Abstract
Biomethane is receiving great attention as a renewable energy gas with lower environmental impacts and diversified sources of production. However, availability of gas infrastructure is an important factor in biomethane development and use. Biomethane can be distributed by the natural gas or local biogas grid. Biomethane can also be road-transported as compressed biomethane (CBG) or liquefied bio-methane (LBG). Biomethane could be distributed via gas hydration technology, where methane molecules are physically trapped within the crystalline structures of frozen host water molecules as gas hydrate compounds. Using life cycle assessment methodology, this study compared the energy performance and climate impact of two gas hydrate scenarios, biogas hydrate and biomethane hydrate, with that of a base case distributing biomethane as CBG. The technical system, from biogas upgrading, hydration, compression and road transport to filling station of biomethane as CBG, was included in the analysis. Results of this study show that distribution of biomethane as gas hydrates had a lower energy performance and higher climate impact than compressed biomethane distribution. The low energy performance was due to high electricity demand in hydrate formation and dissociation processes. The gas hydrate scenarios also had higher climate impacts as a result of high methane losses from hydrate formation and dissociationdissociation and emissions related to energy source use. Biogas upgrading to biomethane also significantly contributed to methane losses and climate impact of the scenarios studied.
Highlights
Biomethane is a versatile biomass-derived renewable energy carrier with the ability to produce energy services and high-value products
The scenarios were a conventional system based on road transport of CBG and two future-oriented scenarios based on gas hydration
The high energy inputs in the gas hydrate scenarios derived from high levels of electricity demand in the hydrate formation and dissociation units
Summary
Biomethane is a versatile biomass-derived renewable energy carrier with the ability to produce energy services and high-value products. The digestion of organic matter results in biogas containing approximately 45–65% by volume (v/v) of methane (CH4) and 25–30% v/v of carbon dioxide (CO2) with the remaining consisting of hydrogen sulfide (H2S), moisture and siloxanes. The energy content of biogas can be increased through drying, cleaning and upgrading, resulting in biomethane with > 97% CH4 (Wellinger et al, 2013). In 2018, total biogas production in Sweden was around 2.1 TWh, of which 1.3 TWh was upgraded to biomethane. 42% of this biomethane was injected to gas grids in south-west Sweden and Stockholm. The remaining biomethane was stored and road-transported as compressed biomethane (CBG; 200 bar) in an “offgrid” solution due to lack of gas grid infrastructure. 44 GWh were converted to liquefied biomethane (LBG) at one plant (Swedish Energy Agency, 2018)
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