Transient Characteristics of a Porous Steam Methane Reforming Reactor

Steam-methane reforming (SMR) remains the workhorse for large-scale hydrogen, yet real plants face transients during start-up, load changes, and control actions. This work develops and validates a two-dimensional transient porous-media CFD model of a single SMR tube in ANSYS Fluent 2024 R2, with user-defined functions (UDFs) implementing reforming kinetics and porous source terms. After mesh/timestep independence and validation against literature data-steam to carbon ratio (S/C)=3 and P = 5 bar, the model is used to quantify how temperature (700-1000 K), pressure (5-20 bar), and S/C (2-5) shape both the dynamic approach to steady state and the final methane conversion. At P=10 bar and S/C=3, raising temperature increases plateau conversion from 15% (700K) to 76%(1000 K) and shortens the response. At 1000 K and S/C=3, lower pressure improves conversion (90% at 5 bar vs 60-65% at 20 bar). Increasing S/C boosts conversion with diminishing returns beyond 4(=96-97%). Transient trajectories exhibit a fast near-wall response followed by a slower core warmup, with outlet compositions (H2, CO2, CH4) settling over 120-300 s depending on conditions.