Techno-economic viability of an electrolyzer-oxygen storage system for continuous biogas desulfurization in Power-to-Gas applications

Power-to-Gas technology enables the long-term storage of electrical energy in the gas grid by converting it to methane. It can be produced using biogas as an environmentally friendly, cost-efficient carbon source and hydrogen from electrolysis. Before being processed in further utilities and injected into the gas grid, biogas must be purified to remove harmful constituents, with hydrogen sulfide being the main pollutant. In this regard, biological desulfurization by air injection into the digester headspace is simple and cost-effective, but nitrogen introduction into the gas grid must be limited to avoid dilution. This can be achieved by the utilization of oxygen provided by the electrolyzer. However, temporal buffering is needed because the electrolyzer is operated intermittently. This study aims to economically evaluate such an oxygen storage system in the context of a Power-to-Gas application by comparing its total specific desulfurization costs with those of alternative processes. Through the simulation of typical agricultural biogas composition in Germany and intermittent electrolyzer operation, data were generated for the economic comparison. Results indicate that the storage system is viable if the electrolyzer operates for about 8,000 annual full-load hours, hydrogen sulfide concentrations exceed 1,680 ppm v , and on-site oxygen provision is preferred. Under these conditions, the desulfurization costs are below 2.82 ct € /Nm 3 ($0.03/Nm 3 ) of an oxygen provision by pressure swing adsorption. For lower electrolyzer full-load hours and hydrogen sulfide concentrations, the system is not competitive. The lowest costs are achieved by buffering times of an inactive electrolyzer by purchased liquid oxygen. • Economic analysis of electrolyzer-O 2 storage for continuous biogas desulfurization. • Economic comparison with O 2 and non-O 2 based desulfurization alternatives. • The O 2 storage system is only economically viable under highly specific conditions. • Electrolyzer-O 2 with liquid O 2 backup yields lowest desulfurization costs. • H 2 loss caused by O 2 in the methanation system adds significant costs.