Simulation of different biogas upgrading processes andLCA for the selection of the best technology

摘要

Biogas is expected to be one of the main energy sources to be employed for reaching the energy policy targets of the European Union (EU), which have been developed with the aim of reducing 40% of greenhouse emissions and of achieving 27% of renewableenergy installed. Indeed, as outlined by Eurostat, from 2000 to 2015 the biogas production in EU has undergone a relevant increase, with a biogas obtained from sewage sludge (17%), landfill gas (9%) and the remaining 74% due to decentralized agricultureplants, centralized co-digestion plants and municipal solid waste.Biomethane, obtained after treatments of cleaning for removal of impurities and of upgrading for removal of carbon dioxide, is a renewable energy that can be employed for the same uses of fossil fuels, in particular natural gas, because both the fuels are composed mainly of the same molecule (methane). It is then recognized as an environmental technology and part of the circular economy, where material and flows are designed for reuse and recycling. In this process, agricultural waste products, as animal manure, residual straw and organic waste from industries and households are recycled and, in addition to biogas, also biofertilizers containing nitrogen, phosphorous and other minerals, are co-produced and can be employed to support plant growth and productivity. For these reasons, biogas production is considered to provide many benefits to the economy and to the society.The use of biomethane is preferred to the one of biogas because of the higher amount of methane, lower amount of other components and therefore higher heating value per unit of mass. Several technologies are available for the upgrading of biogas to biomethane, and the different purification methods can have an impact on the overall system where the biogas plant is located (e.g., the agricultural farm).This work aims at selecting the optimal technology of biogas upgrading of a plant to be located in Europe, on the basis of studies on the energetic performances and on Life Cycle Assessment. The choice of the best technology is fundamental in order to achieve the best performances of the process and to favor the increasing of the number of biogas plants in Europe.Simulations of different upgrading technologies have been carried out by the GASP group of Politecnico di Milano by employing ASPEN Plus, previously set up for a good description of also strongly non-ideal system for chemical absorption and the Life Cycle Assessment has been performed by the Chair Agricultural Systems Engineering of Technical University of Munich in order to analyze the overall performances of the different processes and to determine the best one for theconsidered plant.