Dynamic modelling of methanation reactors during start-up and regulation in intermittent power-to-gas applications.

Power-to-gas is a pathway for the storage of intermittent renewable energy in a chemical form; energy surpluses can be exploited to produce hydrogen (via electrolysis) that can then react with carbon dioxide to produce synthetic methane by using catalytic cooled reactors. Methanation unit has been designed and optimized, defining the number of involved reactors, the number of parallel tubes for each reactor and the staged CO 2 injection to moderate the maximum temperature throughout the reactors. The produced synthetic natural gas (SNG) must have a methane content at least equal to 95 mol.-%, achieved by involving a series of 3 cooled reactors. Dynamic behavior of the as-designed system has been investigated for two cases that can occur when a power-to-gas system is operated intermittently: start-up from reactor hot standby and system operated at partial load. Methanation system requires about 130 s to reach the targeted methane content when it is started up from hot standby. In order to broaden the system rangeability (the minimum percentage of full load), different CO 2 staged injection should be carried out: part of carbon dioxide bypasses first and second reactor and it is directly conveyed to the third one. [Display omitted] • Design of CO 2 methanation unit based on fixed-bed cooled reactors. • Dynamic behavior: start up after hot standby and partial load operation. • Synthetic natural gas quality is achieved after about 130 s from start up. • Carbon dioxide staging should be modified to widen the rangeability (45–100%). [ABSTRACT FROM AUTHOR]