(637b) Ammonia Decomposition to Produce Hydrogen Using Chemical Looping Approaches: Considerations and Results for High Pressure Operation

Authors: 
Kathe, M., The Ohio State University
Petrecca, M., The Ohio State University
Fan, L. S., The Ohio State University
Baser, D., The Ohio State University
A potential solution to reduce transportation costs for H2 is to use ammonia (energy density: 4.25 kW/L). Ammonia (NH3) is proposed to be an alternative H2 carrier, due to its lower transportation costs and it is widely produced on an industrial scale using Haber-Bosch chemistry. From an end-user perspective, if ammonia is used as a H2 carrier and if H2 is still used as the primary energy source, there exists a technological need to convert NH3 back to H2 in an efficient way. OSU has proposed a thermochemical solids looping based NH3 to H2 (ATH) process that can operate at high thermal and H2 production efficiencies. The ATH system can be operated as a two reactor system or a three reactor system, wherein the first the reducer reactor utilizes an intrinsic O2 gradient driven by the reduction potential of NH3 and a metal oxide Fe2O3/Fe3O4) to efficiently crack NH3 to a mixture of N2, H2 and H2O. The reduced metal-oxide from the reducer reactor is re-oxidized in a second reactor oxidizer using H2O as the oxygen source. Depending on the system configuration, the three reactor system adds in a combustor reactor to re-oxidize the metal-oxides. Previous studies have focused on comparing the three reactor system to a two-reactor system and obtaining highest cold-gas efficiencies for each. The earlier chemical looping investigations quantified the thermodynamics of the chemical looping system for atmospheric pressure. So, while the earlier results are promising, it should be noted that various H2 utilization applications require H2 at pressures of ~30-50 bar.

This study seeks to quantify the thermodynamic feasibility associated with high-pressure chemical looping applications for Hydrogen production. This study initially quantifies the H2 production potential of the chemical looping system for higher pressures under isothermal operating conditions. Identified optimal isothermal operating conditions are used for simulating a commercially relevant adiabatic reactor operation. Experimental results are used to provide kinetic parameters to limit design space of the chemical looping system obtained using thermodynamic simulations. The trade-off analysis shows individual and synergistic effects of variables like compression ratios, reactor size, hourly space velocities while using pinch and transshipment type technology for heat exchanger network synthesis. Preliminary results show that operating chemical looping system at higher pressures is feasible and the three reactor system maintains better performance than the two reactor chemical looping system at higher pressures.