Renewable natural gas (RNG) sources
are being considered in future
energy strategy discussions as potential replacements for fossil natural
gas (FNG). While today’s supply of RNG resources is insufficient
to meet U.S. demands, there is significant interest in its viability
to supplement and decarbonize the natural gas supply. However, the
studies compare the life cycle global warming potential (GWP) of various
RNG production pathways are lacking and focus mostly on a singular
pathway. This effort is an attempt to close this gap and provide a
comparison between the life cycle GWP of three major RNG pathways
and the FNG pathway. The three RNG pathways evaluated are anaerobic
digestion (AD), thermal gasification (TG), and power-to-gas (P2G)
using various feedstocks. The functional unit is 1 MJ of compressed
RNG ready for injection into the natural gas transmission network.
The results show that RNG production is not always carbon neutral
or negative. Depending on the pathway, the GWP impact of RNG production
can range from −229 to 27 g CO2e/MJ compressed RNG,
with AD of animal manure and AD of municipal solid waste being the
least and the most impactful pathways, respectively, compared to the
10.1 g CO2e/MJ impact for compressed FNG.
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