Digester Gas Upgrading to Synthetic Natural Gas in Solid Oxide Electrolysis Cells

Abstract

This work focuses on the process design and performance of an innovative plant for digester gas upgrading to synthetic natural gas (SNG). The differences and advantages over traditional upgrading processes are discussed. The main strength of digester gas upgrading via high-temperature electrolysis concerns its higher synthetic natural gas productivity for a given raw digester gas feed. Electrolysis is performed through a solid oxide electrolysis cell (SOEC) system, which is fed with demineralized water and purified digester gas (made up of methane and carbon dioxide). Surplus electricity from intermittent renewable energy sources is used to supply the energy required for the SOEC stacks. The resulting methane-rich syngas is reacted in a series of methanators to yield a high CH4 content output stream. The steam reforming reaction is promoted by means of a nickel catalyst in the cathode (fuel) electrode, which reduces the methane fraction: hence, sulfur, which is present in several types of digester gas (e....