Study on Hydrogen Production Characteristics by Methanol Steam Reforming in a Fresnel Lens-Tapered Cavity Solar Thermal Concentric-Tube Reactor

The endothermic nature of methanol steam reforming (MSR) for hydrogen production induces varying thermal effects along the flow direction, resulting in a non-uniform temperature distribution within the catalytic bed. Optimizing temperature uniformity has been demonstrated to enhance hydrogen production efficiency. In this study, a novel Fresnel lens-driven non-evacuated tapered cavity solar reactor was proposed for methanol steam reforming, which can provide a reference for optimizing hydrogen production using Fresnel lens solar concentrators. The thermal flux distribution on the reactor’s inner walls was determined by Monte Carlo ray-tracing simulations. A three-dimensional CFD model integrating fluid flow, heat and mass transfer, and methanol steam reforming reaction kinetics was developed to investigate the effects of key operational parameters on this novel reactor performance. Multi-objective optimization using response surface methodology revealed that high reactant inlet temperature (Tin > 550 K) and low flow velocity (uin < 0.2 m/s) conditions significantly improve reactor methanol conversion (99.99%) and hydrogen yield (91.48%), but at the cost of increased CO selectivity (SCO > 28%). Conversely, low temperature (Tin < 500 K) and high flow velocity (uin > 0.4 m/s) conditions suppress CO formation (SCO < 0.03%), although with reduced hydrogen production efficiency.