm/s)。另一方面，亦利用表面覆蓋模式進行動力學探討與動力學參數估算與分析，結果顯示表面覆蓋模式於本研究之適用性較佳。

Increasing of carbon dioxide (CO2) concentration in the atmosphere may enhance the global warming effect. In this study, CO2 capture by accelerated carbonation of basic oxygen furnace (BOF) slag is performed under different liquid-to-solid (L/S) ratio and temperature in a slurry reactor. The BOF slag, provided by China Hi-ment Corporation, is rich in calcium content and exhibits alkaline properties, which is beneficial to carbonation reaction. The result indicated that CO2 mass balance within the slurry reactor is quite acceptable and the relative percent difference (RPD) was less than 10%, which indicated that the slurry reactor was a viable method to capture CO2 by BOF slags. The maximum carbonation conversion of BOF slag achieved was 56.99% under an L/S ratio of 20 mL/g, a CO2 flow rate of 0.1 L/min and a pressure of 101.3 kPa at 50 oC for 120 min. In addition, the reaction product was identified as calcite (CaCO3) according to the observations of SEM and XRD. Meanwhile, reaction kinetics of carbonation of BOF slag in the slurry reactor was evaluated by the shrinking core model (SCM) and surface coverage model. Based on the results of SCM, the rate-limiting step was found to be chemical reaction controlled in 20 minutes after carbonation was conducted; and then nd the diffusion provided all the extra carbonation conversion after 60 minutes. However, to define the difference between ash layer and gas film control may need to take further analysis. Effective diffusivity (De) was ranged from 1.66 x 10-6 to 1.8 x 10-6 for different temperature at L/S = 5, the range of De value up to 103 at different L/S ratio. Furthermore, the reaction rate constant (ks) was determined by the surface coverage model, which the reaction time was in a good correlation with the carbonation conversion of BOF slag. It was thus concluded that carbonation of BOF slag in a slurry reactor is a viable method for CO2 capture.