固体氧化物燃料电池发电系统的模拟与优化

固体氧化物燃料电池是21世纪最有希望作为分布式电源和大型电站的清洁高效的发电技术之一。针对1MW固体氧化物燃料电池发电系统,建立了描述SOFC电池堆电化学过程和特性的模型,并在此基础上建立了基于Aspen Plus软件平台的SOFC发电系统模型,对其系统参数进行了灵敏度分析和优化。     

The Development and Application of a Novel Optimisation Strategy for Solid Oxide Fuel Cell‐Gas Turbine Hybrid Cycles

A combined power system with solid oxide fuel cell (SOFC) and gas turbine (GT) is modelled and analysed thermodynamically in this paper. A novel optimisation strategy including the design of optimal parameters is proposed and applied to the hybrid system. Different sources of irreversible losses are specified, and entropy analyses are used to indicate the multi‐irreversibilities existing, and to assess the work potentials of the system. Expressions of the power output and efficiency for both the subsystems and the SOFC‐GT hybrid system are derived. The optimal performance characteristics are presented and discussed in detail through a parametric analysis. The developed model is expected to provide not only a convenient tool to determine the optimal system performance and component irreversibility, but also an appropriate basis to design similar complex hybrid power plants. This new approach can be further extended to other energy conversion settings and electrochemical systems. Decision makers should therefore find the methodology contained in this paper useful in the comparison and selection of advanced heat recovery systems.     

Design and Optimization of an Innovative Solid Oxide Fuel Cell–Gas Turbine Hybrid Cycle for Small Scale Distributed Generation

Distributed power generation and cogeneration is an attractive way toward a more rational conversion of fuel and biofuel. The fuel cell‐gas turbine hybrid cycles are emerging as the most promising candidates to achieve distributed generation with comparable or higher efficiency than large‐scale power plants. The present contribution is devoted to the design and optimization of an innovative solid oxide fuel cell–gas turbine hybrid cycle for distributed generation at small power scale, typical of residential building applications. A 5 kW planar SOFC module, operating at atmospheric pressure, is integrated with a micro gas turbine unit, including two radial turbines and one radial compressor, based on an inverted Brayton cycle. A thermodynamic optimization approach, coupled with system energy integration, is applied to evaluate several design options. The optimization results indicate the existence of optimal designs achieving exergy efficiency higher than 65%. Sensitivity analyses on the more influential parameters are carried out. The heat exchanger network design is performed for an optimal configuration and a complete system layout is proposed. An example of hybrid system integration in a common residential building is discussed.     

Combination of thermochemical recuperative coal gasification cycle and fuel cell for power generation

An integrated power generation cycle combining thermochemical recuperation, brown coal gasification and a solid oxide fuel cell (SOFC) was proposed based on the concept of thermochemical recuperative energy. Process simulation combining the coal gasifier, gas turbine cycle, and SOFC module was conducted using the ASPEN Plus process simulation tool. The simulation indicated that the cycle efficiency increases from 39.5% (HHV) without the SOFC to about 45% (HHV) with the SOFC.     

Technical and economic study of integrated system of solid oxide fuel cell,palladium membrane reactor,and CO2 sorption enhancement unit

This paper deals with the integrated system of solid oxide fuel cell (SOFC), palladium membrane reactor (PMR), and CO₂ sorption enhancement (SE) unit. Three configurations of the SOFC systems fed by biogas are considered, i.e., PMR–SOFC, SE–PMR–SOFC, and SE–PMR–SOFC with a retentate gas recycling (SER–PMR–SOFC). The SOFC system equipped with a conventional reformer (CON–SOFC) is considered as a base case. The simulation results show that the capture of CO₂ in biogas before being fed to PMR (SE–PMR–SOFC) can improve H₂ recovery. The performance of SE–PMR–SOFC can be further enhanced by recycling retentate gas from PMR to CO₂ sorption enhancement unit (SER–PMR–SOFC). Compared to CON–SOFC, both SE–PMR–SOFC and SER–PMR–SOFC give higher power density and thus require smaller stack size (the stack size reduction of 1.55% and 8.27% are observed for SE–PMR–SOFC and SER–PMR–SOFC, respectively). The economic analysis is performed to identify the potential benefits of each SOFC configuration. The results indicate that SE–PMR–SOFC and SER–PMR–SOFC are not cost-effective systems compared with CON–SOFC; however, the capture of CO₂ in these SOFC systems offers an environmental benefit. High %total CO₂ capture and low cost of CO₂ capture are achieved under these SOFC systems.     

Worldwide SOFC Technology Overview and Benchmark

Solid oxide fuel cells (SOFC) are generally considered to be a promising future electricity-generation technology due to their high electrical efficiency. They also display a multi-fuel capability (hydrogen, carbon monoxide, methane, etc.), may play a role in carbon sequestration strategies, and may render the highest electricity generation efficiency in power station design if coupled with a gas turbine. Nevertheless, their development still faces various problems with high-temperature materials, design of cost-effective materials and manufacturing processes, and efficient plant design. This article summarizes world wide efforts in the field of SOFC, presenting an overview of the main SOFC designs and the main developers active in this field. Based on data published in proceedings of international conferences during the last few years, a comparison is made of the results achieved in cell, stack, and system development.     

High Temperature Micro‐Fan for Solid Oxide Fuel Cell Applications

The possibility of using a μ‐fan in tubular solid oxide fuel cells module (SOFC‐M) is shown. The μ‐fan is placed instead of the ejector and fulfills its role. The main advantages of this solution are: lower power demanded by the fuel compressor (blower), more stable working characteristics, and the possibility of more accurate control of the recycled part of the anode gas during part load operation. A comparison of two SOFC‐Ms, with and without the ejector, is also shown and commented.     

Analysis of a solid oxide fuel cell system for combined heat and power applications under non-nominal conditions

In this paper, a model for a solid oxide fuel cell (SOFC) system for decentralized electricity production is developed and studied. The proposed system, operated on natural gas, consists of a planar anode supported fuel cell section and a balance of plant (BoP) which includes gases supply, a fuel processor, a heat management system, an after-burner and a power conditioning system. A reference case is defined and evaluated taking into account the state of the art of the technology and the related technical constrains. Electrical and thermal efficiency of the system, for non-reference conditions are evaluated. In particular, the effect of the deviation from the reference conditions of fuel utilization, gas temperature spring in fuel cell stack, anode off-gas recirculation rate, air inlet temperature and external pre-reforming reaction extent is analyzed. The present study revealed to be a powerful tool for evaluating the SOFC system performance under a wide range of operation and paves the way for defining control strategies in order to maintain high system efficiency under part-load operations.     

Investigation of solid oxide fuel cell short stacks for mobile applications by electrochemical impedance spectroscopy

Solid oxide fuel cells (SOFC) for mobile applications are developed and investigated at the German Aerospace Center (DLR) in Stuttgart. Therefore a light-weight stack design was developed in cooperation with the automotive industry (BMW/Munich, Elring-Klinger/Dettingen, ThyssenKrupp/Essen) and the Research Center Jülich (FZJ). This concept is based on the application of stamped metal sheet bipolar plates, into which the SOFC cells are integrated by brazing technology. For the development and the investigation of the SOFC cells and short stacks, the electrochemical impedance spectroscopy (EIS) is an important and useful characterization method. The paper concentrates on the investigation and on the electrochemical testing of the SOFC short stacks with sintered anode-supported cells (ASC). The short stacks were electrochemically characterized mainly by electrochemical impedance spectroscopy, by current-voltage measurements and by long-term measurements. The cells and stacks were operated at different temperatures, varying fuel gas compositions, different fuel gas flow rates and at different electrical current loads. The influence of these operating conditions on the electrochemical performance of the short stacks is outlined. The nature of losses, e.g. ohmic and the polarization resistances of the electrodes were examined and determined by fitting of the impedance spectra to an equivalent circuit.     

环境压力下吸热燃气轮机循环工程

构建新的循环以提高动力循环效率和发电功率,是能源利用转换领域的基础研究内容之一。本文提出了新型环境压力下吸热燃气轮机循环APGC（ambient pressure gas turbine cycle）,并利用商业软件Aspen Plus建立了APGC燃气动力装置以及燃料电池分析模型,对其在燃料电池装置以及在沼气发电、钢铁行业动力回收中的应用进行模拟和分析,并给出相应的分析结果,显示出APGC独具的优势以及广阔的应用前景。     

Performance analysis of integrated biomass gasification fuel cell (BGFC) and biomass gasification combined cycle (BGCC) systems

Biomass gasification processes are more commonly integrated to gas turbine based combined heat and power (CHP) generation systems. However, efficiency can be greatly enhanced by the use of more advanced power generation technology such as solid oxide fuel cells (SOFC). The key objective of this work is to develop systematic site-wide process integration strategies, based on detailed process simulation in Aspen Plus, in view to improve heat recovery including waste heat, energy efficiency and cleaner operation, of biomass gasification fuel cell (BGFC) systems. The BGFC system considers integration of the exhaust gas as a source of steam and unreacted fuel from the SOFC to the steam gasifier, utilising biomass volatilised gases and tars, which is separately carried out from the combustion of the remaining char of the biomass in the presence of depleted air from the SOFC. The high grade process heat is utilised into direct heating of the process streams, e.g. heating of the syngas feed to the SOFC after cooling, condensation and ultra-cleaning with the Rectisol^® process, using the hot product gas from the steam gasifier and heating of air to the SOFC using exhaust gas from the char combustor. The medium to low grade process heat is extracted into excess steam and hot water generation from the BGFC site. This study presents a comprehensive comparison of energetic and emission performances between BGFC and biomass gasification combined cycle (BGCC) systems, based on a 4th generation biomass waste resource, straws. The former integrated system provides as much as twice the power, than the latter. Furthermore, the performance of the integrated BGFC system is thoroughly analysed for a range of power generations, ～100–997 kW. Increasing power generation from a BGFC system decreases its power generation efficiency (69–63%), while increasing CHP generation efficiency (80–85%).     

不确定性条件下对固体氧化物燃料电池-质子交换膜燃料电池联合系统的综合/设计优化(英文)

Solid oxide fuel cell–proton exchange membrane (SOFC–PEM) hybrid system is being foreseen as a valuable alternative for power generation. As this hybrid system is a conceptual design, many uncertainties involving input values should be considered at the early stage of process optimization. We present in this paper a general-ized framework of multi-objective optimization under uncertainty for the synthesis/design optimization of the SOFC–PEM hybrid system. The framework is based on geometric, economic and electrochemical models and focuses on evaluating the effect of uncertainty in operating parameters on three conflicting objectives:electricity efficiency, SOFC current density and capital cost of system. The multi-objective optimization provides solutions in the form of a Pareto surface, with a range of possible synthesis/design solutions and a logical procedure for searching the global optimum solution for decision maker. Comparing the stochastic and deterministic Pareto surfaces of different objectives, we conclude that the objectives are considerably influenced by uncertainties because the two trade-off surfaces are different.     

Sensitivity Analysis for a Planar SOFC: Size Effects of the Porous Gas Diffusion Layer Underneath the Channel Rib

This paper investigates the size effects of the gas diffusion layer underneath the channel rib on the performance of a planar solid oxide fuel cell (SOFC). Based on 3‐dimensional numerical simulations, the sensitivities of the electrical performance parameters (Nernst potential and current density) and the thermal performance parameters (heat generation and temperature) are examined as a function of variations in the channel rib width and anode thickness. The sensitivity values of the Nernst potential and current density are calculated to guide the design of a cell in a planar SOFC. In particular, the changes in ohmic losses for the interconnectors and anode are analyzed as a function of the variations of the channel rib width and anode thickness. The variations of the mole fractions of hydrogen, oxygen, and water in the active areas of the channel rib and the channel are presented, which provide sensitivity profiles for gas diffusion with respect to changes in the anode thickness.     

Three‐Dimensional Computational Fluid Dynamics Modeling of a Planar Solid Oxide Fuel Cell

A three‐dimensional computational fluid dynamics model was developed to study the performance of a planar solid oxide fuel cell (SOFC). The governing equations were solved with the finite volume method. The model was validated by comparing the simulation results with data from literature. Parametric simulations were performed to investigate the coupled heat/mass transfer and electrochemical reactions in a planar SOFC. Different from previous two‐dimensional studies the present three‐dimensional analyses revealed that the current density was higher at the center along the flow channel while lower under the interconnect ribs, due to slower diffusion of gas species under the ribs. The effects of inlet gas flow rate and electrode porosity on SOFC performance were examined as well. The analyses provide a better understanding of the working mechanisms of SOFCs. The model can serve as a useful tool for SOFC design optimization.     

Power Generation from Biogas using SOFC – Results for a 1 kWe Demonstration Unit

A stand‐alone system for power generation from biogas‐based on a commercial SOFC module in the 1 kW_e range shall demonstrate its applicability to biogas, quantify the efficiency gain compared to conventional combined heat and power technology and justify further development toward SOFC modules in the hundreds of kilowatt range. The system includes biogas cleaning, combined dry and steam reforming, electrochemical oxidation of synthesis gas, offgas burning, and heat usage for steam generation and support of the endothermic reforming reaction. The system demonstrated a performance of 1 kW_e at 52% gross efficiency for a synthetic biogas containing 55 vol.% CH₄ during 500 h in the lab. In addition, the performance using real biogas derived from the wastewater treatment process of a sugar plant was demonstrated for different operating points. Based on the experimentally validated results, it is possible to predict the benefit of operating larger SOFC biogas systems. Investment costs of 2.5 times compared to the conventional technology of a 75 kW_e biogas unit get paid off due to higher electricity revenues over time.     

An adaptable steady state Aspen Hysys model for the methane fuelled solid oxide fuel cell

An adaptable model for the methane fed internal reforming SOFC using the in built features of Aspen Hysys is presented in this paper. The model includes the electrochemistry, the diffusion phenomena and the reforming kinetics in detail. Three potential methods for representing the SOFC are investigated out of which the recycled reforming model is found to be capable of providing reasonable results over a wide range of operating conditions. The electrochemical model that gives good agreement with experimental data is also identified. From the simulations, it is concluded that the developed model is reasonably accurate over a wide operating range and can be used for steady state analysis. The computational challenges in the modelling are discussed. The model will be used for system level optimisation studies of the SOFC system especially in conjuncture with gas turbines and steam turbines.     

Effect of methane slippage on an indirect internal reforming solid oxide fuel cell

Creation of an autothermal system by coupling an endothermic to an exothermic reaction demands matching the thermal requirements of the two reactions. The application studied here is the operation of a solid oxide fuel cell (SOFC) with both direct (DIR) and indirect (IIR) internal reforming of methane. Such internal reforming within a high-temperature fuel cell module can lead to an overall autothermal operation which simplifies the system design and increases efficiency. However, such coupling is not easy to achieve because of the mismatch between the thermal load associated with the rate of steam reforming at typical SOFC temperatures and the local amount of heat available from the fuel cell reactions. Previous results have shown that the use of typical metal-based (e.g. Ni) IIR catalysts leads to full methane consumption but undesirable local cooling at the reformer entrance and the use of less active IIR catalysts (e.g. non-metals or diffusion limited nickel) leads to methane being carried-over into the SOFC anode (methane slippage). In order to evaluate performance in the latter case, a combined DIR and IIR SOFC steady-state model has been developed. Simulation results have shown that, lowering the IIR catalyst activity to prevent local cooling effects at the reformer entrance is not adequate, as the fast kinetics of the direct reforming reaction then lead to full methane conversion and steep temperature gradients in the first 10% of the fuel channel length. It is shown that the simultaneous reduction of the anode DIR reaction rate improves performance considerably. The system behaviour towards changes in current density, operating pressure, and flow configuration (counter-flow vs. co-flow) has been studied. Reduction of both DIR and IIR catalyst activity combined with a counter-flow operation leads to the best performance. System performance with an IIR oxide-based catalyst is also evaluated.     

Mathematical Modelling of Proton‐Conducting Solid Oxide Fuel Cells and Comparison with Oxygen‐Ion‐Conducting Counterpart

Proton‐conducting solid oxide fuel cells (H‐SOFC), using a proton‐conducting electrolyte, potentially have higher maximum energy efficiency than conventional oxygen‐ion‐conducting solid oxide fuel cells (O‐SOFC). It is important to theoretically study the current–voltage (J–V) characteristics in detail in order to facilitate advanced development of H‐SOFC. In this investigation, a parametric modelling analysis was conducted. An electrochemical H‐SOFC model was developed and it was validated as the simulation results agreed well with experimental data published in the literature. Subsequently, the analytical comparison between H‐SOFC and O‐SOFC was made to evaluate how the use of different electrolytes could affect the SOFC performance. In addition to different ohmic overpotentials at the electrolyte, the concentration overpotentials of an H‐SOFC were prominently different from those of an O‐SOFC. H‐SOFC had very low anode concentration overpotential but suffered seriously from high cathode concentration overpotential. The differences found indicated that H‐SOFC possessed fuel cell characteristics different from conventional O‐SOFC. Particular H‐SOFC electrochemical modelling and parametric microstructural analysis are essential for the enhancement of H‐SOFC performance. Further analysis of this investigation showed that the H‐SOFC performance could be enhanced by increasing the gas transport in the cathode with high porosity, large pore size and low tortuosity.     

Analysis of Design Parameters in Anode‐Supported Solid Oxide Fuel Cells Using Response Surface Methodology

Achieving high performance from a solid oxide fuel cell (SOFC) requires optimal design based on parametric analysis. In this paper, design parameters, including anode support porosity, thicknesses of electrolyte, anode support, and cathode functional layers of a single, intermediate temperature, anode‐supported planar SOFC, are analyzed. The response surface methodology (RSM) technique based on an artificial neural network (ANN) model is used. The effects of the cell parameters on its performance are calculated to determine the significant design factors and interaction effects. The obtained optimum parameters are adopted to manufacture the single units of an SOFC through tape casting and screen‐printing processes. The cell is tested and its electrochemical characteristics, which show a satisfactory performance, are discussed. The measured maximum power density (MPD) of the fabricated SOFC displays a promising performance of 1.39 W cm^–2. The manufacturing process planned to fabricate the SOFC can be used for industrial production purposes.     

基于SOFC/MGT/ORC的微型冷热电联供系统性能分析

提出一种基于SOFC/MGT/ORC的微型冷热电联供系统,首先建立并验证了联供系统数学模型,然后给出设计工况下联供系统的输入参数,重点分析在夏季工况下,燃料流率、燃料利用率、蒸汽碳比、压缩机压比等关键操作参数对系统性能的影响。结果表明,在夏季设计工况下,该联供系统发电效率及?效率分别为69.12%、64.4%,同时系统一次能源利用效率可达92.65%,比冬季设计工况高13.1%。