Thermal Energy Storage Using the Boudouard Reaction

This study presents a firm, indefinite storage of solar heat via chemical conversion of simple carbon-based chemicals using both the forward and reverse Boudouard reaction:

C + CO₂↔ 2CO (ΔH = 171 kJ/mol)

This system is intended to be coupled with an external process like a supercritical CO₂ power turbine or a chemical conversion process. Depending on the operational needs, the energy storage reaction may be conducted to optimize performance at temperatures ranging between ca. 900K and 1100K (~600°C to ~800°C) by modifying the initial loading ratio of C and CO₂ into the system. In the thermal energy storage system, when excess heat is present as signaled by high temperatures in the external process, some of the heat is absorbed and stored as chemical energy, and when insufficient heat is supplied by the solar field, as reflected by lower temperatures in the external process, the heat is reinjected into it. In our design, the Boudouard reaction takes place in a fluidized bed reactor in which process solids reside, and where the heat is coupled into or out of the power cycle working fluid through the use of bidirectional heat pipes. The gas reactants/products are stored in packed beds of zeolitic material (copper doped zeolite 5A for CO, and simple ZSM-5 for CO₂). Systems at the 20 MW/320 MWh scale have been designed and modeled.

Current results reflecting system performance, modulating charge and discharge temperatures, and exergetic efficiency will be presented.