• Energy Research

Abstract Currently the role of fuel cells in future power generation is being examined, tested and discussed. However, implementing systems is more difficult because of sealing challenges, slow start-up and complex thermal management and fuel processing. A novel furnace system with a flame-assisted fuel cell is proposed that combines the thermal management and fuel processing systems by utilizing fuel-rich combustion. In addition, the flame-assisted fuel cell furnace is a micro-combined heat and power system, which can produce electricity for homes or businesses, providing resilience during power disruption while still providing heat. A micro-tubular solid oxide fuel cell achieves a significant performance of 430 mW cm−2 operating in a model fuel-rich exhaust stream.

Abstract Flame-assisted fuel cell (FFC) studies have been limited to lower fuel-rich equivalence ratios (∼1–1.7, due to the upper flammability limit and sooting limit) where only small concentrations of H2 and CO can be generated in the exhaust. In this work, a non-catalytic microcombustion based FFC is proposed for direct use of hydrocarbons for power generation. The potential for high FFC performance (450 mW cm−2 power density and 50% fuel utilization) in propane/air microcombustion exhaust is demonstrated. The micro flow reactor is investigated as a fuel reformer for equivalence ratios from 1 to 5.5. One significant result is that soot formation in the micro flow reactor is not observed at equivalence ratios from 1 to 5.5 and maximum wall temperatures ranging from 750 to 900 °C. Soot formation is observed at higher wall temperatures of 950 °C and 1000 °C and equivalence ratios above 2.5. H2 and CO concentrations in the exhaust are found to have a strong temperature dependence that varies with the maximum wall temperature and the local flame temperature.

Abstract The performance of anode-supported solid oxide fuel cells was investigated as the SDC buffer layer thickness was varied between ∼0.4 μm and ∼2.3 μm. The thickness of the buffer layer has a significant effect with the peak performance varying in magnitude by a factor of almost three. A peak power density of 1106 mW cm−2 was achieved at 800 °C and an optimal SDC buffer layer thickness of ∼1.5 μm. The performance variation was complex due to a balance between ohmic and polarization losses, triple phase boundary area, pin holes and interfacial reactions between the BSCF + SDC cathode, SDC buffer layer, and YSZ electrolyte. Understanding this variation is essential in order to compare two fuel cells having a different porous buffer layer thickness.

Abstract Solid oxide fuel cell research and development has faced challenges with slow startup, slow shutdown and a limited number of thermal cycles, which hinders the technology in areas like micro-combined heat and power. A novel micro combined heat and power system, based on a boiler/hot water heater with integrated micro-tubular flame assisted fuel cells (mT-FFCs), is proposed which requires rapid startup, shutdown and thousands of thermal cycles. A 9 cell mT-FFC stack is developed and operated in a two-stage combustor. Rapid startup and shutdown of the fuel cells is demonstrated. The first-stage combustor is ignited, turned off and re-ignited for a total of 3000 on/off, thermal cycles. A maximum heating rate of 966 °C.min −1 and a maximum cooling rate of 353 °C.min −1 is achieved while thermal cycling. Despite the presence of CO in the exhaust, the anode remains porous and crack free after ∼150 h of thermal cycling testing. The mT-FFC stack continues to generate significant power, even after completing the cycling test, and a low voltage degradation rate is reported.

Abstract Direct flame fuel cells (DFFCs) have been investigated as an alternative means of combustion based power generation devices, but current challenges for this technology have included low fuel utilization and efficiency. In order to overcome these obstacles a new micro-tubular flame-assisted fuel cell (mT-FFC) concept is developed in this work and its performance is assessed at different equivalence ratios and temperatures. The concept is based on fuel-rich combustion exhaust, with the combustion equivalence ratio controlled and the exhaust flowing through the fuel cell for complete electrochemical energy conversion. The results were compared to a hydrogen baseline with the same electron potential as the fuel-rich exhaust. The mT-FFC concept offers significant advantages including high fuel utilization and greater performance stability compared to DFFCs.

Combustion based power generation has been accomplished for many years through a number of heat engine systems. Recently, a move towards small scale power generation and micro combustion as well as development in fuel cell research has created new means of power generation that combine solid oxide fuel cells with open flames and combustion exhaust. Instead of relying upon the heat of combustion, these solid oxide fuel cell systems rely on reforming of the fuel via combustion to generate syngas for electrochemical power generation. Procedures were developed to assess the combustion by-products under a wide range of conditions. While theoretical and computational procedures have been developed for assessing fuel-rich combustion exhaust in these applications, experimental techniques have also emerged. The experimental procedures often rely upon a gas chromatograph or mass spectrometer analysis of the flame and exhaust to assess the combustion process as a fuel reformer and means of heat generation. The experimental techniques developed in these areas have been applied anew for the development of the micro-tubular flame-assisted fuel cell. The protocol discussed in this work builds on past techniques to specify a procedure for characterizing fuel-rich combustion exhaust and developing a model fuel-rich combustion exhaust for use in flame-assisted fuel cell testing. The development of the procedure and its applications and limitations are discussed.

Abstract Similar to the original direct flame fuel cell the flame-assisted fuel cell, which has a solid oxide fuel cell (SOFC) operating in combustion exhaust, can potentially simplify the fuel cell system and has applications in micro-Combined Heat and Power. Development and testing of a 9 micro-tubular flame-assisted fuel cell stack is demonstrated in this work. Two different systems are investigated having 1) fixed fuel flow rate and varying air flow rate and 2) fixed total flow rate of air and fuel for the micro-Combined Heat and Power burners. The micro-tubular flame-assisted fuel cell stack achieves a significant performance of 237 mW cm −2 in model methane combustion exhaust at 0.5 V and 790 °C with a lanthanum strontium manganite based cathode. Electrochemical impedance spectroscopy reveals that the fuel cell ohmic losses are unaltered by variations in the exhaust species concentrations while the polarization losses increase with decreasing first-stage combustion fuel-air equivalence ratio. Variations in the combustion exhaust temperature effects both the ohmic and polarization losses.

Abstract In this study, the flame-assisted fuel cell (FFC 1 ) was investigated by using methane/air flames. The confrontation between FFC temperature and fuel concentration at various conditions was investigated which uncovered the complex behavior of FFCs performance. Variations in fuel/air equivalence ratio, fuel flow rate and distance between FFC and burner outlet were studied. A critical distance for FFC placement above the burner outlet was uncovered, which has a significant impact on FFC performance. A high power density of 791 mW cm −2 was achieved which is comparable to the dual chamber solid oxide fuel cell (SOFC) and single chamber SOFC. The short-term test exhibited good stability of the FFCs under operation despite the presence of carbon formation on the anode surface.

Abstract There is an increasing pressure for industry to reduce carbon dioxide (CO 2 ) emissions from combustion processes, resulting in an increased interest in the development of methods to sequester and recycle CO 2 from flue gases. Current methods available to separate nitrogen and CO 2 for environmental benefits, such as chemical looping combustion (CLC), are expensive at the high flow rates encountered in industry. One potential alternative is a ceramic membrane catalytic reactor, which produces pure oxygen and simultaneously conducts oxy-fuel combustion, thus, CO 2 in the product stream can successfully be separated from the nitrogen in air. This work investigates the performance of a perovskite-type SrSc 0.1 Co 0.9 O 3-δ (SSC) and La 0.6 Sr 0.4 Co 0.2 Fe 0.8 O 3-δ (LSCF) membrane reactors for the combustion of methane in various configurations. The ceramic membranes exploited here are oxygen semi-permeable, dense ceramic membranes based on the composite oxides with a high mixed oxygen ionic and electronic conductivity at high temperatures. The prepared SSC and LSCF hollow fibre membranes with catalysts were used to perform reactions with a methane fuel. The oxygen permeability feasibility of the membrane reactors were studied and confirmed. The CO 2 selectivity at various test conditions were also reported with the maximum selectivity achieved for SSC membrane to be 85.4% while LSCF membrane achieved 87.1% CO 2 selectivity.