Effect of altering combustion air flow on a steam power plant: energy and exergy analysis

Energy and exergy analyses were previously performed by the authors of a coal-fired steam power plant. These analyses suggest that the steam generator (and its combustion and heat-transfer processes) is the most inefficient plant device and that significant increases in overall plant efficiency are possible by reducing steam-generator irreversibilities. Here, a possible plant alteration is examined to increase the efficiency of the plant by reducing the irreversibility rate in the steam generator. The modification involves decreasing the fraction of excess combustion air from 0.40 to 0.15. The results show that overall-plant energy and exergy efficiencies both increase by 1.4% when the fraction of excess combustion air decreases from 0.4 to 0.15.Copyright © 2006 John Wiley & Sons, Ltd.     

A study of industrial steam process heating through exergy analysis

This study investigates using exergy analysis the technical factors that influence the feasibility of substituting steam supplied for other energy sources in industrial heating. Some alternative configurations for the steam‐supply system capable of broadening the range of industries able to use the steam for heating are proposed. When examining the feasibility of substituting steam for other energy currencies for providing process heat, exergy analysis quantitatively determines the increase in process efficiency when a lower value energy currency such as steam is used in place of a higher value energy currency such as electricity. Many industries can benefit from using steam for some or all of their heating requirements. An illustrative example for the Bruce Energy Center in Ontario, Canada is presented to demonstrate the importance of using exergy analysis to assess the feasibility of industrial steam process heating. Some alternate reconfigurations of the Center are considered to supply steam at a variety of thermodynamic states, and better match the steam‐state requirements of many industries. The results suggest that exergy analysis should be used as the central tool in process optimization when the use of large quantities of the steam in energy centers is contemplated. Copyright © 2004 John Wiley & Sons, Ltd.     

Energy–exergy analysis and modernization suggestions for a combined‐cycle power plant

Energy and exergy analysis were carried out for a combined‐cycle power plant by using the data taken from its units in operation to analyse a complex energy system more thoroughly and to identify the potential for improving efficiency of the system. In this context, energy and exergy fluxes at the inlet and the exit of the devices in one of the power plant main units as well as the energy and exergy losses were determined. The results show that combustion chambers, gas turbines and heat recovery steam generators (HRSG) are the main sources of irreversibilities representing more than 85% of the overall exergy losses. Some constructive and thermal suggestions for these devices have been made to improve the efficiency of the system. Copyright © 2005 John Wiley & Sons, Ltd.     

Thermodynamic analysis of reheat cycle steam power plants

In this study, a thermodynamic analysis of a Rankine cycle reheat steam power plant is conducted, in terms of the first law of thermodynamic analysis (i.e. energy analysis) and the second law analysis (i.e. exergy analysis), using a spreadsheet calculation technique. The energy and exergy efficiencies are studied as 120 cases for different system parameters such as boiler temperature, boiler pressure, mass fraction ratio and work output. The temperature and pressure values are selected in the range between 400 and 590°C, and 10 and 15 MPa, being consistent with the actual values. The calculated energy and exergy efficiencies are compared with the actual data and the literature work, and good agreement is found. The possibilities to further improve the plant efficiency and hence reduce the inefficiencies are identified and exploited. The results show how exergy analysis can help to make optimum design decisions in a logical manner. Copyright © 2001 John Wiley & Sons, Ltd.     

Efficient design of feedwater heaters network in steam power plants using pinch technology and exergy analysis

A design method is presented based on pinch technology and exergy analysis to reduce heat transfer irreversibility of the feedwater heaters network in steam power plants. In order to show the effects of this method, an extensive study was performed on four steam power plants. The results show that applying this method can decrease the fuel consumption and the condenser load. It also increases the boiler, the feedwater heaters network, and the turbine exergetic efficiencies. On the whole, the results show that applying this method, with a target pinch temperature of 3°C, increases the cycle 2nd law efficiency 0.3–1.3% and the fossil fuel consumption decreases about 64 × 10⁶kg annually for 8000 operating hours per year of the studied steam power plants. Copyright © 2007 John Wiley & Sons, Ltd.     

Energy and exergy analysis of a novel efficient combined process by hydrothermal degradation and superheated steam drying of degradable organic wastes

This paper considers the combination of hydrothermal degradation(HTD)and superheated steam(SHS)drying indisposal and processing of degradable organic wastes in municipal solid wastes(MSW).In SHS drying, a fractionof dryer thermal energy input can be recovered and used to satisfy the heat requirement in maintaining the HTDoperating temperature.Both energy and exergy analysis are applied to the combined process.The analysis coversranges of dryer inlet temperatures of 202.38-234.19℃ and feed water content of 32.5-65%.Thermal energyanalysis shows that the combination of HTD and SHS drying can achieve thermal energy self-sufficiency(TES)by manipulating process variables.The exergy analysis indicates the location,type,and magnitude of the exergylosses during the whole process by applying the second law of thermodynamics.     

Exergy-energy analysis of full repowering of a steam power plant

A 320 MW old steam power plant has been chosen for repowering in this paper. Considering the technical conditions and working life of the power plant, the full repowering method has been selected from different repowering methods. The power plant repowering has been analyzed for three different feed water flow rates: a flow rate equal to the flow rate at the condenser exit in the original plant when it works at nominal load, a flow rate at maximum load, and a flow rate when all the extractions are blocked. For each flow rates, two types of gas turbines have been examined: V94.2 and V94.3A. The effect of a duct burner has then been investigated in each of the above six cases. Steam is produced by a double-pressure heat recovery steam generator (HRSG) with reheat which obtains its required heat from the exhaust gases coming from the gas turbines. The results obtained from modeling and analyzing the energy-exergy of the original steam power plant and the repowered power plant indicate that the maximum efficiency of the repowered power plant is 52.04%. This maximum efficiency occurs when utilizing two V94.3A gas turbines without duct burner in the steam flow rate of the nominal load.     

Performance assessment of a direct steam solar power plant with hydrogen energy storage: An exergoeconomic study

Power generation and its storage using solar energy and hydrogen energy systems is a promising approach to overcome serious challenges associated with fossil fuel-based power plants. In this study, an exergoeconomic model is developed to analyze a direct steam solar tower-hydrogen gas turbine power plant under different operating conditions. An on-grid solar power plant integrated with a hydrogen storage system composed of an electrolyser, hydrogen gas turbine and fuel cell is considered. When solar energy is not available, electrical power is generated by the gas turbine and the fuel cell utilizing the hydrogen produced by the electrolyser. The effects of different working parameters on the cycle performance during charging and discharging processes are investigated using thermodynamic analysis. The results indicate that increasing the solar irradiation by 36%, leads to 13% increase in the exergy efficiency of the cycle. Moreover, the mass flow rate of the heat transfer fluid in solar system has a considerable effect on the exergy cost of output power. Solar tower has the highest exergy destruction and capital investment cost. The highest exergoeconomic factor for the integrated cycle is 60.94%. The steam turbine and PEM electrolyser have the highest share of exergoeconomic factor i.e., 80.4% and 50%, respectively.     

Exergy analysis of a 420 MW combined cycle power plant

Combined cycle power plants (CCPPs) have an important role in power generation. The objective of this paper is to evaluate irreversibility of each part of Neka CCPP using the exergy analysis. The results show that the combustion chamber, gas turbine, duct burner and heat recovery steam generator (HRSG) are the main sources of irreversibility representing more than 83% of the overall exergy losses. The results show that the greatest exergy loss in the gas turbine occurs in the combustion chamber due to its high irreversibility. As the second major exergy loss is in HRSG, the optimization of HRSG has an important role in reducing the exergy loss of total combined cycle. In this case, LP‐SH has the worst heat transfer process. The first law efficiency and the exergy efficiency of CCPP are calculated. Thermal and exergy efficiencies of Neka CCPP are 47 and 45.5% without duct burner, respectively. The results show that if the duct burner is added to HRSG, these efficiencies are reduced to 46 and 44%. Nevertheless, the results show that the CCPP output power increases by 7.38% when the duct burner is used. Copyright © 2007 John Wiley & Sons, Ltd.     

Energy and exergy analysis of a steam power plant in Jordan

In this study, the energy and exergy analysis of Al-Hussein power plant in Jordan is presented. The primary objectives of this paper are to analyze the system components separately and to identify and quantify the sites having largest energy and exergy losses. In addition, the effect of varying the reference environment state on this analysis will also be presented. The performance of the plant was estimated by a component-wise modeling and a detailed break-up of energy and exergy losses for the considered plant has been presented. Energy losses mainly occurred in the condenser where 134 MW is lost to the environment while only 13 MW was lost from the boiler system. The percentage ratio of the exergy destruction to the total exergy destruction was found to be maximum in the boiler system (77%) followed by the turbine (13%), and then the forced draft fan condenser (9%). In addition, the calculated thermal efficiency based on the lower heating value of fuel was 26% while the exergy efficiency of the power cycle was 25%. For a moderate change in the reference environment state temperature, no drastic change was noticed in the performance of major components and the main conclusion remained the same; the boiler is the major source of irreversibilities in the power plant. Chemical reaction is the most significant source of exergy destruction in a boiler system which can be reduced by preheating the combustion air and reducing the air–fuel ratio.     

Exergoeconomic Based Optimization of a Gas Fired Steam Power Plant Using Genetic Algorithm

This research paper mainly deals with exergy, economic, and environmental investigation of a 250 MW steam power plant located in Iran. In order to model this power plant, energy balance equations are used and each part of the power plant is modeled accordingly. Further by introducing the boiler as the main source of irreversibility, two approaches are presented to improve the boiler performance, reduction of excess air, and temperature reduction of gasses leaving the stacks. To study the effect of these two approaches, an objective function including the cost rate of exergy destruction of boiler, fuel cost, and cost rate of environmental impact is presented. The optimization process is done using a genetic algorithm. It is concluded that by optimizing, 20% reduction in the overall cost rate and 88% reduction in the cost rate of environmental impact can be achieved.     

熵与yong及yong分析与yong传递

能量与能质寓于同一的客观属体——能，又分别表征能的不同的客观属性。热力学可划分为基础热力学和应用热力学两大类，相应地形成了分别以熵和yong为核心的两个热力学参数框架体系。yong理论的直接应用是，用分析法；其扩展应用是与经济学结合产生的热经济学，与传输学结合产生炯传递理论。     

Exergy analysis of a coal‐based 210 MW thermal power plant

In the present work, exergy analysis of a coal‐based thermal power plant is done using the design data from a 210 MW thermal power plant under operation in India. The entire plant cycle is split up into three zones for the analysis: (1) only the turbo‐generator with its inlets and outlets, (2) turbo‐generator, condenser, feed pumps and the regenerative heaters, (3) the entire cycle with boiler, turbo‐generator, condenser, feed pumps, regenerative heaters and the plant auxiliaries. It helps to find out the contributions of different parts of the plant towards exergy destruction. The exergy efficiency is calculated using the operating data from the plant at different conditions, viz. at different loads, different condenser pressures, with and without regenerative heaters and with different settings of the turbine governing. The load variation is studied with the data at 100, 75, 60 and 40% of full load. Effects of two different condenser pressures, i.e. 76 and 89 mmHg (abs.), are studied. Effect of regeneration on exergy efficiency is studied by successively removing the high pressure regenerative heaters out of operation. The turbine governing system has been kept at constant pressure and sliding pressure modes to study their effects. It is observed that the major source of irreversibility in the power cycle is the boiler, which contributes to an exergy destruction of the order of 60%. Part load operation increases the irreversibilities in the cycle and the effect is more pronounced with the reduction of the load. Increase in the condenser back pressure decreases the exergy efficiency. Successive withdrawal of the high pressure heaters show a gradual increment in the exergy efficiency for the control volume excluding the boiler, while a decrease in exergy efficiency when the whole plant including the boiler is considered. Keeping the main steam pressure before the turbine control valves in sliding mode improves the exergy efficiencies in case of part load operation. Copyright © 2006 John Wiley & Sons, Ltd.     

Condenser Optimization in Steam Power Plant

In this paper the effects of the condenser design parameters (such as turbine inlet condition, turbine power and condenser pressure) on heat transfer area, cooling water flow-rate, condenser cost and specific energy generation cost are studied for surface type condenser. The results are given in the text and also shown as diagrams.     

Energy,exergy and thermoeconomic analysis of a combined cooling,heating and power (CCHP) system with gas turbine prime mover

In this paper energy, exergy and thermoeconomic analysis of a combined cooling, heating and power (CCHP) system has been performed. Applying the first and second laws of thermodynamics and economic analysis, simultaneously, has made a powerful tool for the analysis of energy systems such as CCHP systems. The system integrates air compressor, combustion chamber, gas turbine, dual pressure heat recovery steam generator (HRSG) and absorption chiller to produce cooling, heating and power. In fact, the first and second laws of thermodynamics are combined with thermoeconomic approaches. Next, computational analysis is performed to investigate the effects of below items on the fuel consumption, values of cooling, heating and net power output, the first and second laws efficiencies, exergy destruction in each of the components and total cost of the system. These items include the following: air compressor pressure ratio, turbine inlet temperature, pinch temperatures in dual pressure HRSG, pressure of steam that enters the generator of absorption chiller and process steam pressure. Decision makers may find the methodology explained in this paper very useful for comparison and selection of CCHP systems. Copyright © 2010 John Wiley & Sons, Ltd.     

火电厂热力系统Yong分析

应用Yong分析方法,对火电厂热力系统进行了诊断。分析了系统中各主要设备和环节的热力学完善性,找出系统中的薄弱环节,并与使用传统的热平衡法取得的结果进行了比较,为火电厂的运行优化和节能技改提供了较为科学的依据。     

Energy and exergy analysis of steam cooled reheat gas–steam combined cycle

This paper deals with parametric energy and exergy analysis of reheat gas–steam combined cycle using closed-loop-steam-cooling. Of the blade cooling techniques, closed-loop-steam-cooling has been found to be superior to air-film cooling. The reheat gas–steam combined cycle plant with closed-loop-steam-cooling exhibits enhanced thermal efficiency (around 62%) and plant specific work as compared to basic steam–gas combined cycle with air-film cooling as well as closed-loop-steam cooling. Further, with closed-loop-steam-cooling, the plant efficiency, reaches an optimum value in higher range of compressor pressure ratio as compared to that in film air-cooling. It has also been concluded that reheat pressure is an important design parameter and its optimum value gives maximum plant efficiency.Component-wise inefficiencies of steam cooled-reheat gas–steam combined cycle based on the second-law-model (exergy analysis) have been found to be the maximum in combustion-chamber (≈30%), followed by that in gas turbine (≈4%).     

Optimization of heat recovery steam generator through exergy analysis for combined cycle gas turbine power plants

This paper proposes a new approach to finding the optimum design parameters of the heat recovery steam generator (HRSG) system to maximize the efficiency of the steam turbine (bottom) cycle of the combined cycle power plant (CCPP), but without performing the bottom cycle analysis. This could be achieved by minimizing the unavailable exergy (the sum of the destroyed and the lost exergies) resulted from the heat transfer process of the HRSG system. The present approach is relatively simple and straightforward because the process of the trial-and-error method, typical in performing the bottom cycle analysis for the system optimization, could be avoided. To demonstrate the usefulness of the present method, a single-stage HRSG system was chosen, and the optimum evaporation temperature was obtained corresponding to maximum useful work for given conditions of water and gas temperatures at the inlets of the HRSG system. Results show that the optimum evaporation temperature obtained based on the present exergy analysis appears similar to that based on the bottom cycle analysis. Also shown is the dependency of number of transfer unit (NTU) on the evaporation temperature, which is another important factor in determining the optimum condition when the construction cost is taken into account in addition to the operating cost. The present approach turned out to be a powerful tool for optimization of the single-stage HRSG systems and can easily be extended to multi-stage systems. Copyright © 2008 John Wiley & Sons, Ltd.     

Exergoeconomic analysis of a combined heat and power (CHP) system

This study deals with exergoeconomic analysis of a combined heat and power (CHP) system along its main components installed in Eskisehir City of Turkey. Quantitative exergy cost balance for each component and the whole CHP system is considered, while exergy cost generation within the system is determined. The exergetic efficiency of the CHP system is obtained to be 38.33% with 51 475.90 kW electrical power and the maximum exergy consumption between the components of the CHP system is found to be 51 878.82 kW in the combustion chamber. On the other hand, the exergoeconomic analysis results indicate that the unit exergy cost of electrical power produced by the CHP system accounts for 18.51 US$ GW^?1. This study demonstrates that exergoeconomic analysis can provide extra information than exergy analysis, and the results from exergoeconomic analysis provide cost‐based information, suggesting potential locations for the CHP system improvement. Copyright © 2007 John Wiley & Sons, Ltd.     

Energy,economy, and ecological (3E)-based performance evaluation of a steam cycle power plant through optimization investigation

Energy, economy, and ecological (3E)-based analysis of steam cycle power plant evaluated through multiobjective investigation. The Montazer Ghaem steam-based power plant situated in Iran is considered for investigation. Cycle efficiency, total cost, and ecological function of steam power cycle are treated as the 3E objective in the analysis. Simultaneous optimization of this performance parameter is executed through a heat transfer search algorithm. Fifteen operating variables of the steam power cycle, which includes different pressure, temperature, and isentropic efficiency are considered during the 3E-based optimization investigation. The dryness fraction of the exhaust stream and condensing temperature are operating constraints considered in the present investigation. The results are presented in the form of Pareto solutions. The results of the Pareto solution indicate that a 6.73% variation in cycle efficiency, 44.67% variation in total cost rate, and 15.63% variation in ecological function (ECF) are observed between extreme values of 3E objectives. The obtained optimum condition is compared with the present actual operating condition of the steam power cycle. Comparative results reveal 5.27% higher cycle efficiency with 15.53% higher ECF as compared to the actual running case. For identical total cost rate of the system, 4.65% higher cycle efficiency with 1.21% rise in ECF was observed as compared to actual running case. Further, the uncertainty propagation of the Pareto points is obtained with different uncertainty levels to identify the robustness of the solutions. Finally, the important operating variables are identified and their effects on the 3E objectives are also investigated.