| High temperature fuel cells are one of the most efficient devices for the electrochemical conversion of chemical energy of hydrocarbon fuels into electricity. In practice, high temperatue fuel cells'efficiency can be further increased by integrating them with a gas turbine (GT) to be a hybrid system. Such systems have been gaining increasing attention in recent years for clean and efficient distributed power generation and become a focus in new technology for energy-use in many contries.This paper has developed the simulation models of the high temperature fuel cells/gas turbine hybrid system at first. Using the developed models, safe operation regime, part-load operating strategies, design and off-desing performances of the hybrid system are investigated. A detail part-load control strategy and suitable startup and shutdown strategies are also introduced. Dynamic performances of the hybrid system with the introduced control strategies are then studied in detail.For the experimental part, electrochemical performances of planar single fuel cell which is developed in our laboratory are tested with various fuel compositions in different operating temperature. For system experiment study, key components such as gas turbine, catalytic combustor, heat exchangers have been designed. Due to the bottleneck problem of pressured solid oxide fuel cell stack fabricating, this paper developed the hybrid system experiment plant which is the first one in China using ambient pressure molten carbonate fuel cell stack. Based on the experiment plant, some preliminary researches have been done.The work performed in this paper can provided the necessary theoretical guide and experimental base for the development and use of high temperature fuel cells/gas turbine hybrid system. Some developments have been achieved as follows.(1) Mathmatical models of high temperature fuel cells and hybrid systemOne-dimensional mathematical models for planar and tubular solid oxide fuel cell (SOFC) have been built with volume-resistance (V-R) method respectively. Detail thermodynamics and electrochemical equations are considered in the modeling. The gas turbine models are developed based on the component performance maps. Other components models are developed by using conservation of mass, energy and state of ideal gas equations. Based on the components; models, steady state and dynamic model of high temperature fuel cells/gas turbine hybrid system are established which can provide the detailed information about the fuel cells when the properties of the hybrid system changed.(2) Single high temperature fuel cell development and performance testAnode-supported planar high temperature solid oxide fuel cell (SOFC) are fabricated which are characterized by X-ray diffraction (XRD), scanning electron microscope (SEM), Thermal Gravity Analysis (TGA) respectively. Experimental plant for single SOFC electrochemical performance test is built. The electrochemical performances of fabricated SOFC single cells are tested with various fuel compositions in different operating temperature. Experimental results indicate that the cathode sintering temperature has a dramatic effect on the performance of the cell. The electrochemical performances of the fabricated celsl with dillented fuels show that SOFC can use low-LHV fuels with high efficiency, which means that SOFC can be a new way for using low LHV fuels such as biogas or syngas in the future.(3) Safe operation regime confirmed and performance study of the hybrid systemBased on the simulation models, performances of the hybrid system at both design and off-design, operating with design fuel and non-deisng fuels are studied. Safe operation regime of hybrid system is accurately plotted considering detail limitations for system safe operation. With the safe regime, three different part-load strategies are introduced. Part-load performance of the hybrid system is analyzed with three strategies respectively. The effects of different operation methods on the system characteristics were analyzed in detail. High fuel flexibility is one of the most important advanateges of high temperature fuel cells. Hybrid system performances with non-desinged fuels are also studied in this paper. (4) Control strategies design and dynamic performance studyThe control strategies of the SOFC-GT hybrid system are designed and the control parameters are optimized. Considering the characteristics of SOFC and hybrid system, detail startup and shutdown swquences which can ensure the system security are studied. Dynamic simulation results show that the control strategies designed in this paper can successfully control the hybrid system during load-change, startup and shutdown processes.(5) Experimental study of high temperature fuel cells/gas turbine hybrid systemThe high temperature fuel cell/gas turbine hybid system experiment plant is developed in this paper. Key components such as catalytic combustor, heat exchangers have been designed. Experimental data during system startup, shutdown, and stable operating process are acquired and analysized in detail.As the first high temperature fuel cell/gas turbine hybrid system experiment plant in China, this work demonstrated the concept of integrating a high temperature fuel cell stack with a gas turbine, and provided the necessary theoretical guide and experimental experience. But because of the bottleneck of fuel cell fabricating technology development, parameters of fuel cells used in this paper is not well matched with gas turbine's, which leads to low system efficiency, thus the advantage of hybrid system is not well represented. Much additional development is no doubtly required to develop a stable, high efficiency hybrid system... |
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