Hydrogen production from methane reforming: Thermodynamic assessment and autothermal reactor design

In this study, a comparative thermodynamic analysis of methane reforming reactions is conducted using an in-house code. Equilibrium compositions are calculated by two distinct methods: (1) evaluation of equilibrium constants and (2) Lagrange multipliers. Both methods result in systems of non-linear algebraic equations, solved numerically using the Scilab (www.scilab.org) function “fsolve”. Effects of temperature, pressure, steam to carbon ratio (S/C) (steam reforming), CH4/CO2 ratio (dry reforming), oxygen to carbon ratio (O/C) (oxidative reforming) and steam to oxygen to carbon ratio (S/O/C) (autothermal reforming) on the reaction products are evaluated. Comparisons between experimental and simulated data, published in the literature, are used to validate the simulated results. We also present and validate a small-scale reactor model for the autothermal reforming of methane (ATR). Using this model, the reactor design is performed and key operational parameters are investigated in order to increase both H2 yield and H2/CO selectivity. The reactor model considers a mass balance equation for each component, and the set of ordinary differential equations is integrated using the Scilab function “ode”. This ATR reactor model is able to describe the influence of temperature on methane conversion profiles, aiming to maximize hydrogen production. The experimental results and the model presented good agreement for methane conversion in all studied temperature range. Through simulated data of methane conversions, hydrogen yields and H2/CO selectivity, it is observed that the best reaction temperature to maximize the yield of hydrogen for the ATR reaction is situated between 723 and 773 K. Inside these bounds, 50% of methane is converted into products. Also, the experimental data indicates that the Ni catalyst activity is not compromised.