本文關(guān)鍵詞： 化學(xué)鏈氧解耦燃燒 Cu 基氧載體 密度泛函理論 抗燒結(jié) 氧載體設(shè)計(jì)　出處：《華中科技大學(xué)》2015年碩士論文　論文類型：學(xué)位論文

【摘要】：化學(xué)鏈燃燒(CLC)是一種新型的燃燒方式,不僅可以提高燃料燃燒效率,而且可以實(shí)現(xiàn)CO2內(nèi)分離,對解決當(dāng)前面臨的CO2排放問題具有重要意義。化學(xué)鏈氧解耦燃燒(CLOU)是一種特殊的化學(xué)鏈燃燒方式,氧載體顆粒可循環(huán)釋放/吸收氣態(tài)氧,可有效提高煤等固體燃料的燃燒速率及效率。其中高性能氧載體是化學(xué)鏈氧解耦燃燒技術(shù)的關(guān)鍵。但是目前對于氧載體的釋氧吸氧微觀機(jī)理和氧載體組分間相互作用機(jī)制的認(rèn)識非常有限,對于氧載體設(shè)計(jì)優(yōu)化的理論研究比較缺乏,制約了這一技術(shù)的發(fā)展。本文基于密度泛函理論(DFT)及熱重分析實(shí)驗(yàn),首先系統(tǒng)地研究了CLOU中應(yīng)用最廣泛的Cu基氧載體的釋氧機(jī)理。恒溫釋氧實(shí)驗(yàn)發(fā)現(xiàn),CuAl2O4釋氧速率隨反應(yīng)進(jìn)行逐漸減慢,而CuO保持勻速率釋氧。DFT計(jì)算表明表面反應(yīng)是CuO釋氧的速控步驟,釋氧快慢不受晶體內(nèi)氧原子遷移路徑的長短限制,因此能夠保持勻速釋氧;而CuAl2O4內(nèi)部氧原子遷移勢壘與表面反應(yīng)勢壘相當(dāng),是釋氧的速控步驟,隨著釋氧過程的進(jìn)行,氧原子遷移路徑更長,造成釋氧速率隨著反應(yīng)進(jìn)行逐漸變慢。同時(shí)對CuFe2O4釋氧進(jìn)行了研究,發(fā)現(xiàn)CuFe2O4的O-O形成勢壘比CuO和CuAl2O4略小,而O-O脫附勢壘顯著高于另兩者;CuFe2O4晶體內(nèi)部的氧原子遷移勢壘同樣比較高,這造成了CuFe2O4釋氧困難。然后通過構(gòu)建合理的負(fù)載型氧載體模型及開展相應(yīng)的程序升溫釋氧實(shí)驗(yàn)(TPD),探索了負(fù)載的抗燒結(jié)機(jī)制和對CuO釋氧活性的影響。DFT計(jì)算表明,CuAl2O4表面與CuO團(tuán)簇間的相互作用可以有效抑制團(tuán)簇的原子擴(kuò)散,進(jìn)而抑制燒結(jié)現(xiàn)象。通過比較CuO與不同負(fù)載的結(jié)合能,并據(jù)此判斷相應(yīng)負(fù)載的抗燒結(jié)能力,發(fā)現(xiàn)Cu-Zr和Cu-MgAl抗燒結(jié)性最好,而Cu-Ti抗燒結(jié)性較差。通過計(jì)算釋氧過程的能量勢壘及TPD實(shí)驗(yàn)研究,發(fā)現(xiàn)CuAl2O4添加并不能有效提高CuO釋氧的速率。DFT計(jì)算表明對于不同負(fù)載的CuO團(tuán)簇,抗燒結(jié)性能好的氧載體反應(yīng)活性反而較低,與TPD實(shí)驗(yàn)結(jié)果相符合。最后,利用DFT計(jì)算方法研究了Cu2O、CuAlO2和CuFeO2吸氧初期的表面反應(yīng)過程。計(jì)算結(jié)果表明自由O2分子的吸附解離最終在Cu2O表面形成了三重位的O3f和四重位的O4f,形成了類似CuO(111)表面的結(jié)構(gòu)。三種氧載體的O2分子的表面吸附解離過程均是放熱過程,說明吸氧過程中表面反應(yīng)相對容易進(jìn)行,同時(shí)進(jìn)一步討論了實(shí)際中限制吸氧過程進(jìn)行的主要因素。
[Abstract]:Chemical chain combustion (CLC) is a new combustion method, which can not only improve the combustion efficiency of fuel, but also realize the separation of CO2. Chemical chain oxygen decoupling combustion (CLOU) is a special chemical chain combustion method. Oxygen carrier particles can recycle and absorb gaseous oxygen. The combustion rate and efficiency of solid fuels such as coal can be improved effectively. Among them, high performance oxygen carrier is the key of chemical chain oxygen decoupling combustion technology. But at present, the microscopic mechanism of oxygen release and oxygen absorption of oxygen carriers and the interaction between oxygen carrier components are very important. The understanding of the mechanism of action is very limited. The lack of theoretical research on oxygen carrier design optimization restricts the development of this technology. This paper is based on density functional theory (DFT) and thermogravimetric analysis (TGA) experiments. Firstly, the oxygen release mechanism of Cu-based oxygen carrier in CLOU was systematically studied. It was found that the oxygen release rate of CuAl2O4 decreased gradually with the reaction at constant temperature. The results show that the surface reaction is the rapid control step of CuO oxygen release, and the speed of oxygen release is not limited by the length of oxygen atom migration path in crystal, so the oxygen release rate can be maintained at a uniform rate. The oxygen atom migration barrier in CuAl2O4 is the same as the surface reaction barrier, which is the speed control step of oxygen release. With the oxygen release process, the oxygen atom migration path is longer. The oxygen release rate of CuFe2O4 decreases gradually with the reaction. It is found that the O-O formation barrier of CuFe2O4 is slightly smaller than that of CuO and CuAl2O4. The O-O desorption barrier was significantly higher than the other two. The oxygen atom transport barrier in CuFe2O4 crystal is also relatively high. This resulted in the difficulty of releasing oxygen, and then through the construction of a reasonable loaded oxygen carrier model and the corresponding temperature programmed oxygen release experiments. The anti-sintering mechanism and the effect on the oxygen release activity of CuO were investigated. The results show that the interaction between CuAl2O4 surface and CuO clusters can effectively inhibit the atomic diffusion of the clusters. By comparing the binding energy of CuO with different loads and judging the anti-sintering ability of the corresponding load, it is found that Cu-Zr and Cu-MgAl have the best sintering resistance. However, the sintering resistance of Cu-Ti is poor. The energy barrier of oxygen release process and the experimental study of TPD are calculated. It was found that the addition of CuAl2O4 could not effectively increase the oxygen release rate of CuO. The results showed that the oxygen carrier reaction activity with good sintering resistance was lower for CuO clusters loaded with different loads. Finally, Cu2O is studied by DFT method. The surface reaction process of CuAlO2 and CuFeO2 at the beginning of oxygen absorption. The results show that the adsorption and dissociation of free O _ 2 molecules finally form triple O _ 3f and quadruple O _ 4f on the surface of Cu2O. The surface adsorption and dissociation process of the O _ 2 molecules of the three oxygen carriers are exothermic, which indicates that the surface reaction is relatively easy to be carried out in the process of oxygen absorption. At the same time, the main factors restricting the process of oxygen absorption are discussed.
【學(xué)位授予單位】：華中科技大學(xué)
【學(xué)位級別】：碩士
【學(xué)位授予年份】：2015
【分類號】：TK16

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本文編號：1449300