Multiscale modeling and industrial validation of the water-gas shift reactor in an ammonia unit using COMSOL multiphysics

The high temperature water-gas shift (HT-WGS) reaction is a central conversion step in ammonia production since it boosts the hydrogen yield and reduces the carbon monoxide content in the synthesis gas mixture before subsequent purification and ammonia synthesis. The industrial reactor was analyzed numerically with COMSOL Multiphysics 6.2. A three-dimensional model was created by combining momentum transport, heat transfer, multicomponent species transport, heterogeneous reaction kinetics, and intraparticle diffusion in porous Fe-Cr catalyst pellets under realistic adiabatic plant operating conditions. The novelty of the approach lies in combining industrial plant validation with simultaneous representation of reactor scale transport and pellet -scale diffusion-reaction processes. The model predictions were compared with the measured axial temperature profile and outlet gas composition obtained from the industrial plant. The model accurately predicted plant data with MAE = 3.50 K, R 2 = 0.950 (temperatures), and MAPE = 5.30% (outlet content). The validated model was used to examine velocity, temperature, pressure, gas-composition, gas–pellet concentration, and intraparticle concentration profiles. A parametric analysis was performed to evaluate the effects of inlet temperature and steam-to-CO ratio on CO conversion. The pressure profile demonstrated an approximately linear decrease across the catalyst bed, dropping from 30 to 28.35 bar. The mole fractions of CO and H 2 O dropped along the reactive bed, while CO 2 and H 2 rose. Increasing the inlet temperature enhanced CO conversion from about 38.5% at 618 K to around 71% at 653–658 K, while increasing the steam-to-CO ratio from 4.0 to 6.0 improved anticipated conversion from approximately 50%–70%. The validated model is a valuable tool for assessing the operation of industrial HT-WGS reactors in ammonia producing facilities.