Process Analysis and Evaluation of Exergy Loss in Solid Oxide Fuel Cell

Comparison study on different SOFC hybrid systems with zero-CO2 emission

Energy analysis and techno-economic assessment of a co-gasification of woody biomass and animal manure, solid oxide fuel cells and micro gas turbine hybrid system

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 investigated the performance of a bioethanol-fed Solid Oxide Fuel Cell (SOFC) system integrated with a distillation column (SOFC-D). Excess heat from the SOFC system was directly utilized in the distillation column where bioethanol (5 mol%) was purified to a desired concentration before feeding to the SOFC system consisting of an air heater, an ethanol/water heater, a reformer, an SOFC preheater, an SOFC stack and an afterburner. The SOFC-D system was simulated using Aspen PlusTM for the distillation portion and MatlabTM for the SOFC portion. The effects of operating parameters; i.e., ethanol concentration, ethanol recovery, fuel utilization and operating voltage on the performance and energy involved in the SOFC-D system (e.g. distillation energy: QD and the net exothermic heat of the SOFC system: QSOFC,Net) were examined. In addition, the performance of the SOFC-D system at the energy sufficient point where QD = QSOFC,Net was considered. The integration of the distillation column with the SOFC system was found to offer superior SOFC performance. The ethanol recovery and fuel utilization significantly influenced the overall electrical efficiency and power density. Quite low performances are obtained when one operated the SOFC-D without an external heat source. The maximum overall efficiency and power density (~35% and 0.22 W cm-2) occured at an ethanol recovery of 80% and Uf of 90%.

Life Cycle Assessment and Life Cycle Costing of a SOFC system for distributed power generation

Recent developments in control and integration of solid oxide fuel cells: From stack to system

This paper addresses how the power and temperature are controlled in a biomass gas fueled solid oxide fuel cell (SOFC) and micro gas turbine (MGT) hybrid system. A SOFC and MGT dynamic model are developed and used to simulate the hybrid system performance operating on biomass gas. The transient behavior of both the SOFC and MGT are discussed in detail. An unstable power output is observed when the system is fed biomass gas. This instability is due to the fluctuation of gas composition in the fuel. A specially designed fuel controller succeeded not only in allowing the hybrid system to follow a step change of power demand from 32 to 35 kW, but also stably maintained the system power output at 35 kW. In addition to power control, fuel cell temperature is controlled by introduction and use of a bypass valve around the recuperator. By releasing excess heat to the exhaust, the bypass valve provided the control means to avoid the self-exciting behavior of system temperature and stabilized the temperature of SOFC at 850 °C.

Field test results of residential SOFC co-generation system at Tokyo Gas T. Ishikawa, S. Yamashita Product Development Dept., Tokyo Gas Lo., LTD., Tokyo, JAPAN We are developing residential SOFC co-generation system in order to commercialize it. One of our activities is to operate SOFC systems in field tests to make sure effects of installation and find technical issues. The detail is as below. A serious accident at nuclear power plants in Fukushima which was triggered by a huge earthquake on 11th March 2011 forces drastic re-formulation of Japan’s energy policy. In a series of discussions on the new energy policy, promoted use of distributed power generation is demanded more than ever as one of the main power systems, with extremely strong expectations for the fuel cell co-generation system. Tokyo Gas has been conducting research and development of solid oxide fuel cell (SOFC) which is expected to achieve the highest efficiency among all distributed power systems. In parallel with it, to verify the applicability of the SOFC for residential use and to identify technical challenges of SOFC, we have started field tests of SOFC systems of multiple manufacturers in the “Solid Oxide Fuel Cell (SOFC) demonstrative research project” with financial support from NEDO (Figure 1) [1][2]. We have installed a total of 23 units of four manufacturers in the field test of over four years (from 2007 to 2010), of which 14 units are still under operation as of April 30, 2012 (table 1). And the operating time has reached 18,600 hours at the longest, with 268,500 hours in total of 23 units. We have acquired the knowledge as shown below during the field tests conducted at general residences which we selected to reflect a variety of electrical and hot water demands (Figure 2). (1) Residential SOFC co-generation system contributes to the saving the preliminary energy consumptions and CO2 emissions by households in Japan (Figure 3, Figure 4). (2) SOFC system shows high electricity efficiency exceeding 45%LHV, and the transition of efficiency indicates that the durability of SOFC system including cell stack is estimated to be almost practical use (Figure 5). (3) SOFC system shows high reliability because of its simple system configuration. We will report the detailed results of SOFC field tests based on the latest data. Acknowledgments Finally, we would like to express our appreciation to NEDO, as this report is prepared mainly based on the results of the project supported by NEDO. Figure 2 Residential Demand (/Month) References [1] Solid Oxide Fuel Cell demonstrative research project final report (2011) http://www.nef.or.jp/sofc/share/pdf/h22y.pdf [2] Y. KAWABATA, T.SEYAMA, T.SOBUE, International Gas Union Research Conference ( 2011 ) Development and Field Test of Residential SOFC Co-generation System with All-ceramics-segmented Cells

Performance analysis of methanol-fueled solid oxide fuel cell system incorporated with palladium membrane reactor

Solid Oxide Fuel Cells (SOFCs) offer the potential for compelling thermo-economic value propositions in wide range of stationary and transportation applications through their potential for high conversion efficiency and their inherent fuel flexibility. Furthermore, many of the core SOFC materials, component, and system technologies have tremendous potential in electrolysis applications where fuels or chemicals could be produced using renewable electricity. However, to date, the wide-spread commercialization of SOFC/SOEC systems has been hampered by their high cost and durability challenges.Fortunately, high temperature solid oxide-based energy conversion systems are well suited for integration with thermal-mechanical energy conversion systems in configurations that offer the potential for significant cost and thermodynamic performance synergies. Specifically, their integration with gas turbines or internal combustion engines offers the potential for ultra-high (>70%) efficiency at an attractive manufacturing cost (<$1/W). In these hybrid systems, engines or turbines are used to convert stack waste exergy to additional useful work resulting in higher overall efficiency and lower power-specific cost (e.g., $/kW) compared to SOFC-only systems.Furthermore, in the case of SOFC and gas turbine hybrid systems, the SOFC stacks are typically located downstream of the gas turbine compressor and are at elevated pressure—enabling increased Nernst potential and decreased overpotentials and thereby higher power density at constant voltage. This benefit translates into a significant power-specific stack cost reduction. Additionally, the gas turbine compressor and recuperator may serve as the SOFC stack blower and recuperator—yielding further cost synergies via the elimination of duplicative balance of plant components.In 2017, ARPA-E launched the INTEGRATE program to develop hybrid system concepts and enabling component technologies that if realized would result in 100kW-scale distributed generation systems with >70% fuel to electricity conversion efficiencies and system manufacturing costs of <$1/W. In the initial two-year Phase I portion of the program, nine teams developed a suite of hybrid system concepts. Given these concepts, the teams then proceeded to develop 1) durable SOFC stacks that are capable of operating at high (~4 bar) pressure, 2) high temperature (>600 °C) and low-cost heat exchangers, and 3) innovative control system approaches. In 2019, three of the original nine teams were selected to design, build and demonstrate 100kW-scale systems by 2023.In the interest of focusing limited financial resources on foundational development risks, while avoiding the weight, volume, and fuel flexibility challenges associated with transportation applications and mitigating the financial risks associated with adopting new technologies at utility (e.g., >100MW) scale, natural gas fueled distributed generation (DG) systems were selected as the initial INTEGRATE application target. These DG systems would offer a fuel to electric power conversion efficiency that is roughly double that of the fossil fueled portion of the US electric grid. Furthermore, as renewable fuels such as hydrogen, ammonia, and bio- or electro- derived hydrocarbons (e.g., renewable natural gas or synthetic kerosene) become available, these systems would be capable of operating on them with relatively minor fuel processing system adjustments.Moving beyond stationary DG applications, SOFC hybrid systems can leverage their fuel flexibility in the pursuit of a decarbonized of long-distance transportation sector—if the systems can be made both light and small enough. To this end, ARPA-E recently launched three programs that have taken on the challenge of developing ultra-efficient, yet compact and light weight carbon-neutral electrified propulsion systems for commercial aviation.One of these programs is focused on carbon-neutral fuel to electric power conversion sub-systems—Range Extenders for Electric Aviation with Low Carbon and High Efficiency (REEACH). In the two-year Phase 1 of this program, six of nine selected teams will develop SOFC/gas turbine/battery hybrid systems that are fueled with renewable natural gas or synthetic kerosene. Phase 1 focuses on system conceptual design and fuel conversion component risk reduction, while full system design and prototype demonstration of a sub-scale fuel-to-electric power conversion device using a carbon-neutral liquid fuel is planned for Phase 2.If the REEACH-envisioned systems are successfully developed, they would enable economically attractive all-electric commercial aircraft up to a narrow body airframe with dramatically reduced (ideally zero) net carbon emissions. Furthermore, INTEGRATE/REEACH hybrid system technologies would also have attractive value propositions in maritime, rail, or heavy-duty vehicle applications.

Solid oxide fuel cell (SOFC) systems are the most advanced power generation system with the highest thermal efficiency. The current trend of research on the SOFC systems is focused on multikilowatt scale systems, which require either internal reforming within the stack or a compact external reformer. Even if the internal reforming within the SOFC stack allows compact system configuration, it causes significant and complicated temperature gradients within the stack, due to endothermic reforming reactions and exothermic electrochemical reactions. As an alternative solution to the internal reforming, an external compact heat exchange reformer (CHER) is investigated in this work. The CHER is based on a typical plate-fin counterflow or coflow heat exchanger platform, and it can save space without causing large thermal stress and degradation to the SOFC stack (i.e., eventually reducing the overall system cost). In this work, a previously developed transient dynamic model of the CHER is validated by experiments. An experimental apparatus, which comprises the CHER, air heater, gas heater, steam generator, several mass flow controllers, and controller cabinet, was designed to investigate steady state reforming performance of the CHER for various hot air inlet temperatures (thermal energy source) and steam to carbon ratios (SCRs). The transient thermal dynamics of the CHER was also measured and compared with simulations when the CHER is used as a heat exchanger with inert gas. The measured transient dynamics of CHER matches very well with simulations, validating the heat transfer model within the CHER. The measured molar fractions of reformate gases at steady state also agree well with the simulations validating the used reaction kinetics. The transient CHER model can be easily integrated into a total integrated SOFC system, and the model can be also used for optimal design of similar CHERs and provides a guideline to select optimal operating conditions of the CHERs and the integrated SOFC system.

Numerical performance analysis of the solid oxide fuel cell for aviation hybrid power system

Cycle analysis of planar SOFC power generation with serial connection of low and high temperature SOFCs

Solid oxide fuel cells (SOFCs) are emerging as energy conversion devices for large-scale electrical power generation because of their high energy conversion efficiency, excellent ability to minimize air pollution, and high fuel flexibility. In this context, this critical review has focussed on the recent advancements in developing a suitable electrolyte for SOFCs which has been required for the commercialization of SOFC technology after emphasizing the literature from the prior studies. In particular, the significant developments in the field of solid oxide electrolytes for SOFCs, particularly zirconia- and ceria-based electrolytes, have been highlighted as important advancements toward the production of sustainable and clean energy. It has been reported that among various electrolyte materials, zirconia-based electrolytes have the potential to be utilized as the electrolyte in SOFC because of their high thermal stability, non-reducing nature, and high mechanical strength, along with acceptable oxygen ion conductivity. However, some studies have proved that the zirconia-based electrolytes are not suitable for low and intermediate-temperature working conditions because of their poor ionic conductivity to below 850°C. On the other hand, ceria-based electrolytes are being investigated at a rapid pace as electrolytes for intermediate and low-temperature SOFCs due to their higher oxygen ion conductivity with good electrode compatibility, especially at lower temperatures than stabilized zirconia. In addition, the most emerging advancements in electrolyte materials have demonstrated that the intermediate temperature SOFCs as next-generation energy conversion technology have great potential for innumerable prospective applications.

Compact subsystems are pivotal to aeronautical applications, inclusive of advanced energy concepts. Regarding size minimization, an “exergogravimetric” approach has recently begun that attempts an exergy-aided weight reduction of advanced energy systems (inclusive of fuel); and this is based upon the added design insights afforded by Second Law considerations. The chief rationale and objective are to leverage the advancements that exergoeconomics affords in the realm of cost-effective thermal system design to aid size-effective thermal system design. A conceptual solid oxide fuel cell (SOFC) system for long-duration unmanned aerial vehicle (UAV) applications has been initially modeled and simulated, inclusive of exergy analysis, and preliminary findings are discussed. Additionally, the concepts and methodologies can be extended to other advanced energy system technologies. There are project-specific and general milestones and conclusions drawn from the initial investigation. Specific to the project, a conceptual SOFC system simulation was completed via physics-based and literature-verified models along with structured language (i.e., MATLAB) numerical implementation. Specific component-level contributions to lost power potential and added mass were preliminarily resolved. Thermal exergy destruction and loss are predominant sources of unutilized specific power potential. Operational and physical degrees-of-freedom were explored, with the aid of exergy analysis, to resolve better design pathways. This included a counterintuitive preliminary finding that larger cell interconnects may facilitate smaller and more efficient system operation. Generally, exergy analyses allow a system design opportunity to gain higher resolution insights (i.e., to component- and spatial-extents) regarding inefficiencies throughout a thermal system, and this is afforded by the comprising blend of 1st Law and 2nd Law considerations. There is also an added means of accounting for 2nd Law effects. The traditional 2nd Law verification point of entropy generation being non-negative does not provide the same level of process analysis closure as does the related constraint that all processes have to account for exergy being stored, converted, destroyed or rejected through any defined control volume. This alternative 2nd Law perspective facilitates verification and validation of simulations.