Experimental investigation of hydrogen production from ammonia decomposition

Abstract

This thesis examines the production of hydrogen from ammonia in a continuous flow, packed bed membrane reactor. The experimental study examines the effects of operating temperature, pressure, and residence time on hydrogen production rate, energy and exergy ratios for the reaction, energy and exergy efficiencies of the overall system, ammonia conversion efficiency, transient ammonia concentration, and ammonia decomposition rate. With the exception of transient ammonia conversion, all of the above underwent increases with respect to operating temperature, pressure and residence time. The increases in operating temperature led to increase catalytic activity and further favouring of the reaction thermodynamics due to the Gibb’s free energy tending towards zero or increasing negatively. The increases in operating pressure resulted in increased residence times and trans – membrane pressure differences which caused increased hydrogen flux. The best results were obtained at 20 bar, 500oC and with a residence time of approximately four seconds. The maximum hydrogen production was approximately 287 mL/min. This lightly undershoots the stoichiometric production rate of approximately 300 mL/min. The maximum energy and exergy ratios for the reaction were 6.77:1 and 1.08:1, respectively. Also, the maximum energy and exergy efficiencies of the overall system were 16.9% and 20.3%, respectively. The maximum ammonia conversion efficiency and minimum ammonia concentration was found to be approximately 95.64% and 4.2%, respectively. The system took approximately 50.0 minutes to reach steady state in this particular scenario. On the results drawn from this experimental work, some technical recommendations to further improve the system’s performance and reliability were made. Also, a potential design for the rail industry was proposed and lightly explained based on the results of this thesis work. Overall, the results of this experimental work were insightful and will be useful as an initial benchmark for future work in the area hydrogen production from ammonia decomposition at UOIT.