Methanation of CO2 - storage of renewable energy in a gas distribution system

This article presents some crucial findings of the joint research project entitled "Storage of electric energy from renewable sources in the natural gas grid-water electrolysis and synthesis of gas components". The project was funded by BMBF and aimed at developing viable concepts for the storage of excess electrical energy from wind and solar power plants. The concept presented in this article suggests the conversion of CO2-containing gases into methane in a pressurized reactor using hydrogen produced via electrolysis. The produced gas can be upgraded to synthetic natural gas (SNG) and fed into the well-developed German natural gas grid. This concept benefits from the high storage capacity of the German gas grid and does not require any extensions of the current gas or power grid. The reaction heat released by the exothermic methanation reaction leads to a temperature rise of the gas in the fixed bed catalyst of the reactor. The conversion of carbon dioxide is limited in accordance to the chemical equilibrium which depends strongly on temperature and pressure. For maximum carbon dioxide conversion, it is convenient to split the methanation into several stages adding cooling sections in between. This article focuses on the methanation process and its transfer onto an industrial scale evaluating the different plant capacities and feedstock mixtures used. The methanation takes place in a staged fixed bed reactor. This staged reactor concept is an in-house development based on know-how from the sulfuric acid production technology.