Exergy and Energy Analysis of Combined Cycle systems with Different Bottoming Cycle Configurations

The paper deals with thermodynamic analysis of cooled gas turbine‐based gas‐steam combined cycle with single, dual, or triple pressure bottoming cycle configuration. The cooled gas turbine analyzed here uses air as blade coolant. Component‐wise non‐dimensionalized exergy destruction of the bottoming cycle has been quantified with the objective to identify the major sources of exergy destruction. The mass of steam generated in different configurations of heat recovery steam generator (HRSG) depends upon the number of steam pressure drums, desired pressure level, and steam temperature. For the selected set of operating parameters, maximum steam has been observed to be generated in the case of triple pressure HRSG = 19 kg/kg and minimum in single pressure HRSG = 17.25 kg/kg. Plant‐efficiency and plant‐specific works are both highest for triple‐pressure bottoming cycle combined cycle. Non‐dimensionalized exergy destruction in HRSG is least at 0.9% for B3P, whereas 1.23% for B2P, and highest at 3.2% for B1P illustrating that process irreversibility is least in the case of B3P and highest in B1P. Copyright © 2012 John Wiley & Sons, Ltd.     

Energy and exergy analysis of internal reforming solid oxide fuel cell–gas turbine hybrid system

The aim of this work is to analyze methane-fed internal reforming solid oxide fuel cell–gas turbine (IRSOFC—GT) power generation system based on the first and second law of thermodynamics. Exergy analysis is used to indicate the thermodynamic losses in each unit and to assess the work potentials of the streams of matter and of heat interactions. The system consists of a prereformer, a SOFC stack, a combustor, a turbine, a fuel compressor and air compressor, recuperators and a heat recovery steam generator (HRSG). A parametric study is also performed to evaluate the effect of various parameters such as fuel flow rate, air flow rate, temperature and pressure on system performance.     

A performance analysis of integrated solid oxide fuel cell and heat recovery steam generator for IGFC system

Solid oxide fuel cell (SOFC) is a promising technology for electricity generation. Sulfur-free syngas from a gas-cleaning unit serves as fuel for SOFC in integrated gasification fuel cell (IGFC) power plants. It converts the chemical energy of fuel gas directly into electric energy, thus high efficiencies can be achieved. The outputs from SOFC can be utilized by heat recovery steam generator (HRSG), which drives the steam turbine for electricity production. The SOFC stack model was developed using the process flow sheet simulator Aspen Plus, which is of the equilibrium type. Various ranges of syngas properties gathered from different literature were used for the simulation. The results indicate a trade-off efficiency and power with respect to a variety of SOFC inputs. The HRSG located after SOFC was included in the current simulation study with various operating parameters. This paper describes IGFC power plants, particularly the optimization of HRSG to improve the efficiency of the heat recovery from the SOFC exhaust gas and to maximize the power production in the steam cycle in the IGFC system. HRSG output from different pressure levels varies depending on the SOFC output. The steam turbine efficiency was calculated for measuring the total power plant output. The aim of this paper is to provide a simulation model for the optimal selection of the operative parameters of HRSG and SOFC for the IGFC system by comparing it with other models. The simulation model should be flexible enough for use in future development and capable of predicting system performance under various operating conditions.     

A performance analysis of integrated solid oxide fuel cell and heat recovery steam generator for IGFC system

Solid oxide fuel cell (SOFC) is a promising technology for electricity generation. Sulfur-free syngas from a gas-cleaning unit serves as fuel for SOFC in integrated gasification fuel cell (IGFC) power plants. It converts the chemical energy of fuel gas directly into electric energy, thus high efficiencies can be achieved. The outputs from SOFC can be utilized by heat recovery steam generator (HRSG), which drives the steam turbine for electricity production. The SOFC stack model was developed using the process flow sheet simulator Aspen Plus, which is of the equilibrium type. Various ranges of syngas properties gathered from different literature were used for the simulation. The results indicate a trade-off efficiency and power with respect to a variety of SOFC inputs. The HRSG located after SOFC was included in the current simulation study with various operating parameters. This paper describes IGFC power plants, particularly the optimization of HRSG to improve the efficiency of the heat recovery from the SOFC exhaust gas and to maximize the power production in the steam cycle in the IGFC system. HRSG output from different pressure levels varies depending on the SOFC output. The steam turbine efficiency was calculated for measuring the total power plant output. The aim of this paper is to provide a simulation model for the optimal selection of the operative parameters of HRSG and SOFC for the IGFC system by comparing it with other models. The simulation model should be flexible enough for use in future development and capable of predicting system performance under various operating conditions.     

Comparative performance analysis of cogeneration gas turbine cycle for different blade cooling means

The paper compares the thermodynamic performance of MS9001 gas turbine based cogeneration cycle having a two-pressure heat recovery steam generator (HRSG) for different blade cooling means. The HRSG has a steam drum generating steam to meet coolant requirement, and a second steam drum generates steam for process heating. Gas turbine stage cooling uses open loop cooling or closed loop cooling schemes. Internal convection cooling, film cooling and transpiration cooling techniques employing steam or air as coolants are considered for the performance evaluation of the cycle. Cogeneration cycle performance is evaluated using coolant flow requirements, plant specific work, fuel utilisation efficiency, power-to-heat-ratio, which are function of compressor pressure ratio and turbine inlet temperature, and process steam drum pressure. The maximum and minimum values of power-to-heat ratio are found with steam internal convection cooling and air internal convection cooling respectively whereas maximum and minimum values of fuel utilisation efficiency are found with steam internal convection cooling and closed loop steam cooling. The analysis is useful for power plant designers to select the optimum compressor pressure ratio, turbine inlet temperature, fuel utilisation efficiency, power-to-heat ratio, and appropriate cooling means for a specified value of plant specific work and process heating requirement.     

Thermodynamic analysis of an integrated power generation system driven by solid oxide fuel cell

A new integrated power generation system driven by the solid oxide fuel cell (SOFC) is proposed to improve the conversion efficiency of conventional energy by using a Kalina cycle to recover the waste heat of exhaust from the SOFC-GT. The system using methane as main fuel consists an internal reforming SOFC, an after-burner, a gas turbine, preheaters, compressors and a Kalina cycle. The proposed system is simulated based on the developed mathematical models, and the overall system performance has been evaluated by the first and second law of thermodynamics. Exergy analysis is conducted to indicate the thermodynamic losses in each components. A parametric analysis is also carried out to examine the effects of some key thermodynamic parameters on the system performance. Results indicate that as compressor pressure ratio increases, SOFC electrical efficiency increases and there is an optimal compressor pressure ratio to reach the maximum overall electrical efficiency and exergy efficiency. It is also found that SOFC electrical efficiency, overall electrical efficiency and exergy efficiency can be improved by increasing air flow rate. Also, the largest exergy destruction occurs in the SOFC followed by the after-burner, the waste heat boiler, the gas turbine. The compressor pressure ratio and air flow rate have significant effects on the exergy destruction in some main components of system.     

Exergy analyses and parametric optimizations for different cogeneration power plants in cement industry

The cement production is an energy intensive industry with energy typically accounting for 50–60% of the production costs. In order to recover waste heat from the preheater exhaust and clinker cooler exhaust gases in cement plant, single flash steam cycle, dual-pressure steam cycle, organic Rankine cycle (ORC) and the Kalina cycle are used for cogeneration in cement plant. The exergy analysis for each cogeneration system is examined, and a parameter optimization for each cogeneration system is achieved by means of genetic algorithm (GA) to reach the maximum exergy efficiency. The optimum performances for different cogeneration systems are compared under the same condition. The results show that the exergy losses in turbine, condenser, and heat recovery vapor generator are relatively large, and reducing the exergy losses of these components could improve the performance of the cogeneration system. Compared with other systems, the Kalina cycle could achieve the best performance in cement plant.     

Thermodynamic analysis of an LNG fuelled combined cycle power plant with waste heat recovery and utilization system

This paper has proposed an improved liquefied natural gas (LNG) fuelled combined cycle power plant with a waste heat recovery and utilization system. The proposed combined cycle, which provides power outputs and thermal energy, consists of the gas/steam combined cycle, the subsystem utilizing the latent heat of spent steam from the steam turbine to vaporize LNG, the subsystem that recovers both the sensible heat and the latent heat of water vapour in the exhaust gas from the heat recovery steam generator (HRSG) by installing a condensing heat exchanger, and the HRSG waste heat utilization subsystem. The conventional combined cycle and the proposed combined cycle are modelled, considering mass, energy and exergy balances for every component and both energy and exergy analyses are conducted. Parametric analyses are performed for the proposed combined cycle to evaluate the effects of several factors, such as the gas turbine inlet temperature (TIT), the condenser pressure, the pinch point temperature difference of the condensing heat exchanger and the fuel gas heating temperature on the performance of the proposed combined cycle through simulation calculations. The results show that the net electrical efficiency and the exergy efficiency of the proposed combined cycle can be increased by 1.6 and 2.84% than those of the conventional combined cycle, respectively. The heat recovery per kg of flue gas is equal to 86.27 kJ s^?1. One MW of electric power for operating sea water pumps can be saved. The net electrical efficiency and the heat recovery ratio increase as the condenser pressure decreases. The higher heat recovery from the HRSG exit flue gas is achieved at higher gas TIT and at lower pinch point temperature of the condensing heat exchanger. Copyright © 2006 John Wiley & Sons, Ltd.     

Energetic and exergetic performance analyses of a combined heat and power plant with absorption inlet cooling and evaporative aftercooling

In this paper, exergy method is applied to analyze the gas turbine cycle cogeneration with inlet air cooling and evaporative aftercooling of the compressor discharge. The exergy destruction rate in each component of cogeneration is evaluated in detail. The effects of some main parameters on the exergy destruction and exergy efficiency of the cycle are investigated. The most significant exergy destruction rates in the cycle are in combustion chamber, heat recovery steam generator and regenerative heat exchanger. The overall pressure ratio and turbine inlet temperature have significant effect on exergy destruction in most of the components of cogeneration. The results obtained from the analysis show that inlet air cooling along with evaporative aftercooling has an obvious increase in the energy and exergy efficiency compared to the basic gas turbine cycle cogeneration. It is further shown that the first-law efficiency, power to heat ratio and exergy efficiency of the cogeneration cycle significantly vary with the change in overall pressure ratio and turbine inlet temperature but the change in process heat pressure shows small variation in these parameters.     

Energy,exergy, and environmental (3E) assessments of an integrated molten carbonate fuel cell (MCFC), Stirling engine and organic Rankine cycle (ORC) cogeneration system fed by a biomass-fueled gasifier

In this paper, a novel syngas-fed combined cogeneration plant, integrating a biomass gasifier, a molten carbonate fuel cell (MCFC), a heat recovery steam generator (HRSG) unit, a Stirling engine, and an organic Rankine cycle (ORC), is introduced and thermodynamically analyzed to recognize its potentials compared to the previous solo/combined systems. For the proposed system, energetic, exergetic as well as environmental evaluations are performed. Based on the results, the gasifier and the fuel cell have a significant contribution to the exergy destruction of the system. Through a parametric study, the current density and the stack temperature difference are known as the main effective factors on the plant performance. Meanwhile, dividing the whole system into three sub-models, i.e., model (1): power production plant including the gasifier and MCFC without including Stirling engine, HRSG, and ORC unit, model (2): the cogeneration system without ORC unit, and model (3): the whole cogeneration system, an environmental impact assessment is carried out regarding CO₂ emission. Considering paper as biomass revealed that maximum value of exergy efficiency is 50.18% with CO₂ emissions of 28.9 × 10⁻² t.MWh⁻¹ which compared to the solo MCFC system indicates 28.40% increase and 13.3 × 10⁻² t.MWh⁻¹ decrease in exergy efficiency and CO₂ emission, respectively.     

Exergy analysis of an integrated solid oxide fuel cell and organic Rankine cycle for cooling, heating and power production

The study examines a novel system that combined a solid oxide fuel cell (SOFC) and an organic Rankine cycle (ORC) for cooling, heating and power production (trigeneration) through exergy analysis. The system consists of an SOFC, an ORC, a heat exchanger and a single-effect absorption chiller. The system is modeled to produce a net electricity of around 500 kW. The study reveals that there is 3-25% gain on exergy efficiency when trigeneration is used compared with the power cycle only. Also, the study shows that as the current density of the SOFC increases, the exergy efficiencies of power cycle, cooling cogeneration, heating cogeneration and trigeneration decreases. In addition, it was shown that the effect of changing the turbine inlet pressure and ORC pump inlet temperature are insignificant on the exergy efficiencies of the power cycle, cooling cogeneration, heating cogeneration and trigeneration. Also, the study reveals that the significant sources of exergy destruction are the ORC evaporator, air heat exchanger at the SOFC inlet and heating process heat exchanger.     

Performance Improvement of Combined Cycle Power Plant Based on the Optimization of the Bottom Cycle and Heat Recuperation

Many F class gas turbine combined cycle(GTCC)power plants are built in China at present because of less emis-sion and high efficiency.It is of great interest to investigate the efficiency improvement of GTCC plant.A com-bined cycle with three-pressure reheat heat recovery steam generator(HRSG)is selected for study in this paper.In order to maximize the GTCC efficiency,the optimization of the HRSG operating parameters is performed.Theoperating parameters are determined by means of a thermodynamic analysis,i.e.the minimization of exergylosses.The influence of HRSG inlet gas temperature on the steam bottoming cycle efficiency is discussed.Theresult shows that increasing the HRSG inlet temperature has less improvement to steam cycle efficiency when itis over 590℃.Partial gas to gas recuperation in the topping cycle is studied.Joining HRSG optimization with theuse of gas to gas heat recuperation,the combined plant efficiency can rise up to 59.05% at base load.In addition,the part load performance of the GTCC power plant gets much better.The efficiency is increased by 2.11% at75% load and by 4.17% at 50% load.     

Engineering design and exergy analyses for combustion gas turbine based power generation system

This paper presents the engineering design and theoretical exergetic analyses of the plant for combustion gas turbine based power generation systems. Exergy analysis is performed based on the first and second laws of thermodynamics for power generation systems. The results show the exergy analyses for a steam cycle system predict the plant efficiency more precisely. The plant efficiency for partial load operation is lower than full load operation. Increasing the pinch points will decrease the combined cycle plant efficiency. The engineering design is based on inlet air-cooling and natural gas preheating for increasing the net power output and efficiency. To evaluate the energy utilization, one combined cycle unit and one cogeneration system, consisting of gas turbine generators, heat recovery steam generators, one steam turbine generator with steam extracted for process have been analyzed. The analytical results are used for engineering design and component selection.     

The effect of elevated inlet air temperature and relative humidity on cogeneration system

The effect of elevated inlet air temperature and relative humidity on a gas turbine (GT) cogeneration system performance was investigated. The analysis was carried out on a GT of a capacity 171 MW at ISO condition, which is integrated with a dual pressure heat recovery steam generator (HRSG), the cogeneration system had been tested under Kuwait summer climate conditions. A computational model was developed and solved using engineering equation solver professional package to investigate the performance of a dual pressure GT‐HRSG system. The suggested HRSG is capable of producing high‐pressure superheated steam at 150 bar and 510°C to operate a power generation steam turbine cycle, and a medium pressure saturated steam at 15 bar to run a thermal vapor compression (TVC) desalination system. In this research, the influence of elevated inlet air temperature and relative humidity on the energy assessment of the suggested cogeneration system was thoroughly investigated. Results indicated that operating GT under elevated values of inlet air temperatures is characterized by low values of net power and thermal efficiency. At elevated inlet air temperatures, increasing relative humidity has a small positive impact on GT cycle net power and thermal efficiency. Integrating the GT with HRSG to generate steam for power generation and process heat tends to increase energy utilization factor of the system at elevated inlet air temperatures. Increasing inlet air temperature plays a negative impact on power to heat ratio (PHR), while relative humidity has no effect on PHR. Copyright © 2009 John Wiley & Sons, Ltd.     

Energy and exergy analyses of an integrated SOFC and coal gasification system

This paper examines an integrated gasification and solid oxide fuel cell (SOFC) system with a gas turbine and steam cycle that uses heat recovery of the gas turbine exhaust. Energy and exergy analyses are performed with two different types of coal. For the two different cases, the energy efficiency of the overall system is 38.1% and 36.7%, while the exergy efficiency is 27% and 23.2%, respectively. The effects of changing the reference temperature on the exergy destruction and exergy efficiency of different components are also reported. A parametric study on the effects of changing the pressure ratio on the component performance is presented.     

Thermoeconomic modeling and parametric study of hybrid SOFC–gas turbine–steam turbine power plants ranging from 1.5 to 10 MWe

Detailed thermodynamic, kinetic, geometric, and cost models are developed, implemented, and validated for the synthesis/design and operational analysis of hybrid SOFC–gas turbine–steam turbine systems ranging in size from 1.5 to 10 MWe. The fuel cell model used in this research work is based on a tubular Siemens-Westinghouse-type SOFC, which is integrated with a gas turbine and a heat recovery steam generator (HRSG) integrated in turn with a steam turbine cycle. The current work considers the possible benefits of using the exhaust gases in a HRSG in order to produce steam which drives a steam turbine for additional power output. Four different steam turbine cycles are considered in this research work: a single-pressure, a dual-pressure, a triple pressure, and a triple pressure with reheat. The models have been developed to function both at design (full load) and off-design (partial load) conditions. In addition, different solid oxide fuel cell sizes are examined to assure a proper selection of SOFC size based on efficiency or cost. The thermoeconomic analysis includes cost functions developed specifically for the different system and component sizes (capacities) analyzed. A parametric study is used to determine the most viable system/component syntheses/designs based on maximizing total system efficiency or minimizing total system life cycle cost.     

联产制冷的能效性能探讨

利用汽轮机抽汽作为吸收式制冷驱动热源的联产制冷，将供电、制冷有机结合在一起，不仅满足制冷要求也改善联产机组效率。通过引入抽汽yong增益概念，揭示了汽轮机抽汽特性规律，在此基础上从联产制冷目的yong效率角度比较了几种制冷方式，分析了汽轮机抽汽参数和相对内效率等因素对联产制冷能效性能影响规律，抽汽的yong增益比是联产制冷yong效率影响起决定作用的因素，所得结论对联产制冷吸收机的合理选用匹配提供有益的指导。     

Thermo‐Economic Analysis and Multiobjective Optimization of Dual Pressure Combined Cycle Power Plant with Supplementary Firing

The heat recovery steam generator (HRSG) and duct burner are parts of a combined cycle which have considerable effect on the steam generation. The effect of the gas turbine, duct burner and HRSG on power generation is investigated to reduce exergy destruction and power loss in the gas turbine. The results show that with an increase in duct burner flow rate, pressure loss in the recovery boiler increases, steam generation increases on the HP side while it decreases on the LP side. With a reduction in the HP pinch point, thermal recovery increases while the LP pinch point does not have a significant effect. Then, power loss due to pressure drop in the gas turbine and the electricity cost are considered as two objective functions for optimization. Finally, the sensitivity analysis on ambient temperature, compressor pressure ratio, fuel lower heating value, duct burner fuel rate, condenser pressure and main pressure are performed and results are reported. It is concluded that with an increment in compressor pressure ratio, the duct burner flow rate and consequently steam generation increases while electricity cost decrease.     

Exergy based performance analysis of a solid oxide fuel cell and steam injected gas turbine hybrid power system

This paper presents exergy analysis of a hybrid solid oxide fuel cell and gas turbine (SOFC/GT) system in comparison with retrofitted system with steam injection. It is proposed to use hot gas turbine exhaust gases heat in a heat recovery steam generator to produce steam and inject it into gas turbine. Based on a steady-state model of the processes, exergy flow rates are calculated for all components and a detailed exergy analysis is performed. The components with the highest proportion of irreversibility in the hybrid systems are identified and compared. It is shown that steam injection decreases the wasted exergy from the system exhaust and boosts the exergetic efficiency by 12.11%. Also, 17.87% and 12.31% increase in exergy output and the thermal efficiency, respectively, is demonstrated. A parametric study is also performed for different values of compression pressure ratio, current density and pinch point temperature difference.     

Thermodynamic,exergoeconomic and exergoenvironmental analyses and optimization of a solid oxide fuel cell-based trigeneration system

This study proposes a trigeneration system based on solid oxide fuel cell (SOFC) for generating power, cooling and heating simultaneously. The system mainly contains a SOFC, a gas turbine (GT), an organic Rankine cycle (ORC), a steam ejector refrigerator (SER) and a heat exchanger. The thermodynamic, exergoeconomic and exergoenvironmental models of proposed trigeneration system are developed, and the effects of design parameters on system performances are analyzed. The results indicate that the system average product cost and environmental impact per unit of exergy increase with SOFC inlet temperature and working pressure, the pinch point temperature difference and evaporating pressure of Generator, while decrease with the current density of fuel cell. Finally, optimization is performed to achieve the optimal exergy-based performance. It is revealed that though the system exergy efficiency is decreased by 7.64% after optimization, the system average product cost and environmental impact per unit of exergy are significantly reduced.