Gas Turbine Hybrid Cycle Research Articles

Thermodynamic sensitivity analysis of SOFC integrated with blade cooled gas turbine hybrid cycle

In the area of clean energy production along with higher efficiency, integrated combine power system, specifically gas turbine (GT) cycle with solid oxide fuel (SOFC) system, is gaining the attention of researchers. Thermodynamic modeling for the SOFC-GT hybrid cycle has been presented in this paper. For the proposed hybrid cycle, a high-temperature SOFC has successfully integrated with the recuperated-blade cooled gas turbine cycle. The gas turbine outlet waste heat has perfectly utilized the recuperator to power the fuel cell system. However, to maintain the temperature of the gas turbine blade within the permissible limit, air–film blade cooling scheme has been used. The SOFC-GT hybrid cycle has been operated under steady-state conditions, and a developed MATLAB program has been used to solve the governing equations for the components of the hybrid cycle. The impact of main operating parameters such as the temperature intake turbine (TIT), compression ratio (rpc), fuel utilization ratio (UF), and recirculation ratio are examined. From the obtained result, it can be revealed that the integration of the SOFC has seen significant improves overall hybrid cycle efficiency. The performance of fuel cell (SOFC) increases notably as the level of recuperation increases. To check the influence of main operating parameters, a sensitivity analysis has been performed for the hybrid cycle, and the maximum efficiency of 73% has been achieved. Moreover, to extend this research, an exclusive performance map has been plotted for power plant designers.

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.

Using inlet guide vane to improve load following ability of solid oxide fuel cell and gas turbine hybrid cycle

High efficiency and high reliability with low emission of solid oxide fuel cell make them one of the best choices for distributed generation systems. Furthermore, the gas turbine power generation systems are completely developed in recent decades. Hybrid cycle of SOFC and gas turbine gathers these points and introduces the highest possible efficient system for building heating and power. The behavior of this cycle can be studied from a model of fuel cell, gas turbine and balance of plant. For each component a model is developed and the performance of the overall system analyzed by integrating each model. Load variation for SOFC-GT hybrid cycle in residential application is very wide. To adjust the net power and choosing best operation point for SOFC-GT hybrid cycle, an inlet guide vane (IGV) is used in the inlet of the compressor. In this study by using a dynamic model, transient effect of IGV angle on performance of SOFC-GT hybrid cycle is investigated. Also this model can be used for designing a controller for safe operation of this cycle while satisfying constraints of the hybrid cycle. Results showed that by using IGV, the off-design performance of the SOFC-GT cycle is enhanced.

Robust Multi-Objective Optimization of Solid Oxide Fuel Cell–Gas Turbine Hybrid Cycle and Uncertainty Analysis

Chemical process optimization problems often have multiple and conflicting objectives, such as capital cost, operating cost, production cost, profit, energy consumptions, and environmental impacts. In such cases, multi-objective optimization (MOO) is suitable in finding many Pareto optimal solutions, to understand the quantitative tradeoffs among the objectives, and also to obtain the optimal values of decision variables. Gaseous fuel can be converted into heat, power, and electricity, using combustion engine, gas turbine (GT), or solid oxide fuel cell (SOFC). Of these, SOFC with GT has shown higher thermodynamic performance. This hybrid conversion system leads to a better utilization of natural resource, reduced environmental impacts, and more profit. This study optimizes performance of SOFC–GT system for maximization of annual profit and minimization of annualized capital cost, simultaneously. For optimal SOFC–GT designs, the composite curves for maximum amount of possible heat recovery indicate good performance of the hybrid system. Further, first law energy and exergy efficiencies of optimal SOFC–GT designs are significantly better compared to traditional conversion systems. In order to obtain flexible design in the presence of uncertain parameters, robust MOO of SOFC–GT system was also performed. Finally, Pareto solutions obtained via normal and robust MOO approaches are considered for parametric uncertainty analysis with respect to market and operating conditions, and solution obtained via robust MOO found to be less sensitive.

Exergy, economic and environmental analysis and multi-objective optimization of a SOFC-GT power plant

Thermodynamic, exergy, economic and environmental analysis of a solid oxide fuel cell and gas turbine hybrid cycle have been done in this paper. Also, multi-objective optimization of this cycle has been done by NSGA-II algorithm. In order to defining of the optimum design point, interactive fuzzy multi-objective method has been used. At optimum point, the cost function value, 0.0435 (US$/s) and exergy efficiency approximately 57.7% have been obtained. As well, sensitivity analysis of fuel cost per energy unit into objective functions has been done. In addition, rising inlet temperature of gas turbine from 900 up to 1600 (K), has caused an increase in output power up to 8.5% and entropy generation about 30% and a reduction in exergy efficiency from 61.9% to 51.7%. By evaluation of entropy generation rate, it has been concluded that most of enthalpy generation rate (32%) is related to combustion chamber. Increasing of fuel cell stack temperature causes an increase in exergy efficiency from 56.6% up to 60.2% and about 34.8% in output power of the cycle and a reduction in exergy efficiency from 62.8% to 59.1% and 8.4% in fuel cell power. Also, payback time of this cycle is about 3.12 years.

Thermodynamic assessment of advanced SOFC-blade cooled gas turbine hybrid cycle

This paper focuses on novel integration of high temperature solid oxide fuel cell coupled with recuperative gas turbine (with air-film cooling of blades) based hybrid power plant (SOFC-blade cooled GT). For realistic analysis of gas turbine cycle air-film blade cooling technique has been adopted. First law thermodynamic analysis investigating the combine effect of film cooling of blades, SOFC, applied to a recuperated gas turbine cycle has been reported. Thermodynamic modeling for the proposed cycle has been presented. Results highlight the influence of film cooling of blades and operating parameters of SOFC on various performance of SOFC-blade cooled GT based hybrid power plant. Moreover, parametric investigation has also been done to examine the effect of compressor pressure ratio, turbine inlet temperature, on hybrid plant efficiency and plant specific work. It has been found that on increasing turbine inlet temperature (TIT) beyond a certain limit, the efficiency of gas turbine starts declining after reaching an optimum value which is compensated by continuous increase in SOFC efficiency with increase in operating temperature. The net result is higher performance of hybrid cycle with increase in maximum cycle temperature. Furthermore, it has been observed that at TIT 1600 K and compression ratio 20, maximum efficiency of 73.46% can been achieved.

Comparison of Single-stage and Two-stage Tubular SOFC-GT Hybrid Cycles: Energy and Exergy Viewpoints

In this work, single-stage and two-stage tubular solid oxide fuel cell (SOFC)/gas turbine hybrid cycles are comparatively examined from the energy and exergy viewpoints. For this purpose, mass, energy and exergy balances are applied to all components of the cycles. The behavior of tubular solid oxide fuel cell modeled in this study is validated with the experimental test data of tubular SOFC developed by Siemens Westinghouse. The results of simulation show that two-stage SOFC-GT hybrid cycle not only generate more power,but also it has high efficiency in comparison to single-stage SOFC-GT. The values of first law efficiency and Exergetic Performance Coefficient (EPC) are increased from 60.69% and 1.405 in single-stage SOFC-GT to 63.93% and 1.725 in two-stage SOFC-GT respectively. This means that for equivalent generated power of single and two-stage SOFC-GT hybrid cycles, the amount of exergy destruction for two-stage SOFC-GT cycle is less than single-stage SOFC-GT. Also exergy destruction of all components of the hybrid cycles is calculated separately and results are compared. Finally a parametric study is performed to find out optimal values for solid oxide fuel cell design parameters. Effects of these parameters are evaluated on efficiency, generated power and total exergy destruction of the hybrid cycles.

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

AbstractDistributed 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.

Process integration and optimization of a solid oxide fuel cell – Gas turbine hybrid cycle fueled with hydrothermally gasified waste biomass

Due to its suitability for using wet biomass, hydrothermal gasification is a promising process for the valorization of otherwise unused waste biomass to synthesis gas and biofuels. Solid oxide fuel cell (SOFC) based hybrid cycles are considered as the best candidate for a more efficient and clean conversion of (bio) fuels. A significant potential for the integration of the two technologies is expected since hydrothermal gasification requires heat at 673–773K, whereas SOFC is characterized by heat excess at high temperature due to the limited electrochemical fuel conversion.This work presents a systematic process integration and optimization of a SOFC-gas turbine (GT) hybrid cycle fueled with hydrothermally gasified waste biomass. Several design options are systematically developed and compared through a thermodynamic optimization approach based on First Law and exergy analysis.The work demonstrates the considerable potential of the system that allows for converting wet waste biomass into electricity at a First Law efficiency of up to 63%, while simultaneously enabling the separation of biogenic carbon dioxide for further use or sequestration.

Study on a novel solid oxide fuel cell/gas turbine hybrid cycle system with CO2 capture

SUMMARY A novel solid oxide fuel cell (SOFC)/gas turbine (GT) hybrid cycle system with CO2 capture is proposed based on a typical topping cycle SOFC/GT hybrid system. The H2 gas is separated from the outlet mixture gas of SOFC1 anode by employing the advanced ceramic proton membrane technology, and then, it is injected into SOFC2 to continue a new electrochemical reaction. The outlet gas of SOFC1 cathode and the exhaust gas from SOFC2 burn in the afterburner 1. The combustion gas production of the afterburner1 expands in the turbine 1. The outlet gas of SOFC1 anode employs the oxy-fuel combustion mode in the afterburner 2 after H2 gas is separated. Then, the combustion gas production expands in the turbine 2. To ensure that the flue gas temperature does not exceed the maximum allowed turbine inlet temperature, steam is injected into the afterburner 2. The outlet gas of the afterburner 2 contains all the CO2 gas of the system. When the steam is removed by condensation, the CO2 gas can be captured. The steam generated by the waste heat boiler is used to drive a refrigerator and make CO2 gas liquefied at a lower temperature. The performance of the novel quasi-zero CO2 emission SOFC/GT hybrid cycle system is analyzed with a case study. The effects of key parameters, such as CO2 liquefaction temperature, hydrogen separation rate, and the unit oxygen production energy consumption on the new system performance, are investigated. Compared with the other quasi-zero CO2 emission power systems, the new system has the highest efficiency of around 64.13%. The research achievements will provide the valuable reference for further study of quasi-zero CO2 emission power system with high efficiency. Copyright © 2011 John Wiley & Sons, Ltd.

Innovative Hybrid Cycle Solid Oxide Fuel Cell‐Inverted Gas Turbine with CO2 Separation

AbstractDecentralized power generation and cogeneration of heat and power is an attractive way toward a more rational conversion of fossil or biofuel. In small‐scale power production fuel cell–gas turbine hybrid cycles are an emerging candidate to reach higher or comparable efficiency than large‐scale power plants. The present contribution introduces an innovative concept of hybrid cycle that allows targeting high efficiency together with carbon dioxide separation and maintaining the fuel cell operating under atmospheric condition. The system consists in a planar module of solid oxide fuel cell operating at atmospheric pressure, an oxy‐combustion unit, and two separated gas turbine units driven in an inverted Brayton cycle. A thermodynamic optimization approach, based on the system energy integration, is used to analyze several design options. Optimization results demonstrate that the proposed hybrid system enables higher energy conversion efficiency with respect to an equivalent state of the art pressurized hybrid system, whilst avoiding fuel cell pressurization technical problems, and enabling the carbon dioxide separation. The potential of designs achieving 80% First Law efficiency is shown.

Comparison between two optimization strategies for solid oxide fuel cell–gas turbine hybrid cycles

This paper compares the performance characteristics of a combined power system with solid oxide fuel cell (SOFC) and gas turbine (GT) working under two thermodynamic optimization strategies. Expressions of the optimized power output and efficiency for both the subsystems and the SOFC-GT hybrid cycle are derived. Optimal performance characteristics are discussed and compared in detail through a parametric analysis to evaluate the impact of multi-irreversibilities that take into account on the system behaviour. It is found that there exist certain new optimum criteria for some important design and operating parameters. Engineers should find the methodologies developed in this paper useful in the optimal design and practical operation of complex hybrid fuel cell power plants.

05/02256 Analysis and optimization of a solid oxide fuel cell and intercooled gas turbine (SOFC-ICGT) hybrid cycle

05/02256 Analysis and optimization of a solid oxide fuel cell and intercooled gas turbine (SOFC-ICGT) hybrid cycle

Dynamic Modeling on the Hybrid Molten Carbonate Fuel Cell-Gas Turbine Bottoming Cycle

The intention of this paper is to present the dynamic models for the molten carbonate fuel cell (MCFC)-gas turbine hybrid cycle. This paper analyzes the performance of various components in the hybrid power plant, such as the compressor, turbine, recuperator, generator, fuel cell stack, etc. The modular simulation models of these components are presented. Based on the dynamic simulation modeling principle, one bottoming hybrid MCFC-microturbine cycle was studied to carry out the simulation. The simulation result can reflect the dynamic response of the hybrid power plant.

Analysis and optimization of a solid oxide fuel cell and intercooled gas turbine (SOFC–ICGT) hybrid cycle

Abstract The power generation community faces a major challenge: to protect the environment while producing a plentiful supply of clean low-cost energy. “21st Century Energy Plants” (Vision 21 Plants) have been proposed and conceptualized to meet the energy and environmental challenges. The solid oxide fuel cell and intercooled gas turbine (SOFC–ICGT) hybrid cycle introduced in this work is one example of a Vision 21 Plant. The system includes an internal-reforming tubular-SOFC, an intercooled gas turbine, a humidifier, and other auxiliary components. A recently developed thermodynamic analysis computer code entitled advanced power systems analyses tools (APSAT) was applied to analyze the system performance of the SOFC–ICGT cycle. Sensitivity analyses of several major system parameters were studied to identify the key development needs and design and operating improvements for this hybrid cycle. A novel optimization strategy including a design of experiments (DOEx) approach is proposed and applied to the hybrid system. Using this optimization strategy, a system electrical efficiency higher than 75% (net ac/lower heating value (LHV)) could be achieved when the system was designed to operate under a high operating pressure (50 bara) and with a low percent excess air (EA) (55%) in the SOFC.

Efficiency Upgrading of an Ambient Pressure Molten Carbonate Fuel Cell Plant Through the Introduction of an Indirect Heated Gas Turbine

The efficient end environmentally friendly production of electricity is undoubtedly one of the 21st century priorities. Since renewable sources will be able to guarantee only a share of the future demand, the present research activity must focus on innovative energy devices and improved conversion systems and cycles. Great expectations are reserved to fuel cell systems. The direct conversion from chemical to electrical energy eliminates environmental problems connected with combustion and bypass the stringent efficiency limit due to Carnot’s principle. Still in infancy, high-temperature fuel cells present the further advantage of feasible cycle integration with steam or gas turbines. In this paper, a molten carbonate fuel cell plant is simulated in a cycle for power generation. The introduction of an external combustion gas turbine is evaluated with the aim of efficiency and net power output increase. The results show that the proposed cycle can be conveniently used as a source of power generation. As compared to internal combustion gas turbine hybrid cycles found in the literature the plant is characterized by fuel cell greater simplicity, due to the absence of pressurization, and gas turbine increased complexity, due to the presence of the heat exchange system.