Production of synthetic natural gas from industrial carbon dioxide

The Power-to-Gas strategy has become a mainstream topic for decarbonization and development of renewables and flexibility in energy systems. One of the key arguments for decarbonizing the gas network is to take advantage of existing network infrastructure, gradually transitioning to lower fossil carbon sources of methane from Power-to-Gas. This work proposes the techno-economic investigation of an integrated system considering an advanced CO₂ capture process, in terms of solvent and process configuration, to treat about 10% of a cement plant's flue gas and convert the captured CO₂ into synthetic natural gas using renewable hydrogen generated from a large-scale wind powered electrolyzer. An optimized heat recovery system is proposed, drastically decreasing the external hot utility demand of the CO₂ capture unit. In addition, it leads to the production of complementary electricity (about 1.06 MW), reducing thus also the electrical demand of the integrated process. The synthetic natural gas produced has a composition (CH₄ 92.9 mol.%, CO₂ 3.7 mol.%, and H₂ 3.4 mol.%) and a Wobbe index (46.72 MJ/m³), corresponding to specification for gas grid injection at 50 bar in Germany. With an overall system efficiency of 72.6%, the process produces 0.40 ton synthetic natural gas per ton of captured CO₂. The cost of the synthetic natural gas produced is higher when compared to the present natural gas market price, but cost reductions and possible commercial use of coproducts like oxygen, represent a likely alternative. Costs are mainly driven by high capital investments (the electrolyzer), and the price of renewable electricity, which is expected to decrease in the coming years.