Abstract
The synthesis of a Substitute Natural Gas (SNG) that is compatible with the gas grid composition requirements by using surplus electricity from renewable energy sources looks a favourable solution to store large quantities of electricity and to decarbonise the gas grid network while maintaining the same infrastructure. The most promising layouts for SNG production and the conditions under which SNG synthesis reduces the environmental impacts if compared to its fossil alternative is still largely untapped. In this work, six different layouts for the production of SNG and electricity from biomass and fluctuating electricity are compared from the environmental point of view by means of Life Cycle Assessment (LCA) methodology. Global Warming Potential (GWP), Cumulative Energy Demand (CED) and Acidification Potential (AP) are selected as impact indicators for this analysis. The influence of key LCA methodological aspects on the conclusions is also explored. In particular, two different functional units are chosen: 1 kg of SNG produced and 1 MJ of output energy (SNG and electricity). Furthermore, different approaches dealing with co-production of electricity are also applied. The results show that the layout based on hydrogasification has the lowest impacts on all the considered cases apart from the GWP and the CED with SNG mass as the functional unit and the avoided burden approach. Finally, the selection of the multifunctionality approach is found to have a significant influence on technology ranking.
Highlights
In recent years, renewable energies are increasingly gaining relevance towards the achievement of environmental, economic and political objectives and for a diversification of the energy mix
The layout having the lowest global warming potential years horizon (GWP) impact (À0.45 kg CO2 eq/ kg substitute of natural gas (SNG)) is the SOFC6 due to its higher production of electricity which results in higher credits
The LCA of six different layouts for the production of SNG from biomass and electrolytic hydrogen was performed according to three impact indicators (GWP, acidification potential (AP), CEDnr), and compared with the natural gas impacts
Summary
Renewable energies are increasingly gaining relevance towards the achievement of environmental, economic and political objectives and for a diversification of the energy mix. Due to the use of a significant amount of power, electrolysis is an expensive process, but it could become costcompetitive and environmentally sustainable when powered by surplus electricity from renewable energy sources [1] Such a surplus could occur either because the grid is not demanding for additional power or because it could create grid instability. A large variety of final fuels were proposed from the syngas obtainable from biomass gasification: methanol, ethanol, dimethyl ether (DME), substitute of natural gas (SNG) [2] For the latter fuel, several different concepts for SNG production from biomass gasification were analysed [3], due to its promising overall energy efficiencies (up to 50%) especially in the presence of heat integration [4,5]. Feeding the biomass syngas to a pressurised Solid Oxide Electrolyser (SOEC) would further improve the plant efficiency, mainly because the methanation reaction starts occurring directly in the SOEC [11]
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