Numerical analysis on ammonia decomposition for hydrogen production in a membrane reactor assisted by a parabolic trough solar collector

Abstract

Ammonia (NH3) has emerged as a promising hydrogen storage carrier due to its considerable hydrogen storage density, storage and transportation convenience, and zero carbon emissions during endothermic decomposition. By utilizing a parabolic trough solar collector to provide heat and integrating NH3 decomposition with a membrane reactor, a clean and sustainable method of hydrogen production can be achieved. This paper establishes a comprehensive numerical model for NH3 decomposition within a parabolic trough solar receiver/membrane reactor (PTSMR). The model incorporates heat and mass transfer in porous catalyst beds, membrane permeation, and reaction dynamics to accurately capture the intricate phenomena under actual operating conditions. Special attention is paid to the influences of inlet temperature, flow rate, flow pattern, and reaction pressure on NH3 conversion and hydrogen recovery. The results demonstrate that the temperature distribution within the PTSMR exhibits non-uniformity, and the temperature at the bottom is always higher than that at the top, especially at the outlet, where the temperature difference is more than 100K. The NH3 conversion rate in counterflow is higher than that in parallel flow, while the hydrogen recovery rate in parallel flow is higher due to the reverse permeation of hydrogen in counterflow. For a 2-mm-thickness catalyst bed, the addition of membranes increases NH3 conversion rate by 9% at a reaction pressure of 5 bar, compared to a 3% increase for an 8-mm-thickness catalyst bed. The PTSMR with a 2-mm-thickness catalyst bed obtains the optimum hydrogen yield rate.