Thermodynamic analysis of alternative approaches to chemical looping combustion

In this article, we review and clarify some of the points made by previous authors(1, 2)regarding chemical looping combustion (CLC). Although much of the recent interest in chemical looping combustion has been associated with carbon sequestration, our primary interest here is its potential to increase the thermodynamic efficiency of converting fuel chemical energy into useful work. We expand on several points about the details of CLC that we feel have not previously been sufficiently explored and suggest alternative (and possibly more practical) approaches that exploit some of the same thermodynamic concepts. We illustrate our key points with first and second law analyses of ideal conceptual processes, which, in addition to CLC, also include isothermal, nonequilibrium, preheated combustion and combustion with thermochemical recuperation. Our results suggest that a significant portion of the potential efficiency benefit of CLC might be achieved without the need to handle and transport large quantities of solid oxygen-storage material. Exploitation of this fact may lead to approaches for power generation from hydrocarbon fuel combustion that can achieve second law efficiencies 10-15% higher than those that are currently possible.