The Techno-Economic Potential of Power to Gas for Synthetic Natural Gas Production through Biogas Upgrading

Abstract

Raw biogas can be upgraded to produce pipeline grade synthetic natural gas (SNG) via thermo-catalytic hydrogenation of CO2. This method reduces green house gas (GHG) emissions through offsetting fossil natural gas consumption while providing a financially profitable avenue for private sector investment. The H2 needed for the system is generated via water electrolysis using surplus or inexpensive electricity. This study assesses the economic feasibility of constructing a SNG production facility for landfill gas upgrading via thermocatalytic hydrogenation of CO2. A power-to-gas (PtG) setup is utilized to produce a comprehensive process flow diagram consisting of actively cooled heat exchanger type methanation reactors, alkaline electrolysers and auxiliary process units. The overall system is simulated in steady state using Aspen HYSYS to provide process stream specifications and utility requirements. Base equipment costs obtained from the chemical process model allow generation of further economic outlooks to determine feasible scenarios for the technology. Factors including payout period, net present worth and internal rate of return are calculated and show that profitable outcomes highly depend on the price of electricity and selling price of SNG. Production cost range from $13-45/GJ with electricity prices in the $0.04/kWh to $0.18/kWh range. SNG selling prices at or above $20/GJ are found to be necessary in order to provide economic scenarios attractive to investors.