Jeongmin Ahn

Combustion Characterization and Model Fuel Development for Micro-tubular Flame-assisted Fuel Cells

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.

Review and analysis of fuel cell-based, micro-cogeneration for residential applications: Current state and future opportunities

Micro-cogeneration or micro-combined heat and power, which can meet both the electrical and thermal needs of the residential sector, is growing and can offer reduced energy usage and emission. Micro-combined heat and power differs from typical combined heat and power plants in size and in the way these systems are often controlled to follow the space heating load as opposed to the electrical load. Among the different technologies available, fuel cell-based micro-combined heat and power fundamentally differs from the combustion-based technologies and has the potential to achieve high electrical efficiency, low emissions, reduced noise, and reduced energy consumption for the residential sector. However, these benefits are not always realized by fuel cell micro-combined heat and power as they depend on factors such as start-up/shutdown time, turndown capability, and the application, among other things. While the opportunities are clear and well-documented in the literature, the means of assessing fuel cell micro-combined heat and power energy usage, efficiency, and emissions varies. Advanced models and methods, such as the quasi-two-dimensional or three-dimensional approach, have been developed for fuel cell system analysis, but simplified models are often used as part of the building integrated micro-combined heat and power assessment. Many of the building integrated micro-combined heat and power assessments only investigate the average annual energy usage and the associated greenhouse gas emissions of the micro-combined heat and power systems without fully accounting for the seasonal and day-to-day variations in the load and supply. Differences in the fuel cell models used for building integrated micro-combined heat and power assessment has led to conflicting results and conclusions about the potential for this technology in the residential sector. A literature review is conducted in this work to assess the opportunities and obstacles for fuel cell micro-combined heat and power in the residential sector and the methods of assessing these systems. The review reveals that certain fuel cell model types, such as the black box approach, tend to give inconsistent results when the assumptions do not align with the actual operation of the fuel cell micro-combined heat and power system. Recommendations are made for employing these models while assessing building integrated fuel cell micro-combined heat and power systems. A unified approach that integrates more sophisticated fuel cell micro-combined heat and power models into building integrated energy performance simulation platforms is recommended.

Effect of Scale on the Performance of Heat-Recirculating Reactors

Extinction limits and combustion temperatures in heat-recirculating excess enthalpy reactors employing both gas-phase and catalytic reaction have been examined previously, with an emphasis Reynolds number (Re) effects and possible application to microscale combustion devices. However, Re is not the only parameter needed to characterize reactor operation. In particular, the use of a fixed reactor size implies that residence time (thus Damkohler (Da), the ratio of residence to chemical time scales) and Re cannot be adjusted independently. To remedy this situation, in this work geometrically similar reactors of different physical sizes were tested with the aim of independently determining the effects of Re and Da. It is found that the difference between catalytic and non-catalytic combustion limits narrow as scale decreases. Moreover, to assess the importance of wall thermal conductivity, reactors of varying wall thickness were studied; results were consistent with theoretical predictions. From these results the effect of scale on microscale reactor performance and implications for practical microcombustion devices are discussed.

A Thermally Self-Sustaining Miniature Solid Oxide Fuel Cell

A thermally self-sustaining miniature power generation device was developed utilizing a single-chamber solid oxide fuel cell (SOFC) placed in a controlled thermal environment provided by a spiral counterflow “Swiss roll” heat exchanger and combustor. With the single-chamber design, fuel/oxygen crossover due to cracking of seals via thermal cycling is irrelevant and coking on the anode is practically eliminated. Appropriate SOFC operating temperatures were maintained even at low Reynolds numbers (Re) via combustion of the fuel cell effluent at the center of the Swiss roll. Both propane and higher hydrocarbon fuels were examined. Extinction limits and thermal behavior of the integrated system were determined in equivalence ratio—Re parameter space and an optimal regime for SOFC operation were identified. SOFC power densities up to 420 mW/cm^2 were observed at low Re. These results suggest that single-chamber SOFCs integrated with heat-recirculating combustors may be a viable approach for small-scale power generation devices.

Flame-Assisted Fuel Cell Operating With Methane for Combined Heating and Micro Power

Solid Oxide Fuel Cells (SOFCs) operating in a Flame-assisted Fuel Cell (FFC) setup have potential for Combined Heating and micro Power applications. The feasibility of a FFC furnace operating with natural gas is investigated by using methane/ air flames. The confrontation between the FFCs operating temperature and fuel concentration under various conditions was investigated which uncovered the complex performance behavior. Variations in the fuel/ air equivalence ratio, fuel flow rate and distance between the FFC anode and burner outlet were studied. A critical distance for FFC placement above the burner outlet was uncovered, which has a significant impact on the FFCs performance. A high power density of 791mW.cm−2 was achieved which is comparable to the dual chamber SOFC and single chamber SOFC. Carbon coking was observed on the anode surface, but was not detrimental to FFC performance during testing.Copyright

Integrated Anaerobic Digester and Fuel Cell Power Generation System for Community Use

New York State is expected to experience future population growth that is increasingly concentrated in urban areas, where there is already a heavy burden on the existing energy, water and waste management infrastructure. To meet aggressive environmental standards (such as that established by the State’s “80x50” goal), future electrical power capacity must produce substantially fewer greenhouse gas emissions than currently generated by coal- or natural gas-fired power plants. Currently, biogas is combusted to produce heat and electricity via an internal combustion engine generator set. A conventional internal combustion engine generator set is 22–45 % efficient in converting methane to electricity, thus wasting 65–78 % of the biogas energy content unless the lower temperature heat can be recovered. Fuel cells, on the other hand, are 40–60 % efficient in converting methane to electrical energy, and 80–90 % efficient for cogeneration if heat (> 400 °C) is recovered and utilized for heating and cooling in the community power system. This current research studies the feasibility of a community biomass-to-electricity power system which offers significant environmental, economic and resilience improvements over centrally-generated energy, with the additional benefit of reducing or eliminating disposal costs associated with landfills and publicly-owned treatment works (POTWs). Flame Fuel Cell (FFC) performance was investigated while modifying biogas content and fuel flow rate. A maximum power density peak at 748 mWcm-2 and an OCV of 0.856 V was achieved. It should be noted that the performance obtained with the model biofuel is comparable to the performances of direct methane fueled DC-SOFC and SC-SOFC. The common trends also concluded an acceptable range for optimal performance. Although the methane to CO2 ratios of 3:7 and 2:8 produced power, they are not the strongest ratios to have optimal performance, meaning that operation should stay between the 6:4/4:6 ratio range. Lastly, the amount of air added to the biogas mixture is crucial to achieving the optimal performance of the cell. The data obtained confirmed the feasibility of a biofuel driven fuel cell CHP device capable of achieving higher efficiency than existing technologies. The significant power output produced from the sustainable biogas composition is competitive with current hydrocarbon fuel sources. This idea can be expanded for a community waste management infrastructure.Copyright

Novel Structured Electrolyte for All-Solid-State Lithium Ion Batteries

In this study, a multi-layer structure solid electrolyte (SE) for all-solid-state electrolyte lithium ion batteries (ASSLIBs) was fabricated and characterized. The SE was fabricated by laminating ceramic electrolyte Li1.3Al0.3Ti1.7(PO4)3 (LATP) with polymer (PEO)10-Li(N(CF3SO2)2 electrolyte and gel-polymer electrolyte of PVdF-HFP/ Li(N(CF3SO2)2. It is shown that the interfacial resistance is generated by poor contact at the interface of the solid electrolytes. The lamination protocol, material selection and fabrication method play a key role in the fabrication process of practical multi-layer SEs.Copyright

A ceramic-membrane-based methane combustion reactor with tailored function of simultaneous separation of carbon dioxide from Nitrogen

Today, industry has become more dependent on natural gases and combustion processes, creating a tremendous pressure to reduce their emissions. Although the current methods such as chemical looping combustion (CLC) and pure oxygen combustion have several advantages, there are still many limitations. A ceramic membrane based methane combustion reactor is an environmentally friendly technique for heat and power generation. This work investigates the performance of a perovskite-type SrSc0.1Co0.9O3-δ (SSC) membrane reactor for the catalytic combustion of methane. For this purpose, the mixed ionic and electronic conducting SSC oxygen-permeable planar membrane was prepared by a dry-pressing technique, and the SSC powder catalyst was spray coated on the permeation side of the membrane. Then, the prepared SSC membrane with the catalyst was used to perform the catalytic combustion of methane. The oxygen permeability of the membrane reactor was studied. Also, the methane conversion rates and CO2 selectivity at various test conditions were reported.Copyright

Thermal Transpiration Based Propulsion

Thermal transpiration based propulsion is studied. Thermal transpiration describes flowing of the gas through a narrow channel with an imposed temperature gradient. As gas flows from the cold to hot side in the chamber, a pressure gradient is created across the channel induced by the temperature gradient. Between the two sides of the chamber an aerogel substance, which functions as an excellent insulator, is used as a thermal transpiration membrane and allows gas diffuse to the hot chamber. The induced pressure gradient is the driving factor in the propulsion of air, or any gas, into the chamber and through the porous membrane. The use of a porous substance such as aerogel as the transpiration membrane and a pressure gradient served as the two requirements in order to successfully achieve thermal transpiration. The gas diffusion through the aerogel transpiration membrane indicates that the average pore size of the aerogel must be comparable with the free path of the molecules. This concept can be taken further if the outlet chamber served as a combustion reactor. The flowing gas is motivated by the heat produced from the combustion process. Along with the exceptionally low thermal conductivity of the aerogel, the gas flow permits the propulsion device to be self-sustaining. The implications of providing a self-sustaining heat source signify that no external electrical heating is required. The effectiveness of this device can be measured as a function of the porous size of the membrane and the temperature difference applied to the system and pressure gradient created.© 2014 ASME

Single-phase ceramic membranes integrated with combustion processes

La0.6Sr0.4Co0.2Fe0.8O3-δ (LSCF6428) hollow fibre oxygen-permeable membranes were fabricated by extrusion technique. The oxygen permeability of a blank hollow fibre membrane was investigated with helium as sweeping gas. The oxygen permeation flux result was reported, agreeing very well with previous work. Then the hollow fibre membrane was packed with LSCF6428 catalyst and assembled as hollow fibre membrane reactor for methane combustion, aiming to separate the CO2 in the combustion exhaust from the nitrogen in air. The CO2 selectivity at various conditions was studied.Copyright