(613d) Global Optimization of Ideal Gibbs Reactor for Carbon Dioxide Capturing

An increment of carbon dioxide concentration in the atmosphere has been related to increases in the average world temperature, supporting norms that regulate atmospheric carbon dioxide emissions from various industrial sources. One of the most common operations in industrial processes is the burning of a fuel to produce energy. This suggests high temperature streams containing carbon dioxide exit the combustion process. In this work we propose a methodology for the removal of carbon dioxide from water-air mixtures via calcium oxide adsoportion, based on Gibbs free energy minimization in a multiphase system.

The case study presented in this work consists of a first step in which a gaseous mixture of oxygen, nitrogen, water and carbon dioxide reacts at constant temperature and pressure with solid carbon oxide fixed in a batch reactor. The possible reacting products are calcium carbonate and calcium hydroxide. In a second step the bed is regenerated using steam at a higher temperature. The total Gibbs minimization problem is non-linear due to the presence of condensed species, which ultimately yield a total Gibbs free energy equation that is a combination of a linear equation, a negative entropy and a positive entropy functions. The problem is reduced into variables that bound the feasible region of the problem and by the Weirstrass theorem we establish the existence of a minimum. After evaluating the bounds of the variables we establish 9 possible cases for the position of the global minimum and inspection of the cases yields the equilibrium composition of the system.