(221a) Nuclear Hydrogen Initiative Calcium-Bromine Cycle: Determine the Feasibility of Using Cold Plasma Dissociation for H2 Generation, and Molten-Spray Contactor for Ca·Br2 Regeneration

Authors: 
Henry, M. - Presenter, Argonne National Laboratory
Lottes, S. A. - Presenter, Argonne National Laboratory
Lyczkowski, R. W. - Presenter, Argonne National Laboratory


The Calcium-Bromine (Ca-Br) cycle being investigated is a hybrid cycle for hydrogen production employing both heat and electricity. It is particularly attractive because nearly one-half the required thermodynamic energy for water-splitting is delivered as Gen-4 heat at around 1025K (725oC) and it is envisioned that this temperature will facilitate the engineering of materials when compared to other higher temperature cycles. The work during the current fiscal year reported here focuses on two special aspects of the Ca-Br cycle:

- Determine the feasibility of using cold plasma dissociation for H2 generation from HBr (consideration is being given in the broadest sense to alternate electrical routes that will produce H2 from HBr).

- Determine the feasibility of using a molten-spray contactor for CaBr2 regeneration in a continuous mode recognizing that there is a eutectic phase with CaO

The thermodynamic basis for a three-stage Ca-Br water-splitting cycle builds upon pioneering work done on the 4-stage University of Tokyo UT-3 process, but Ca-Br employs a plasma-chemical stage for the recovery of HBr as H2 and Br2 as a substitute for the final two stages of UT-3. Earlier process design studies on the 3-stage Ca-Br cycle investigated operation in a semi-continuous mode and found that the practical efficiency was 39 - 45%. This current approach is an advance from earlier process design studies, because a continuous rather than semi-continuous mode will be tested in the laboratory. In the earlier semi-continuous mode, the mass and heat balance includes carrying the thermal load of the Calcium titanate used to support the calcium reagent through the temperature cycling between 1025 K and 850 K, thereby creating inefficiencies. Additonally, as batch vessels shift in their chemical environments between reducing and oxidizing atmospheres there are attendant complications with trace gases adsorbed in the system. Of critical importance is that the work reported here focuses on two special aspects of the Ca-Br cycle that will move the system from a semi-batch mode to continuous operations eliminating these issues.