In Chapters 5 and 6, we discussed gas turbine cycles and Rankine cycles used in power generation, with a focus on how to improve the cycle efficiency and recover the maximum availability from the primary energy source. We also discussed the conditions under which one chooses to build a plant running on a gas cycle or a two-phase cycle, and related these to the characteristics of the primary energy source. High-temperature energy sources can be effectively utilized in a gas turbine cycle, which exhausts its stream at atmospheric pressure (unless the cycle is closed, but this is not currently practiced). Lower-temperature sources must use two-phase Rankine cycles, and must be operated in a closed cycle mode to achieve the desired efficiency. In both cases, reheat and regeneration are effective approaches to raising the thermal efficiency.

Thermodynamics is central to the analysis of energy conversion processes and systems. Although excluding rate processes, equilibrium thermodynamics’ analysis can be used to examine the efficiency and specific work of a process or a series of processes executing work and heat transfer interactions with other systems, experiencing mass transfer, undergoing chemical and electrochemical reactions, or a combination of all of these events. Non-equilibrium and rate processes can indeed impact efficiency, and are necessary to determine the power as well as other performance measures such as size and emissions. Non-equilibrium effects will be examined in later chapters. In this chapter, the basic laws of equilibrium thermodynamics are reviewed, with an emphasis on some of the origins of the different statements, the meaning of the quantities appearing in these laws, the most relevant forms of the laws to be used in analysis of energy conversion, and some conclusions regarding how these systems should be designed. The early coverage is independent of the working fluid, and focuses on the energy conversion process. Pure substance, ideal gases, and mixtures of ideal gases and their equations of state are also mentioned.

The performance of fuel cells at finite current, or finite power, is presented in this chapter, focusing on the sources of loss, how each loss mechanism is modeled, and how the design parameters and operating conditions contribute to each. In particular, we examine the role of chemical kinetics and transport processes in fuel cell efficiency. At finite current, fuel cells cannot achieve the ideal thermodynamic efficiency, corresponding to the maximum work or the Gibbs free energy of the overall reaction, due to a number of intrinsic loss mechanisms. These include: (1) non-electrochemical, or thermochemical, reactions, occurring on the surfaces or within the fuel channel; (2) potential loss associated with finite-rate electrochemical reactions; (3) decrease in reactants concentrations because of finite-rate transport processes; and (4) losses associated with the transport of ions and electrons across different elements. All of these mechanisms depend on the current drawn from the cell. Some small losses are observed even at open-circuit conditions, mostly due to electron and fuel leakage across the electrodes. Modeling these losses is tackled in some detail in this chapter.

In this chapter, methods proposed for integrating CO2 capture into power cycles are presented. While “carbon capture” is used to describe this technology, the word refers to producing a separate stream of pure CO2 at the “tailpipe” of the power plant. Moreover, while the term is sometimes used to describe separating CO2 from the combustion products of air combustion-based power plants (or any air combustion process), it is actually meant to refer to any technology that uses hydrocarbon fuels in electricity generation power plants while producing a pure stream of CO2 for storage (or reuse). These technologies include three broad categories: post-combustion capture, pre-combustion capture, and oxy-combustion capture. It is also mostly assumed that in a carbon capture power plant, CO2 is delivered in the liquid phase, at pressures above 75 bar and temperature around 32 °C.