Efficient Generation of H<sub>2</sub>/NH<sub>3</sub> Fuel Mixtures for Clean Combustion
Rok Sitar, Javishk Shah, J. Douglas Way, Colin A. Wolden
Abstract
Ammonia (NH3) is an attractive carbon-free fuel, though it often requires the addition of a promoter such as hydrogen (H2) to ensure efficient and complete combustion. Herein, we describe the construction and operation of a catalytic membrane reformer (CMR) for the efficient generation of H2/NH3 fuel mixtures. A fraction of the ammonia is decomposed, and the released hydrogen is extracted through a membrane, where it combines with the remaining ammonia, which is used as a sweep gas. The use of ammonia as a sweep stream increased hydrogen recovery by as much as 60% and reduced the CMR operating temperature to as low as T = 350 °C. Dynamic control of the H2/NH3 ratio is achieved by adjusting the sweep flowrate, and the rejection of N2 enhances fuel quality. The use of the sweep enables high H2 recovery under isobaric operation, producing high-pressure H2/NH3 fuel mixtures without the need for compression. A simple reactor model was developed that accurately captures reformer performance across the range of operating conditions explored, and the excellent durability of the CMR was demonstrated through nominally unchanged performance over >1500 h of operation. This compact reformer provides on-demand generation of H2/NH3 fuel mixtures from a single fuel source that may serve as drop-in replacements for hydrocarbons to provide clean combustion with minimal equipment modification. Finally, the CMR concept may be applied for hydrogen enrichment of other fuels, and we successfully demonstrate the generation of H2/CH4 mixtures using methane as the sweep gas.