Towards H2-rich gas production from unmixed steam reforming of methane: Thermodynamic modeling

► Thermodynamic predictions are consistent with experimental results from USR isothermal tests under fuel/steam feed. ► The reacted NiO to CH4 (NiOreacted/CH4) molar ratio is a very important parameter that affects the product gas composition and decreases with time. ► In absence of CaO, NiO reduction reactions dominate the equilibrium system at the beginning of fuel flow, resulting in high CO2 selectivity, negative steam conversion and low concentrations of H2. ► At the end of fuel/steam feed, the reforming reaction is the most important chemical mechanism. In absence of CaO, H2 production reaches ∼75 mol%. ► During fuel flow, the energy demand increases with time. ► In absence of CaO, H2 at a concentration of 73 mol% can be obtained under thermo-neutral conditions. ► In the presence of CaO sorbent, H2 at concentrations over 98 mol% can be produced continuously under fuel/steam feeds. ► Carbonation reaction provides the heat for steam reforming. Thus, the heat released during air flow due to Ni oxidation can be used to decompose calcite into CaO. With a suitable duration of fuel/steam feed, as well as the right calcite to Ni molar ratios during air feed, the process can run auto-thermally.