Influence of the Contamination of Fuel with Fly Ash Originating from Biomass Gasification on the Performance of the Anode-Supported SOFC

The integration of solid oxide fuel cells (SOFCs) with biomass gasification reactors raises the possibility of solid particle contamination of the gaseous fuel entering the cell. Technical specifications from SOFC manufacturers, among other sources, claim that SOFCs do not tolerate the presence of solid particles in fuel. However, there is very limited literature on the experimental investigation of feeding SOFCs with particulate matter aerosols. In this study, a standard 5 × 5 cm anode-supported SOFC was fueled by two types of aerosols, namely, (1) inert powder of grain sizes and concentration equivalent to gasifier fly ash and (2) a real downdraft gasifier fly ash, both suspended in a gaseous fuel mixture. For reference, cells were also investigated with a dust-free fuel gas of the same composition. A straightforward negative influence of the inert powder aerosol could not be confirmed in experiments with a duration of 6 days. That said, the introduction of carbonaceous fly ash aerosol caused slow but irreversible damage to the SOFC. The degradation mechanisms were studied, and the presence of carbon-containing particles was found to clog the pores of the SOFC anode. The maximum measured power density of the SOFC equaled 855 mW/cm2 (850 °C, reference fuel). Feeding inert aerosol fuel caused no rapid changes in power density. A moderate drop in performance was observed throughout the experiment. The contamination of fuel with fly ash resulted in an initial performance gain and a ca. 25% performance drop longer term (43 h of contamination). Post-mortem analysis revealed contamination on the walls of the gas channels, with some visible alumina or fly ash spots in the anode area

Setup of a test bench and testing the single solid oxide fuel cell at various temperatures

RES Master´s Thesis Verkefnið er unnið í tengslum við Háskóla Íslands og Háskólann á AkureyriSolid Oxide Fuel Cells (SOFCs) are a promising source of electricity. They are efficient devices that allow direct harnessing the Gibbs free energy of reactions between fuel and an oxidant. The ongoing project in the Fuel Cell laboratory in Perugia, Italy is a part of their coordination with the Energy Research Center of Netherlands (ECN). This project was devoted to single SOFCs testing, which helps in understanding the influence of different circumstances on the SOFC performance. In this thesis is a detailed outline of the testing procedures and an expanded discussion of the results. The main objectives of this work were to: finish building the single SOFC test bench, create a model that allowed time and gas consumption forecasting for different tests, design the sulphur tolerance system, create a model for cell temperature evaluation, study recent scientific achievements in SOFC with special emphasis on single cells testing, prepare the laboratory testing procedures, perform the tests of the ASC2 Cell by InDEC B.V. The results are presented in graphs in the body of the work and in detailed tables as an appendix. The measurements gave results worse than expected, but the temperature dependence is clear. The conclusions for future development of the test bench are that the temperature measuring should be improved and software development should continue

Carbon as a fuel for efficient electricity generation in carbon solid oxide fuel cells

In this paper, the impact of the physicochemical properties of carbonaceous solid fuels on the performance of a direct carbon solid oxide fuel cell (DC-SOFC) was investigated. High-purity synthetic carbon powders such as carbon black N-220 and Carbo Medicinalis FP5 were chosen for analytical and electrochemical investigations in a DC-SOFC. The research focussed on choosing an optimised, cost-effective, high-purity carbon powder which could be applied as a solid reference fuel for all tests performed on a single DC-SOFC cell as well as on DC-SOFC stack constructions. Most of the electrochemical investigations described in this paper were performed using square DCSOFCs with dimensions of 5 × 5 cm. The relationship between structure, physicochemical properties, and electrochemical reactivity in a DC-SOFC was analysed

Solid Oxide Fuel Cells coupled with a biomass gasification unit

A possibility of fuelling a solid oxide fuel cell stack (SOFC) with biomass fuels can be realized by coupling a SOFC system with a self-standing gasification unit. Such a solution enables multi-fuel operation, elasticity of the system as well as the increase of the efficiency of small-scale biomass-to-electricity conversion units. A system of this type, consisting of biomass gasification unit, gas purification unit, SOFC stack, anode off-gas afterburner and peripherals was constructed and operated successfully. During the process, biomass fuel (wood chips) was gasified with air as gasification agent. The gasifier was capable of converting up to 30 kW of fuel to syngas with efficiencies up to 75%. Syngas leaving the gasification unit is delivered to a medium temperature adsorber for sulphur compounds removal. Steam is added to the purified fuel to maintain steam to carbon ratio higher than 2. The syngas then is passed to a SOFC stack through a fuel preheater. In such a configuration it was possible to operate a commercial 1.3 kW stack within its working regime. Conducted tests confirmed successful operation of a SOFC stack fuelled by biomass-sourced syngas

Analysis of a Micro-CHP Unit with in-series SOFC Stacks Fed by Biogas

AbstractThis paper presents results of a recent evaluation of a conceptual micro-CHP units in two alternative configurations. Parallel and in-series connections of two identical commercial electrolyte-supported SOFC stacks were under evaluation. In order to achieve high overall fuel utilization in the system enabling high electrical efficiency, both concepts were analyzed with respect to operational regimes typical for SOFC stacks. Numerical analysis included several possible configurations of complete a system with fuel processor, SOFC stacks and BoP components. Evaluation of the in-series connection was performed using experimental setup with a commercial SOFC stack to reproduce operating conditions obtained from the model. Validation of the concept was necessary to qualitatively and quantitatively determine possibility of operating second stack on lean fuel originating from the anodic compartments of the first stack. Results of the comparative analysis presented in this paper were used to aid in defining optimal outline of a micro-CHP power system. Predictions of the models were in agreement with preliminary experiments, proving the concept of in-series stacks configuration viable. Electrical efficiency increases for the system with two in-series stacks, and value of 46%LHV can be achieved in the micro-CHP system with SOFC

Impact of Sweep Gas on the Degradation of an La_0.6Sr_0.4Co_0.8Fe_0.8O₃ Anode in a Solid Oxide Electrolysis Cell

The degradation of solid oxide electrolysis (SOE) cells with different anode sweep gases was studied in 1000 h-long measurements in order to investigate the impact of sweep gas composition on cell performance. Cathode-supported electrolysis cells with an La0.6Sr0.4Co0.2Fe0.8O3 air electrode (active area of 4 × 4 cm2) were tested under a constant current (−0.25 A/cm2) in the electrolysis mode while supplying the cathode side with 70% H2O–30% H2 mixtures at 800 °C and using oxygen, nitrogen, and steam as sweep gases. It was demonstrated that the degradation of the anode in steam conditions resulted in more than a 2-fold increase in both, polarization and ohmic resistance (from 0.20–0.25 to 0.6–0.65 Ω cm2 compared to relatively stable values of 0.15–0.2 Ω cm2 for N2), as a consequence of the phase decomposition. Strontium played an important role in steam-induced degradation, migrating from the volume of the electrode layer to the surface of the electrolyte. As a result, the Sr-enriched layer demonstrated susceptibility to Cr poisoning. The cell purged with N2 demonstrated enhanced performance, while the use of oxygen led to degradation originating from the well-described delamination process. DRT analysis demonstrated some similarity of the spectra for steam and N2, namely the presence of a slow process at τ≈0.5 s, which might be associated with hindered oxygen transport due to point defect association in the perovskite structure. The results of this study showed that Sr-containing materials likely cannot be used as an SOE anode in high humidity conditions

Analysis of Soot Deposition Mechanisms on Nickel-Based Anodes of SOFCs in Single-Cell and Stack Environment

Solid oxide fuel cells (SOFCs) can be fueled with various gases, including carbon-containing compounds. High operating temperatures, exceeding 600 °C, and the presence of a porous, nickel-based SOFC anode, might lead to the formation of solid carbon particles from fuels such as carbon monoxide and other gases with hydrocarbon-based compounds. Carbon deposition on fuel electrode surfaces can cause irreversible damage to the cell, eventually destroying the electrode. Soot formation mechanisms are strictly related to electrochemical, kinetic, and thermodynamic conditions. In the current study, the effects of carbon deposition on the lifetime and performance of SOFCs were analyzed in-operando, both in single-cell and stack conditions. It was observed that anodic gas velocity has an impact on soot formation and deposition, thus it was also studied in depth. Single-anode-supported solid oxide fuel cells were fueled with gases delivered in such a way that the initial velocities in the anodic compartment ranged from 0.1 to 0.7 m/s. Both cell operation and post-mortem observations proved that the carbon deposition process accelerates at higher anodic gas velocity. Furthermore, single-cell results were verified in an SOFC stack operated in carbon-deposition regime by dry-coupling with a downdraft 150 kWth biomass gasifier

Influence of the Contamination of Fuel with Fly Ash Originating from Biomass Gasification on the Performance of the Anode-Supported SOFC

The integration of solid oxide fuel cells (SOFCs) with biomass gasification reactors raises the possibility of solid particle contamination of the gaseous fuel entering the cell. Technical specifications from SOFC manufacturers, among other sources, claim that SOFCs do not tolerate the presence of solid particles in fuel. However, there is very limited literature on the experimental investigation of feeding SOFCs with particulate matter aerosols. In this study, a standard 5 × 5 cm anode-supported SOFC was fueled by two types of aerosols, namely, (1) inert powder of grain sizes and concentration equivalent to gasifier fly ash and (2) a real downdraft gasifier fly ash, both suspended in a gaseous fuel mixture. For reference, cells were also investigated with a dust-free fuel gas of the same composition. A straightforward negative influence of the inert powder aerosol could not be confirmed in experiments with a duration of 6 days. That said, the introduction of carbonaceous fly ash aerosol caused slow but irreversible damage to the SOFC. The degradation mechanisms were studied, and the presence of carbon-containing particles was found to clog the pores of the SOFC anode. The maximum measured power density of the SOFC equaled 855 mW/cm2 (850 °C, reference fuel). Feeding inert aerosol fuel caused no rapid changes in power density. A moderate drop in performance was observed throughout the experiment. The contamination of fuel with fly ash resulted in an initial performance gain and a ca. 25% performance drop longer term (43 h of contamination). Post-mortem analysis revealed contamination on the walls of the gas channels, with some visible alumina or fly ash spots in the anode area