Fuel Cell Turbine Hybrid Research Articles

A Degradation Diagnosis Method for Gas Turbine—Fuel Cell Hybrid Systems Using Bayesian Networks

Abstract This paper aims to develop and test Bayesian belief network-based diagnosis methods, which can be used to predict the most likely degradation levels of turbine, compressor, and fuel cell (FC) in a hybrid system based on different sensors measurements. The capability of the diagnosis systems to understand if an abnormal measurement is caused by a component degradation or by a sensor fault is also investigated. The data used both to train and to test the networks are generated from a deterministic model and later modified to consider noise or bias in the sensors. The application of Bayesian belief networks (BBNs) to fuel cell—gas turbine hybrid systems is novel, thus the results obtained from this analysis could be a significant starting point to understand their potential. The diagnosis systems developed for this work provide essential information regarding levels of degradation and presence of faults in a gas turbine, fuel cell and sensors in a fuel cell—gas turbine hybrid system. The Bayesian belief networks proved to have a good level of accuracy for all the scenarios considered, regarding both steady-state and transient operations. This analysis also suggests that in the future a Bayesian belief network could be integrated with the control system to achieve safer and more efficient operations of these plants.

Surge and Stall Detection Using Acoustic Analysis for Gas Turbine Hybrid Cycles

Abstract Compressor dynamics were studied in a gas turbine—fuel cell hybrid power system having a larger compressor volume than traditionally found in gas turbine systems. This larger compressor volume adversely affects the surge margin of the gas turbine. Industrial acoustic sensors were placed near the compressor to identify when the equipment was getting close to the surge line. Fast Fourier transform (FFT) mathematical analysis was used to obtain spectra representing the probability density across the frequency range (0–5000 Hz). Comparison between FFT spectra for nominal and transient operations revealed that higher amplitude spikes were observed during incipient stall at three different frequencies, 900, 1020, and 1800 Hz. These frequencies were compared to the natural frequencies of the equipment and the frequency for the rotating turbomachinery to identify more general nature of the acoustic signal typical of the onset of compressor surge. The primary goal of this acoustic analysis was to establish an online methodology to monitor compressor stability that can be anticipated and avoided.

Compressor Instability Analysis Within a Hybrid System Subject to Cycle Uncertainties

The dynamic modeling of energy systems can be used for different purposes, obtaining important information both for the design phase and control system strategies, increasing the confidence during experimental phase. Such analysis in dynamic conditions is generally performed considering fixed values for both geometrical and operational parameters such as volumes, orifices, but also initial temperatures, pressure. However, such characteristics are often subject to uncertainty, either because they are not known accurately or because they may depend on the operating conditions at the beginning of the relevant transient. With focus on a gas turbine fuel cell hybrid system (HS), compressor surge may or may not occur during transients, depending on the aforementioned cycle characteristics; hence, compressor surge events are affected by uncertainty. In this paper, a stochastic analysis was performed taking into account an emergency shut-down (ESD) in a fuel cell gas turbine HS, modeled with TRANSEO, a deterministic tool for the dynamic simulations. The aim of the paper is to identify the main parameters that impact on compressor surge margin. The stochastic analysis was performed through the response sensitivity analysis (RSA) method, a sensitivity-based approximation approach that overcomes the computational burden of sampling methods. The results show that the minimum surge margin occurs in two different ranges of rotational speed: a high-speed range and a low-speed range. The temperature and geometrical characteristics of the pressure vessel, where the fuel cell is installed, are the two main parameters that affect the surge margin during an emergency shut down.

Multicoordination Control Strategy Performance in Hybrid Power Systems

This paper evaluates a state-space methodology of a multi-input multi-output (MIMO) control strategy using a 2 × 2 tightly coupled scenario applied to a physical gas turbine fuel cell hybrid power system. A centralized MIMO controller was preferred compared to a decentralized control approach because previous simulation studies showed that the coupling effect identified during the simultaneous control of the turbine speed and cathode airflow was better minimized. The MIMO controller was developed using a state-space dynamic model of the system that was derived using first-order transfer functions empirically obtained through experimental tests. The controller performance was evaluated in terms of disturbance rejection through perturbations in the gas turbine operation, and setpoint tracking maneuver through turbine speed and cathode airflow steps. The experimental results illustrate that a multicoordination control strategy was able to mitigate the coupling of each actuator to each output during the simultaneous control of the system, and improved the overall system performance during transient conditions. On the other hand, the controller showed different performance during validation in simulation environment compared to validation in the physical facility, which will require a better dynamic modeling of the system for the implementation of future multivariable control strategies.

Open Loop and Closed Loop Performance of Solid Oxide Fuel Cell Turbine Hybrid Systems During Fuel Composition Changes

The dynamic behavior of a solid oxide fuel cell gas turbine hybrid system (SOFC/GT) from both open and closed loop transients in response to sudden changes in fuel composition was experimentally investigated. A pilot-scale (200–700 kW) hybrid facility available at the U.S. Department of Energy, National Energy Technology Laboratory was used to perform the experiments using a combination of numerical models and actual equipment. In the open loop configuration, the turbine speed was driven by the thermal effluent fed into the gas turbine system, where the thermal effluent was determined by the feedforward fuel cell control system. However, in the closed loop configuration, a load-based speed control system was used to maintain the turbine speed constant at 40,500 rpm by adjusting the load on the turbine, in addition to the implementation of the fuel cell system control. The open loop transient response showed that the impacts of fuel composition changes on key process variables, such as fuel cell thermal effluent, turbine speed, and cathode feed stream conditions, in the SOFC/GT systems were propagated over the course of the test, except for the cathode inlet temperature. The trajectories of the aforementioned variables are discussed in this paper to better understand the resulting mitigation/propagation behaviors. This will help lead to the development of novel control strategies to mitigate the negative impacts experienced during fuel composition transients of SOFC/GT systems.

Technical challenges in operating an SOFC in fuel flexible gas turbine hybrid systems: Coupling effects of cathode air mass flow

Considering the limited turndown potential of gasification technologies, supplementing a fuel cell turbine hybrid power system with natural gas provides flexibility that could improve economic viability. The dynamic characterization of fuel composition transients is an essential first step in completing the system identification required for controls development. In this work, both open loop and closed loop transient responses of the fuel cell in a solid oxide fuel cell (SOFC) gas turbine (GT) hybrid system to fuel composition changes were experimentally investigated using a cyber-physical fuel cell system. A transition from methane lean syngas to methane rich gases with no turbine speed control was studied. The distributed performance of the fuel cell was analyzed in detail with temporal and spatial resolution across the cell.Dramatic changes in fuel cell system post combustor thermal output or “thermal effluent” resulting from anode composition changes drove turbine transients that caused significant cathode airflow fluctuations, by as much as 8% in less than a minute. In comparing the open loop responses to identical tests conducted under closed loop conditions without significant airflow changes, it was discovered that the cathode airflow change was a major linking event in short-term system transient response. The results suggested that modulating cathode air flow in response to fuel composition changes offers promise for the dynamic control of SOFC/GT hybrid systems with fuel flexibility.

Control Impacts of Cold-Air Bypass on Pressurized Fuel Cell Turbine Hybrids

A pressure drop analysis for a direct-fired fuel cell turbine hybrid power system was evaluated using a hardware-based simulation of an integrated gasifier/fuel cell/turbine hybrid cycle, implemented through the hybrid performance (Hyper) project at the National Energy Technology Laboratory, U.S. Department of Energy (NETL). The Hyper facility is designed to explore dynamic operation of hybrid systems and quantitatively characterize such transient behavior. It is possible to model, test, and evaluate the effects of different parameters on the design and operation of a gasifier/fuel cell/gas turbine hybrid system and provide means of evaluating risk mitigation strategies. The cold-air bypass in the Hyper facility directs compressor discharge flow to the turbine inlet duct, bypassing the fuel cell, and exhaust gas recuperators in the system. This valve reduces turbine inlet temperature while reducing cathode airflow, but significantly improves compressor surge margin. Regardless of the reduced turbine inlet temperature as the valve opens, a peak in turbine efficiency is observed during characterization of the valve at the middle of the operating range. A detailed experimental analysis shows the unusual behavior during steady state and transient operation, which is considered a key point for future control strategies in terms of turbine efficiency optimization and cathode airflow control.

Fuel Composition Transients in Fuel Cell Turbine Hybrid for Polygeneration Applications

Transient impacts on the performance of solid oxide fuel cell/gas turbine (SOFC/GT) hybrid systems were investigated using hardware-in-the-loop simulations (HiLSs) at a test facility located at the U.S. Department of Energy, National Energy Technology Laboratory. The work focused on applications relevant to polygeneration systems, which require significant fuel flexibility. Specifically, the dynamic response of implementing a sudden change in fuel composition from syngas to methane was examined. The maximum range of possible fuel composition allowable within the constraints of carbon deposition in the SOFC and stalling/surging of the turbine compressor system was determined. It was demonstrated that the transient response was significantly impact the fuel cell dynamic performance, which mainly drives the entire transient in SOFC/GT hybrid systems. This resulted in severe limitations on the allowable methane concentrations that could be used in the final fuel composition when switching from syngas to methane. Several system performance parameters were analyzed to characterize the transient impact over the course of 2 h from the composition change.

Avoiding Compressor Surge During Emergency Shutdown Hybrid Turbine Systems

A new emergency shutdown procedure for a direct-fired fuel cell turbine hybrid power system was evaluated using a hardware-based simulation of an integrated gasifier/fuel cell/turbine hybrid cycle (IGFC), implemented through the Hybrid Performance (Hyper) project at the National Energy Technology Laboratory, U.S. Department of Energy (NETL). The Hyper facility is designed to explore dynamic operation of hybrid systems and quantitatively characterize such transient behavior. It is possible to model, test, and evaluate the effects of different parameters on the design and operation of a gasifier/fuel cell/gas turbine hybrid system and provide a means of quantifying risk mitigation strategies. An open-loop system analysis regarding the dynamic effect of bleed air, cold air bypass, and load bank is presented in order to evaluate the combination of these three main actuators during emergency shutdown. In the previous Hybrid control system architecture, catastrophic compressor failures were observed when the fuel and load bank were cut off during emergency shutdown strategy. Improvements were achieved using a nonlinear fuel valve ramp down when the load bank was not operating. Experiments in load bank operation show compressor surge and stall after emergency shutdown activation. The difficulties in finding an optimal compressor and cathode mass flow for mitigation of surge and stall using these actuators are illustrated.

선박동력용 SOFC/ST 하이브리드시스템의 성능 평가

연료전지시스템의 고효율화를 목적으로 수소가 가진 화학적 에너지를 최대한 전력화하기 위하여 연료전지에서 발생하는 폐열을 적극 활용할 필요가 있다. 이런 목적에 폐열을 이용하는 증기터빈과 연료 전지를 결합시킨 SOFC/ST 하이브리드시스템이 적합하다. 본 논문은 SOFC/ST 하이브리드시스템에 대한 셀의 작동온도와 전류밀도, 연소기 출구 온도, 보일러 출구 가스온도가 시스템의 성능에 미치는 영향 등을 시뮬레이션을 통하여 검토한 것으로 증기터빈의 일정 조건에서는 연료전지 스택에서 다량의 폐열이 발생하는 경우가, 연료전지의 일정 조건에서는 연소기에 추가적 연료 공급을 억제하는 경우에서 하이브리드시스템의 효율이 증가됨을 확인하였다.

Examination of the Effect of System Pressure Ratio and Heat Recuperation on the Efficiency of a Coal-Based Gas Turbine Fuel Cell Hybrid Power Generation System With CO2 Capture

This paper examines two coal-based hybrid configurations that employ separated anode and cathode streams for the capture and compression of CO2. One configuration uses a standard Brayton cycle, and the other adds heat recuperation ahead of the fuel cell. Results show that peak efficiencies near 55% are possible, regardless of cycle configuration, including the cost in terms of energy production of CO2 capture and compression. The power that is required to capture and compress CO2 is shown to be approximately 15% of the total plant power.

125 固体酸化物形燃料電池・マイクロガスタービン複合発電システムにおける各種燃料毎の総合効率評価とシステム最適化(学生賞IV,一般講演)

125 固体酸化物形燃料電池・マイクロガスタービン複合発電システムにおける各種燃料毎の総合効率評価とシステム最適化(学生賞IV,一般講演)

Scaling a Solid Oxide Fuel Cell Gas Turbine Hybrid System to Meet a Range of Power Demand

In recent years there has been significant interest in using the heat generated from the normal operation of a solid oxide fuel cell (SOFC) to supplant the normal combustion process of a gas turbine system. By doing this a gas turbine fuel cell hybrid power generation system is formed. Because the heat produced by a SOFC is utilized by the turbine to produce work, the hybrid system can have an overall system efficiency that greatly exceeds those of either the stand alone SOFC system, or the stand alone gas turbine system. One of the most critical problems that must be addressed in gas turbine fuel cell hybrid technology is temperature control. A hybrid system that is designed to operate efficiently for a given base load may not be easily extended to accommodate peek load. In this paper a simple hybrid system configuration using a standard SOFC and a single compressor-turbine pair is presented. This simple system is used to establish the effect that key configuration parameters have on system temperatures. The configuration model is then scaled over a range of fuel input and power output to show the limitations of the system. The system is modeled using the ASPEN PLUS® simulation software with special modules to calculate fuel cell performance.

Basic Electrochemical Thermodynamic Studies of Fuel Cells and Fuel Cell Hybrids

It is important to understand the maximum possible thermal efficiency a device is capable of obtaining and then what of this it actually achieves. In this paper it is shown that the thermal efficiency is a product of the voltage efficiency and the maximum possible thermal efficiency. One can mathematically demonstrate that for any elemental direct anodic oxidation reaction for a simple hybrid system, any fuel cell, and any operating temperature, any pressure, the maximum reversible work is equal to the free energy of reaction at the standard state. This is useful in defining an intrinsic fuel cell exergetic efficiency. An equation for thermal efficiency as a product of exergetic efficiency and maximum possible thermal efficiency is developed and presented for loosely integrated fuel cell turbine hybrids. From these simple studies alone one would conclude that the efficiency potential of fuel cells is expanded through simple fuel cell turbine hybrids.

Basic Electrochemical Thermodynamic Studies of Fuel Cells Using MALT2

There are at least four basic fuel cell thermodynamic features: maximum intrinsic thermal efficiency (electrical efficiency), reversible potential, and two new ones—intrinsic cooling requirement and intrinsic exergetic efficiency. A basic electrochemical thermodynamic analysis of fuel cells using MALT reveals that it is probably for thermodynamic reasons that cooling strategies other than excess oxidant, such as water cooling, have generally been adopted for lower temperature fuel cells such as polymer electrolyte fuel cell (PEFC) and phosphoric acid fuel cell (PAFC). One can mathematically demonstrate that for a simple hybrid system, any fuel cell, any operating temperature, and any pressure, the maximum reversible work is equal to the free energy of reaction at the standard state. This study gives information of new opportunity fuels having increasing importance is all future energy scenarios. The results of this analysis show that ammonia and direct methanol give greater maximum intrinsic thermal efficiency than hydrogen oxidation. From these simple studies alone, one would conclude that the great payoff in terms of theoretical efficiency potential for research is direct carbon fuel cell (DCFT), PEFC, and direct oxidation of methane, intermediate temperature solid oxide fuel cell (SOFC), and simple fuel cell turbine hybrids.

Distributed generation—Molten carbonate fuel cells

High efficiency and ultra-clean molten carbonate fuel cell (MCFC) technology development by FuelCell Energy, with support from the U.S. Department of Energy (DOE), has progressed to commercial power plants for stationary applications such as distributed generation. Lessons learned from this development will also be valuable to DOE for the ongoing Solid State Energy Conversion Alliance (SECA) solid oxide fuel cell (SOFC) development and cost reduction, for fuel cell turbine hybrids, and for hydrogen economy development with FutureGen.

U.S. DOE fossil energy fuel cells program

The U.S. Department of Energy's (DOE) Office of Fossil Energy's (FE) National Energy Technology Laboratory (NETL), in partnership with private industry, educational institutions and national laboratories, is leading the development and demonstration of high efficiency, high temperature solid oxide fuel cells (SOFCs) and fuel cell turbine (FCT) hybrid power generation systems for stationary markets including auxiliary power units (APUs), distributed generation (DG) and large, coal-based central power plants. The DOE FE fuel cells program has three aspects: the Solid State Energy Conversion Alliance (SECA), Fuel Cell Coal Based Systems for central power, and the High Temperature Electrochemistry Center (HiTEC). The SECA goal is to decrease SOFC system cost to US$ 400 per kilowatt (kW) by 2010 for stationary markets. DOE FE is ultimately concerned with coal-based central power plants such as FutureGen. The goal is to aggregate SECA-type fuel cells into larger systems and to produce a very high efficiency megawatt-class FCT hybrid for testing at FutureGen. The low-cost, US$ 400 kW −1 SECA FCT hybrid is a key component to achieving 60% efficiency by 2020. Advanced aspects of solid oxide technology are part of HiTEC R&D. Technical progress and advances are discussed for all three program aspects.

General fuel cell hybrid synergies and hybrid system testing status

FCT hybrid power systems offer the highest efficiency and the cleanest emissions of all fossil fuelled power. The engineering for the highest possible efficiency at lowest cost and weight depends on general system architecture issues and the performance of the components. Presented in this paper are system studies which provide direction for the most efficient path toward achieving the most beneficial result for this technology. Ultimately, fuel cell-turbine (FCT) hybrid systems applicable to integrated gasification combined cycle power systems will form the basis for reaching the goals for advanced coal-based power generation. The FCT hybrid power island will also be important for the FutureGen plant and will provide new options for carbon dioxide capture and sequestration as well as power and hydrogen generation. The system studies presented in this paper provide insight to current technology ‘benchmarks’ versus expected benefits from hybrid applications. Discussion is also presented on the effects of different balance of plant arrangements and approaches. Finally, we discuss the status of US DOE is sponsored projects that are looking to help understand the unique requirements for these systems. One of these projects, Hyper, will provide information on FCT dynamics and will help identify technical needs and opportunities for cycle advancement. The methods studied show promise for effective control of a hybrid system without the direct intervention of isolation valves or check valves in the main pressure loop of the system, which introduce substantial pressure losses, allowing for realization of the full potential efficiency of the hybrid system.

U.S. Department of Energy′s Solid Oxide Fuel Cells: Technical Advances

AbstractFor Abstract see ChemInform Abstract in Full Text.

U.S. Department of Energy's Solid Oxide Fuel Cells: Technical Advances

The U.S. Department of Energy's (DOE) Office of Fossil Energy's (FE) National Energy Technology Laboratory (NETL), in partnership with private industries, is leading the development and demonstration of high‐efficiency solid oxide fuel cells (SOFCs) and fuel cell turbine hybrid power generation systems for distributed generation (DG) markets. The DOE FE DG program has three aspects: the Solid State Energy Conversion Alliance (SECA), Central Power Systems, and the High Temperature Electrochemistry Center (HiTEC). NETL is partnering with Pacific Northwest National Laboratory in developing new directions in research under SECA for the development and commercialization of modular, low‐cost, and fuel‐flexible SOFC systems. The SECA initiative, through advanced materials, processing, and system integration research and development (R&D) will bring the fuel cell cost to $400 per kilowatt (kW) by 2010 for stationary and auxiliary power unit markets. The SECA program is currently structured to include six competing industry teams supported by a crosscutting core technology program. DOE is ultimately concerned with coal‐based central power plants. Advanced aspects of solid oxide technology are part of HiTEC R&D.