燃料电池/燃气轮机混合动力系统中的燃气轮机运行特性分析

对燃料电池/燃气轮机混合动力系统中的燃气轮机在系统设计点和部分工况下的运行特性进行了分析。对系统部分负荷工况,分析了四种不同运行方式下燃气轮机的特性。结果表明,与单独运行相比,在混合动力系统中燃气轮机的运行特性会发生明显的变化。在系统设计点,由于压气机和透平间较多部件的存在导致压损增大使燃气轮机的输出功下降。部分工况下,燃气轮机的运行特性对混合动力系统的特性有较大的影响。     

Performance characteristics of a solid oxide fuel cell/gas turbine hybrid system with various part-load control modes

The purpose of this study is to compare the part-load performance of a solid oxide fuel cell/gas turbine (SOFC/GT) hybrid system in three different control modes: fuel-only control, rotational speed control, and variable inlet guide vane (VIGV) control. While the first mode maintains a constant air supply and reduces the supplied fuel to achieve part-load operation, the other modes are distinguished by the simultaneous controls of the air and fuel supplied to the system. After the performance analysis of a SOFC/GT hybrid system under part-load operating conditions, it was concluded that the rotational speed control mode provided the best performance characteristics for part-load operations. In spite of worse performance than the rotational speed control mode, the VIGV control mode can be a good candidate for part-load operation in a large-scale hybrid system in which the rotational speed control is not applicable. It was also found that, in spite of a relatively small contribution to the total system power generation, the gas turbine plays an important role in part-load operation of a SOFC/GT hybrid system.     

Performance characteristics of part-load operations of a solid oxide fuel cell/gas turbine hybrid system using air-bypass valves

In spite of the high-performance characteristics of a solid oxide fuel cell/gas turbine (SOFC/GT) hybrid system, it is difficult to maintain high-level performance under real application conditions, which generally require part-load operations. The efficiency loss of the SOFC/GT hybrid system under such conditions is closely related to that of the gas turbine. The power generated by the gas turbine in a hybrid system is much less than that generated by the SOFC, but its contribution to the efficiency of the system is important, especially under part-load conditions. Over the entire operating load profile of a hybrid system, the efficiency of the hybrid system can be maximized by increasing the contribution of power coming from the high efficiency component, namely the fuel cell. In this study, part-load control strategies using air-bypass valves are proposed, and their impact on the performance of an SOFC/GT hybrid system is discussed. It is found that air-bypass modes with control of the fuel supply help to overcome the limits of the part-load operation characteristics in air/fuel control modes, such as variable rotational speed control and variable inlet guide vane control.     

Design and partial load exergy analysis of hybrid SOFC–GT power plant

This paper presents a full and partial load exergy analysis of a hybrid SOFC–GT power plant. The plant basically consists of: an air compressor, a fuel compressor, several heat exchangers, a radial gas turbine, mixers, a catalytic burner, an internal reforming tubular solid oxide fuel cell stack, bypass valves, an electrical generator and an inverter. The model is accurately described. Special attention is paid at the calculation of SOFC overpotentials. Maps are introduced, and properly scaled, in order to evaluate the partial load performance of turbomachineries. The plant is simulated at full-load and part-load operation, showing energy and exergy flows trough all its components and thermodynamic properties at each key-point. At full-load operation a maximum value of 65.4% of electrical efficiency is achieved. Three different part-load strategies are introduced. The off-design operation is achieved handling the following parameters: air mass flow rate, fuel mass flow rate, combustor bypass, gas turbine bypass, avoiding the use of a variable speed control system. Results showed that the most efficient part-load strategy corresponded to a constant value of the fuel to air ratio. On the other hand, a lower value of net electrical power (34% of nominal load) could be achieved reducing fuel flow rate, at constant air flow rate. This strategy produces an electrical efficiency drop that becomes 45%.     

Part-load performance characteristics of a lean burn catalytic combustion gas turbine system

The purpose of this study is to compare the part-load performance of a lean burn catalytic combustion gas turbine (LBCCGT) system in three different control modes: varying fuel, bleeding off the fuel mixture flow after the compressor and varying rotational speed. The conversions of methane species for chemical process are considered. A 1D heterogeneous plug flow model was utilized to analyze the system performance. The actual turbomachinery components were designed and predicted performance maps were applied to system performance research. The part-load characteristics under three control strategies were numerically investigated. The main results show that: the combustor inlet temperature is a significant factor that can significantly affect the part-load characteristics of the LBCCGT system; the rotational speed control mode can provide the best performance characteristics for part-load operations; the operation range of the bleed off mode is narrower than that of the speed control mode and wider than that of the fuel only mode; with reduced power, methane does not achieve full conversion over the reactor at the fuel only control mode, which will not warrant stable operation of the turbine system; the thermal efficiency of the LBCCGT system at fuel only control strategy is higher than that at bleed off control strategy within the operation range.     

Performance analysis for the part-load operation of a solid oxide fuel cell–micro gas turbine hybrid system

In this paper, the performance evaluation of a solid oxide fuel cell (SOFC)–micro gas turbine (MGT) hybrid power generation system under the part-load operation was studied numerically. The present analysis code includes distributed parameters model of the cell stack module. The conversions of chemical species for electrochemical process and fuel reformation process are considered. Besides the temperature distributions of the working fluids and each solid part of cell module by accounting heat generation and heat transfers, are taken into calculation. Including all of them, comprehensive energy balance in the cell stack module is calculated. The variable MGT rotational speed operation scheme is adopted for the part-load operation. It will be made evident that the power generation efficiency of the hybrid system decreases together with the power output. The major reason for the performance degradation is the operating temperature reduction in the SOFC module, which is caused by decreasing the fuel supply and the heat generation in the cells. This reduction is also connected to the air flow rate supplement. The variable MGT rotational speed control requires flexible air flow regulations to maintain the SOFC operating temperature. It will lead to high efficient operation of the hybrid system.     

Molten carbonate fuel cell (MCFC)-based hybrid propulsion systems for a liquefied hydrogen tanker

This study proposes a molten carbonate fuel cell (MCFC)-based hybrid propulsion system for a liquefied hydrogen tanker. This system consists of a molten carbonate fuel cell and a bottoming cycle. Gas turbine and steam turbine systems are considered for recovering heat from fuel cell exhaust gases. The MCFC generates a considerable propulsion power, and the turbomachinery generates the remainder of the power. The hybrid systems are evaluated regarding system efficiency, economic feasibility, and exhaust emissions. The MCFC with a gas turbine has higher system efficiency than that with a steam turbine. The air compressor consumes substantial power and should be mechanically connected to the gas turbine. Although fuel cell-based systems are less economical than other propulsion systems, they may satisfy the environmental regulations. When the ship is at berth, the MCFC systems can be utilized as distributed generation that is connected to the onshore-power grid.     

Operation window and part-load performance study of a syngas fired gas turbine

Integrated coal gasification combined cycle (IGCC) provides a great opportunity for clean utilization of coal while maintaining the advantage of high energy efficiency brought by gas turbines. A challenging problem arising from the integration of an existing gas turbine to an IGCC system is the performance change of the gas turbine due to the shift of fuel from natural gas to synthesis gas, or syngas, mainly consisting of carbon monoxide and hydrogen. Besides the change of base-load performance, which has been extensively studied, the change of part-load performance is also of great significance for the operation of a gas turbine and an IGCC plant.In this paper, a detailed mathematical model of a syngas fired gas turbine is developed to study its part-load performance. A baseline is firstly established using the part-load performance of a natural gas fired gas turbine, then the part-load performance of the gas turbine running with different compositions of syngas is investigated and compared with the baseline. Particularly, the impacts of the variable inlet guide vane, the degree of fuel dilution, and the degree of air bleed are investigated. Results indicate that insufficient cooling of turbine blades and a reduced compressor surge margin are the major factors that constrain the part-load performance of a syngas fired gas turbine. Results also show that air bleed from the compressor can greatly improve the working condition of a syngas fired gas turbine, especially for those fired with low lower heating value syngas. The regulating strategy of a syngas fired gas turbine should also be adjusted in accordance to the changes of part-load performance, and a reduced scope of constant TAT (turbine exhaust temperature) control mode is required.     

Performance analysis on various system layouts for the combination of an ambient pressure molten carbonate fuel cell and a gas turbine

This study analyses hybrid systems combining a molten carbonate fuel cell (MCFC) operating at ambient pressure and a gas turbine. Various possible system layouts, with the major difference among these layouts being the heating method of the turbine inlet gas, are proposed and their design performances are simulated and comparatively analyzed. Power of the MCFC in the hybrid system is explained in terms of the cathode inlet air temperature. Power of the gas turbine differs among various layouts because of large difference in the turbine inlet temperature. The direct firing in front of the turbine allows far higher turbine inlet temperature, and thus greater gas turbine power than the indirect heating of the inlet gas. The optimum pressure ratio of the directly fired system is higher than that of the indirectly fired system. The directly fired system allows not only much larger system power and higher optimum efficiency but also greater flexibility in the selection of the design pressure ratio of the gas turbine. In addition, the directly fired system can better accommodate the specifications of both current micro gas turbines and advanced gas turbines than the indirectly fired system.     

Analysis of the design of a pressurized SOFC hybrid system using a fixed gas turbine design

Design characteristics and performance of a pressurized solid oxide fuel cell (SOFC) hybrid system using a fixed gas turbine (GT) design are analyzed. The gas turbine is assumed to exist prior to the hybrid system design and all the other components such as the SOFC module and auxiliary parts are assumed to be newly designed for the hybrid system. The off-design operation of the GT is modeled by the performance characteristics of the compressor and the turbine. In the SOFC module, internal reforming with anode gas recirculation is adopted. Variations of both the hybrid system performance and operating condition of the gas turbine with the design temperature of the SOFC were investigated. Special focus is directed on the shift of the gas turbine operating points from the original points. It is found that pressure loss at the fuel cell module and other components, located between the compressor and the turbine, shifts the operating point. This results in a decrease of the turbine inlet temperature at each compressor operating condition relative to the original temperature for the GT only system. Thus, it is difficult to obtain the original GT power. Two cell voltage cases and various degrees of temperature difference at the cell are considered and their influences on the system design characteristics and performance are comparatively analyzed.     

Molten carbonate fuel cell and gas turbine hybrid systems as distributed energy resources

Molten carbonate fuel cell (MCFC)/gas turbine (GT) hybrid system has attracted a great deal of research effort due to its higher electricity efficiency. However, its technology has remained at the conceptual level due to incomplete examination of the related issues, challenges and variables. To contribute to the development of system technology, the MCFC/GT hybrid system is analyzed and discussed herein. A qualitative comparison of the two kinds of MCFC/GT hybrid system, indirect and direct, is hindered by the many variables involved. However, the indirect system may be preferred for relatively small-scale systems with the micro-GT. The direct system can be more competitive in terms of system efficiency and GT selection due to the optionality of system layouts as well as even higher GT inlet temperature. System layout is an important factor influencing the system efficiency. The other issues such as GT selection, system pressurization and part-load operation are also significant.     

Methodologies for predicting the part-load performance of aero-derivative gas turbines

Prediction of the part-load performance of gas turbines is advantageous in various applications. Sometimes reasonable part-load performance is sufficient, while in other cases complete agreement with the performance of an existing machine is desirable. This paper is aimed at providing some guidance on methodologies for predicting part-load performance of aero-derivative gas turbines. Two different design models – one simple and one more complex – are created. Subsequently, for each of these models, the part-load performance is predicted using component maps and turbine constants, respectively. Comparisons with manufacturer data are made. With respect to the design models, the simple model, featuring a compressor, combustor and turbines, results in equally good performance prediction in terms of thermal efficiency and exhaust temperature as does a more complex model. As for part-load predictions, the results suggest that the mass flow and pressure ratio characteristics can be well predicted with both methods. The thermal efficiency and exhaust temperature, however, are not well predicted below 60–70% load when using turbine constants and assuming constant efficiencies for turbomachinery.     

Performance characteristics of a MW-class SOFC/GT hybrid system based on a commercially available gas turbine

The ultimate purpose of a SOFC/GT hybrid system is for distributed power generation applications. Therefore, this study investigates the possible extension of a SOFC/GT hybrid system to multi-MW power cases. Because of the matured technology of gas turbines and their commercial availability, it was reasonable to construct a hybrid system with an off-the-shelf gas turbine. Based on a commercially available gas turbine, performance analysis was conducted to find the total appropriate power for the hybrid system with consideration of the maximum allowable cell temperature. In order to maintain high performance characteristics of the hybrid system during part-load operations, it was necessary to find the optimal control strategy for the system according to the change in power required. The results of the performance analysis for part-load conditions showed that supplied fuel and air must be changed simultaneously. Furthermore, in order to prevent performance degradation, it was found that both cell temperature and turbine inlet temperature must be maintained as close as possible to design-point conditions.     

Thermal performance prediction of a solar hybrid gas turbine

The present work focuses on a modelling procedure to simulate the operation of a solar hybrid gas turbine. The method is applied to a power generation system including an heliostat field, a receiver and a 36 MW commercial gas turbine. Heat is provided by concentrated solar power and integrated by fossil fuel. A detailed modelling of the gas turbine (GT) is proposed to predict the performance of commercial GT models in actual operating conditions. Advanced software tools were combined together to predict design and off-design performance of the whole system: TRNSYS® was used to model the solar field and the receiver while the gas turbine simulation was performed by means of Thermoflex®. A detailed comparison between the solarized and the conventional gas turbine is reported, taking into account GT electric power, efficiency and shaft speed. All thermodynamic parameters such pressure ratio, air flow and fuel consumption were compared. The main advantage of solarization is the fossil fuel saving, but it is balanced by a relevant penalty in power output and efficiency.     

压气机静叶可调对燃气轮机和联合循环变工况性能的影响

本文叙述了压气机采用可调静叶对单轴恒速燃气轮机变工况性能的影响。通过计算得到了燃气轮机变工况性能曲线,分析了不同的最大排气温度对静叶调节区的影响,以及在部分负荷下机组效率变化的影响。叙述了压气机静叶调节时对由单轴恒速燃气轮机组成的联合循环的影响,指出这时能改善部分负荷下的效率,因而得到了实际应用。     

燃气轮机驱动压缩机组负荷控制参数波动问题研究

西气东输工程燃气轮机驱动压缩机组控制系统负荷控制功能不完善,造成机组在压力自动控制模式下,燃机、压缩机的转速和排气温度等重要参数在运行过程中极不稳定,并呈现周期性振动特性,对燃机重要部件造成严重的低周疲劳损伤。本文对机组的控制方式进行了研究,分析了机组功率、转速、排气温度波动的机理,通过合理调整控制器参数解决了机组关键参数波动的问题,显著改善了机组的运行稳定性和可靠性,对于提高机组的使用寿命、降低热部件的疲劳损耗具有主要作用。所做工作对机组控制系统的设计和调整具有参考价值。     

基于BP神经网络的9F燃气轮机压气机离线水洗周期优化

基于BP神经网络,对某9F燃气轮机机组历史运行数据进行了建模与分析,提出了一种燃气轮机压气机叶片积垢导致其性能下降的分析方法,得到了燃气轮机压气机效率、压气机压比、压气机流量、燃气轮机功率四个性能参数偏差值随燃气轮机实际运行小时的变化曲线。结果表明,可将上述四个性能参数的实际运行值与理想状态下的运行值(神经网络预测值)偏差3%、3%、4%、5%作为压气机离线水洗的判据。据此,对9F燃气轮机机组现有的离线水洗周期进行优化,得出当前燃气轮机压气机积垢状态实际运行指导小时数为3 000 h。该方法为燃气轮机离线水洗周期优化提供了一种思路,具有一定的工程应用价值。     

Improving hybrid SOFC‐GT systems performance through turbomachinery design

A methodology to improve the performance of a hybrid solid oxide fuel cell gas turbine (SOFC‐GT) system for the whole operating range is proposed. The method suggests a way to estimate the geometric parameters of the turbomachinery components for a hybrid SOFC‐GT system. It is based on the search of the compressor and turbine operating lines giving the optimum system efficiency both in design and part load operation. Turbomachinery models are used to calculate the geometry that produces the desired performance maps and the corresponding operating lines. Based on the new turbomachinery design, the hybrid system shows a clear efficiency advantage for the whole operating range. Copyright © 2014 John Wiley & Sons, Ltd.     

Catalytic combustion and system performance assessment of MCFC-MGT hybrid system

The catalytic combustor is applied as an off-gas and startup combustor for a molten carbonate fuel cell-micro-gas turbine (MCFC-MGT) hybrid system (HS) so as to utilize the waste energy of fuel cell off-gas. Three types of catalysts are prepared over a cordieritic honeycomb support. One is Pt catalyst which is not cost effective and less high temperature stability. CeZrO₂ and LaMnO₃ have been selected as an additive for another two Pt catalysts to improve the performance. Tests have been completed in realistic conditions and reaction feed close to the MCFC-MGT hybrid system. Simulations are carried out with a fluid mechanical code that incorporates detailed transport and heat loss mechanisms. The simulation results are compared with the Pt catalyst test results. The agreement confirms the accuracy of simulation. The model can be used to develop an MCFC-MGT hybrid system with an off-the-shelf gas turbine and assess the performances during part-load operation. From the experimental results, the reaction starts at 620 K for 1 vol.% CH₄ using Pt catalyst, while the temperature is above 800 K for the addition of additive. For the 50% CH₄ conversion, the preheated temperature of the three catalysts is 713 K, 870 K and 950 K respectively. While all of the catalysts exhibit good performance when using the MCFC off-gas as fuel. The results of performance analysis for part-load conditions show that the cell operation temperature and turbine inlet temperature (TIT) should be maintained as close as possible to the design value to prevent the performance degradation.     

Part-load,startup, and shutdown strategies of a solid oxide fuel cell-gas turbine hybrid system

Current work on the performance of a solid oxide fuel cell (SOFC) and gas turbine hybrid system is presented. Each component model developed and applied is mathematically defined. The electrochemical performance of single SOFC with different fuels is tested. Experimental results are used to validate the SOFC mathematical model. Based on the simulation model, a safe operation regime of the hybrid system is accurately plotted first. Three different part-load strategies are introduced and used to analyze the part-load performance of the hybrid system using the safe regime. Another major objective of this paper is to introduce a suitable startup and shutdown strategy for the hybrid system. The sequences for the startup and shutdown are proposed in detail, and the system responses are acquired with the simulation model. Hydrogen is used instead of methane during the startup and shutdown process. Thus, the supply of externally generated steam is not needed for the reforming reaction. The gas turbine is driven by complementary fuel and supplies compressed air to heat up or cool down the SOFC stack operating temperature. The dynamic simulation results show that smooth cooling and heating of the cell stack can be accomplished without external electrical power.