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Please use this identifier to cite or link to this item: http://hdl.handle.net/10805/2107

Title: LIFE CYCLE ASSESSMENT OF DISTRIBUTED ENERGY PRODUCTION USING BIOFUEL FROM WASTE
Authors: EVANGELISTI, SARA
Tutor: BORELLO, DOMENICO
LETTIERI, PAOLA
MICANGELI, ANDREA
Keywords: LIFE CYCLE ASSESSMENT
MICRO CHP
DISTRIBUTED ENERGY
ANAEROBIC DIGESTION
ORGANIC FRACTION OF MUNICIPAL SOLID WASTE
Issue Date: 12-Jul-2013
Abstract: Municipal Solid Waste can be a potential renewable and non-seasonal resource for energy production. Alternative uses of waste, in fact, become increasingly interesting both from a waste management perspective – to reduce the amount of increasing waste deposited at landfill - and from an energy system perspective – to get the targets in terms of share of renewable and greenhouse gas reduction. In Europe, in recent years a lot of attention has raised around the possibility to use the Organic Fraction of Municipal Solid Waste (OFMSW) for the production of energy through anaerobic digestion. In this process, the bio-waste is metabolized by bacteria under anaerobic conditions producing a gas – i.e. biogas. Digestate, a by-product of the anaerobic digestion process, can be used as a valid substitute to conventional mineral fertilisers. Production and collection of OFMSW usually takes place at district level, hence making it a great potential as non-seasonal energy feedstock. The biogas can then be used as a fuel for Combined Heat and Power (CHP) production, through systems directly installed at dwelling level. This perfectly matches with the Distributed Generation paradigm, where the energy is produced at, or near to its point of use. The aim of this thesis was to evaluate the environmental impact of a waste-to-energy system in a distributed generation paradigm. OFMSW was considered as main feedstock to produce biogas, which was fed to different micro CHP units to generate energy for those dwellings that generated the waste. Three different technologies were investigated: Solid Oxide Fuel Cell (SOFC), Micro Gas Turbine (MGT), Stirling Engine. A secondary objective of the work was to demonstrate the feasibility of the waste-to-energy closed loop at residential level. In order to achieve this, a Life Cycle Assessment with system expansion was performed considering two case studies: the Borough of Greenwich in the Greater London area (UK) and the municipality of Livorno (IT), in Toscany region. They were compared in terms of energy generation and waste disposal strategies. The analysis was based on a comparative assessment of two sub – systems: Waste Management scenarios – where alternative waste treatments for the OFMSW were investigated and a Distributed Generation scenarios – where three different micro-CHP technologies were analysed, together with two different ways of using biogas and three different operating strategies. Moreover, a reference scenario for the production of energy at a residential level was assumed in the two case studies and possible reductions in terms of several environmental impacts categories were evaluated. Results showed that, although anaerobic digestion is potentially the best option in term of GHG emissions for the treatment of the organic waste, the amount of biogas produced with this fraction was not enough to cover the energy demand of the dwellings that generated the waste. Furthermore, when normalised per tons of OFMSW produced in the two geographical contexts, 851 and 856 kg CO2 eq were saved in UK and Italy respectively, when AD was considered as alternative waste treatment compared to the landfill plant with energy recovery. The potential emissions’ savings were reduced to 30 and 35 kg CO2 eq per kg of OFMSW treated in UK and Italy respectively, if an incineration plant with electricity and heat production was considered as displaced process. The robustness of the first sub-model was investigated through a sensitivity analysis. The most critical assumption concerned the quantity and quality of the energy substituted by the biogas production. Fuel cell micro – CHP could clearly reduce the environmental impacts of UK and IT homes compared with their current average value. There was however great difficulty in estimating the magnitude of these reductions, because of the influence of key parameters assumed in the design phase of the micro CHP units, i.e. the H to P ratio of the dwellings and the operating strategy adopted. Another important issue was the type of technology that substituted the new system. Results showed that this can determine when the micro CHP system represents a saving or a burden in terms of emissions. Conclusions showed that the definition of the future energy scenario in which the process will be embedded is a key issue to determine the actual environmental benefits due to the introduction of waste to energy systems in the distributed generation paradigm. This depends on macro- national and European strategies and highlights the importance of a holistic approach to inform decision-makers on the best solution for waste to energy policies.
URI: http://hdl.handle.net/10805/2107
Research interests: Energy from waste, Life cycle assessment, distributed energy system, fuel cells, biomethane production
Personal skills keywords: Life Cycle Analysis practitioner
Sustainable Technologies for Energy and Envrionment
Mechanical Engineer
Appears in PhD:SVILUPPO SOSTENIBILE E COOPERAZIONE INTERNAZIONALE

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