(733b) Separation Work and the Thermodynamics of CO2 Capture From Flue Gas

The economics and process selection for CO2 capture from flue gases is influenced to a significant extent by the energy requirements for the process. This paper presents a thermodynamic framework for estimating the energy requirements of CO₂ capture processes. The presented thermodynamic framework is general in nature and applies to CO₂ capture using absorption in amines and can be applied to any separation involving a mixture of gases.   

Of specific interest are the processes using a first step of selectively capturing the gas to be separated by a solvent followed by stripping of the absorbed /adsorbed gas in a second step. Among the many possibilities these will include liquid absorption cycles, mostly amine based and chemical looping using materials such as calcium oxide or sodium carbonate-bicarbonate. While the capture process occurs spontaneously, stripping and regeneration of the solvent that releases the purified gas requires energy. Given the very large commercial scale of these processes it is of utmost importance to minimize the energy requirements. For example, the heat provided to the stripper reboiler may constitute more than 80% of the total energy requirements of the gas capture operations. It is then important to develop a conceptual understanding of the factors affecting the energy requirements. These include, rich and lean loadings, stripper pressure, energy losses in cross flow heat exchangers and the type of solvent deployed. The model being presented provides the lower bound for the energy consumption. The analysis will address the minimum separation work from a solvent and its relation to the minimum separation work from an ideal gas mixture. The model provides a criterion for solvent selection and for improving the process configuration . The results will be compared with reported experimental and industrial results.