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# Production of Synthetic Natural Gas from Carbon Dioxide and Renewably Generated Hydrogen: A Techno-Economic Analysis of a Power-to-Gas Strategy

[+] Author and Article Information
William Becker

Department of Mechanical Engineering, Colorado School of Mines, Golden, CO USA
becker0210@gmail.com

Michael Penev

National Renewable Energy Laboratory, Golden, CO USA
michael.penev@nrel.gov

Robert J. Braun

Department of Mechanical Engineering, Colorado School of Mines, Golden, CO USA
rbraun@mines.edu

1Corresponding author.

ASME doi:10.1115/1.4041381 History: Received May 22, 2018; Revised August 14, 2018

## Abstract

Power-to-gas to energy systems are of increasing interest for low carbon fuels production and as a low-cost grid-balancing solution for renewables penetration. However, such gas generation systems are typically focused on hydrogen production, which has compatibility issues with existing natural gas pipeline infrastructures. This study presents a power-to-synthetic natural gas (SNG) plant design and a techno-economic analysis of its performance for producing SNG by reacting renewably generated hydrogen from low-temperature electrolysis with captured carbon dioxide. The study presents a "bulk" methanation process that is unique due to the high concentration of carbon oxides and hydrogen. Carbon dioxide, as the only carbon feedstock, has much different reaction characteristics than carbon monoxide. Thermodynamic and kinetic considerations of the methanation reaction are explored to design a system of multi-staged reactors for the conversion of hydrogen and carbon dioxide to SNG. Heat recuperation from the methanation reaction is accomplished using organic Rankine cycle units to generate electricity. The product SNG has a Wobbe index of 47.5 MJ/m3 and the overall plant efficiency (H2/CO2 to SNG) is shown to be 78.1% LHV (83.2% HHV). The nominal production cost for SNG is estimated at 38.8 $/MMBTU (132$/MWh) with 3 $/kg hydrogen and a 65% capacity factor. At U.S. DOE target hydrogen production costs (2.2$/kg), SNG cost is estimated to be as low as 28.6 $/MMBtu (97.6$/MWh or 1.46 \$/kgSNG).

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