Biogas as an energy vector

Biogas is a sustainable energy vector with diverse input sources (e.g. landfills and anaerobic digestion of waste materials, wastewater treatment sludge, manure from animal production, or energy crops) and diverse applications. The nature of the substrate and the design of the biogas production process determines the composition of raw biogas. All types of biogas must be cleaned and upgraded before delivering to the consumers and in practice, the key challenge of the biogas supply chain is its cleaning and upgrading to consumers quality. The physicochemical technologies used to clean and upgrade the raw biogas are reliable, mature and at high technology readiness levels. This paper critically reviews the biogas supply chain including feedstock supply, biogas production and upgrading/cleaning processes, potential hazards of biogas contaminants, product specification based on applications, and biogas/biomethane uses. The biogas cleaning and upgrading technologies with emphasis on cost comparison are assessed. In summary, the upgrading technology alternatives and their associated costs are found substantially affected by the project-specific circumstances. For instance, upgrading with chemical scrubbing might be preferred in the availability of cheap on-site thermal energy. If the biomethane is planned to be injected into high-pressure natural gas pipelines, those upgrading methods operating at relatively high pressures (e.g. membranes) would be preferred. If the biomethane injection point to the gas grid is located distant from the production site, the distribution cost will also play a determinative role in the overall biogas supply chain economics. Among all these factors, plant capacity seems to be a pivotal element in the economics of biogas supply chain. Amendments to national and sub-national support schemes are also an important factor affecting investment decisions.