Greenhouse Gas Emissions of Biomethane for Transport: Uncertainties and Allocation Methods

Abstract

Employing a life-cycle assessment approach, this paper studies greenhouse gas (GHG) emissions resulting from biomethane used as transportation fuel. It focuses on both GHG allocation methodologies and uncertainties regarding GHG emissions from biomethane. The goal is to calculate GHG emissions of two types of biomethane used in transportation: that produced from biowaste feedstock and that extracted from dedicated energy crop feedstocks. The effects of allocation methods used for digestate and those of other factors arising during the life cycle of biomethane are studied. The GHG emissions of biomethane produced from biowaste with digestate use are approximately 22 gCO2eq MJ–1; those of biomethane extracted from dedicated energy crops are 61 gCO2eq MJ–1. However, using the substitution method for digestate decreases biowaste emissions by 10 gCO2eq MJ–1 and dedicated energy crop emissions by 22 gCO2eq MJ–1. The highest emissions uncertainties are related to land use change, cultivation processes, digestate use, and technology selections in digestion and upgrading. Using technology with high energy consumption or methane leakages will significantly increase total emissions. On the other hand, use of renewable energy in processes is one option for decreasing total emissions. It appears that biomethane could be produced with lower emissions than previous studies have shown by optimizing production and implementing new technology. The utilization of digestate in replacing mineral fertilizers, resulting in additional GHG emission reductions, is a key issue which should be accorded more attention in the future. For one to achieve reliable results, factors related to biomethane production and allocation methods for digestate emissions should always be chosen on a case-by-case basis.

Life cycle assessment of small-scale combined heat and power plant: Environmental impacts of different forest biofuels and replacing district heat produced from natural gas

“…LCA offers a powerful tool to analyze environmental impacts, including climate change effects of energy production methods. LCA has been conducted on photovoltaic systems (Sherwani and Usmani, 2010), biogas (Ishikawa et al, 2006), biomethane (Uusitalo et al, 2014),bioethanol production (Sandilands et al, 2009), and wind power production (Schleisner, 2000). Caserini et al (2010) state that GHG savings can be obtained in comparison to conventional fuels if biomass supplying distance is less than 600 km.…”

Assessing Land Use Efficiencies and Land Quality Impacts of Renewable Transportation Energy Systems for Passenger Cars Using the LANCA® Method

“…The EU-28 mix for corn silage methane production from the GaBi database has been used here and has been augmented by adding distribution and refueling. Biomethane may be distributed via natural gas grids or via refueling infrastructure for natural gas [43]. The electricity used in distribution and refueling processes consumes approximately 1 MJ kg −1 methane [43].…”

“…Biomethane may be distributed via natural gas grids or via refueling infrastructure for natural gas [43]. The electricity used in distribution and refueling processes consumes approximately 1 MJ kg −1 methane [43].…”