search query: @instructor Santarelli, Massimo / total: 1
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Author: | Tjaden, Bernhard |
Title: | System analysis of biogas fuelled solid oxide fuel cell |
Publication type: | Master's thesis |
Publication year: | 2013 |
Pages: | 63 Language: eng |
Department/School: | Insinööritieteiden korkeakoulu |
Main subject: | Energiatekniikka (Ene-47) |
Supervisor: | Järvinen, Mika |
Instructor: | Santarelli, Massimo ; Nordgren, Thomas |
OEVS: | Electronic archive copy is available via Aalto Thesis Database.
Instructions Reading digital theses in the closed network of the Aalto University Harald Herlin Learning CentreIn the closed network of Learning Centre you can read digital and digitized theses not available in the open network. The Learning Centre contact details and opening hours: https://learningcentre.aalto.fi/en/harald-herlin-learning-centre/ You can read theses on the Learning Centre customer computers, which are available on all floors.
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Location: | P1 Ark Aalto 6142 | Archive |
Keywords: | biogas solid oxide fuel cell electrochemical model system analysis |
Abstract (eng): | Biogas is a widely available resource which offers large potential for providing carbon neutral electricity. Anaerobic digestion processes can be used to produce biogas from a wide selection of biological substances which makes it a readily available and local energy source. This thesis investigates energetic and economic performance of a small scale solid oxide fuel cell system running on biogas. In this analysis, biogas is considered to be produced from the following sources: livestock effluents, energy crops, agricultural waste and organic waste. For adequate system setup, a database containing biogas compositions of anaerobic digesters with a power output < 100 kWel for the above mentioned substrates is established and used, to analyse chemical build-up and design the gas cleaning and reforming unit. The database shows, that average CH4 content throughout all substrates lies in the range of 55 %mol. However, large seasonal and daily variations are observed and are independent of used matter. Main contaminants are made up by H2S which leads to catalyst deactivation in reformer and fuel cell. This makes effective gas cleaning necessary, for which ZnO and activated carbons are the most practical solutions. The energy model of the solid oxide fuel cell plant is designed and analysed using the software Aspen Plus® and is set up in such a way, that different kind of reforming options are compared with each other. For the electrochemical modelling of the solid oxide fuel cell stack, data from literature are used in order to account for polarisation losses under varying operating conditions. In addition, cost functions are directly implemented into the system, allowing investment cost as well as economic profitability calculations. The system analysis shows, that highest electric efficiencies of 50.63 % on higher heating value basis is achieved when steam reforming is applied. This value lays around 15 % points above average electric efficiencies of biogas engines based on lower heating value. Highest total plant efficiency (electric plus thermal) of 74.14 % is reached under partial oxidation reforming as exothermic reforming reactions increase thermal output of the plant. Total overnight costs of steam and partial oxidation reforming amount to 113,937 euros and 95,693 euros, respectively. For economic profitability calculation, net present value and payback period are determined by applying German, Italian and Finnish subsidy laws. Hereby, due to highest feed-in tariffs, Italy provides the most economically friendly environment for biogas fuelled SOFCs with payback periods of 17 years and 7.6 years for steam and partial oxidation reforming, respectively. As a conclusion, it can be stated, that solid oxide fuel cells using biogas as fuel feature higher electric efficiencies compared to gas engines. However, specific investment costs are in the range of 3,828 euros/kWel to 4,557 euros/kWel for partial oxidation reforming and steam reforming, exceeding specific investment costs of biogas engines by 1,000 euro/kWel and 1,700 euro/kWel, respectively. This makes such systems only profitable when applying Italian and German subsidies. Even though auto thermal reforming was analysed, it showed neither thermodynamic nor economic advantages over steam or partial oxidation reforming. |
ED: | 2013-10-16 |
INSSI record number: 47321
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