利用超重力旋轉填充床於碳捕獲及空氣污染物減量與鹼性廢棄物再利用之研究

Carbon Capture via a Rotating Packed Bed Process for Air Emission Reduction and Reuse of the Alkaline Waste Byproduct

方雲柯(Yun-Ke Fang)

指導教授 ： 蔣本基

國立臺灣大學/工學院/環境工程學研究所/碩士(2017年)

https://doi.org/10.6342/NTU201702138

摘要

本研究開展對於利用整合式的超重力技術應用於二氧化碳捕捉之研究，並同時探究其在空氣污染物防治的效能與鹼性廢棄物改質再利用之可行性。超重力技術具有所需接觸反應時間短，且操作溫度與壓力相對較低的特點，在模廠設備實驗中可同時去除煙氣中二氧化碳、氮氧化物、二氧化硫與細懸浮微粒。碳捕捉所用材料之流化床飛灰富含大量鹼性成分，通過碳捕捉程式之改質作用，可添加進入水泥中進行再利用。本研究之內容包括研究不同操作條件及不同操作流程對於碳酸化反應之影響：研究不同轉速和液固比操作及溶劑條件下，通過直接碳酸化及間接碳酸化流程，比較得到各參數對於碳捕捉能力之影響。研究發現，旋轉填充床轉速的提高可大幅加快反應進程，提高碳酸化程度。通過多次浸出或採用pH-swing法，間接碳酸化流程之碳捕捉能力與直接碳酸化相當；探究浸出及碳酸化過程中涉及之化學反應及質傳動力學：研究運用縮核模型及整體反應模型對飛灰之浸出過程進行了描述，模型之間的比較得到，產物層擴散與化學反應的聯合作用為飛灰浸出之主要控制步驟，整體反應模型在擬合過程中也得到了比較好的相關性。碳酸化之進程由表面覆蓋模型描述其鈣轉化率，由鈣離子濃度模型描述其溶液中鈣離子的變化量；通過模廠實驗驗證超重力技術對於煙道氣中空氣污染物的減量效能：通過模廠實驗，超重力技術被證明可有效去除煙氣中污染物。其中二氧化碳、二氧化硫及氮氧化物之去除率分別可達96.3±2.1%, 99.4±0.3% and 95.9±2.1%,對於顆粒物的去除率可達83.4±2.6%。此外，實驗發現設備對在脫硫效能上有極為良好的表現，在設備最大進氣流量下（11.16m3/min），可達到98.8±0.4%之去除率。驗證改質後飛灰用作輔助性凝膠材料之可行性：改質後飛灰被嘗試用作輔助性凝膠材料添加進入水泥。通過可行性分析發現其成分與波特蘭水泥接近，且毒性溶出分析符合相關標準。根據取代後水泥性能分析發現其最佳添加規範為10%碳酸化後飛灰取代。利用環境、經濟和工程面分析全面評估超重力之技術效能：通過3E分析發現，超重力技術可有效降低環境衝擊，並增加經濟效益。通過圖解法優化得到現場最佳操作條件為進氣量： 4.23 m3/min; 轉速: 600 rpm; 液固比: 40ml-tap water/g-fly ash。

關鍵字

超重力技術 ； 二氧化碳捕捉 ； 空氣污染物減量 ； 水泥取代 ； 3E分析

並列摘要

This study focused on the development of high gravity technology applicable in carbon capture for the air emission reduction and also investigated reuse of the alkaline waste byproduct. High gravity technology using in carbon capture process have advantages of high mass transfer coefficient and can be operated in atmospheric pressure and ambient temperature. In the on-site experiments, CO2, SO2, NOx and particle matters can be reduced simultaneously. Besides, the fly ash of circulating fluidized bed (CFB) used in carbon capture process can be reused to substitute Portland cement after stabilization. The research objectives including exploration of the effect of operating conditions on carbonation behavior in rotating packed bed (RPB): The effect of two operation parameters including rotating speed and liquid-to-solid ratio on the carbon capture capacity of fly ash were investigated for both direct and indirect carbonation processes. The results showed that rotating speed of RPB can increase reaction rate and the carbonation efficiency significantly. After leaching for four times or applying pH-swing method, the capture capacities of fly ash in direct and indirect carbonation process were not much changed; models are developed to describe the reaction kinetics and mass transfer, during the leaching and carbonation process. A shrinking core model and an entire reaction model were used to describe the leaching process of alkaline waste. The comparison results among models showed that the process was mainly controlled by the combination effect of product layer diffusion and reaction. In the carbonation process, a surface coverage model was used for the description of calcium conversion and a calcium concentration model was used for the prediction of calcium concentration in solution; the performance of high gravity technology was demonstrated on air emission control via on-site experiments: According to the on-site experimental results，high gravity technology can reduce air emissions in flue gas simultaneously. The reduction efficiencies of CO2, SO2 and NOx can reach 96.3±2.1%, 99.4±0.3% and 95.9±2.1% respectively. The reduction efficiency of particle matters (PM) reached 83.4±2.6%. Besides, experimental results show that, in a higher gas flow rate (11.16m3/min), high gravity technology still has potential to reduce sulfur dioxide in flue gas at a high efficiency (98.8±0.4%); The feasibility to use stabilized fly ash for substituting Portland cement in making concreate was investigated: Fresh fly ash and modified fly ash by different stabilization process are all feasible for Portland cement substitution according to their similar constitutions with ordinary Portland cement (OPC). Besides, to ensure the safety of using such substitution materials, the process must proceed by the TCLP test. The performance test in workability, durability and compressive strength shows that carbonated fly ash has a better performance comparing with other materials. The recommended substitution ratio is 10 w.t.%; comprehensively evaluation of the process from the perspective of environmental, economic and engineering aspects The following optimized operation conditions were obtained by the 3E (environmental, economic and engineering) analysis for the on-site operation, gas flow rate: 4.23 m3/min; rotating speed: 600 rpm; liquid-to-solid ratio: 40ml-tap water/g-fly ash. Besides, the environmental and economic analyses show that the High Gravity Carbonation (HiGCarb) process can not only reduce environmental impaction by air emission reduction and alkaline wastes utilization, but also can gain economic profits by comprehensive valorization of wastes.

並列關鍵字

High gravity technology ； carbon capture ； air emissions control ； cement substitution ； 3E analysis

參考文獻

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