Dynamic modeling of an evaporation cooled micro-structured reactor - The case of CO$_2$ methanation

Converting renewable electricity and captured $\mathrm{CO_2}$ into synthetic natural gas is a key element of the energy transition.
Compact micro-structured reactors with evaporative cooling are promising for this Power-to-Gas pathway, but their safe operation requires robust thermal stability.
This work develops an open-source dynamic model to investigate the coupled effects of heat release from $\mathrm{CO_2}$ methanation, heat conduction through the reactor wall, and two-phase flow boiling in a plate-type microreactor.
A parametric study reveals an exceptionally narrow operating window of only $\pm 2 °C$ in coolant temperature, bounded by reaction extinction and temperature excursions.
Two coolant distribution strategies are compared. The spatially redistributed configuration achieves conversions sufficient for injection into the German natural gas grid while producing superheated steam suitable for electrolyzer integration.
Cooling failure simulations reveal a pronounced asymmetry: downstream failures are benign, whereas upstream failures induce irreversible steady-state shifts via hysteresis driven by positive feedback between heat release and hotspot migration.
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Even sub-threshold failures produce permanent hotspot migration, and a critical failure duration of approximately 5 s is identified beyond which recovery requires controlled shutdown.
These findings establish temperature exceedance as an insufficient health indicator and provide a quantitative basis for model-based monitoring and control of this reactor class.