CO2 Reutilization in the Residential Sector Through Power to Gas and Oxyfuel Combustion

Abstract

A novel concept of Power-to-gas (PtG) has been investigated as a versatile technology for storage and utilization of carbon dioxide coming from energy installations. The proposed PtG solution takes advantage of the synergies of different processes to integrate energy storage efficiently with carbon utilization to produce a ‘CO2 neutral’ natural gas. PtG converts surplus electricity into synthetic natural gas by combining H2 from water electrolysis and CO2 through methanation reaction and oxyfuel combustion. This carbon capture option releases thermal energy from the synthetic fuel producing a near-pure stream of CO2 that close the carbon loop used for methanation. Under this framework, the present work proposes to study and validate the hybridization between Power-to-Gas energy storage technology and CO2 oxyfuel combustion in the residential sector. This combination is a novel strategy focused on solving: (i) the intermittent and seasonal electricity generation from renewable resources; (ii) the large energy and economic penalties associated with CO2 capture and utilization (especially at small scale); (iii) and the development of energy storage systems of small-medium size and high flexibility.

This hybridization allows managing the excess of renewable electricity in the Power-to-Gas installation and producing hydrogen (stored energy) and oxygen (by-product). Subsequently, oxygen is used to meet the needs of the oxyfuel combustion process, in this case, in the residential sector, with two important advantages: a high concentration CO2 flow is obtained, and the oxygen production neither requires an air separation unit (ASU) nor additional energy requirements. The stored hydrogen and the captured carbon dioxide are combined by methanation to produce synthetic natural gas stored for future uses. From CO2 capture point of view, the proposed hybrid system presents an additional advantage: there would also be no penalty associated with the compression and underground storage of captured CO2, since it is reused in the oxyfuel burner along with the oxygen, obtained in the electrolyzer, closing the carbon cycle. A PtG installation with recycled CO2 utilization has been designed to fully supply the thermal heating demand and partially the electrical demand of a single-family house located in the northeast of Germany, from a photovoltaic generator. The PtG system's characteristics, the CO2 storage and utilization strategy, the equipment necessary and energy balances are presented and illustrated with a case study. The proposed design can supply the 87% of the energy consumed by a single-family home and avoid the emissions of 2.8 tons of CO2 every year.

Keywords: Power-to-Gas, oxyfuel combustion, methanation, residential sector