Efficient Combustion: A Process Synthesis Approach to Improve the Efficiency of Coal-Fired Power Stations

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• 作者：Baraka Celestin Sempuga ; Bilal Patel ; Diane Hildebrandt ; David Glasser
• 刊名：Industrial & Engineering Chemistry Research
• 出版年：2012
• 出版时间：July 4, 2012
• 年：2012
• 卷：51
• 期：26
• 页码：9061-9077
• 全文大小：727K
• 年卷期：v.51,no.26(July 4, 2012)
• ISSN：1520-5045

文摘

Much of our energy reserves are locked in the chemical potential of chemicals such as fossil fuels. The majority of CO₂ emissions caused by human activities come from the combustion of these fuels. Typically, the fuel is burned with oxygen (air), and heat is released. This heat is then used to drive power cycles to produce, for example, electricity in a power plant or motion in the motor car engine. Often, the performance of these processes is assessed in term of thermal efficiency (畏_th), which considers how much of the energy released in the combustion process is turned into work. This is not a good representation of how efficient the process is, however, as an idealized Carnot engine, which takes heat from a heat source at a temperature T_H and rejects heat to a heat sink at the reference temperature T₀ = 298.15 K, is reversible and thus takes all of the work potential (exergy) of heat and converts this to work. Thus, the Carnot engine might have only 40% efficiency in terms of converting heat to work (畏_th), but because it is fully reversible, it generates no entropy, and therefore, it is 100% efficient in terms of recovering the work potential of heat. However, there is a much more fundamental efficiency that should be considered, namely, how much of the chemical potential of the fuel is turned into work. When combustion processes are considered in this way, it becomes clear that some of the major inefficiencies are in the chemical transformations that produce heat, rather than in the power cycles that convert heat to work. A very important question remains: Is it possible to do these transformations more efficiently and thereby conserve the work potential or chemical potential in fuel? This article shows, from a fundamental thermodynamic analysis, that it is not possible to combust carbon-based materials efficiently, that is, that the process of combustion of carbon-based materials is irreversible and that a considerable amount of the chemical potential of the fuel is lost during the combustion process. However, other substances or chemistries are explored in this work, and it is shown that some of these have the potential for more reversible combustion. These options are explored, and their potential implementation is examined by considering a coal-based power plant as an example. In particular, it is shown that CO₂ emissions could be significantly reduced by using different chemical pathways to do the combustion and by combining power and chemical production.