PhD student, Technical University of Denmark, Department of Energy Conversion and Storage
The integration of solid oxide fuel cells with biogas as fuel.
It is general agreed that due to the increasing amount of renewable energy in the electricity production different energy conversion and storage technologies are needed to ensure a 100% availability of electricity. One attractive medium is fuel derived from biomass. Biogas consists basically of methane and carbon dioxide plus some traces of other gases such as sulfur components. Biomass is a rare resource and has to be used in an efficient way. Whereas in commercial biogas power plants biogas is burned off with low efficient combustion engines, solid oxide fuel cells (SOFC’s) could be a more efficient way. Furthermore most biogases are unattractive for combustion engines due to their low heating values. With SOFC’s it is possible to convert hydrogen or carbon containing fuels, as for example biogas, directly into electricity and the side product heat in a high efficient way. The aim of this PhD thesis is the integration of SOFC’s with biogas as fuel. With an industrial partner, the potential of using real biogas from a landfill unit and making it available in the SOFC through reforming will be explored. The activities will be related to the cell level, the stack level and the system level. On the cell level the composition of the biogas and the needed reactant will be variated and analyzed. This is important to prevent carbon formation on the anode side of the fuel cell. On the stack level, investigations will be carried out to determine the durability and degradation mechanisms of the SOFC-Stack. On the system level, theoretical studies will be carried out for the whole system integration, including system layout, capacities, and efficiencies.
Abstract: Heterogeneous catalysis studies were conducted on two crushed solid oxide fuel cell (SOFC) anodes in fixed‐bed reactors. The baseline anode was Ni/ScYSZ (Ni/scandia and yttria stabilized zirconia), the other was Ni/ScYSZ modified with Pd/doped ceria (Ni/ScYSZ/Pd‐CGO). Three main types of experiments were performed to study catalytic activity and effect of sulfur poisoning: (i) CH4 and CO2 dissociation; (ii) biogas (60% CH4 and 40% CO2) temperature‐programmed reactions (TPRxn); and (iii) steady‐state biogas reforming reactions followed by postmortem catalyst characterization by temperature‐programmed oxidation and time‐of‐flight secondary ion mass spectrometry. Results showed that Ni/ScYSZ/Pd‐CGO was more active for catalytic dissociation of CH4 at 750 °C and subsequent reactivity of deposited carbonaceous species. Sulfur deactivated most catalytic reactions except CO2 dissociation at 750 °C. The presence of Pd‐CGO helped to mitigate sulfur deactivation effect; e.g. lowering the onset temperature (up to 190 °C) for CH4 conversion during temperature‐programmed reactions. Both Ni/ScYSZ and Ni/ScYSZ/Pd‐CGO anode catalysts were more active for dry reforming of biogas than they were for steam reforming. Deactivation of reforming activity by sulfur was much more severe under steam reforming conditions than dry reforming; a result of greater sulfur retention on the catalyst surface during steam reforming.
Pub.: 25 Feb '16, Pinned: 03 Jul '17
Abstract: The present work investigates electricity production using a high efficiency electrochemical generator that employs as fuel a biogas from the dry anaerobic digestion of the organic fraction of municipal solid waste (OFMSW). The as-produced biogas contains several contaminants (sulfur, halogen, organic silicon and aromatic compounds) that can be harmful for the fuel cell: these were monitored via an innovative mass spectrometry technique that enables for in-line and real-time quantification. A cleaning trap with activated carbons for the removal of sulfur and other VOCs contained in the biogas was also tested and monitored by observing the different breakthrough times of studied contaminants. The electrochemical generator was a commercial Ni anode-supported planar Solid Oxide Fuel Cell (SOFC), tested for more than 300 h with a simulated biogas mixture (CH4 60 vol.%, CO2 40 vol.%), directly fed to the anode electrode. Air was added to promote the direct internal conversion of CH4 to H2 and CO via partial oxidation (POx). The initial breakthrough of H2S from the cleaning section was also simulated and tested by adding ∼1 ppm(v) of sulfur in the anode feed; a full recovery of the fuel cell performance after 24h of sulfur exposure (∼1 ppm(v)) was observed upon its removal, indicating the reliable time of anode exposure to sulfur in case of exhausted guard bed.
Pub.: 02 Aug '14, Pinned: 03 Jul '17
Abstract: The feasibility of operating a solid oxide fuel cell on biogas has been studied over a wide compositional range of biogas, using a small tubular solid oxide fuel cell system operating at 850 °C. In addition the response of the SOFC towards waste ammonia has been studied. It is possible to run the SOFC on biogas, even at remarkably low levels of methane, at which conventional heat engines would not work, thus offering a valuable and environmentally friendly use for poor-quality biogas that is currently wasted by detrimental venting to the atmosphere. The power output varies with methane content of the biogas, with maximum power production occurring at 45% methane, corresponding to maximal production of H2 and CO through internal dry reforming. Direct electrocatalytic oxidation of methane does not contribute to the power output of the cell. For biogas with higher methane contents methane decomposition becomes significant, leading to increased H2 production, and hence transiently higher power production, and deleterious carbon deposition and thus eventual cell deactivation. SOFCs are tolerant to ammonia, actually utilising the ammonia present in biogas to produce electrical power, at the same time acting as an environmental clean-up device breaking down the ammonia pollutant to N2 and water, with no formation of any undesirable nitrogen oxides.
Pub.: 01 Sep '03, Pinned: 03 Jul '17
Abstract: Novel integration of in situ near infrared (NIR) thermal imaging, vibrational Raman spectroscopy, and Fourier-transform infrared emission spectroscopy (FTIRES) coupled with traditional electrochemical measurements has been used to probe chemical and thermal properties of Ni-based, solid oxide fuel cell (SOFC) anodes operating with methane and simulated biogas fuel mixtures at 800 °C. Together, these three non-invasive optical techniques provide direct insight into the surface chemistry associated with device performance as a function of cell polarization. Specifically, data from these complementary methods measure with high spatial and temporal resolution thermal gradients and changes in material and gas phase composition in operando. NIR thermal images show that SOFC anodes operating with biogas undergo significant cooling (ΔT = -13 °C) relative to the same anodes operating with methane fuel (ΔT = -3 °C). This result is general regardless of cell polarization. Simultaneous Raman spectroscopic measurements are unable to detect carbon formation on anodes operating with biogas. Carbon deposition is observable during operation with methane as evidenced by a weak vibrational band at 1556 cm(-1). This feature is assigned to highly ordered graphite. In situ FTIRES corroborates these results by identifying relative amounts of CO2 and CO produced during electrochemical removal of anodic carbon previously formed from an incident fuel feed. Taken together, these three optical techniques illustrate the promise that complementary, in situ methods have for identifying electrochemical oxidation mechanisms and carbon-forming pathways in high temperature electrochemical devices.
Pub.: 20 Nov '13, Pinned: 03 Jul '17
Abstract: The development of fuel cells is promising to enable the distributed generation of electricity in the near future. The main candidate fuel for these devices is hydrogen, however, the infrastructure for its production and distribution is currently lacking. In a short to medium term, processing of fossil fuels will play a significant role in hydrogen generation for fuel cells and the use of renewable source – as biogas – is collecting increasing interest at international level. In this work, we consider the use of biogas to feed a solid oxide fuel cell (SOFC) studying separately in details the reforming and the power production. The biogas reforming process was investigated using a thermodynamic and chemical simulation tool. The influence of various operating parameters, such as steam to carbon ratio, carbon deposition and temperature, on the reforming performances was validated, analyzed in-depth and results are presented. Then a model able to provide the polarization curve of the SOFC was implemented and validated. The SOFC model was run using the syngas compositions obtained for three different reforming operating temperatures from 600 to 800 °C. When the temperature increased, the hydrogen molar composition in the syngas increased, whereby the results obtained by the numerical analysis showed an improvement of the SOFC performance as the reforming temperature increased. Afterwards, the reforming/SOFC model was integrated in a hybrid renewable power plant, for an off-grid application. In the proposed case study, a wind turbine and a photovoltaic panel array are used as main energy sources, while the SOFC, together with a battery and a diesel generator, is used as backup system, due to the intrinsic intermittency of main power sources. Three different scenarios, based on different amounts of biogas produced by a biowaste anaerobic digester, have been simulated and analyzed, demonstrating that the power plant is able to achieve 100% renewable operation, provided that the digester produces at least 436 m3/day on average.
Pub.: 22 Apr '17, Pinned: 03 Jul '17
Abstract: Solid Oxide Fuel Cells (SOFCs) perform well on light hydrocarbon fuels, and the use of biogas derived from the anaerobic digestion (AD) of municipal wastewater sludges could provide an opportunity for the CH4 produced to be used as a renewable fuel. Greenhouse gas (GHG), NOx, SOx, and hydrocarbon pollutant emissions would also be reduced. In this study, SOFCs were operated on AD derived biogas. Initially, different H2 dilutions were tested (N2, Ar, CO2) to examine the performance of tubular SOFCs. With inert gases as diluents, a decrease in cell performance was observed, however, the use of CO2 led to a higher decrease in performance as it promoted the reverse water-gas shift (WGS) reaction, reducing the H2 partial pressure in the gas mixture. A model was developed to predict system efficiency and GHG emissions. A higher electrical system efficiency was noted for a steam:carbon ratio of 2 compared to 1 due to the increased H2 partial pressure in the reformate resulting from higher H2O concentration. Reductions in GHG emissions were estimated at 2400 tonnes CO2, 60 kg CH4 and 18 kg N2O. SOFCs were also tested using a simulated biogas reformate mixture (66.7% H2, 16.1% CO, 16.5% CO2, 0.7% N2, humidified to 2.3 or 20 mol% H2O). Higher humidification yielded better performance as the WGS reaction produced more H2 with additional H2O. It was concluded that AD-derived biogas, when cleaned to remove H2S, Si compounds, halides and other contaminants, could be reformed to provide a clean, renewable fuel for SOFCs.
Pub.: 19 Sep '16, Pinned: 03 Jul '17
Abstract: In the context of the paradigm of Carbon Recovery and Re-utilization (or CRR), this work investigates the role of electrochemical generators (such as high-temperature fuel cells) to perform CRR as a practical secondary effect.
Pub.: 13 Feb '17, Pinned: 03 Jul '17
Abstract: The Life Cycle Assessment (LCA) of biogas-fed Solid Oxide Fuel Cell (SOFC) integrated with a CO2 recovery system is presented in this work. The goal of the work is to evaluate the environmental performance of an SOFC fueled with sewage biogas and to compare it with traditional technologies (internal combustion engines and microturbines) using the same fuel. CO2 recovery is performed through a tubular photobioreactor, fixing the recovered carbon in the form of a micro-algae.
Pub.: 11 Mar '17, Pinned: 03 Jul '17