Power-to-gas (P2G) plays a significant role in the future energy system. The surplus renewable electricity can be transformed into substitute natural gas (SNG) through water electrolysis and subsequent methanation. At present, the energy conversion efficiency of a power-to-gas plant is relatively low, and extra energy is required to obtain CO2 for methanation. To solve the above problems, this work proposed an efficient power-to-gas system based on renewable hydrogen and biomass gasification: the high temperature electrolysis relied on the renewable power produces hydrogen as the middle energy carrier, and provides O2 as gasification agent for gasifier; the renewable hydrogen combined with syngas from biomass gasification will be used for CO2/CO coexistence methanation process, which can break through the conventional idea of water gas shift process and avoid CO2 separation consumption. Besides, process heat of gasification and methanation are recycled and utilized for electrolysis. The electrochemical model of the high temperature electrolysis is established and the whole system is simulated by Aspen plus. The parametric analysis are conducted and the results show that the heat consumption of electrolysis increases with temperature rising while the change of power requirement is the contrary; the gasification cold gas efficiency of biomass can reach 83% at 1123 K; in the co-methanation process, the recommended values of Ru is 3.0. The energy/exergy analyses of the whole power-to-gas system illustrate the thermal efficiency of the novel plant can reach up to 77.4%, which is 15 percentage points higher than the traditional SNG production pathways.
Keywords renewable hydrogen, steam/oxygen biomass gasification, CO2/CO co-methanation, thermodynamic analyses