Could biological biogas upgrading be a sustainable substitution for water scrubbing technology? A case study in Denmark

Abstract

Biological upgrading of biogas, a sub-category of “power to gas” technology, has provoked great interest because it enables the secure storage of surplus renewable electricity within existing gas pipeline infrastructure in the form of biomethane yielding low storage costs and high environmental benefit. However, a barrier to commercialization of this technology is evaluation of sustainability aspects in comparison with alternatives, e.g., water scrubbing. Although many studies have assessed techno-economic aspects of biological biogas upgrading technology, there is a lack of sufficient research over its sustainability aspects. As such, this study uses life cycle assessment to investigate the environmental and life cycle cost impacts of biological biogas upgrading vs water scrubbing using a case study in Denmark. Consequential life cycle assessment with marginal data for 2030 (i.e., the minimum time frame needed to commercialize this technology) was used to model and compare the environmental impacts of the two upgrading technologies. Similarly, a comprehensive economic analysis was also performed regarding technological development in 2030, scaling effects, probable electricity prices, as well as potential policy scenarios. The results demonstrate that biological upgrading can be a sustainable alternative to water scrubbing if surplus electricity in 2030 can be purchased at 50% of the regular electricity price paid by consumers when the amount of electricity production copes with the demand (i.e., 22.36 €/MW hel) and if the CAPEX of electrolyzer and methanation systems can be decreased to approximately one-third of reported prices in 2020 via technological learning and scaling effect. Having considered a case study biogas plant in Denmark treating 240000 t/year agro-industrial waste, the results were improved by net environmental savings of 5.46 kilopoints, levelised energy cost of 50.55 €/MW h biomethane, net present value of 24.18 million €, internal rate of return of 20%, and payback period of 5.18 years, even in the case that a subsidy is not granted to biomethane. The sensitivity analysis demonstrated that economic profitability and the production cost of biomethane would be highly associated with the price of surplus electricity and the subsidy granted for biomethane production.