Can power to methane systems be sustainable and can they improve the carbon intensity of renewable methane when used to upgrade biogas produced from grass and slurry?. (15th October 2018)

• Record Type: Journal Article
• Authors: Vo, Truc T.Q.; Rajendran, Karthik; Murphy, Jerry D.
• Is Part Of: Applied energy. Volume 228(2018)
• Page Start: 1046
• Page End: 1056
• Publication Date: 2018-10-15
• Subjects: Life cycle assessment -- Sustainability criteria -- Advanced biofuels -- Power to gas -- Biological methanation -- Co-digestion; Power (Mechanics) -- Periodicals; Energy conservation -- Periodicals; Energy conversion -- Periodicals; 621.042
• DOI: 10.1016/j.apenergy.2018.06.139
• Languages: English
• ISSNs: 0306-2619

Abstract

Highlights: Increasing the slurry to grass ratio improves sustainability of biogas. Power to gas (P2G) can be used to upgrade biogas to biomethane. The carbon intensity of hydrogen is higher than the electricity it is produced from. P2G systems using the Irish electricity mix reduce sustainability of biomethane. Renewable electricity levels of 85% allow biomethane be sustainable. Abstract: The recast of the renewable energy directive (RED recast) considers power to gas (P2G) an advanced transport biofuel if a 70% greenhouse gas savings as opposed to the fossil fuel displaced is achieved. Power to methane systems can store electricity as gas and the system can be optimised in sourcing CO2 from biogas to upgrade biogas to biomethane. The crucial question in this work is whether P2G systems can be sustainable and if they can improve the sustainability of biomethane systems using traditional upgrading systems. This work evaluates a comparative lifecycle assessment of grass and slurry (50:50 wet weight equivalent to 80:20 volatile solid weight) biomethane using P2G and/or amine scrubbing as an upgrading method. The sustainability of P2G upgrading systems is heavily dependent on the carbon intensity of the source of electricity. Using a 41% decarbonised electricity mix the sustainability was reduced using P2G and would not be deemed sustainable under criterion set by the RED recast. Maintaining a maximum of 2% fugitive CH4 emissions, using 74% slurry (wet weight) in a grass slurry feedstock, allowing for 0.6 t carbon sequestration per hectare per annum in grasslands and using an electricity mix with 85% renewable electricity the whole system including P2G upgrading could satisfy the GHG savings of 70%. However, the traditional system employing amine scrubbing had higher levels of sustainability.