Simultaneous production of biomethane and food grade CO2 from biogas: an industrial case study

Abstract

This work presents a case study on the first large-scale industrial biogas upgrading process with simultaneous purification of methane and CO₂ in one of Europe's largest biogas production and purification plants in Northern Italy. A preliminary study was performed on a pilot plant, constructed as a model of the industrial plant where the final experiments were performed. The full-scale anaerobic digestion plant has a digestive capacity of 400 000 tonnes of biomass per year and it can treat 6250 m³ h⁻¹ of biogas. The first objective was a biogas upgrading process that achieves distribution grid-quality methane via different purification steps. The second objective and most innovative aspect is the further purification of CO₂ from a useless waste product to a high purity gas for the food and beverage industry. The chemical purity of different process streams was analysed by a certified laboratory and was compared with the guidelines of the European Industrial Gas Association and International Society of Beverage Technologists (EIGA/ISBT) for CO₂ used in the food industry. The microbiological purity was found to be far below the limit values defined in the European Collaborative Action. With a purity of 96.3 vol%, methane respects the purity requirement for the household network. With a purity of 98.1 vol% before, and 99.9 vol% after the final distillation process, CO₂ proves to be chemically and microbiologically suitable for food applications, thus closing the CO₂ loop in biogas production. An evaluation of the economic and energetic aspects and a comparison with alternative purification processes highlights the profitability of the process.