Three-pipeline gas grid: A new concept for power-to-gas associated with complete carbon capture and utilization

A three-pipeline gas grid is proposed, consisting of an empowerment of the existing natural gas distribution grid,by adding two additional pipelines conveying respectively oxygen and carbon dioxide. The aim is to serve the power-to-gas and advanced gas-to-power systems currently under development, making it is possible to transfer carbon from the methane to the carbon dioxide pipeline and vice versa, without ever releasing it into the atmosphere. In order to evaluate the feasibility of the concept, the functioning of the power-to-gas system is assessed on the basis of a simulation model, embedding first principle models of an alkaline electrolyzer and of a cooled isothermal packed bed Sabatier reactor. A design point is selected, where the power supplied to the power-to-gas system is 4 MW, the operating pressure is 30 bar, and the temperatures of the electrolyzer and of the Sabatier reactor are 80 ◦C and 370 ◦C respectively. It is estimated that the first principle efficiency is 51.7% at design point, and tends to increase in off-design conditions where the power input is reduced. The estimated efficiency appears interesting in the context of the three-pipeline gas grid scheme, also considering the advantages offered in terms of carbon capture and utilization.