以超重力程序去除多種空氣污染物之模式與評估之研究

Modeling and Assessment of High-gravity Process for Multiple Air Pollutants Removal

陳則綸(Tse-Lun Chen)

指導教授 ： 蔣本基

國立臺灣大學/工學院/環境工程學研究所/博士(2021年)

https://doi.org/10.6342/NTU202100064

摘要

目前發展同步去除多種空氣污染物之新穎技術實為研究發展的新趨勢，且必須同時考量其能源效率、經濟可行性以及可能的環境衝擊；超重力技術是由傳統填充塔改良為旋轉式填充床，進一步減少能源消耗、提升氣液質傳效率，可作為同步去除多種空氣污染物以及二氧化碳礦化與再利用之創新技術。本研究主要探討以超重力技術進行多種空氣污染物去除，以及都市焚化爐飛灰進行二氧化碳礦化之效能、質傳與動力學模式，以及環境衝擊與經濟成本評估等研究；本研究目前各研究目標之工作項目與重點成果，簡述如下：

(1) 評估超重力技術同步淨化多種空氣污染物之績效：本研究於國內重點產業建立整合式超重力技術空污防制技術示範，探討煙道尾氣之多種空氣污染物（包含：硫氧化物、氮氧化物、二氧化碳與懸浮微粒）去除績效評估，使用含高濃度鈣離子與高pH之飛灰水洗液作為吸收劑，臭氧作為氧化劑，評估不同操作參數之影響（包含：超重力因子，液固比與氣液比），實驗結果發現，SO2、NOx與PM之最高去除率分別為96.3±2.1%、99.4 ± 0.3%、95.9 ± 2.1%與83.4 ± 2.6%。此外，反應後吸收劑可回收高純度碳酸鈣，其平均孔隙直徑、BET比表面積以及孔隙體積分別為7.76 µm、2.796 ± 0.096 m2 g-1與0.8377 cm3 g-1，品質可與一般工業用碳酸鈣產品相比。另外藉由圖像法整合不同實驗數據平衡系統能耗與空污減量之關聯性。此外，本研究引用半理論模式與水滴-液膜之懸浮微粒蒐集模式分析懸浮微粒於超重力旋轉填充床內的去除機制，了解水滴、液膜以及填充材對於懸浮微粒去除效率之影響。

(2) 建立超重力系統中對於多種空氣污染物去除之質傳模式
本研究基於雙模理論分析超重力旋轉填充床中NOx-SO2-CO2 氣液質傳行為，基於理論模型與實驗數據，計算各項污染物的氣項質傳係數(KGa)、液項質傳係數(kL) 、以及單位質傳高度(HTU)，並推估由化學反應貢獻於去除績效的增進因子(E)，同時評估不同操作條件下各別污染物的單位能耗，最後整合模式分析、實驗數據與能耗分析結果，推測三種污染物在同一系統中的各別增進因子；研究結果表明，SO2之KGa 遠高於CO2與NOx之KGa，在高鹼度與高鈣離子濃度的吸收劑作用下，且超重力因子較低的情況下，CO2與NOx的吸收貢獻主要來自於化學反應（即增進因子E），隨著超重力因子提升，質傳係數會被提升並抵銷化學反應的貢獻度且HTU也會下降，；此外，本研究分析單位污染物去除能耗，其中各別污染物最佳能耗為0.103 kWh/t-NOx、0.047 kWh/t-SO2以及134.62 kWh/CO2，可對應出NOx、SO2與CO2的KGa分別為1.25 1/s、1.08 1/s與1.7 1/s，其操作條件為超重力因子233.8、氣液比69.5以及，最後以圖解法得到NOx、SO2與CO2的增進因子為1.8、5.9與1.6，可進一步說明本研究SO2去除是來自於化學吸收而非受高質傳作用。

(3) 評估超重力技術結合二氧化碳礦化對於都市焚化飛灰穩定化效果
利用實驗室規模超重力旋轉填充床進行都市焚化飛灰穩定化，結合碳酸化以及水洗程序，探討不同液固比與超重力因子對於飛灰礦化與可溶性氯鹽脫除之效果，結果發現氯鹽萃取率隨著液固比減少而有些微提升，最高氯鹽萃取率為36.35 %，CO2礦化則隨著超重力因子提升而上升，最大單位補碳量為258.5 g-CO2/kg-FA；XRD與SEM結果表明，反應前MSWI-FA主要成分為 KCl、CaClOH、CaSO4與NaCl，經過水洗與碳酸化處理可將反應後飛灰轉化為CaCO3沉澱，且飛灰經碳酸化與水洗後可去除84%的總氯鹽含量；此外，透過能耗與水耗分析發現，當液固比為30時，可獲得最佳的單位補碳與脫氯之能耗0.11 kWh/kg-CO2與1.08 kWh/g-Cl，以及脫氯耗水量1.13 L/g-Cl。

(4) 建立二氧化碳礦化與飛灰中鈣離子溶出行為之反應動力式
本研究分析以超重力旋轉填充床進行MSWI-FA 泥漿的碳酸化與鈣離子濃度於常溫常壓下之反應動力式，使用表面覆蓋模式預測碳酸鈣轉換率"δ" _"Ca" 與反應常數ks，使用史崔特-費普士方程式 (Streeter-Phelps formula) 描述碳酸化期間鈣離子溶出與沉澱行為的反應動力，探討不同液固比與超重力因子對於反應常數之影響，並比較文獻中不同與鹼性廢棄物（如精煉渣、轉爐石、副產石灰、粉煤灰以及焚化飛灰）之動力學反應變化；研究結果發現，"δ" _"Ca" 與ks會隨著超重力因子提升而增加，表示飛灰顆粒可被反應物覆蓋之表面會逐漸減少，當液固比降低時，kp會有些微的上升，且MSWI-FA之kp高於其他廢棄物，說明MSWI-FA有著較多的表面覆蓋率；此外，本研究使用史崔特-費普士方程式描述碳酸化期間，鈣離子溶出與沉澱為競爭行為，當反應剛開始時，因超重力場可提升加速碳酸化反應，使鈣離子濃度會急速消耗，此時沉澱反應常數kd會大於溶出反應常數ka，當pH值降至中性時，此時水中碳酸離子為優勢種，進而降低碳酸鈣沉澱反應，並導致鈣離子濃度再度上升。

(5) 從工程面、環境面與經濟面建立系統最佳化與最適化操作情境
本研究依據超重力對於多種空氣污染物去除以及焚化飛灰穩定化成果，結合技術經濟評估(TEA)與環境衝擊評估(LCA)，同時運用決策分析工具的TOPSIS方法分析其工程面、環境面與經濟面之綜合效益，本研究以國內某焚化廠安裝超重力技術為例，設計兩種操作情境與現有的濕式洗滌塔系統（即BAU情境）進行比較，超重力系統主要可貢獻的效益包含直接與間接的碳權收益（透過鹼性廢棄物補碳）、飛灰穩定化與再利用、及純碳酸鈣產品等；結果顯示，超重力系統可提升空氣污染物的去除效益，同時可兼具飛灰再利用，可同步降低環境衝擊與提升經濟效益，從TOPSIS的結果可提出超重力系統優先操作方案，提供未來超重力技術規模放大之參考。

關鍵字

超重力旋轉填充床 ； 多種空氣污染物同步減量 ； 質傳模式 ； 二氧化碳礦化 ； 反應動力學 ； 系統最佳化

並列摘要

The criterions of criterial air pollution (i.e., NOx, SOx and PM) control technology are included enhancement of energy efficiency, effectiveness of economic benefit and mitigation of environmental impact. To develop the novel and promising technology for simultaneous multiple air pollutants removal is the urgent issue. High-gravity (HiGee) technology is an attractive method for air pollution control, CO2 capture and wastes utilization. In the present study, a proposed high-gravity process for multiple air pollutant abatement couple with CO2 mineralization using municipal solid wastes incineration (MSWI) fly ash was invesigated from several aspects, in terms of mass transfer, reaction kinetics, process simulation, environmental impact assessmen and cost-benefit analysis. The research outcomes were sumerrized as followings:
1. Performance Evaluation of HiGee Process for Multiple Air Pollutants Abatement
An integrated approach to demonstrate simultaneous air pollution reduction (e.g., CO2, SO2, NOx, and PM) with green alkaline solution can be achieved via HiGee process in the domestic industeries. The multiple air pollutants reduction with fly ash leachate utilizing as a green solvent via a HiGee process can be substantially established. Ozone was used as an oxidizer for NOx removal. Effect of key operating parameters including high-gravity factor, liquid-solid ratio, and gas-liquid ratio was investigated. Results indicated that the maximal CO2, SO2, NOx, and PM removal efficiencies of 96.3 ±  2.1%, 99.4  ±  0.3%, 95.9  ± 2.1%, and 83.4  ±  2.6% were respectively achieved. Precipitated CaCO3 generated from the carbonation reaction in the HiGee RPB was identified with microspore size of 7.76 µm, BET surface area of 2.796 ± 0.096 m2 g-1, and porous volume of 0.8377 cm3 g-1. Its propertises could be compared with the commercial product. Balance of energy consumption and air pollutant reduction was determined with a graphical presention approach. Moreover, the mechanism of PM collection in the RPB was investigated with the semi-theoratical model and droplet and film based PM collection model to understand the removal efficiency among the droplet, film and packing materials.
2. Determination of Mass Transfer Performance and Energy Consumption for NOx-SO2-CO2 Simultaneous removal in the HiGee System
The mass transfer rate for NOx-SO2-CO2 absorption using alkaline solid wastes in a HiGee RPB towards a green process intensification was determined from the theoretical model. The performance of SO2 removal efficiencies and KGa values were dramatically superior than that of NOx and CO2 because of the lower SO2 concentration in flue gas and mass transfer resistance between solvent and SO2 gas. In addition, the analysis of energy consumption against the estimated KGa values under various key operating variables for identification of the favorable operating factors (i.e., β of 233.8, GLR of 69.5 and LSR of 40) was investigated. Result indicated that the available energy consumptions of 0.103 kWh per t-NOx, 0.047 kWh per t-SO2 and 134.62 kWh per t-CO2 were found at the β of 233.8 and the estimated KGa values of NOx, SO2 and CO2 up to 1.25 s-1, 1.08 s-1 and 1.7 s-1 could be determined. The enhancement factor of NOx, SO2 and CO2 were exhibited as 1.8, 5.9 and 1.6, respectively. It could briefly conclude that less enhanced mass transfer and the higher chemical enhancement on SO2.
3. Stabilization and Solidification of MSWI Fly Ash Coupling CO2 Mineralization via the HiGee Process
To develop an integrated wet-extraction and carbonation process for MSWI-FA stabilization, solidification and utilization via the high-gravity process. A benchtop experiment demonstrated the dechlorination and CO2 sequestration of MSWI-FA and the carbonated product could be applied as a supplementary cementitious material in the cement mortar. The effects of liquid-to-solid ratio and high gravity factor were evaluated. Physical, chemical and thermal characteristics of raw, wet-extracted, and carbonated MSWI-FA were identified in terms of the mean diameter, micropore area, micropore volume, and chemical compositions.. Results indicated that a chloride extraction ratio of 36.35% and a CO2 capture capacity of 258.5 g-CO2 kg-FA-1 were achieved in the batch experiment. Results of mineralogy and morphology presented main soluble chloride species were NaCl, KCl, and CaClOH in the raw ash. Moreover, considering available performance and water usage with minimum energy consumption, the operation with L/S of 30 corresponding with 0.11 kWh kg-CO2-1, 1.13 L g-Cl-1 and 1.08 kWh g-Cl-1 is suggested.
4. Reaction Kinetics of CO2 Mineralization of Different Akaline Solid Wastes via the HiGee Process
The reaction kinetic of aqueous carbonation by CO2 mineralization and the dynamic changes of Ca2+ concentration using different calcium based ASW via a HiGee RPB under ambient temperature and pressure was demonstrated. The rate constant of mineralization was determined under different operating conditions using surface coverage model. The dynamic changes of "C" _(〖"Ca" 〗^"2+" ) during carbonation was successfully elucidated using the Streeter-Phelps formula. The determination of rate constant of leaching (ka) and the precipitation kinetics (kd) can be described the competition between Ca2+ leaching and CaCO3 precipitation. When the conversion (δCa) increased, rate constent (ks) was increased while reaction coefficient of the active surface sites (kp) decreased. It indicated that more reactant is converted, the higher reaction rate is obtained and more available reactive position is reduced. In addition, . the Ca2+ leaching kinetic was superior to the precipitation kinetic due to the less bicarbonate/carbonate ions from the dissolved CO2 in the slurry. It represents that the CaCO3 precipitation might be achieved as the large amount bicarbonate/carbonate ions exist at the alkaline condition (i.e. pH > 10) .
5. System Optimization from Engineering-Environmental-Economic Aspects
The multi-criteria engineering, environmental and economic analysis of HiGee system for flue gas purification and MSWI-FA stabilization and utilization were conducted exemplified by a MSW incineration plant. The combination of TEA and LCA was applied for the evaluation the engineering performance, environmental impact and economic cost. Two HiGee scenarios was designed to compare to the existing wet-scrubber (i.e., BAU scenario). In TEA results, major benefits of HiGee system including direct/indirect carbon credit, CaCO3 byproduct revenue, and FA utilization revenue. Compared to the BAU case, the environmental midpoint impact could be reduced by installing the HiGee process, e.g., a decrease in the indicators related to ecotoxicity and water quality degradation up to 30~32%. From the perspectives of engineering, environment and economy, results of TOPSIS method indicated the prioritized alternative was scenario 1, which owned a relative lower environmental impact and acceptable engineering performance and economic cost.

並列關鍵字

high-gravity rotating packed bed ； multiple air pollutants abatement ； mass transfer model ； CO2 mineralization ； reaction kinetics ； system optimization

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