Entropy generation analyses of Endex and conventional calcium looping processes for CO2 capture

Endex thermoreactive processes, in which an exothermic reaction is coupled thermokinetically to an endothermic reaction, in principle are more efficient than conventional processes. The purpose of this research is to quantify rigorously and in detail the thermodynamic efficiency advantage of an Endex calcium looping process for CO2 capture from flue gas streams, relative to a comparable conventional process, by entropy generation analysis. The theoretical background of second law analysis is reviewed, control volumes are defined and modelled, and the entropy generation rates are computed of all identified subprocesses. The Endex process is found to have superior relative second law efficiency by a factor of approximately 1.8, achieved mainly by a large reduction in the entropy penalty of regeneration at the expense of a modest increase in the entropy penalty of separation. The subprocesses most worthy (and unworthy) of optimization are identified. Results indicate that the Endex process is a promising candidate for thermal engineering optimization, because entropy generation is distributed relatively evenly across many subprocesses rather than concentrated in one or two.