From conventional to renewable natural gas: can we expect GHG savings in the near term?

• Published in: Biomass & bioenergy Vol. 131; p. 105396
• Main Authors: Serra, Rut, Niknia, Iman, Paré, David, Titus, Brian, Gagnon, Bruno, Laganière, Jérôme
• Format: Journal Article
• Language: English
• Published: Elsevier Ltd 01.12.2019
• Subjects: Bioenergy; Carbon sequestration parity time; GHG mitigation; Renewable natural gas; Thermochemical conversion; Wood residues; Renewable natural gas; Thermochemical conversion; Bioenergy; GHG mitigation; Wood residues; Carbon sequestration parity time
• ISSN: 0961-9534; 1873-2909
• DOI: 10.1016/j.biombioe.2019.105396

Displacement of fossil fuels by forest bioenergy can contribute to climate change mitigation by reducing greenhouse gas (GHG) emissions. However, GHG savings are not realised until the avoided fossil emissions offset the loss of atmospheric carbon (C) that would have been sequestered if the biomass was not used for bioenergy (i.e. time to C sequestration parity). We estimated the potential for mitigating GHG emissions and the timing of these atmospheric benefits when substituting conventional natural gas (NG) with renewable natural gas (RNG) produced from different forestry feedstocks within three Canadian provinces, and assessed the uncertainty among these estimates. We calculated the GHG balance of RNG using the alternative fate of biomass and the use of NG as base-case scenarios. Immediate to long-term time to C sequestration parity was typically in the order of residues burned < mill residues < harvest residues decaying on site < salvaged trees. The potential GHG savings from using harvest and mill residues to produce RNG within the three provinces ranged from 52.4 to 77.8 Mt CO2eq a−1. Sensitivity analyses suggest that time to C sequestration parity in the best-case scenarios relative to the baseline can be reduced up to 17 years by using harvest residues that decay rapidly (based on feedstock species, size and geographic region), and reduced up to 8 years by improving the efficiency of the thermochemical conversion process. These two considerations are key for ensuring significant GHG reductions from RNG use within a timescale that helps Canada meet its GHG mitigation targets. •Immediate GHG benefits for RNG produced with residues otherwise burned on site.•No short-term C sequestration parity time for RNG produced with forest residues.•C sequestration parity time >100 years for RNG produced with salvaged trees.•Potential net GHG savings of 52.4–77.8 Mt CO2eq.year−1 for RNG use.