(115a) Optimal CO2 Capture Solvent Properties for Partial Capture and Natural Gas Power Plants

A major class of work on absorption-based capture systems is the prediction of separation plant performance for various solvents and solvent mixtures.  Equilibrium or rate-based models are used to compute the imposed load (reduction in net electrical work output from a power plant) for separation using a given solvent, possibly optimizing over process parameters (such as stripper pressure).  This analysis is repeated for each solvent considered.  While this type of work shows the potential of each solvent, it does not show how an energetically-optimal solvent would behave. 

In our modeling approach, we choose a specific process architecture, but do not choose a specific solvent.  Instead of taking solvent properties as fixed, we treat them as model inputs that can be adjusted along with the system operating conditions.  By adjusting the solvent properties as well as process parameters, we find the properties of the energetically-optimal solvent for a given process configuration, and the imposed load when using that solvent in that process.  This value of imposed load is a more informative target than the thermodynamic minimum work or the work requirement with a specific solvent since it reveals the potential of a given process configuration.

We will discuss the properties of optimal solvents for natural gas and partial capture coal cases with varying solvent type and kinetic behavior.  The model is not dependent on any particular solvent chemistry, and hence is applicable to many classes of solvents.  Models for ionic liquids and non-aqueous co-solvents are obtained by setting the solvent composition appropriately.  Although the model is at its core a thermodynamic model, kinetic effects can be modeled by changing the rich loading.  We find that optimal thermodynamic behavior is a function of kinetic behavior and equipment size.