Thermodynamic model and parametric analysis of a tubular SOFC module

This project was conducted under the Co-operative Agreement No. DE-FE0027584 with the US Department Energy to developed advanced Solid Oxide Fuel Cell (SOFC) Technologies. The overall objective of this project was to advance SOFC technology at the cell and stack level to enhance cell robustness and durability, increase performance, and reduce balance-of-plant (BOP) requirements. By reducing system complexity combined with the increases in power density and efficiency, the ultimate goal of the project was to increased reliability and to reduce capital and operating costs of installed systems. The project was focused on pathways that will reduce the cost of the SOFC cell and stack, including the following areas: Robust, redox tolerant cell technology Lower cost cell manufacturing through advances in cell design, which will reduce the amount of material, energy and time used in the fabrication of SOFCs High performance, low temperature electrolyte based on improvement of established materials Innovative SOFC stack architecture which truly integrates Balance of Plant functionality into the stack level design Thermal management of the fuel cell stack for increased durability and expanded window of operation Novel stack design amenable for use in sub-MW to multi-MW-scale power plants and having low replacement cost The incorporation of balance-of-plant (BOP) equipment into the stack platform increased the economic viability of smaller scale systems. The project objectives were met by a multi-prong approach, including new cell design complemented with modifications to existing cell technology, as well as a new stack design incorporating components typically included in the BOP, such as heat exchangers, oxidizer, fuel reformers, and recycle systems. The project culminated with demonstration of a stack test validating the viability of the cell and stack improvements. A cost model was also developed to estimate costs for the advanced stack technology at high volume manufacturing levels. The net outcome of the project is SOFC cell and stack technology with costs significantly below current DOE targets without compromising and, in some cases, improving on the performance and degradation rate demonstrated with the current state-of-the-art stack design. The results of this project advanced the reliability, robustness, and endurance of low-cost SOFC technology that ultimately are ready to be deployed in coal power systems with greater than 60 percent efficiency (based on higher heating value of fuel) and the capability for ≥97% CO2 capture at a cost-of-electricity that is approximately 40 percent below presently available Integrated Gasification Combined Cycle systems.

Review: 469 refs.

Exergoeconomic evaluation of an ethanol-fueled solid oxide fuel cell power plant

<div class="htmlview paragraph">Delphi Automotive Systems and BMW are jointly developing Solid Oxide Fuel Cell (SOFC) technology for application in the transportation industry primarily as an on-board Auxiliary Power Unit (APU). In the first application of this joint program, the APU will be used to power an electric air conditioning system without the need for operating the vehicle engine.</div> <div class="htmlview paragraph">The SOFC based APU technology has the potential to provide a paradigm shift in the supply of electric power for passenger cars. Furthermore, by supplementing the conventional fuel with reformate in the internal combustion engine, extremely low emissions and high system efficiencies are possible. This is consistent with the increasing power demands in automobiles in the new era of more comfort and safety along with environmental friendliness.</div> <div class="htmlview paragraph">Delphi Automotive Systems and BMW were successful in demonstrating an Auxiliary Power Unit (APU) based on Solid Oxide Fuel Cell (SOFC) technology in February, 2001. A SOFC APU generates power using hydrogen and carbon monoxide reformed from fuels such as gasoline, diesel, or natural gas. The proof-of-concept unit and the advantages of using a SOFC APU will be activities in the development of a second generation APU. This development has been targeted towards resolving the fundamental issues with the following key subsystems: fuel cell stack, fuel reformers, and energy and thermal management. Major focus has also been directed at system integration challenges to make a more robust and efficient product.</div>

SummaryA design study was undertaken of a 100 kW natural gas solid oxide fuel cell (SOFC)/gas turbine (GT) hybrid system to evaluate the impacts of the reforming process under a broad range of SOFC fuel utilizations. An equilibrium reformer model and a one‐dimensional SOFC model are employed to perform system study for this hybrid, while balance of plant model is built in Ebsion to simulate the associated performance of GT cycle. Fifty design cases with varied external fuel reforming temperatures are analyzed based on different SOFC fuel utilization levels. With the decrease of reforming temperature, optimal fuel utilization in terms of efficiency shift from 90% with external reforming to 60% with internal reforming. Highest efficiency up to 74% was achieved with internal reforming, but this came with 1275 K cathode inlet air temperature and 1673 K turbine inlet temperature, which no current fuel cell and few GTs can tolerate. High fuel pre‐reforming rates provided a higher design flexibility and showed opportunities of efficiency improvement with appropriate thermal integration strategy. And the feasibility of achieving high efficiencies in the hybrid system with thermally integrated external reforming will be explored in our future work.Novelty StatementBoth fuel reforming process and fuel utilization could affect the heat and energy balance in the hybrid gas solid oxide fuel cell (SOFC)‐gas turbine (GT) system. However, the optimal design condition considering different fuel reforming approaches and SOFC fuel utilization levels was not determined in the literature. In addition, appropriate integration strategies, used to balance the heat and power between the two subsystems (SOFC and GT), are imperative under different fuel reforming approaches and SOFC fuel utilization levels. But, the feasibility of those thermal integration strategies has not been examined in existing studies. This work studied the coupling effects of SOFC fuel utilization and fuel reforming process on system performance of a natural gas hybrid SOFC/GT cycle. Highest efficiency up to 74% was achieved with internal reforming, but this came with 1275 K cathode inlet air temperature and 1673 K turbine inlet temperature, which no current fuel cell and few GTs can tolerate. High fuel pre‐reforming rates provided a higher design flexibility and showed opportunities of efficiency improvement with appropriate thermal integration strategy.

Advances in solid oxide fuel cell technology

Recently, while eco-friendly energy storage/conversion technologies have been attracting attention, researches have been reported to improve performance and provide multiple functions by applying three-dimensional nano-/micro-structures to energy devices. In general energy devices, the electrolyte and electrodes located on both sides have been designed to have a flat interface, but in the end, developed structures in consideration of three-dimensional efficiency should be required. Among them, in solid oxide fuel cells (SOFCs), which have advantages such as high efficiency and fuel flexibility, studies on the use of advanced cell structures were conducted to lower the operating temperature. Although micro-SOFC using etching or laser processing has been reported, there are limitations in practical operation due to poor material/structural stability and low pattern resolution. In this paper, we developed a novel ceramic micropatterning process by imprinting a pyramid-shaped polymer mold made by soft lithography on the anode support. Furthermore, we have implemented a three-dimensional SOFC with record-high cell performance through the combination of thin film process and large-area cell manufacturing technology. For microscale patterning of the anode, polymer-ceramic anode films with low elastic modulus was prepared by the tape casting process, and the anode support with pyramidal patterns was fabricated through the subsequent imprinting process. The imprinted pattern was maintained after the sintering process. Then, through RF sputtering and pulsed laser deposition (PLD) process, the nanoscale anode functional layer (nAFL), Y2O3-stabilized ZrO2 (YSZ), Gd0.1Ce0.9O1.95 (CGO) and La0.6Sr0.4CoO3- δ (LSC) layer were deposited to fabricate a full cell. To analyze the electrochemical effect of three-dimensional electrode/electrolyte interface, 3DA-cell with ceramic micropatterning process and Planar-cell with flat interface were compared. Interestingly, 3DA-cell showed higher performance than Planar-cell at all operating temperatures, and resulted in 55 % enhanced maximum power density (PDmax) and 19 %, 52 % decreased polarization, ohmic resistance at 500 °C, respectively. Notably, the CGO-based 3DA-cell using CGO as the main electrolyte material recorded a high PDmax of 0.931 W/cm2 at 500 °C. Therefore, to find the factors that improve the electrochemical performance, the microstructures of two different cells were analyzed by scanning electron microscope (SEM), transmission electron microscopy (TEM) and 3D reconstruction method. From the 3D reconstruction result, the nAFL/YSZ interface area, CGO/LSC interface area, and active TPB length of AFL of 3DA-cell increased by about 33 %. 23 %, and 64 % compared to Planar-cell, whereas pore volume ratio of AFL did not change. Therefore, it was confirmed that the increase of the electrode/electrolyte interface area by ceramic micropatterning had a direct effect on the improvement of cell performance, and the internal structure of AFL was not affected by the imprinting process. Furthermore, to demonstrate the versatility of ceramic micropatterning process, a 5 cm x 5 cm large-area three-dimensional thin film SOFC was fabricated and its performance was evaluated. As a result, we set a new milestone in SOFC technology by reporting a power of ~ 13 W at 500 °C, and confirmed the consistency of our process through a cell reproducibility test. Additionally, the stability of the three-dimensional structure was verified through the operation without notable degradation for 500 hours under the condition of 5 A and 8 A current load. This work exhibits an outstanding breakthrough to accomplish high-performance, high-stable large-area SOFCs, and can accelerate commercialization to the portable and transportation devices.

SOFCpower-HTceramix' mission is to offer new energy solutions in the deregulated electricity market, based upon its highly efficient Solid Oxide Fuel Cell (SOFC) technology. SOFCpower develops SOFC stacks and thermally integrated stacks (HoTbox{trade mark, serif}) for OEM companies commercializing new power generators and co-generation systems. Since 2008, SOFCpower has implemented a cost-effective pilot production line for cells, stacks and HoTbox{trade mark, serif} power modules for residential co-generation with a capacity of 2 MW/y in Trento (IT). Furthermore, investments on testing facilities and infrastructures have been made in the same site in order to ensure quality of production and to certify stack durability. As a consequence, it was possible to speed-up cell and stack development and to progress in stack robustness and reproducibility of its performance, achieving electrical efficiency above 50% at stack level without internal reforming. The paper gives an up-date on the status of the manufacturing line and the test bench installation. Performance and stability data for SOFCpower stacks produced within the pilot manufacturing plant are presented, as well an up-date on progresses made on the development of large stacks (> 1 kW).

Development of nickel based cermet anode materials in solid oxide fuel cells – Now and future

Hydrogen generation from natural gas for the fuel cell systems of tomorrow

In conventional gas turbine systems combustion results in high exergy losses (∼30%) of fuel exergy input. Replacing the combustor with a high temperature fuel cell, like the Solid Oxide Fuel Cell (SOFC), will significantly reduce these exergy losses. As the SOFC electrochemically converts the natural gas, exergy losses are far lower (∼10%) compared to combustion. Natural gas entering a SOFC system has to be reformed first to hydrogen and carbon monoxide by steam reforming. Here it is chosen to use the heat generated by the fuel cell to drive the endothermic reforming reactions: internal reforming. The SOFC-GT system has the advantage that both fuel cell and gas turbine technology contribute to power production. In earlier work [1] several fuel cell system configurations with PEMFC, MCFC or SOFC, were analyzed studying the exergy flows. Here is focused on the SOFC-GT configuration, to get a detailed understanding of the exergy flows and losses through all individual components. Several configurations, combining the SOFC with the GT are possible. The selected operating conditions should prevent carbon deposition. Systems studies are performed to get more insight in the exergy losses in these combined systems. Exergy analysis facilitates the search for the high efficient SOFC-GT hybrid systems. Using exergy analysis, several useful configurations are found. Exergy losses are minimized by varying pressure ratio and turbine inlet temperature. Sensitivity studies, of equivalent cell resistance and fuel cell temperature, show that total system exergy efficiencies of more than 80% are conceivable, without using a bottoming cycle.

This paper deals with an exergetic performance analysis of a gas turbine cycle integrated with SOFCs with internal reforming. As the efficiency of a gas turbine cycle is mainly defined by the maximum temperature at the turbine inlet, this temperature is fixed at 1573 K for the analysis. In the cycle considered, the high-temperature gaseous flow from the turbine heats the input flows of natural gas and air, and is used to generate pressurized steam which is mixed with natural gas at the SOFC stack inlet to facilitate its conversion. The application of SOFCs provides the opportunity to reduce the exergy losses of the most irreversible process in the system: fuel combustion. Depending on the SOFC stack efficiency, the energy efficiency of the combined cycle reaches 70–80% which compares well to the efficiencies of 54–55% typical of conventional combined power generation cycles. Parametric studies are also undertaken to investigate how energy and exergy efficiencies of the integrated system change with variations in operating conditions. An increase in the efficiency of SOFCs is attained by increasing the fuel cell active area. Achieving the highest efficiency of the SOFC stack leads to a significant and non-proportional increase in the stack size and cost, and simultaneously to a decrease in steam generation, reducing the steam/methane ratio at the anode inlet and increasing the possibility of catalyst coking. Accounting for these factors, likely operating conditions of the SOFC stack in combination with a gas turbine cycle are presented.

Solid oxide fuel cells (SOFCs) have been attracting considerable attention as ecologically friendly and highly efficient power sources with a variety of applications. Modern directions in the SOFCs technology are related to lowering the SOFC operating temperature that require both advanced materials design and development of versatile technologies to fabricate SOFC with thin-film electrolyte membrane to decrease ohmic losses at decreased temperatures. Electrophoretic deposition (EDP) is one of the most technologically flexible and cost-effective methods for the thin film formation currently available. This review highlights challenges and approaches presented in literature to the formation dense thin films based on oxygen-conducting and proton conducting electrolytes, as well as multilayer and composite electrolyte membranes.

Liquid biofuels for solid oxide fuel cells: A review

In this paper the operation and performance of a high temperature solid oxide fuel cell (SOFC) stack on biomass syn-gas from a demonstration biomass gasification combined heat and power (CHP) plant is investigated. The objective of this work is to develop a computer simulation model of a biomass-SOFC CHP system, flexible enough for use in industry, capable of predicting system performance under various operating conditions and using diverse fuels. The biomass gasifier is of the dual fluidised bed (DFB) type with steam as the gasifying agent and is operated at atmospheric pressure. The tubular SOFC configuration, developed by Siemens Power Generation Inc (SPGI), is selected. It is considered to be the most advanced design and is approaching commercialisation. The SOFC stack model, developed using the chemical process flowsheet simulator Aspen Plus, is of equilibrium type and is based on Gibbs free energy minimisation. The SOFC model performs heat and mass balances and considers the ohmic, activation and concentration losses for the voltage calculation. Data available in the literature on the SPGI SOFC operating on natural gas is used to validate the model. The system model predicts thermodynamic condition and composition of all internal flow streams, the heat generated by the SOFC stack, voltage (V), current (I) and efficiency. Operating parameters are varied over a wide range, parameters such as fuel utilisation factor (Uf), current density (j) and steam to carbon ratio (STCR) have significant influence. The results indicate that there must be a trade-off between voltage, efficiency and power with respect to j and the SOFC stack should be operated at low STCR and high Uf, within certain limits. SOFC stack operation on biomass syn-gas is compared to operation on natural gas and as expected there is a drop in performance, which is attributed to increased input fuel and air flow due to the lower quality of the fuel gas. The optimum realistic operating conditions with regard to SOFC stack performance are identified. High electrical efficiencies are predicted making these systems very attractive for CHP applications.