Hao Zhang , Xiaomi Zhang , Dazhi Yang , Bai Liu , Yong Shuai , Bachirou Guene Lougou , Qian Zhou , Xing Huang , Fuqiang Wang
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To delve further into such phenomenon and potentially unveil the underlying scientific principles, this study conducts a reaction kinetic analysis and lab-scale systematic experiments on a novel methane-assisted two-step thermochemical process using iron-based oxygen carriers. Despite the fact that the reaction kinetics analysis of iron oxides indicates that isothermal cycles at reaction temperatures of 573–1173 K do not provide significant advantages in terms of energy conversion efficiency, surprisingly, the experiments conducted with the prepared cobalt–nickel ferrite materials conclude oppositely. More specifically, the observed increase in material reactivity with rising oxidation temperature contributes to an approximately two-fold enhancement in the CO yield under isothermal conditions, as well as a noteworthy improvement of about 15% in solar-to-fuel efficiency. This energy efficiency improvement could be attributed, at least in part, to the stable reaction temperature during isothermal cycling, which effectively mitigates the challenges associated with solid-phase sensible heat recovery caused by significant temperature fluctuations, particularly when operating at high feed flow rates. Accordingly, the applicability of isothermal cycles is linked to two crucial factors: the reactivity of the oxygen carrier and the specific operating conditions employed. The experiments herein conducted showed that the catalytic activity of the material reached a relatively stable state after 24 h of reaction, resulting in a peak CO yield of 20.5 mL min<span><math><msup><mrow></mrow><mrow><mo>−</mo><mn>1</mn></mrow></msup></math></span> g<sup>−1</sup> and a CO<span><math><msub><mrow></mrow><mrow><mn>2</mn></mrow></msub></math></span> conversion exceeding 90%. 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引用次数: 0
摘要
出于热力学和反应动力学的考虑,传统的两步太阳能热化学过程通常依赖于非等温循环条件,以有效地将内热还原反应和放热氧化反应结合起来。然而,最近基于热力学模拟和材料表征对等温循环的讨论引发了不同意见,因为某些在等温循环条件下运行的反应过程已证明有可能实现更高的能量转换效率。为了进一步深入研究这种现象并揭示其潜在的科学原理,本研究对使用铁基氧载体的新型甲烷辅助两步热化学过程进行了反应动力学分析和实验室规模的系统实验。尽管铁氧化物的反应动力学分析表明,反应温度为 573-1173 K 的等温循环在能量转换效率方面并不具有显著优势,但令人惊讶的是,用制备的钴镍铁氧体材料进行的实验却得出了相反的结论。更具体地说,随着氧化温度的升高,观察到的材料反应性的增加使等温条件下的一氧化碳产量提高了约两倍,太阳能转化为燃料的效率也显著提高了约 15%。能效的提高至少部分归功于等温循环过程中稳定的反应温度,这有效缓解了固相显热回收因温度大幅波动而带来的挑战,尤其是在高进料流速下运行时。因此,等温循环的适用性与两个关键因素有关:氧载体的反应性和采用的特定操作条件。实验表明,该材料的催化活性在反应 24 小时后达到了相对稳定的状态,一氧化碳产量峰值为 20.5 mL min-1 g-1,二氧化碳转化率超过 90%。通过深入分析,我们发现了几种在反应系统设置下提高效率的优化措施。
Comparison of non-isothermal and isothermal cycles in a novel methane-assisted two-step thermochemical process
As driven by thermodynamics and reaction kinetics considerations, conventional two-step solar thermochemical processes typically rely on non-isothermal cycling conditions to effectively couple the endothermic reduction and exothermic oxidation reactions. Nevertheless, recent discussions on isothermal cycles based on thermodynamics simulation and material characterization have sparked dissenting opinions, as certain reaction processes operating under isothermal cycling conditions have demonstrated the possibility of achieving higher energy conversion efficiency. To delve further into such phenomenon and potentially unveil the underlying scientific principles, this study conducts a reaction kinetic analysis and lab-scale systematic experiments on a novel methane-assisted two-step thermochemical process using iron-based oxygen carriers. Despite the fact that the reaction kinetics analysis of iron oxides indicates that isothermal cycles at reaction temperatures of 573–1173 K do not provide significant advantages in terms of energy conversion efficiency, surprisingly, the experiments conducted with the prepared cobalt–nickel ferrite materials conclude oppositely. More specifically, the observed increase in material reactivity with rising oxidation temperature contributes to an approximately two-fold enhancement in the CO yield under isothermal conditions, as well as a noteworthy improvement of about 15% in solar-to-fuel efficiency. This energy efficiency improvement could be attributed, at least in part, to the stable reaction temperature during isothermal cycling, which effectively mitigates the challenges associated with solid-phase sensible heat recovery caused by significant temperature fluctuations, particularly when operating at high feed flow rates. Accordingly, the applicability of isothermal cycles is linked to two crucial factors: the reactivity of the oxygen carrier and the specific operating conditions employed. The experiments herein conducted showed that the catalytic activity of the material reached a relatively stable state after 24 h of reaction, resulting in a peak CO yield of 20.5 mL min g−1 and a CO conversion exceeding 90%. Thorough analyses reveal several optimization measures for enhancing efficiency under the setting of the reaction system.
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