系統式發展優化超重力碳酸化程序於碳捕集再利用

Systematic Approach to Development and Optimization of High-Gravity Carbonation (HiGCarb) Process for Carbon Capture and Utilization

潘述元(Shu-Yuan Pan)

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(2016年)

https://doi.org/10.6342/NTU201601300

摘要

使用鹼性固體廢棄物進行加速碳酸化係具有應用潛力之二氧化碳(CO2)捕獲與再利用技術。本研究以系統式面向發展優化超重力碳酸化程序於碳捕集再利用，並使用轉爐碴與冷軋廢水，於鋼鐵廠現場進行技術驗證。本研究目標包括：（一）建立整合式熱分析方法，準確量測固體廢棄物碳酸化轉換效率；（二）鑑別超重力碳酸化程序關鍵操作參數，進行程序碳捕獲績效評估；（三）結合程序化學路徑、反應動力學與質量傳輸現象，建立超重力碳酸化程序預測模式；（四）建立程序生命週期系統邊界與物料盤查清單，量化超重力碳酸化程序之環境衝擊；及（五）建立3E（工程、環境、經濟）三角評估模型，最優化超重力碳酸化程序操作。本研究各研究目標之工作項目與重點成果，簡述如下：
於「建立整合式熱分析方法，準確量測固體廢棄物碳酸化轉換效率」目標，由於文獻中測量固體廢棄物中碳酸鈣含量之準則與方法論皆不盡相同，本研究首先建立一套整合式熱分析方法，用以準確測量反應後產物之碳酸化性質，例如：碳酸化轉換率與碳酸鈣含量。此整合式熱重分析方法包含：熱重分析（TG）、微商熱重分析（DTG）、示差掃描熱分析（DSC）。高純度碳酸鈣以不同比例添加於不同程度之碳酸化轉爐碴，用以建立轉確整合式熱分析方法（TG/DTG）。結果顯示本研究所提出整合式方法（TG/DTG）可準確符合示差掃描熱分析（DSC）之結果，同時，熱分析裂解尾氣經過質譜儀（MS）與傅立葉紅外線光譜（FTIR）定性，以確認轉爐碴於不同加熱區段分解之化合物種類。此外，本研究應用阿瑞尼亞式（Arrhenius）與金式覺方程式（Kissinger），計算轉爐碴中碳酸鈣之熱分解動力學與熱力學參數，並與文獻所得數據進行比較。
於「鑑別超重力碳酸化程序關鍵操作參數，進行程序碳捕獲績效評估」目標，評估關鍵操作參數於二氧化碳去除之績效，包括：旋轉床轉速、液固比、氣體流量及漿體流量。研究結果指出於氣液比為40時，最高CO2去除效率可達97.3%，每日捕獲容量可達165公斤CO2。此外，反應後轉爐碴以不同比例（包括：0%、10%、及20%）添加於水泥砂漿，作為輔助性水泥膠結材料，並進行水泥砂漿之功能性質，包括：物化性質、表面結構、晶相改變、抗壓強度與蒸壓膨脹。研究結果指出使用較高碳酸化程度之轉爐碴於水泥砂漿中，其早期強度與耐久性質皆較純波特蘭水泥優異，顯示碳酸化轉爐碴具有潛力應用於高早期強度水泥。
於「結合程序化學路徑、反應動力學與質量傳輸現象，建立超重力碳酸化程序預測模式」目標，首先透過定量X光繞射分析（QXRD）與Rietveld精鍊模型，確定超重力碳酸化程序之化學路徑。根據上述結果，研析轉爐碴中金屬溶出行為，並應用表面覆蓋模式建立超重力碳酸化程序動力學模式，所得模式參數與不同反應器比較。另一方面，透過古典理論模式計算超重力碳酸化程序之關鍵質傳模式參數，包括：氣相質傳係數（KGa）與單位質傳高度（HTU）等。研究結果發現於液固比介於13.3–20.0時，超重力碳酸化程序之單位質傳高度約為7.8–28.0公分，此質傳效果較傳統反應器來得優異。本研究成功結合化學路徑、反應動力學與質量傳輸現象，建立超重力碳酸化程序預測模式。
於「建立程序生命週期系統邊界與物料盤查清單，量化超重力碳酸化程序之環境衝擊」目標，本研究運用生命週期評估（LCA），以煉鋼廠為案例，比較整合超重力碳酸化程序於煉鋼程序後，於環境衝擊面之減緩效益。由於本程序反應後產物可再利用作為水泥添加材料，可於煉鋼業及水泥業間建立廢棄物資源化供應鏈，改善工業對於環境衝擊。本項目評估之單元操作程序包括：爐碴研磨、攪拌、鼓風機、壓縮機、泵、及旋轉填充床等。根據生命週期評估結果，整合超重力碳酸化程序後，每噸轉爐碴直接淨捕獲容量約為282公斤CO2，並由於產品再利用可再間接避免約997公斤CO2額外排放。
於「建立3E（工程、環境、經濟）三角評估模型，最優化超重力碳酸化程序操作」目標，本項目同時從工程面、環境面與經濟面之3E角度，全面性評估超重力碳酸化程序。超重力碳酸化程序之CO2來源可直接從煉鋼廠煙囪排氣取得，且不需要額外CO2運輸與儲存；同時，反應後產品可再利用作為輔助性水泥膠結材料，因此可間接避免水泥廠之CO2排放與環境衝擊。本研究根據CO2捕獲效率選定九組不同超重力碳酸化情境，並透過Delphi方法從3E角度決定共16種關鍵績效指標，用以評估超重力碳酸化程序。根據3E評估模式結果，隨者CO2捕獲效率去除效率增加，程序能源消耗與環境衝擊亦隨之減小，使得超重力碳酸化程序更加具環境友善與經濟成本效益。

關鍵字

旋轉填充床 ； 整合式熱分析 ； Rietveld精修 ； 質量傳輸 ； 動力學 ； 生命週期評估 ； 3E三角模型

並列摘要

Accelerated carbonation of alkaline solid wastes is an attractive and promising method for CO2 capture and resource utilization. In this study, high-gravity carbonation (HiGCarb) process using alkaline wastes, i.e., basic oxygen furnace slag (BOFS) and cold-rolling mill wastewater (CRW), for CO2 mineralization and utilization was evaluated using field operation data from the steelmaking industry. In this study, the objectives are to (1) set-up a quality assurance and quality control (QA/QC) program for carbonation conversion of alkaline solid wastes; (2) evaluate the effect of key operating factors on the carbonation conversion of BOFS by the HiGCarb process for CO2 fixation; (3) develop integrated prediction models for the HiGCarb process by combining process chemistry, reaction kinetics and mass transfer; (4) quantify the environmental benefits and impacts of the HiGCarb process via a life cycle assessment (LCA); and (5) establish a 3E (Engineering, Environmental and Economic) triangle model for system optimization.
1. Establishment of QA/QC Program for Carbonation Conversion of Alkaline Solid Wastes
The evaluation criteria of CaCO3 content in alkaline solid wastes and the way to interpret thermal analysis profiles were found to be quite different among the literature. In this research, an integrated thermal analyses for determining carbonation parameters such as carbonation degree and CaCO3 content in BOFS were proposed based on thermogravimetric (TG), derivative thermogravimetric (DTG), and differential scanning calorimetry (DSC) analyses. Different quantities of reference CaCO3 standards, carbonated BOFS samples and synthetic CaCO3/BOFS mixtures were prepared for evaluating the data quality of the proposed method using TG/DTG analysis. The results indicate that the CaCO3 contents in BOFS determined by the modified method using TG/DTG can be consistent with those obtained by DSC analysis. Moreover, the evolved gas analysis was performed by mass spectrometer (MS) and Fourier transform infrared spectroscopy (FTIR) for detection of the gaseous compounds released during heating, in order to further confirm the TG/DTG/DSC results. Lastly, the decomposition kinetics (i.e., apparent activation energy, kinetic exponent and pre-exponential factor) and thermodynamics (i.e., changes of entropy, enthalpy, and Gibbs free energy) of CaCO3 in BOFS was evaluated using Arrhenius equation and Kissinger equation, and compared to those reported in the literature.
2. Performance Evaluation of HiGCarb Process for Carbon Capture and Utilization
The effect of key operating factors including rotation speed, liquid-to-solid ratio, gas flow rate, and slurry flow rate on CO2 removal efficiency was studied. The results indicated that maximal CO2 removal of 97.3% was achieved using BOFS at a gas-to-liquid (G/L) ratio of 40, with a capture capacity of 165 kg CO2 per day. In addition, the BOFS product with different carbonation degrees was used as supplementary cementitious materials in cement mortar at various substitution ratios (i.e., 0, 10 and 20%). The performance of the BOFS/cement mortar, including physico-chemical properties, morphology, mineralogy, compressive strength and autoclave soundness, was evaluated. The results indicated that the BOFS mortar with a higher carbonation degree (i.e., 48%) exhibited a higher mechanical strength in the early stage, compared to pure Portland cement mortar, and possessed superior soundness to fresh BOFS mortar, suggesting its suitability for use as high-early strength cement.
3. Development of Integrated Prediction Models for HiGCarb Process
To establish the kinetic and mass transfer models for HiGCarb process, the process chemistry of accelerated carbonation for BOFS with CRW was evaluated using quantitative X-ray diffraction (QXRD) via Rietveld refinement. In addition, the leaching behavior of various metal ions from BOFS matrix into different types of liquid agents (reaction kinetics) was studied. Moreover, the reaction kinetics of accelerated carbonation for BOFS/CRW in the HiGCarb process was determined by introducing the surface coverage model. The reaction kinetics for carbonation with different alkaline wastes in various types of reactors (e.g., HiGCarb, slurry reactor, and autoclave reactor) was compared accordingly. Furthermore, the mass transfer characteristics such as the overall gas-phase mass transfer coefficient (KGa) and height of a transfer unit (HTU) were illustrated based on theoretical theory. The results indicated that the HTU value of HiGCarb was 7.8–28.0 cm with L/S ratios between 13.3 and 20.0, which was superior to that of conventional reactors. It suggests that the reaction mechanisms, kinetics, and mass transfer of accelerated carbonation of BOFS in the HiGCarb process should be well interpreted and expressed by the developed models.
4. Quantification of Environmental Benefits and Impacts via Life-cycle Assessment (LCA)
To critically evaluate the benefits of integrating the HiGCarb process in the steelmaking industry, the performance before (i.e., business as usual, BAU) and after integration of HiGCarb process was evaluated. Significant environmental benefits can be realized by establishing the waste-to-resource supply chain between the steelmaking and cement industries, i.e., from waste treatment to cement production. The power consumption of the main unit operation (and/or equipment) for the HiGCarb process such as BOFS grinding, stirring, blowers, air compressors, pumps, and RPB reactor were evaluated. According to the results of the life-cycle assessment, the net CO2 capture amount by the HiGCarb process was 282 kg-CO2/t-BOFS, accompanied by a CO2 avoidance of 997 kg-CO2/t-BOFS due to the product utilization.
5. System Optimization by 3E (Engineering, Environmental and Economic) Triangle Model
The HiGCarb process was comprehensively evaluated according to engineering, environmental, and economic (3E) criteria using a cradle-to-gate life-cycle approach. The CO2 source for HiGCarb can be introduced directly from the industrial stacks, eliminating the need for additional CO2 capture, concentration, and transportation prior to the HiGCarb process. In addition, the reacted product is suited as cement substitution material, avoiding environmental burden from the cement industry, also an intensive CO2 emission source. In this study, nine scenarios were selected based on the overall CO2 capture performance in flue gas via the HiGCarb process. A total of 16 key performance indicators were selected by Delphi method for evaluating the HiGCarb process via the 3E triangle model. According to the results of 3E triangle model, an increase in CO2 capture performance should simultaneously reduce the potential costs and environmental impacts, which make integration of the HiGCarb process into the steelmaking industry more economically viable and environmentally friendly.

並列關鍵字

rotating packed bed ； integrated thermal analysis ； Rietveld refinement ； mass transfer ； kinetics ； life cycle assessment ； 3E triangle model

參考文獻

Liu, C.F., Shih, S.M., 2002. A surface coverage model for the reaction of Ca(OH)2 with SO2 at low temperatures. J Chin Inst Chem Eng 33, 407-413.

Power, I.M., Harrison, A.L., Dipple, G.M., Wilson, S.A., Kelemen, P.B., Hitch, M., Southam, G., 2013b. Carbon Mineralization: From Natural Analogues to Engineered Systems. Reviews in Mineralogy and Geochemistry 77, 305-360.

Abo-El-Enein, S.A., Heikal, M., Amin, M.S., Negm, H.H., 2013. Reactivity of dealuminated kaolin and burnt kaolin using cement kiln dust or hydrated lime as activators. Constr Build Mater 47, 1451-1460.

Al-Saleh, Y.M., Vidican, G., Natarajan, L., Theeyattuparampil, V.V., 2012. Carbon capture, utilisation and storage scenarios for the Gulf Cooperation Council region: A Delphi-based foresight study. Futures 44, 105-115.

Alvarez, D., Abanades, J.C., 2005. Determination of the Critical Product Layer Thickness in the Reaction of CaO with CO2. Ind Eng Chem Res 44, 5608-5615.