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

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.