Solid Oxide Fuel Cell Hybrid Research Articles

Simulation and exergy analysis of a hybrid Solid Oxide Fuel Cell (SOFC)–Gas Turbine System

The simulation and exergy analysis of a hybrid Solid Oxide Fuel Cell–Gas Turbine (SOFC–GT) power system are discussed in this paper. In the SOFC reactor model, it is assumed that only hydrogen participates in the electrochemical reaction and that the high temperature of the stack pushes the internal steam reforming reaction to completion; the unreacted gases are assumed to be fully oxidized in the combustor downstream of the SOFC stack. Compressors and GTs are modeled on the basis of their isentropic efficiency. As regards the heat exchangers and the heat recovery steam generator, all characterized by a tube-in-tube counterflow arrangement, the simulation is carried out using the thermal efficiency-NTU approach. Energy and exergy balances are performed not only for the whole plant but also for each component in order to evaluate the distribution of irreversibility and thermodynamic inefficiencies. Simulations are performed for different values of operating pressure, fuel utilization factor, fuel-to-air and steam-to-fuel ratios and current density. Results showed that, for a 1.5 MW system, an electrical efficiency close to 60% can be achieved using appropriate values of the most important design variables; in particular, the operating pressure and cell current density. When heat loss recovery is also taken into account, a global efficiency of about 70% is achieved.

Influences of The Type and Thickness of Electrolyte on Solid Oxide Fuel Cell Hybrid System Performance

This paper sets out the results of mathematical modeling and numerical simulations with regard to the influences of the type and thickness of electrolyte on Solid Oxide Fuel Cell Hybrid System (SOFC-HS) performance. A change of electrolyte materials can result in total hybrid system efficiency increasing from around 48% HHV (53% LHV) to about 65% HHV (72% LHV) in an environment where turbine inlet temperature and gas turbine subsystem pressure ratio remain unchanged. The governing equations of SOFC-HS modeling are given. An adequate simulator of the SOFC stack was made and described. Based on this simulator, a model of the 260kWe Siemens Westinghouse unit was built. The performance of this SOFC-HS with different electrolyte materials and thicknesses is shown, and some characteristics are given and described. The advantages and disadvantages of different electrolyte types from a hybrid system performance point of view are indicated.

Concept and system design for a ZEBRA battery–intermediate temperature solid oxide fuel cell hybrid vehicle

This paper explores the combination of a sodium–nickel chloride (ZEBRA) battery and an intermediate temperature solid oxide fuel cell (IT-SOFC) to form a hybrid power system that is intended for automotive applications. A range of vehicle types, drive cycles and fuels are investigated and compared in terms of their suitability for the pairing of this particular fuel cell and battery technology. In order to avoid the problem of stop–start cycles and load transients on the SOFC, a nominally ‘always-on’ strategy is investigated for the fuel cell. Sizing of the system is performed for each vehicle/drive cycle by adopting the minimum fuel cell power and battery energy in order to preserve charge neutrality over a 24 h period, while accommodating the requisite vehicle performance characteristics. Weight and volume estimates are reported for the hybrid system and opportunities for efficiency improvement brought about by synergistic operation of the fuel cell and the battery are discussed.

Project ABSOLUTE: A ZEBRA Battery/Intermediate Temperature Solid Oxide Fuel Cell Hybrid for Automotive Applications

Project ABSOLUTE (advanced battery solid oxide fuel cell linked unit to maximize efficiency), aims to combine a sodium-nickel chloride battery and an intermediate temperature solid oxide fuel cell (IT-SOFC) to form an all-electric hybrid package that surpasses the efficiency and performance of a purely fuel cell driven vehicle, as well as extending the range of a purely battery driven electric vehicle. This paper discusses the project background, the ABSOLUTE hybrid concept, the methodology adopted, the vehicle types and drive cycles that best suit the hybrid and system control considerations. Results from a battery and IT-SOFC system model are presented.

Influence of the anodic recirculation transient behaviour on the SOFC hybrid system performance

This paper addresses the off-design and transient response of a high efficiency hybrid system based on the coupling of a recuperated micro-gas turbine (mGT) with a tubular solid oxide fuel cell (SOFC) reactor. The work focuses on the anodic side where an ejector exploits the pressure energy of the fuel to recirculate part of the exhaust gas, in order to maintain a proper value for the steam-to-carbon ratio (STCR) and to support the reforming reactions. Two different stand-alone time-dependent ejector models are presented and validated against experimental data. Then, the most suitable model for cycle simulations, in term of calculation time, has been employed for the transient analysis of the entire hybrid system. The SOFC hybrid system transient behaviour is presented and discussed at several operating conditions from an electrochemical, fluid dynamic and thermal point of view.

Characterization and quantification of uncertainty in solid oxide fuel cell hybrid power plants

Distributed power generation is one of the most powerful applications of fuel cell technology. Several types of configurations have been hypothesized and tested for these kinds of applications at the conceptual level, but hybrid power plants are one of the most efficient. These are designs that combine the fuel cell cycle with other thermodynamic cycles to provide higher efficiency. The power plant in focus is the high pressure (HP)–low pressure (LP) solid oxide fuel cells (SOFC)/steam turbine (ST)/gas turbine (GT) configuration which is a part of the vision-21 program, which is a new approach, the U.S. Department of Energy's (DOE's) Office of Fossil Energy has begun, for developing 21st century energy plants that would have virtually no environmental impact. The overall goal is to effectively eliminate—at competitive costs—environmental concerns associated with the use of fossil fuels, for producing electricity and transportation fuels. In this design, coal is gasified in an entrained bed gasifier and the syn-gas produced is cleaned in a transport bed desulfurizer and passed over to cascaded SOFC modules (at two pressure levels). This module is integrated with a reheat GT cycle. The heat of the exhaust from the GT cycle is used to convert water to steam, which is eventually used in a steam bottoming cycle. Since this hybrid technology is new and futuristic, the system level models used for predicting the fuel cells’ performance and for other modules like the desulfurizer have significant uncertainties in them. Also, the performance curves of the SOFC would differ depending on the materials used for the anode, cathode and electrolyte. The accurate characterization and quantification of these uncertainties is crucial for the validity of the model predictions and hence is the main focus of this paper. This work performs a two-level uncertainty analysis of the fuel cell module: uncertainty associated with (1) model and (2) material used for anode, cathode and electrolytes. Following that the paper deals with the uncertainty analysis of the desulfurization reaction module based in particular on the activation energy and frequency factors for different sorbents used. This paper lays the basis for two analyses: (1) the effect of uncertainties on the trade-off surface obtained through a multi-objective optimization framework; (2) development of the “value of research” framework which is concerned with analyzing the trade-offs between allocation of resources for the reduction of uncertainties and benefits accrued to the objectives through this reduction [K. Subramanyan, U. Diwekar, The ‘value of research’ methodology applied to the solid oxide fuel cell/steam turbine/gas turbine hybrid power plant design, Ind. Eng. Chem. Res., submitted for publication].

04/02808 Probabilistic analysis of a solid-oxide fuel-cell based hybrid gas-turbine system: Gorla, R. S. R. Applied Energy, 2004, 78, (1), 63–74

Two, simple, solid-oxide fuel-cell (SOFC) power systems fed by hydrogen and methane, respectively, are examined. While other models available in the literatures focus on complicated hybrid SOFC and gas-turbine (GT) power systems, this study focuses on simple SOFC power systems with detailed thermodynamic modeling of the SOFC. All performance-related parameters of the fuel-cell such as respective resistivity of the components, anode and cathode exchange current density, limiting current density, flow diffusivity, etc. are all expressed as a function of temperature, while the flow through of each nodes of the system is described as a function of thermodynamic state. Full analysis of the energy and exergy at each node of the system is conducted and their respective values are normalized by the lower heating value (LHV) of the fuel and its chemical exergy, respectively. Thus, the normalized electrical energy outputs directly indicate the first law and second law efficiencies, respectively, of the fuel-cell power systems.

Novel concepts for CO 2 capture

This paper describes the possibilities for power generation with CO 2 capture using envisaged key technologies: gas turbines, membranes and solid oxide fuel cells (SOFCs). First, the underlying programs in the Netherlands and at ECN are introduced. Then the key technologies are introduced, and concepts using these technologies are discussed. A literature overview of systems for power generation with fuel cells in combination with CO 2 capture is presented. Then a novel concept is introduced. This concept uses a water gas shift membrane reactor to convert the CO and H 2 in the SOFC anode off-gas to gain a CO 2 rich stream, which can be used for sequestration without elaborate treatment. Several implementation schemes of the technique are discussed such as atmospheric systems and hybrid SOFC–GT systems.

Ejector performance influence on a solid oxide fuel cell anodic recirculation system

This work deals with the design and off-design performance evaluation of an anodic recirculation system based on ejector technology for solid oxide fuel cell hybrid applications. The analysis presented here has been divided into three parts: (i) ejector design taking into account all the thermodynamic, fluid dynamic and chemical constraints, such as steam to carbon ratio (two ejector geometries have been considered: constant area mixing section, constant pressure mixing section); (ii) stand-alone ejector design and off-design performance analysis; (iii) influence on the whole hybrid system—SOFC, reformer, anode recirculation-design and off-design performance of the ejector primary flow conditions (hybrid system part-load conditions).

Integrated model framework for the evaluation of an SOFC/GT system as a centralized power source

New power generation technologies are expected to reduce various environmental impacts of providing electricity to urban regions for some investment cost. Determining which power generation technologies are most suitable for meeting the demand of a particular region requires analysis of tradeoffs between costs and environmental impacts. Models simulating different power generation technologies can help quantify these tradeoffs. An Internet-based modelling infrastructure called DOME (distributed object-based modelling environment) provides a flexible mechanism to create integrated models from independent simulation models for different power generation technologies. As new technologies appear, corresponding simulation models can readily be added to the integrated model. DOME was used to combine a simulation model for hybrid SOFC (solid oxide fuel cell) and gas turbine system with a power generation capacity and dispatch optimization model. The integrated models were used to evaluate the effectiveness of the system as a centralized power source for meeting the power demand in Japan. Evaluation results indicate that a hybrid system using micro-tube SOFC may reduce CO2 emissions from power generation in Japan by about 50%. Copyright © 2004 John Wiley & Sons, Ltd.

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

A solid oxide fuel cell (SOFC) is expected to be applied to the distributed energy systems because of its high thermal efficiency and exhaust gas utilization. The exhaust heat from the SOFC can be transferred to the electric power by a gas turbine, and the high efficiency power generation can be achieved by constructing the SOFC and gas turbine hybrid system. In this study, we analyze the local processes in the electrodes and electrolyte of unit SOFC taking into account the heat conduction, mass diffusion, electrode reactions and the transport of electron and oxygen ion. The temperature and concentration distributions perpendicular to the electrolyte membrane are shown. The effects of the operating conditions on the cell performance are also shown. Furthermore, the entropy generation and exergy loss of each process in the electrodes and electrolyte are analyzed and the reason for generating the exergy loss in the SOFC is clarified. It is noted that two electrode reactions are responsible for the major exergy loss.

A Thermodynamic Analysis of Tubular Solid Oxide Fuel Cell Based Hybrid Systems

The goals of a research program recently completed at the University of California, Irvine were to develop analysis strategy for solid oxide fuel cell (SOFC) based systems, to apply the analysis strategy to tubular SOFC hybrid systems and to identify promising hybrid configurations. A pressurized tubular SOFC combined with an intercooled-reheat gas turbine (SureCell™ cycle) is chosen as the base cycle over which improvements are sought. The humid air turbine (HAT) cycle features are incorporated to the base cycle resulting in the SOFC-HAT hybrid cycle which shows an efficiency of 69.05 percent while the base cycle has an efficiency of 66.23 percent. Exergy analysis identified the superior efficiency performance of the SOFC component. Therefore, an additional cycle variation added a second SOFC component followed by a low pressure combustor in place of the reheat combustor of the gas turbine of the SOFC-HAT hybrid. The resulting dual SOFC-HAT hybrid has a thermal efficiency of 75.98 percent. The single SOFC-HAT hybrid gives the lowest cost of electricity (3.54¢/kW-hr) while the dual SOFC-HAT hybrid has the highest cost of electricity (4.02¢/kW-hr) among the three cycles with natural gas priced at $3/GJ. The dual SOFC-HAT hybrid plant cost is calculated to be significantly higher because the fraction of power produced by the SOFC(s) is significantly higher than that in the other cases on the basis of $1100/kw initial cost for the SOFC. The dual SOFC-HAT hybrid can only be justified in favor of the single SOFC-HAT hybrid when the price of natural gas is greater than $14/GJ or if a severe carbon tax on the order of $180/ton of CO2 is imposed while natural gas price remains at $3/GJ.

Energy and exergy analysis of simple solid-oxide fuel-cell power systems

Two, simple, solid-oxide fuel-cell (SOFC) power systems fed by hydrogen and methane, respectively, are examined. While other models available in the literatures focus on complicated hybrid SOFC and gas-turbine (GT) power systems, this study focuses on simple SOFC power systems with detailed thermodynamic modeling of the SOFC. All performance-related parameters of the fuel-cell such as respective resistivity of the components, anode and cathode exchange current density, limiting current density, flow diffusivity, etc. are all expressed as a function of temperature, while the flow through of each nodes of the system is described as a function of thermodynamic state. Full analysis of the energy and exergy at each node of the system is conducted and their respective values are normalized by the lower heating value (LHV) of the fuel and its chemical exergy, respectively. Thus, the normalized electrical energy outputs directly indicate the first law and second law efficiencies, respectively, of the fuel-cell power systems.

Advances in solid oxide fuel cell technology

High temperature solid oxide fuel cells (SOFCs) offer a clean, pollution-free technology to electrochemically generate electricity at high efficiencies. These fuel cells provide many advantages over traditional energy conversion systems including high efficiency, reliability, modularity, fuel adaptability, and very low levels of NO x and SO x emissions. Furthermore, because of their high temperature of operation (∼1000°C), natural gas fuel can be reformed within the cell stack eliminating the need for an expensive, external reformer. Also, pressurized SOFCs can be successfully used as replacements for combustors in gas turbines; such hybrid SOFC–gas turbine power systems are expected to reach efficiencies over 70%. This paper reviews the materials and fabrication methods used for the different cell components, and discusses the performance of cells fabricated using these materials; it also discusses the materials and processing studies that are under investigation to reduce the cell cost. Finally, the paper summarizes the recently built power generation systems that employed state-of-the-art SOFCs. A new design SOFC that combines the seal-less feature of tubular cells and a flattened air electrode with integral ribs is also described; this new design has a shortened current path and hence lower cell resistance and higher power output than tubular cells.

The generalised Huggins-Mayer form of born repulsive potentials for NaCl-type alkali halides

This paper reports a review of an environmentally clean and efficient source of energy such as solid oxide fuel cell hybrid systems. Due to climate concerns, most nations are seeking alternative means of generating energy from a clean, efficient and environmental-friendly method. However, this has proven a big hurdle for both academic and industry researchers over many years. Currently, practical and technically feasible solution can be obtained via an integration of a microturbine and a fuel cell (hybrid systems). Combining the two distinct systems in a hybrid arrangement the efficiency of the microturbine increases from 25 to 30% to the 60–65% range. Hence, this paper outlines an engineering power generation solution towards the acute global population growth, the growing need, environmental concerns, intelligent use of energy with attendant environmental and hybrid system layouts concerning arising problems and tentative proposed solutions. Furthermore, advantages of a solid oxide fuel cell hybrid systems with respect to the other technologies are identified and discussed rationally. Special attention is devoted to modelling with software and emulator rigs and system prototypes. The paper also reviews the limitations and the benefits of these hybrid systems in relationship with energy, environment and sustainable development. Few potential applications, as long-term potential actions for sustainable development, and the future of such devices are further discussed.