A 6-kW thermally self-sustained two-stage CO2 methanation reactor: design and experimental evaluation of steady-state performance under full-load conditions

This study designed and evaluated a 6-kW, two-stage CO2 methanation reactor, with the aim of effectively recovering the heat generated by the reaction and condensation of the by-product H2O, securing a high CO2 conversion (≥99%) under low pressure without any external thermal input for catalyst temperature control, i.e., thermally self-sustained. The H2 feed was split, with the majority being fed into the first reactor and the remainder into a second reactor. The heat-carrier flow was also split between the stages and, thereby, the second reactor was cooled by supplying only a fraction of the heat-carrier that had been heated in the first reactor. Reactor inner diameters of 16 and 25 mm, as well as parallel and counter flow heat exchange configurations were compared in the second reactor, using a 1-kW test rig. The results showed that the use of a 16-mm reactor diameter and a parallel flow configuration in the second reactor realize a higher total heat recovery with the 99% CO2 conversion. The steady-state performance of the designed 6-kW two-stage reactor was evaluated at 200 kPa (G) under full load. The reactor consequently recovered more than 70% of the total generated heat at 99% CO2 conversion, increasing the heat-carrier temperature from room temperature (inlet heat-carrier temperature) to 137 °C (outlet heat-carrier temperature).