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

Based on mathematical modelling and numerical simulations, the control strategy for a Solid Oxide Fuel Cell Hybrid System (SOFC-HS) is presented. Adequate maps of performances with three independent parameters are shown. These independent parameters are as follows: stack current, fuel mass flow and turbine-compressor shaft speed. To control external load, those parameters should be appropriately chosen. The control system is purposed to meet many constraints: e.g. stack temperature, steam-to-carbon ratio, compressor surge limitation etc. The aim is to achieve maximum efficiency of power generated within those constraints. Governing equations of SOFC-HS modelling are given. An adequate simulator for the SOFC module was produced and described. Based on this simulator, the control strategy was obtained. The performance of this SOFC-HS is shown in various working environments.

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.

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

Due to the intermittent nature of renewable energy and the rigid operation of existing coal plants, the need for flexible power generation technology is eminent. Hybrid energy systems have shown potential for flexible, grid following dynamics while maintaining higher efficiencies. The work below focuses on the performance analysis of a proposed 100 kW pressurized Internal Combustion Engine (ICE) and Solid Oxide Fuel Cell (SOFC) hybrid system. The un-utilized fuel from the SOFC stack provided the chemical energy to operate the engine. A turbocharger was used to deliver the necessary air flow for both the stack and engine. An external reformer was utilized to provide fuel syngas to the fuel cell stack. Four alternative SOFC/ICE cycles were presented and analyzed. All components of the four cycles were numerically modeled using two different software. The SOFC and reformer were simulated using a 1-dimensional model written in MathWorks ® MATLAB/Simulink. The IC engine and balance of plant (BOP) model was developed using STEAG EBSILON® Professionals. These models were developed to evaluate several options for heat recovery and the anode exhaust cooling before feeding into the engine. The study was conducted by variating fuel utilization and anode methane content through reformer operating temperature, ranging from 70 to 90% and 600 to 1000 K, respectively. Additionally, a study on the effects of anode off-gas recirculation was conducted by variating the recirculation rate between 0, 25 and 70%. Furthermore, current density effects were analyzed when operating the stack at 0.2, 0.4, and 0.55 A/cm2 . At each design point, hardware was re-sized to 4 match the desired conditions. The cycle performance and fuel cell distributed profiles are discussed. Results indicated that both the stack and engine are thermally disconnected thus behaving as topping and bottoming cycles. The highest efficiency attained was 62% at a reformer operating temperature of 800 K and 90% fuel utilization. An optimal balance was found when the thermal load required for on-anode reformation is well matched with the heat generated from the electrochemical hydrogen oxidation reaction across the fuel cell.

This paper mainly studied the solid oxide fuel cell (SOFC)–micro gas turbine (MGT) hybrid power system. The key parameters that greatly influence the overall system performance have been studied and optimized. The thermodynamic potential of improving the hybrid system performance by integrating SOFC with the advanced thermal cycle system is analyzed. The optimization rules of main parameters of SOFC-MGT hybrid power system with the turbine inlet temperature (TIT) of MGT as a constraint condition are revealed. The research results show that TIT is a key parameter that limits the electrical efficiency of hybrid power system. With the increase of the cell number, both the power generation efficiency of the hybrid cycle power system and TIT increase. Regarding the hybrid system with the fixed cell number, in order to get a higher electrical efficiency, the operating temperature of SOFC should be enhanced as far as possible. However, the higher operating temperature will result in the higher TIT. Increasing of fuel utilization factor is an effective measure to improve the performance of hybrid system. At the same time, TIT increases slightly. Both the electrical efficiency of hybrid power system and TIT reduce with the increase of the ratio of steam to carbon. The achievements obtained from this paper will provide valuable information for further study on SOFC-MGT hybrid power system with high efficiency. Copyright © 2010 John Wiley & Sons, Ltd.

An advanced coal based power plant system that has an electrical efficiency of 60% on an HHV basis is defined. The solid oxide fuel cell (SOFC) hybrid has been shown to be an essential requirement in order to achieve such a high efficiency. The coal is gasified utilizing a high pressure air-blown advanced transport reactor (ATR). A thermo-economic analysis of this integrated gasification fuel cell (IGFC) plant is performed by comparing it to an integrated gasification combined cycle (IGCC) plant that utilizes a gas turbine combined cycle for power generation. Results of this thermo-economic analysis indicate that the required “break even” cost of the SOFC system is $400/kW on an installed cost basis such that the cost of electricity of IGFC plant is the same as that of the IGCC plant. Coproduction of H2 and capture of carbon emissions may be incorporated in the design without causing a major thermal penalty on the system performance when high temperature separation membranes are employed. An O2-blown gasifier is required for such applications. The technology development needs are addressed.

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

The main objective is to identify and assess advanced improvements to the Brayton Cycle (such as but not limited to firing temperature, pressure ratio, combustion techniques, intercooling, fuel or combustion air augmentation, enhanced blade cooling schemes) that will lead to significant performance improvements in coal based power systems. This assessment is conducted in the context of conceptual design studies (systems studies) that advance state-of-art Brayton cycles and result in coal based efficiencies equivalent to 65% + on natural gas basis (LHV), or approximately an 8% reduction in heat rate of an IGCC plant utilizing the H class steam cooled gas turbine. H class gas turbines are commercially offered by General Electric and Mitsubishi for natural gas based combined cycle applications with 60% efficiency (LHV) and it is expected that such machine will be offered for syngas applications within the next 10 years. The studies are being sufficiently detailed so that third parties will be able to validate portions or all of the studies. The designs and system studies are based on plants for near zero emissions (including CO{sub 2}). Also included in this program is the performance evaluation of other advanced technologies such as advanced compression concepts and the fuel cell based combined cycle. The objective of the fuel cell based combined cycle task is to identify the desired performance characteristics and design basis for a gas turbine that will be integrated with an SOFC in Integrated Gasification Fuel Cell (IGFC) applications. The goal is the conceptualization of near zero emission (including CO{sub 2} capture) integrated gasification power plants producing electricity as the principle product. The capability of such plants to coproduce H{sub 2} is qualitatively addressed. Since a total systems solution is critical to establishing a plant configuration worthy of a comprehensive market interest, a baseline IGCC plant scheme is developed and used to study how alternative process schemes and power cycles might be used and integrated to achieve higher systems efficiency. To achieve these design results, the total systems approach is taken requiring creative integration of the various process units within the plant. Advanced gas turbine based cycles for Integrated gasification Combined cycle (IGCC) applications are identified by a screening analysis and the more promising cycles recommended for detailed systems analysis. In the case of the IGFC task, the main objective is met by developing a steady-state simulation of the entire plant and then using dynamic simulations of the hybrid Solid Oxide Fuel Cell (SOFC)/Gas Turbine sub-system to investigate the turbo-machinery performance. From these investigations the desired performance characteristics and a basis for design of turbo-machinery for use in a fuel cell gas turbine power block is developed.

The objective of this work is the development of a simulation model for a hybrid Solid Oxide Fuel Cell (SOFC)/Micro Gas Turbine (MGT) system, flexible and robust enough, capable to predict the system performance under various operating conditions. The hybrid system consists of a high temperature SOFC, based on a tubular configuration developed by Siemens Power Generation Inc, and a recuperated small gas turbine (GT) validated using data for the Capstone C30. The design and off-design performance of the system is examined by means of performance maps. Moreover, operating parameters such as fuel utilization factor, steam to carbon ratio and current density are varied over a wide range and the influence on system performance is studied. The optimum operating conditions are discussed with regard to overall system performance under part load operation. The results show that high electrical efficiencies can be achieved making these systems appropriate for distributed generation applications.

In this paper, methodology to estimate GHG emissions from electricity generation sector using Iran as an example was first explained. Then different scenarios to reduce GHG emissions were evaluated for two countries: Canada and Iran. The results demonstrated that there were great potentials for GHG emission reduction in both countries. These potentials were evaluated by introducing eight different scenarios, including power stations' fuel switching to natural gas, replacement of existing power plants with natural gas combined cycle, Integrated Gasification Combined Cycle (IGCC), Solid Oxide Fuel Cell (SOFC), hybrid SOFC, and SOFC-IGCC hybrid power stations, and installation of CO2 capture systems.

A hybrid system that combines a solid oxide fuel cell (SOFC) with a proton exchange membrane fuel cell (PEMFC) is presented in this paper. The SOFC stack acts as both an electricity producer and the fuel reformer for the PEMFC stack to generate additional power. A thermoeconomic model for the design optimization of a 220 kW SOFC-PEMFC hybrid system is developed in this work. Optimization of two objectives, i.e., the life cycle cost and the net electrical efficiency, are considered individually to find the optimum system configuration and component designs. Then, a multiparameter sensitivity analysis is performed to estimate the relative importance of the decision variables on the objectives. The optimization results indicate that the life cycle cost of the hybrid system is 3800–5,600 $/kW, and the maximum net electrical efficiency can reach around 63%, which is higher than an SOFC-only system, a reformer-PEMFC system, and an SOFC-gas turbine (GT) system with a similar output power. The sensitivity analysis shows that minimizing the size of the SOFC is most crucial to the system cost optimization. The hydrogen utilization factor in the SOFC is found to be sensitive to the net electrical efficiency.

In this paper, a simple multi-closed Proportional-Integral-Derivative (PID) controller is presented for a 5 kW solid oxide fuel cell (SOFC) system. Referring to the presented detailed dynamic model, the external load performance, control parameters and control objectives are studied and discussed. In order to achieve the goal of fast load tracing and high efficiency. Then the designed multi-loop control strategy is introduced and its responses on the external load change and system efficiency are investigated. Results show that the presented multi-loop PID control strategy can not only improve the system efficiency, but also gain the fast tracking of the output power.

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.

The paper presents a simulation of a hybrid solid oxide fuel cell-gas turbine (SOFC-GT) power generation system fueled by natural gas. In the system considered, the unreacted fuel from a topping solid oxide fuel cell is burnt in an afterburner to feed a bottoming gas turbine and produce additional power. Combustion gas expands in the gas turbine after having preheated the inlet air and fuel and it is used to generate steam required by the reforming reactions. A novel thermodynamic model has been developed for the fuel cell and implemented into the library of a modular object-oriented Process Simulator, CAMELPro™. The relevant plant performance indicators have been analyzed to evaluate the incremental increase in efficiency brought about by the introduction of the gas turbine and heat regeneration system. Simulations were performed for different values of the main plant parameters. This paper is an updated version of a paper published in the ECOS'08 proceedings.

FuelCell Energy is developing a Hybrid Solid Oxide Fuel Cell (SOFC)-Battery Energy System for Large Displacement Unmanned Undersea Vehicle (LDUUV) propulsion as part of the Office of Naval Research’s LDUUV Innovative Naval Prototype (INP) Energy Program. The project objective is the development of an air-independent refuelable power system with high energy density suitable for long duration underwater missions. The Hybrid SOFC-Battery system will be capable of generating 1800kWhr of electricity over a 70 day mission with no exhaust discharged outside of the vehicle at any time. The energy system is fueled by JP-10 logistic fuel, utilizes liquid O2 for air-independent operation, and is compact enough to fit within a 42-inch square by 120-inch long LDUUV power section. Phase I of the project includes process design and cost analysis, development of a 3-D CAD model of the energy system, breadboard testing of components and the integrated system, as well as completion of a Preliminary Hazard Analysis (PHA).