Behavior of ilmenite as oxygen carrier in chemical-looping combustion
Behavior of ilmenite as oxygen carrier in chemical-looping combustion
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DOI：
10.1016/j.fuproc.2011.10.020
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发表时间：
2012-02-01
影响因子：
7.5
通讯作者：
Gayan, P.
中科院分区：
文献类型：
--
作者：
Cuadrat, A.;Abad, A.;Gayan, P.
对于二氧化碳排放存在限制的未来前景，化学循环燃烧（CLC）已被认为是一项有前景的技术，可以降低发电厂二氧化碳捕集相关的成本。在 CLC 中，固体氧载体以循环方式将氧气从空气转移到燃料中，避免它们之间的直接接触。 CO2 本质上是在单独的流中获得的。对于该过程，载氧体在两个互连的流化床反应器之间循环。为了使 CLC 适用于固体燃料，氧载体与固体燃料气化产生的气体发生反应，该气化就在燃料反应器中进行。钛铁矿。一种由 FeTiO3 组成的天然矿物，是一种低成本且有前景的材料，可在 CLC 中大规模使用。本研究的目的是分析钛铁矿作为 CLC 中氧载体的行为。特别关注在使用 CH4、H-2 和 CO 作为还原气体的间歇式流化床反应器中连续氧化还原循环期间钛铁矿颗粒的化学和物理特性的变化。与 H-2 的反应比与 CO 的反应更快，并且在流化床中实现了接近完全的 H-2 转化。 CH4 的反应活性较低。钛铁矿的反应活性随着循环次数的增加而增加，特别是对于 CH4。还通过使用 CO + H-2 合成气混合物的 100 次循环测试来评估钛铁矿的结构变化及其在大量循环下的行为变化。为了观察两种还原气体的相互影响，还进行了不同 H-2:CO 比例的测试，结果表明反应速率是 H-2 和 CO 各自反应速率的总和。还研究了钛铁矿的氧化反应。观察了氧化反应的活化过程，并区分了反应发展的两个步骤。氧化反应速度快，每次循环后都能达到完全氧化。发现低磨损值并且在流化床操作期间没有观察到反流化。在活化过程中，颗粒的孔隙率从低孔隙率值增加到27.5%。观察到颗粒中出现了外壳，其中富集了 Fe。 Fe 从 TiO2 中偏析导致氧传输能力下降。 100 次氧化还原循环后，R-OC 从最初的 R-OC = 4.0% 降低至 2.1%。 (C) 2011 Elsevier B.V. 保留所有权利。
For a future scenery where will exist limitation for CO2 emissions, chemical-looping combustion (CLC) has been identified as a promising technology to reduce the cost related to CO2 capture from power plants. In CLC a solid oxygen-carrier transfers oxygen from the air to the fuel in a cyclic manner, avoiding direct contact between them. CO2 is inherently obtained in a separate stream. For this process the oxygen-carrier circulates between two interconnected fluidized-bed reactors. To adapt CLC for solid fuels the oxygen-carrier reacts with the gas proceeding from the solid fuel gasification, which is carried out right in the fuel-reactor. Ilmenite. a natural mineral composed of FeTiO3, is a low cost and promising material for its use on a large scale in CLC. The aim of this study is to analyze the behavior of ilmenite as oxygen-carrier in CLC. Particular attention was put on the variation of chemical and physical characteristics of ilmenite particles during consecutive redox cycles in a batch fluidized-bed reactor using CH4, H-2 and CO as reducing gases. Reaction with H-2 was faster than with CO, and near full H-2 conversion was obtained in the fluidized-bed. Lower reactivity was found for CH4. Ilmenite increased its reactivity with the number of cycles, especially for CH4. The structural changes of ilmenite, as well as the variations in its behavior with a high number of cycles were also evaluated with a 100 cycle test using a CO + H-2 syngas mixture. Tests with different H-2:CO ratios were also made in order to see the reciprocal influence of both reducing gases and it turned out that the reaction rate is the sum of the individual reaction rates of H-2 and CO. The oxidation reaction of ilmenite was also investigated. An activation process for the oxidation reaction was observed and two steps for the reaction development were differenced. The oxidation reaction was fast and complete oxidation could be reached after every cycle. Low attrition values were found and no defluidization was observed during fluidized-bed operation. During activation process, the porosity of particles increased from low porosity values up to values of 27.5%. The appearance of an external shell in the particle was observed, which is Fe enriched. The segregation of Fe from TiO2 causes that the oxygen transport capacity. R-OC, decreases from the initial R-OC = 4.0% to 2.1% after 100 redox cycles. (C) 2011 Elsevier B.V. All rights reserved.