| 摘要: | 本研究嘗試分別利用焚化底渣(以下簡稱底渣)與電弧爐還原碴(以下簡稱還原碴)，在控制液固比及模擬焚化爐煙道氣排氣濃度等條件下，探討前述底渣或還原碴捕捉二氧化碳之可行性。實驗控制條件分別包括液固比(0.2-0.4)，模擬煙道氣10%二氧化碳及15 ppm二氧化硫。研究過程除評估前述底渣及還原碴對二氧化碳捕捉效果外，亦期進一步探討二氧化硫對加速碳酸鹽反應捕捉二氧化碳之競爭影響。
研究結果顯示，底渣與還原碴均屬於高鈣含量的灰渣類廢棄物，且經過加速碳酸鹽反應，並控制液固比條件為0.2時，底渣及還原碴捕捉二氧化碳之效果，分別為42.5 g/kg及69.1 g/kg，此係還原碴具有較高之比表面積與孔隙率，故有較佳之二氧化碳捕捉效果。當液固比增加至0.3時，底渣及還原碴對二氧化碳的捕捉量，分別增加至78.3 g/kg及82.7 g/kg，可見控制適當液固比條件，有助於加速碳酸鹽之反應，提升二氧化碳之捕捉效果。然而，當液固比增加至0.4時，底渣及還原碴對二氧化碳的捕捉量，則分別降低至41.1 g/kg及63.2 g/kg。此係液固比過高，水分佔據灰渣及還原碴的孔隙，造成二氧化碳擴散率降低，導致二氧化碳不易與灰渣及還原碴的含鈣物質接觸與反應，二氧化碳之捕捉效果明顯降低。此外，以液固比控制0.3時，二氧化碳捕捉率最佳之狀況下，煙道氣中含有15 ppm之二氧化硫，由於二氧化硫將與二氧化碳共同競爭鈣離子，導致底渣及還原碴對二氧化碳之捕捉量，明顯降低至54.7 g/kg及77.1 g/kg。
加速碳酸鹽反應後底渣及還原碴之重金屬穩定化分析結果顯示，底渣經加速碳酸鹽反應前後之鎘(Cd)、鉛(Pb)、硒(Se)、砷(As)、汞(Hg)及六價鉻(Cr6+)，皆低於儀器偵測濃度，而總鉻(Cr)溶出濃度則由初始0.33 mg/L降低至低於儀器檢測濃度。還原碴反應前後之銅(Cu)、鋅(Zn)、鉻(Cr)、鎘(Cd)、鉛(Pb)、硒(Se)、砷(As)及汞(Hg)，皆低於儀器偵測濃度，至於六價鉻(Cr6+)溶出濃度，則由初始之0.06±0.02 mg/L降低至低於儀器檢測濃度。整體而言，底渣與還原碴經加速碳酸鹽反應後，不僅具有二氧化碳捕捉之效果，同時有助於達成灰渣及還原碴之重金屬穩定化及無害化之目的。
;This research investigated that the feasibility of carbon dioxide capture by municipal solid waste incinerator (MSWI) bottom ash and electric arc furnace (EAF) reductive slag using the accelerated carbonation system combined with semi-dry rotary kiln. The experiments were conducted by controlling liquid-solid ratio (ranged from 0.2 to 0.4), 10% carbon dioxide concentration and 15 ppm sulfur dioxide concentration.
The experimental results showed that MSWI bottom ash and EAF reductive slag were alkaline solid residues containing high calcium content. In the case of liquid-to-solid ratio 0.2, the carbon dioxide captured by bottom ash and reductive slag were 42.5 g/kg and 69.1 g/kg, respectively. When the liquid-solid ratio was increased to 0.3, the carbon dioxide captured by bottom ash and reductive slag were significantly increased to 78.3 g/kg and 82.7 g/kg, respectively. Consequently, controlling the appropriate liquid-solid ratio could exhibit a good CO2 capture performance. However, in the case of liquid-solid ratio 0.4, the carbon dioxide captured by bottom ash and reductive slag were slightly decreased to 41.1 g/kg and 63.2 g/kg, respectively. This is because the higher moisture content of ash could tend to block the pores of alkaline residues, hence, it will be resulted in a decrease in carbon dioxide diffusion. On the other hand, due to the reductive slag had a higher specific surface area than that of bottom ash, it can provide the higher porosity and perform a good potential for carbon dioxide diffusion. Therefore, reductive slag exhibited a good carbon dioxide capture efficiency than that of bottom ash.
With sulfur dioxide (SO2) addition, a competitive reaction between calcium ion and sulfur ion could occur during accelerated carbonation process. It implied that carbon dioxide capture efficiency could decreased with an increase in SO2 concentration. In the case of liquid-to-solid ratio 0.3, the carbon dioxide was captured by bottom ash and reductive slag were decreased from 78.3g/kg to 54.7 g/kg, and from 82.7 g/kg to 77.1 g/kg with SO2 concentration increased from 0 ppm to 15 ppm, respectively.
Based on the analysis results of heavy metals stabilization in carbonated residues, all the tested heavy metals from carbonated bottom ash and reductive slag were in compliance with current Taiwan EPA regulation thresholds. In case of bottom ash after accelerated carbonation reaction, the Cr concentration was significantly decreased from 0.33 mg/L to the analytical detection limit. Meanwhile, in case of reductive slag, the Cr6+ concentration was also significantly decreased from 0.06±0.02 mg/L to the analytical detection limit after accelerated carbonation reaction. It could conclude that the accelerated carbonation has a good potential for enhancing the Cr and Cr6+ stabilization in bottom ash and reductive slag.In summary, this research has been successfully developed and proven the performances of accelerated carbonation reaction system combined with semi-dry rotary kiln. The multiple purposes of resources reduction, harmless of alkaline solid residues, and carbon dioxide sequestration by accelerated carbonation have been conducted in this research. |
