Integrating renewables in biomethane production plants: an economic and environmental assessment

This thesis presents an evaluation of the practicality of using heat pumps to heat feedstock within anaerobic digesters for biomethane production. Given the increasing production of biogas and biomethane in both advanced and developing countries, incorporating alternative forms of renewable energy for this purpose not only enhances production capabilities but also contributes to environmental improvement. Thus, utilizing a heat pump to fulfilll the heat demand of the anaerobic digestion process in biomethane production will amplify environmental benefits. In the introductory section of the thesis, an overview of the anaerobic digestion process will be provided, which is the method utilized in this case study for biogas production, along with an exploration of various technologies employed for upgrading biogas into purer biomethane. Additionally, a concise summary of trends in biogas and biomethane production will be presented. In this case study, an anaerobic digestion plant is used to produce biomethane, situated in Turin, located in northwest Italy. The facility operates for 31 days each month and mesophilic temperature conditions (37°C) are utilized for the anaerobic digestion processes. In the following section, the selection of feedstocks, determination of digester size, and estimation of biogas and biomethane production quantities will be detailed. Additionally, five scenarios will be proposed to address the energy consumption needs of the project, encompassing both heat and electricity requirements. In Scenario 1, the heat demand is satisfied by a ground-source heat pump, and the electricity demand is fulfilled through a combination of PV panels and sourcing from the national grid while in the second scenario, the entire electricity demand is covered only by the PV panels. In Scenario 3, a combined heat and power unit is employed to fully meet both the heat and electricity demand. Any surplus electricity demand is fulfilled through the Italian national grid network. In Scenario 4, the heat demand is satisfied using a ground-source heat pump, while the electricity demand is fulfilled by the Italian national grid network. Finally, in scenario 5, the heat demand is met by the wood chips boiler, while the PV panels fulfil the electricity demand. In the subsequent section, a comprehensive cost analysis will be undertaken, encompassing an examination of the capital costs, operational costs, and revenues associated with all parts and elements of the project. A comparison will be drawn between the three scenarios to assess their respective financial implications. In the final section, a comparative analysis will be conducted to assess the environmental impact of the anaerobic digester operation. This analysis will provide valuable insights into the potential contributions toward reducing greenhouse gas (GHG) emissions through integrating renewable energy technologies. In conclusion, an overall comparison was conducted to gain a comprehensive understanding of the advantages and disadvantages of each scenario.