Solid Oxide Fuel Cell Power Plant Research Articles

Solid Oxide Cell Technology for Power Generation, Hydrogen Production and Energy Storage

The progress in maturation of solid oxide cell technology has led to development of new applications that would explode its presence in many areas, far beyond power generation. The solid oxide cell technology has the potential to have a formidable presence in production of hydrogen and, eventually, long duration storage of electric power.Following the successful operation of a 200 kW SOFC system under a project supported by Department Energy/NETL, FuelCell Energy (FCE) is pursing the development of SOC based plant configurations from subMW to electrolysis, and further, to energy storage.Multi-faceted evolution of the technology has been underway since the earlier demonstration of SOFC power plant. FCE has developed state-of-the-art lightweight Compact SOFC Architecture (CSA) stacks that are packaged in compact modules with adaptability for use in a variety of configurations and capacities. The CSA stacks can operate directly on a variety of fuels - natural gas, biogas, and hydrogen- without any modification. FCE’s existing fuel cell pilot manufacturing line for CSA cells and stacks includes robotics and automation such as cell screen printing, interconnect subassembly, seal application, QC, as well as stack assembly and conditioning. Via a design for manufacturing approach, as well as focus on minimization of raw material, recent detailed cost studies show a path to low factory stack production cost (<100/kW) at high volumes (1,000 MW/year). The large market existing for power generation equipment, in the range of 200-300kW, is a significant driver for development of high efficiency SOFC products that would easily cater to early-adopters prior to wide-spread acceptance. The accelerated interest in hydrogen as the fuel source will widen the market for SOFC deployment even more. Under a project supported by DOE, FCE is working on design of MW-class SOFC power plants as future extension of the subMW SOFC plant products.FCE is developing a first-of-a-kind 250kW Solid Oxide Electrolyzer Cell (SOEC) system with the hydrogen production capacity of 150kg/day. The overarching goal of the project is to verify that the integration of Solid Oxide Electrolysis Cell (SOEC) systems within nuclear plants will maximize the plants’ efficiency and flexibility and will increase their revenue by switching between electric power generation and hydrogen production. Hybrid nuclear-hydrogen production operations are expected to help the present and future nuclear plants diversify and increase profitability.The 250kW SOEC system is planned to be demonstrated and operated at Idaho National Laboratory (INL). The project will culminate in verification and validation testing and solidify SOEC technology as a low cost and efficient means for hydrogen production integrated within the nuclear power plant environment. The SOEC system will be interfaced with a High-Level front-end Controller (HLC) simulating communications from a nuclear plant and the electric grid. The HLC will determine an optimized hydrogen production schedule to meet all contractual obligations, while maximizing revenue from the integrated operations.FCE is also developing energy storage systems based on the Company’s Solid Oxide Fuel Cell (SOFC) technology. Reversible Solid Oxide Fuel Cell (RSOFC) technology is suitable for medium to long-duration energy storage achieving high round trip electric efficiencies near 70% (electricity-in to electricity-out) at an expected levelized cycle cost of ≤ $0.05 / kWh-cycle.FCE is currently conducting operational tests of an RSOFC prototype system to accomplish the of validation and verification of engineering/pilot-scale RSOFC technology in a relevant environment. A bread-board pilot demonstration system is being utilized to verify cell materials and stack design improvements as well as to validate power electronics and system control strategies that will be utilized for optimization of efficiency, transient response, and lifetime characteristics.

Performance Assessment of the Heat Recovery System of a 12 MW SOFC-Based Generator on Board a Cruise Ship through a 0D Model

The present work considers a 12 MW Solid Oxide Fuel Cell (SOFC) power plant integrated with a heat recovery system installed on board an LNG-fuelled cruise ship of about 175,000 gross tonnes and 345 m in length. The SOFC plant is fed by LNG and generates electrical power within an integrated power system configuration; additionally, it provides part of the thermal energy demand. A zero-dimensional (0D) Aspen Plus model has been built-up to simulate the SOFC power plant and to assess the performances of the proposed heat recovery system. The model has been validated by comparing the results obtained with data from the literature and commercial SOFC modules. The integrated system has been optimized in order to maximize steam production since it is the most requested thermal source on board. The main design outcome is that the steam produced is made by the recovered water from the SOFC exhaust by about 50–60%, thus reducing the onboard water storage or production. Additionally, results indicate that such an integrated system could save up to about 14.4% of LNG.

Internal Conversion in the Membrane-Supported SOFC

Steam reforming is a highly endothermic process of hydrogen or synthesis gas production from methane or other hydrocarbon fuels. Metals from group VIII of the Periodic table are catalysts for steam reforming; nickel is the most commonly used among them. Platinoid catalysts: rhodium, ruthenium and palladium are more active, but less frequently used due to their high cost. Nickel catalysts have proven their effectiveness due to the simplicity of their production, stability and chemical activity [1]. It is known that the heat required for the endothermic process of steam reforming can be provided by an electrochemical reaction in a stack of high-temperature solid oxide fuel cells [2,3]. In the case of internal reforming, the process of steam reforming of methane proceeds directly at the anode of a solid oxide fuel cell (SOFC) due to the high operating temperature and the presence of nickel in the composition [4,5]. The advantage of internal reforming is not only thermal, but also chemical integration of reforming agent and generator – the water vapor produced during the SOFC anodic electrochemical reaction can be used for reforming without the need for anode recycling organization. Also, the endothermic effect of steam reforming can be used to control the temperature of the stack. As it was shown in work [6] feeding of the mixture containing 30% of methane into the electrolyte-supported SOFC stack to the input leads to 22% of methane observed at the output. Thus, based on the literature data, we cannot expect a high conversion rate in the process of internal methane reforming. Therefore, studies of the internal methane conversion process were carried out on an experimental short stack of two 100x100 mm electrolyte-supported SOFCs. A whole series of experiments were carried out on H2+CH4+H2O mixtures with different sets of conditions – an increase in the ratio and consumption of methane, and then a decrease in temperature. The ranges of methane consumption and other key parameters of the experiment were based on the results of the analysis of available literature data on the experimental study of the kinetics of methane steam conversion on cermet SOFC anodes. Prior to the experiments, discussions were mainly caused by the probable carbon deposition at the anodes and the associated rapid performance degradation, the capabilities of the anodes for internal conversion were upper estimated according to the fuel consumption of SOFCs, so it was assumed that, at worst case, the conversion provides only its internal consumption needs. The results of experiments at an operating temperature of 850°C showed that the kinetics of internal conversion was largely underestimated. The assembly of two SOFCs converts methane up to concentrations not exceeding the calculated equilibrium ones, up to the maximum available flow rate on the equipment used – 187 ml/min – even without current passing. This fuel flow rate is capable of providing a current of up to 53 A, while the rated operating current of these SOFCs is about 20 A, up to 30 A on methane-rich fuel. This means, that the conversion capabilities of SOFC even in the absence of current are at least twice higher than their own needs. The current further stimulates the conversion by generating additional steam. In order to discover the limits of conversion capabilities, the temperature was lowered to 750°C. The result of the conversion at maximum flow rate proceeding up to equilibrium values was repeated. Thus, in the course of the experiments, it was not possible to obtain methane concentrations in the exhaust gas that significantly exceed the equilibrium ones. This result turned out to be extremely unexpected and undoubtedly positive, since it demonstrates an extremely high potential of internal conversion and opens the way to a sharp decrease in the requirements for the degree of conversion of fuel supplied to SOFC, abandonment of a bulky fuel processor, reduction of costs for SOFC cooling and, thereby, an increase in efficiency and reducing the mass and dimensions of SOFC power plants. This work was carried out with financial support from the Russian Scientific Foundation, grant no. 17-79-30071.

Методика расчёта режимов электрохимических энергоустановок с твёрдооксидным электролитом

Fuel cell power plants (FCPPs) are considered as one of the key future energy technologies. Along with machine-based power generation technologies (gas turbine units, diesel generator sets, combined cycle plants, Stirling engine plants, etc.), FCPPs can also be used in cogeneration plants for combined generation of electricity and heat. Fuel cells can find use in Russia for distributed electricity generation, including autonomous power supply to consumers based on the use of pipeline and liquefied natural gas, liquefied hydrocarbon gases, as well as renewable energy sources, especially in cogeneration modes of operation. A procedure for calculating the operation modes of a fuel cell power plant is proposed, assuming that the combustible elements contained in the fuel are fully oxidized, transforming into inert gases. The flowrates of products before and after the reactions at the FCPP inlet and outlet are determined by using the material balance method. The material and energy balances of fuel cells are calculated taking as an example an SOFC-type FCPP with a solid oxide electrolyte for direct internal conversion of methane and also during operation on pure hydrogen in a combination with a windmill. The possibility of storing energy in hydrogen storage devices is estimated. In view of their highest electric and cogeneration efficiencies, solid oxide FCPPs using natural gas (methane) as fuel (reducing agent) and atmospheric oxygen (air) as oxidizer are considered to be promising ones for cogeneration-type electric power sources. The required methane and air flowrates are determined assuming that the oxygen content in air is equal to 21%. The potential fuel capacity was calculated for the installation’s electric power equal to 15 MW and its heat load in the cogeneration mode equal to 6 MW. This thermal power is removed from the FCPP fuel cell unit through a delivery water heater for its further use. The hydrogen storage device can be made as a gas tank or a gas cylinder. Obviously, pressurized gaseous hydrogen storing systems are simple and do not require special equipment for retrieving gas from the storage.

Renewed sanitation technology: A highly efficient faecal-sludge gasification–solid oxide fuel cell power plant

Sustainable development goals for 2030 aim at the extensive reduction of the global sanitation breach; this might be achieved by renewed sanitation technologies and while providing sanitation recover valuable products such as energy. Consequently, this work presents a gasification–solid oxide fuel cell (SOFC) power plant that was configured for high-efficiency energy recovery from faecal sludge. The main limitations of faecal sludge gasification are the production of impurities, such as tar, and the high energy requirements for both the endothermic gasification process and removing the high moisture content in the feedstock. However, results from this work indicate that a superheated steam dryer combined with an indirectly heated multistage gasifier and a gas-cleaning unit can overcome the mentioned limitations. The external heat for the gasifier is supplied by the process heat available and a microwave plasma torch, and there is sufficient heat to drive a micro steam turbine. Thermodynamic calculations indicated that the plant could reach a net electrical efficiency of the order of 65%. As a result, a gasification–SOFC power plant is more suitable for energy recovery than any other process such as biochar production by pyrolysis; hence, it might become a technology that is financially feasible and can be used globally for sanitation purposes.

SOFC power plant with circulating fluidized bed gasifier

Coal is used all over the world to meet the energy needs of industry and housing and communal services. The main requirements of coal using are environmental safety and efficiency. Increasing these parameters can be realized with the combination of a gasifier and fuel cells. The paper includes a variant of the thermal scheme of the power plant, which uses coal as a fuel, with its further gasification and conversion into electrical energy in a solid oxide fuel cell (SOFC) stacks. The developed scheme differs from traditional circuits by using a gasifier with an inhibited circulating fluidized bed (ICFB). In addition, the anode-off gases are used in the combustion chamber of the gasifier to maintain endothermic gasification reactions. This technologies combination allows increasing the energy system efficiency. The paper also includes the results of tests of an ICFB gasifier and analyze the available electrical power of the SOFC stacks. Analysis dependence EMF from the produced generator gas composition showed no significant effect on the available power of the electrochemical generator. Developed scheme allow excluding from the process the gas cleaning from tar after gasifier, which allowed to increase the efficiency and reduce the metal capacity of the developed equipment.

Multi-objective design and operation of Solid Oxide Fuel Cell (SOFC) Triple Combined-cycle Power Generation systems: Integrating energy efficiency and operational safety

Energy efficiency is one of the main pathways for energy security and environmental protection. In fact, the International Energy Agency asserts that without energy efficiency, 70% of targeted emission reductions are not achievable. Despite this clarity, enhancing the energy efficiency introduce significant challenge toward process operation. The reason is that the methods applied for energy-saving pose the process operation at the intersection of safety constraints. The present research aims at uncovering the trade-off between safe operation and energy efficiency; an optimization framework is developed that ensures process safety and simultaneously optimizes energy-efficiency, quantified in economic terms. The developed optimization framework is demonstrated for a solid oxide fuel cell (SOFC) power generation system. The significance of this industrial application is that SOFC power plants apply a highly degree of process integration resulting in very narrow operating windows. However, they are subject to significant uncertainties in power demand. The results demonstrate a strong trade-off between the competing objectives. It was observed that highly energy-efficient designs feature a very narrow operating window and limited flexibility. For instance, expanding the safe operating window by 100% will incur almost 47% more annualized costs. Establishing such a trade-off is essential for realizing energy-saving.

Application of a two-level rolling horizon optimization scheme to a solid-oxide fuel cell and compressed air energy storage plant for the optimal supply of zero-emissions peaking power

We present a new two-level rolling horizon optimization framework applied to a zero-emissions coal-fueled solid-oxide fuel cell power plant with compressed air energy storage for peaking applications. Simulations are performed where the scaled hourly demand for the year 2014 from the Ontario, Canada market is met as closely as possible. It was found that the proposed two-level strategy, by slowly adjusting the SOFC stack power upstream of the storage section, can improve load-following performance by 86% compared to the single-level optimization method proposed previously. A performance analysis indicates that the proposed approach uses the available storage volume to almost its maximum potential, with little improvement possible without changing the system itself. Further improvement to load-following is possible by increasing storage volumes, but with diminishing returns. Using an economically-focused objective function can improve annual revenue generation by as much as 6.5%, but not without a significant drop-off in load-following performance.

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

A SOFC (solid oxide fuel cell) system integrated with an ethanol steam reforming unit is evaluated using exergoeconomic analysis. The exergy destruction cost, total production cost, relative cost difference, exergoeconomic factor and thermoeconomic cost of electricity are studied. The TCOE (thermoeconomic cost of electricity) is compared with electricity cost from similar processes and fuels. A sensitivity analysis has been carried out in order to have a good insight into SOFC power plant performance, focusing on ethanol steam reformer temperature (823 < TESR < 973 K), SOFC stack unit cost (1500–400 $ kW) and fuel price (0.002 < ethanol price < 0.01 $ MJ−1). Results suggest that the SOFC unit constitutes the most important component in the process. A reduction in the investment cost and in exergy destruction within the stack may reduce the total production cost (Ctot), total investment costs (Ztot) and exergy destruction cost (CD) by 18%, 73% and 19% respectively, as well as the electricity cost (TCOE) by 21%. The higher production cost corresponds to higher ethanol price, due to the specific exergy cost of streams. In the best scenario, the electricity cost using ethanol as feedstock reaches 0.04 $ kWh−1, which is comparable and competitive with natural gas (0.06 $ kWh−1) using SOFC technology.

Control and Operation Of a Solid Oxide Fuel-Cell Power Plant In an Isolated System

Control and Operation Of a Solid Oxide Fuel-Cell Power Plant In an Isolated System

Design and Balance-of-Plant of a Demonstration Plant With a Solid Oxide Fuel Cell Fed by Biogas From Waste-Water and Exhaust Carbon Recycling for Algae Growth

The design and balance-of-plant of a novel anaerobic digestion (AD) biogas solid oxide fuel cell (SOFC) plant is assessed. Biogas from waste-water treatment plant is the fuel feeding the SOFC system. Simultaneous multigeneration of electricity, heat and a fuel (algae, in our case) via exhaust carbon recycling is accomplished in the proposed plant configuration. CO2 capture from the SOFC anode exhaust is carried out through an oxy-combustion reactor that completes the oxidation of spent fuel still available downstream of the fuel cell. The captured CO2, after water condensation, is thus fed to an array of photo-bioreactors where C biofixation in algae is achieved. The design of the main plant sections, including the gas cleaning unit, fuel processor, SOFC “hot-box,” oxy-combustor, CO2/H2O condensation unit and photo-bioreactors, is provided. A system analysis of a full-scale version of the biogas SOFC power plant with optimized heat integration is finally analyzed to fully understand the potential of the proposed integrated energy system. An overall electrical efficiency exceeding 52% (LHV basis) was calculated. Sensitivity analyses have been carried out in order to study the influence of fuel utilization, internal reforming, biogas composition and steam-to-carbon ratio on both SOFC and overall plant performance.

Modelling a grid-connected SOFC power plant into power systems for small-signal stability analysis and control

SUMMARY This paper presents a systematic procedure to establish mathematical models of a solid oxide fuel cell (SOFC) power plant integrated in a multi-machine power system for power system small-signal stability analysis and control. First, the paper describes comprehensively how a grid-connected SOFC power plant can be modeled into a multi-machine power system. The model established can be used for power system small-signal stability analysis. Second, a localized model of the grid-connected SOFC power plant is proposed. This localized model can be used for the design of a power system stabilizer attached to the SOFC power plant to improve power system small-signal stability. The design proposed is simple because establishment of the localized model does not need to obtain and validate the information of the entire multi-machine power system. In the paper, an example four-machine power system integrated with a SOFC power plant is presented. The example demonstrates the effectiveness of the stabilizer designed by the proposed method based on the localized model, which is confirmed by the modal computation and non-linear simulation. Copyright © 2012 John Wiley & Sons, Ltd.

Effect of grid-connected solid oxide fuel cell power generation on power systems small-signal stability

This study investigates one of the most fundamental issues of integrating fuel cell (FC) generation into power systems – its effect on power system small-signal stability when it operates jointly with conventional power generation. The study first presents a comprehensive mathematical model of the solid oxide fuel cell (SOFC) power plant integrated with the single-machine infinite-bus power system. Based on the model, conventional damping torque analysis is carried out to study the effect of SOFC power generation on power system small-signal stability. The analysis concludes that system small-signal stability can be affected either positively or negatively by the SOFC power plant when system operating conditions change. Two examples of power systems with gird-connected SOFC power plants are presented. Small-signal stability of the first example of single-machine power system was examined when the power system operated at different load conditions and levels of mixtures of conventional and FC power generation. The second example is a four-machine two-area power system where the power supplied by the gird-connected SOFC power plant is variable. Results of simulation using full non-linear model of the power systems and the SOFC power plants are given. All the results from the example power systems confirm and further demonstrate the analysis presented and conclusions obtained.

SOFC Module Material Development at Fuel Cell Energy

FuelCell Energy (FCE) is engaged in the development of Solid Oxide Fuel Cell (SOFC) power plants under DOE's Solid State Conversion Alliance (SECA) Coal-Based Program. The ultimate goal of the project is to develop Multi-MW SOFC power plants suitable for integration with coal gasifiers and cable of capturing >90% of carbon in coal syngas. FCE is currently utilizing the SOFC stacks developed by Versa Power Systems (VPS) as building blocks for development of the sub-MW and MW scale fuel cell modules. The design of an SOFC stack module is comprised of an assembly of stack blocks to provide targeted dc power. Advanced materials are being developed for gas seals between stacks, mechanical and electrical connections of stack blocks, and thermal as well as electrical insulation within modules. This paper is a review of the progress in development of conducting module gasket (CMG), non-conducting gasket (PH) and electrical contacting paste materials.

Fuzzy neural control of a hybrid fuel cell/battery distributed power generation system

An innovative control strategy is proposed of hybrid distributed generation (HDG) systems, including solid oxide fuel cell (SOFC) as the main energy source and battery energy storage as the auxiliary power source. The overall configuration of the HDG system is given, and dynamic models for the SOFC power plant, battery bank and its power electronic interfacing are briefly described, and controller design methodologies for the power conditioning units and fuel cell to control the power flow from the hybrid power plant to the utility grid are presented. To distribute the power between power sources, the fuzzy switching controller has been developed. Then, a Lyapunov based-neuro fuzzy algorithm is presented for designing the controllers of fuel cell power plant, DC/DC and DC/AC converters; to regulate the input fuel flow and meet a desirable output power demand. Simulation results are given to show the overall system performance including load-following and power management of the system.

Nonlinear model predictive control of SOFC based on a Hammerstein model

To protect solid oxide fuel cell (SOFC) stack and meet the voltage demand of DC type loads, two control loops are designed for controlling fuel utilization and output voltage, respectively. A Hammerstein model of the SOFC is first presented for developing effective control strategies, in which the nonlinear static part is approximated by a radial basis function neural network (RBFNN) and the linear dynamic part is modeled by an autoregressive with exogenous input (ARX) model. As we know, the output voltage of the SOFC changes with load variations. After a primary control loop is designed to keep the fuel utilization as a steady-state constant, a nonlinear model predictive control (MPC) based on the Hammerstein model is developed to control the output voltage of the SOFC. The performance of the MPC controller is compared with that of the PI controller developed in [Y.H. Li, S.S. Choi, S. Rajakaruna, An analysis of the control and operation of a solid oxide fuel-cell power plant in an isolated system, IEEE Trans. Energy Convers. 20 (2) (2005) 381–387]. Simulation results demonstrate the potential of the proposed Hammerstein model for application to the control of the SOFC, while the excellence of the nonlinear MPC controller for voltage control of the SOFC is proved.

SECA Coal-Based Multi-MW SOFC Power Plant Development

Coal is one of the primary sources of electric power generation in the world. FuelCell Energy is developing a cost-competitive, highly efficient, multi-MW solid oxide fuel cell (SOFC) power system using coal-derived synthesis gas. Design of the coal-based SOFC plant is to include greater than 90 percent CO2 separation from the coal-derived syngas as a prerequisite to carbon sequestration. Focus of the coal-based SOFC power plant development is on SOFC cell and stack scale-up and optimization, stack manufacturing capacity development, and MW class module engineering design and development. Simultaneously, power plant engineering is being conducted for design of a baseline multi-MW (~400 MWe) power plant with near zero emissions. Currently, scale-up of SOFC cell area and stack size (number of cells) and fuel cell improvements for both performance and longevity in operation are being implemented in the core fuel cell technology. Also, preliminary engineering design and analysis for a 5 MW proof-of-concept SOFC power plant system is being conducted.

Static VAr compensator based reactive power management for SOFC power plants

This paper reports the dynamic behavior of a solid-oxide fuel cell (SOFC) power plant including a battery bank and a static Volt–Ampere-reactive power compensator system (static VAr compensator or SVC) for active and reactive power flow controllers. First, the necessities of the reactive power management as well as the load following capability of distributed generation (DG) systems are emphasized. Then, a decoupled active and reactive power management control strategies are described. In the proposed system, while the active power management is achieved using the SOFC power plant with the aid of the battery; the reactive power management is achieved using an SVC system which totally prevents the reactive loading interactions with the dc bus. The simulation results of the integrated overall system indicate the viability of the proposed management strategies.

Efficiency analyses of solid oxide fuel cell power plant systems

In this paper, the effects of fuel utilization, air-to-fuel ratio (A/F) and pre-reforming rate on the plant efficiency, including heat and electric efficiencies, of sequential-type and fully recuperative-type of solid oxide fuel cell (SOFC) power plant are studied with the GCTool software developed by American Argonne National Laboratory (ANL). Methane is chosen as fuel, air as oxidant, and the pressure drop due to stream transported in the duct and components is considered in both types of power plant systems. A full analysis of the state at each node of the system is conducted. The results reveal that the A/F factor is the most important factor on system efficiency, and the pre-reforming rate of fuel is insignificant to the efficiency, but it can be used as an auxiliary tuner for the operating temperature of the solid oxide fuel cells in addition to A/F value. Under the same settings, overall plant efficiency is higher in the sequential type than in the fully recuperative type of SOFC power plants. On the other hand, for electric efficiency, the opposite trend is observed.

Solid Oxide Fuel Cell System Development in VTT

The Finnish solid oxide fuel cell (SOFC) project (FINSOFC) was initiated in 2002 as a five-year project. It forms the core of the publicly funded SOFC research in Finland. The purpose of the project is to support the industry in its development of SOFC systems and components and other possible SOFC-based business to be created in the future. The project is coordinated by the VTT Technical Research Centre of Finland in cooperation with universities and industrial enterprises. The project is executed in close cooperation with several European partners both bilaterally and within Real-SOFC. The focus is to construct and run a natural gas-fueled 5kWe SOFC power plant demonstration connected to heat and electricity grids. The power plant demonstration contains a stack and all BOP components from fuel processing to power conditioning and grid connections. The aim is also to thoroughly understand the behavior of the system. The subprojects needed to do this are (i) fuel processing, (ii) testing of fuel cells and stacks, (iii) construction of a 5kWe power station demonstration, and (iv) system modeling.