Thermodynamic Benchmarking of CO2 Capture Systems: Exergy Analysis Methodology for Adsorption Processes

Exergy analyses of carbon capture systems provide a directly cross-comparable figure of merit (the exergy efficiency), and identify the process steps in each system that are most in need of improvement. In order to perform an exergy analysis of adsorption systems, the exergy of an adsorbed phase must be defined; however, the thermodynamics of these phases are different from those of bulk phases so bulk phase exergy expressions cannot be used directly. The exergy of an adsorbed phase is derived from fundamental principles. Restrictions on adsorbed-phase equations of state and mixing rules, as well as the definition of the dead state, are discussed. Examples relevant to carbon capture are presented; however, the expression derived here applies generally to adsorption processes.