(350f) Chemical Looping Based Technology for High Efficiency Production of H2 from Ammonia (NH3)

Authors: 
Kathe, M., The Ohio State University
Fan, L. S., The Ohio State University
Clelland, K., The Ohio State University
Hydrogen (H2) is widely considered to be an integral part in solving the issues surrounding the consumption of fossil fuels. As a carbon neutral fuel, H2 can be used as an energy source with minimal emissions for a wide range of uses including chemical production and transportation. One of the most advantageous properties of using H2 as a fuel source lies in its high specific energy of 39.8 kWh/kg (HHV). Despite the advantages offered by the widespread utilization of H2, market penetration is prohibited by the high transportation costs associated with its low volumetric energy density of 1.55kWh/L and thus high compression losses in the storage of H2. In an effort to overcome these limitations, the use of ammonia (NH3) as a hydrogen carrier to minimize transportation and storage costs has been proposed. This vision for improving the market penetration of H2, is contingent upon development of high efficiency H2 from NH3 processes. OSU has developed a chemical looping based NH3 to H2 (ATH) process that can operate at high thermal and H2 production efficiencies. The OSU chemical looping approach consists of two reactors to convert NH3 to H2. The first reactor, namely the reducer reactor utilizes an intrinsic O2 gradient driven by the reduction potential of NH3 and a metal oxide like Fe3O4, ZrO2, WO3 to efficiently crack NH3 to a mixture of N2, H2 and H2O. The reduced metal-oxide from the reducer reactor is re-oxidized in an oxidizer using H2O as the oxygen source. This ensures ~1.5 moles of H2 production per mole of NH3 (nearly 100% H2 production efficiency). This presentation will initially focus on the thermodynamic rationale for developing a chemical looping based NH3 to H2 process. This will be followed by the heat balance approach to achieving the maximum H2 production efficiency while maintaining a high energy efficiency values. The relevant experimental data (using Thermo-gravimetric Analyzer and a fixed bed reactor) that identifies key design conditions associated with the kinetics of the reducer and the oxidizer reactor will be presented. A series of directed sensitivity studies that identify the trends associated with the chemical looping system and the design parameters that need to be de-risked in further scale up of this technology will be discussed.