博士 / 國立臺灣科技大學 / 機械工程系 / 105 / Chemical looping combustion (CLC) is classified as an emerging clean combustion process, where metal oxide (MexOy) as oxygen carrier is used to provide the oxygen sources for the combustion reaction, thereby achieving the inherent CO2 capture for the indirect contact between fuel and air. It is widely discussed that the development of the oxygen carriers, reactor design and fuel selection are the critical issues for the CLC process. Especially the development of oxygen carriers, the transfer ability of the heat and oxygen within the fuel/air reactor, avoiding the air direct connecting to the fuel are concerned. Of the feasible candidates, iron-based oxygen carrier (hematite, Fe2O3) is the most promising oxygen carrier for the commercial CLC application, because of its relative thermal stability, mechanical strength and low price. Unfortunately, the poor reduction kinetics of Fe2O3 is the major drawback during the high temperature operation, attributing to the three intermediate states in the reduction period. Therefore, the feasibility of using alkali- and alkaline earth-metals contained in the seawater can be utilized as the catalytic agents for Fe2O3 oxygen carrier in chemical looping combustion process was investigated to improve the reduction kinetics in this study.
The reduction kinetics of Fe2O3 oxygen carrier in fuel gases and different ratios of Fe2O3/Al2O3 as oxygen carriers are primarily discussed. The initial reduction temperature is found to be strongly depended on the fuels with the order of carbon monoxide > syngas > hydrogen. The Fe2O3/Al2O3 oxygen carrier with 60wt% Fe2O3 (FA32) shows successful attrition behavior, reaction activity and thermal stability in the CLC process. Furthermore, the formation mechanism for sodium-contained solution preparation via air atmospheric pressure plasma jet (Air-APPJ) method is also investigated, as well as assessing the sodium-modified FA32 oxygen carrier. With the Sodium dopant loading in the FA32 oxygen carrier increasing from 1 wt. % to 10 wt. %, Nax_FA32 samples with different crystalline structure and surface morphology caused the fuel conversion ability and the stability performance in the practical operation process. The enhanced properties such as the reduction behavior, thermal stability and attrition resistance of Na1_FA32 without degradation were feasibly achieved in the lab-scaled semi-fluidized bed reactor (semi-FzBR). Optimistic results were attributed to the promotion of the pore structure and the improvement on the selectivity of the fuel conversion from the sodium promoter.
Moreover, the use of seawater as a precursor to prepare the alkali- and alkaline earth- dopants using an Air-APPJ method. A three-step of the preparation route is proposed as ultrasonic atomization, plasma oxidation and dissolution. Based on the formation mechanism, dopants without any chlorine-containing residues modifying inreactive FA32 oxygen carrier (Na1_inFA32_seawater) has been established, which led to an improved reduction performance as compared to the raw FA32 and inreactive FA32 oxygen carriers. The high gas yield for syngas as fuel (Ysyngas) around 0.93 after fifty redox cycles for the Na1_inFA32_seawater oxygen carrier is achieved. It can be anticipated that the alkali- and alkaline earth metals-modified Fe2O3/Al2O3 samples from seawater by an Air-APPJ system as an oxygen carrier candidate in a reversible CLC process would be notably attractive.
| Identifer | oai:union.ndltd.org:TW/105NTUS5489031 |
| Date | January 2017 |
| Creators | Wei-Chen Huang, 黃薇臻 |
| Contributors | Yu-Lin Kuo, 郭俞麟 |
| Source Sets | National Digital Library of Theses and Dissertations in Taiwan |
| Language | zh-TW |
| Detected Language | English |
| Type | 學位論文 ; thesis |
| Format | 184 |
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