Comparative analysis of thermodynamic theoretical models for energy consumption of CO2 capture
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CO2 capture is considered an effective technology to control the CO2 level in the atmosphere, but its development has been restricted due to its high energy requirement during CO2 concentration. Theoretical thermodynamic models have been used not only to predict energy consumption, but also to elucidate the energy conversion mechanism. However, the existing theoretical models have been applied without a clear consideration of boundaries, conditions, and limitations in thermodynamic images. Consequently, the results from such theoretical models can lead to a misunderstanding of the energy conversion mechanism during CO2 capture. A comparative analysis of three theoretical thermodynamic models, namely the mixture gas separation (MGS), carbon pump (CP), and thermodynamic carbon pump (TCP) models, was presented in this paper. The characteristics of these models for determining the energy consumption of CO2 capture were clarified and compared in relation to their practical application. The idealization levels of these models were demonstrated through comparison of theoretical estimates of the energy required for CO2 concentration. The correctness and convenience of the CP model were proved through a comparison between the CP and MGS models. The TCP model proposed in this study was proved to approach the ideal status more closely than the CP model. Finally, an application of the TCP model was presented through a case study on direct capture of CO2 from the air (DAC).
Key wordsCO2 capture Energy consumption Theoretical model Carbon pump
目的:碳捕集能耗较高的技术瓶颈,亟待热力学理论在 交叉研究中解决。热力学理论工具在碳捕集技术 能耗水平评估方面的准确性、有效性和局限性都 尚未明确,且碳捕集能耗研究的共性规律仍未被 把握。本文对现有能耗分析模型进行对比以揭示 碳捕集技术能耗的实质,并提出普适性和针对性 恰当的能耗分析模型,以明确碳捕集能耗水平的 “天花板”。
创新点:1. 提出热力学碳泵模型,分析碳捕集技术理想能 耗;2. 对比不同碳捕集能耗分析模型,通过案例 分析说明其不同特点和理想化程度的差异。 方法: 1. 通过概念比拟,类比热泵概念,提出热力学碳 泵概念,并阐述碳捕集过程是通过热或功驱动的 二氧化碳从低浓度向高浓度逆向富集的非自发 过程(图2 和3),实现碳捕集技术实质的理想化 概括;2. 通过热力学理论推导,获得基于热力学 碳泵模型的碳捕集最小理想能耗(公式(13)); 3. 通过案例分析,论证热力学碳泵模型相对混合 气体分离模型和碳泵模型的理想化程度是否更 高(图9),以及其中碳源、汇的无限质容假设是 否更接近理想状态。
结论:1. 通过碳泵模型可以得到碳捕集技术的理想能 耗,并且碳泵模型相对混合气体分离模型在使用 时更便捷。2. 热力学碳泵模型相对碳泵模型的理 想化程度更高;因为忽略碳源、汇由传质引起的 不可逆性,热力学碳泵模型计算所得最小理想能 耗比碳泵模型计算所得理想能耗更小。3. 通过热 力学碳泵模型分析直接空气碳捕集技术表明,其 最小理想能耗是相同反应条件下烟气处理技术 的4.916 倍。
关键词碳捕集 能耗 理论模型 热力学碳泵
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