Dynamic operation of two-stage CO2 methanation reactor: Start-up by H2 combustion and load change by independent control of heat-carrier flow rate

This study suggested and evaluated methods for attaining the fast start-up and load change of a two-stage CO2 methanation reactor. For start-up, catalysts inside the reactor need to be heated from the cold state to a temperature exceeding the methanation activation temperature (>150 °C). The proposed method combusts H2 using methanation catalysts as the H2 combustion catalyst. For load change (a change in the CH4 production rate), the flow rates of the feed gases (H2 and CO2) need to be varied from the current value to the target value. The proposed method determines the ramp rate of the heat-carrier flow rates independently of the feed gas flow rates. Both methods were experimentally evaluated using a previously developed 6-kW two-stage CO2 methanation reactor. The start-up was conducted from room temperature (25 °C) and the load was varied between 60 % and 100 %. For comparison, conventional start-up using a 3.5-kW heat-carrier heater was also conducted. The results show that the proposed start-up method could light off two-stage methanation in as little as 4 min while the conventional method took 26 min. Also, the proposed load change method realized a 2-s feed gas flow rate change without any reaction blow-outs.