Exergy Analysis Method Research Articles

Evaluation and optimization of BOG Re–condenser in the LNG reservoir process

The liquefied natural gas (LNG) is a product of condensation of natural gas in very low temperature and stored at ambient pressure in the cryogenic tanks. For using, the LNG is re-gasified and supplied to power and chemical plants as fuel and material. Recently, the demand of using LNG has increased significantly because it is abundant, low price and CO2 emission. Therefore, the LNG plays an important role in the global energy system as an input to power generation, heating and material in industry. Many projects of LNG receiving terminal are being constructed in Vietnam and operated in the next few years. However, during storage in the cryogenic tank, a considerable amount of LNG evaporates by solar absorption and generates boil–off gas (BOG) which causes of loss increasing and unsafety. As a result, the BOG generation problem is highlighted for operation optimization in the future. In this study, a retrofit BOG re–condensation process was proposed based on the existing plant at LNG Dapeng receiving terminal, China. The previous study evaluated the process only on energy analysis, hence the irreversibility was not realized. As a result, the total lost, 1130.9 (kW), in term of exergy loss is really high. Therefore, the exergy analysis method was considered to optimize the operating parameters of the process. The results indicated that the exergy loss was decreased by 2.6 times compares to the previous process, it reduces to only 434.9 (kW). In addition, BOG was completely condensed and optimum operating pressure of the condenser is determined in the range of 8–9 bars. Thus, the results give the engineers more options to select the optimum conditions for reduction of energy consumption and environment savings.

Advanced exergy and exergoeconomic analysis of an integrated system combining CO2 capture-storage and waste heat utilization processes

To solve the problem regarding the purification of coal syngas, a system that integrates the CO2 capture and storage process and the waste heat utilization processes is proposed herein and analyzed using advanced exergy and exergoeconomic analysis methods. The purpose is to obtain the distribution of the exergy destruction rate and the cost rate of each block in the integrated process. The total exergy efficiency of the system was found to be 17.56%. Moreover, the total exergy destruction was 36424 kW, of which the CO2 capture and storage process accounted for 43.15%, the organic Rankine cycle process accounted for 32.35%, and the absorption refrigeration cycle process accounted for 24.50%. The exergy destruction ratio of the whole system was 82.44%. In this process, the optimization of the blocks such as the distillation column, absorber, and Evaporator 2 is to be considered a priority. Advanced exergy and energy efficiency analysis can provide guidance for the optimization of system irreversibility and help to determine the improvement potential of each block. In addition, certain strategies are proposed for the improvement of each block on the basis of the results, which can provide a theoretical flowchart for the efficient operation of the integration process.

Exergy destruction analysis of a low-temperature Compressed Carbon dioxide Energy Storage system based on conventional and advanced exergy methods

Compressed Carbon dioxide Energy Storage (CCES) system is a novel energy storage technology, which provides a new method to solve the unstable problem of renewable energy. Since the CCES system using low-temperature thermal energy storage can avoid the technical difficulties from high-temperature thermal energy storage, the low-temperature Compressed Carbon dioxide Energy Storage (LT-CCES) system has more obvious application feasibility compared with the high-temperature energy storage system. As the research on energy conversion, transfer, and loss in CCES system under low-temperature heat storage is still missing, while it is important to understand the energy losses for the further optimization of this kind of system, in this paper, the conventional exergy analysis and advanced exergy analysis were utilized to analyze the thermodynamic characteristics of a LT-CCES system consisting of CO2 Brayton cycle, low-temperature thermal energy storage and cold energy storage, whose thermal energy storage temperature is below 200 °C. As the advanced exergy analysis takes into account the correlation between system components as well as the technical limitations of each component, exergy destruction can be split into more detailed parts (i.e., avoidable exergy destruction, unavoidable exergy destruction, endogenous exergy destruction, and exogenous exergy destruction), which makes the results of the advanced exergy analysis different from those of conventional exergy analysis. The results showed that, advanced exergy analysis pointed out that HEX3 should be given priority as endogenous avoidable exergy destruction in HEX3 was the largest, while the results from the conventional exergy analysis showed that HEX1 should be given priority. For all the components, the two methods indicated that the compressor should be given the highest priority for improvement, followed by the turbine. Besides, as the total exergy efficiency of the system was 55.3% under the real condition and the total exergy efficiency was 76.7% under the unavoidable condition, there was still room for improvement of the system. In brief, based on the advanced exergy analysis method, the real component that should be paid attention can be determined, which gives the designers a more profound understanding of exergy destruction in the LT-CCES system.

Comparison of Exergy and Various Energy Analysis Methods for a Main Marine Steam Turbine at Different Loads

This paper present energy and exergy analysis of the main marine steam turbine, which is used for the commercial LNG (Liquefied Natural Gas) carrier propulsion, at four different loads. Energy analysis is performed by using four different methods. The presented analysis allows distinguishing advantages and disadvantages of all observed energy analysis methods and its comparison to exergy analysis of the same steam turbine. Each analysis is based on the measurement results obtained in main turbine exploitation conditions. Main turbine is composed of two cylinders – High Pressure Cylinder (HPC) and Low Pressure Cylinder (LPC). At low turbine loads, the dominant power producer is HPC, while at middle and high loads the dominant power producer is LPC. Energy analysis Method 1 which is based on the same principles as exergy analysis, should be avoided if the majority of turbine losses are not known. Other observed energy analysis methods can be applied in the analysis of any steam turbine, with a note that increase in ideal (isentropic) steam expansion process divisions will result with an increase in energy losses and with a decrease in energy efficiency. Energy analysis Method 2 which consist of only one ideal (isentropic) steam expansion process, for the whole turbine and at all observed loads, results with the lowest energy losses (in the range between 639.98 kW and 6434.17 kW) as well as with the highest energy efficiency (in a range between 53.70% and 79.40%) in comparison to other applicable energy analysis methods. For the observed loads, whole main turbine exergy destruction is in range from 608.64 kW to 5922.86 kW, while the exergy efficiency range of the whole turbine is between 54.94% and 80.73%. Exergy analysis and all three applicable energy analysis methods show that increase in the main turbine load results with simultaneous increase in turbine losses and efficiencies (both energy and exergy).

Theoretical study on a modified single‐stage autocascade refrigeration cycle with auxiliary phase separator

Abstract In order to improve the cycle performance of a conventional single-stage autocascade refrigeration cycle (ARC), an auxiliary separator is considered to be introduced. In the modified autocascade refrigeration cycle (MARC), the auxiliary separator located after an expansion device is used to further collect the vapor enriched with low-boiling components. In this case, the MARC enables to improve the cycle performances by utilizing more zeotropic mixture enriched with the low-boiling components to realize a higher evaporation pressure at the given evaporation temperature in the evaporator of the cycle. The performances of the MARC and ARC are compared utilizing energy, exergy and exergo-economic analysis methods, and several important parameters are also discussed in detail. The results indicate that the MARC using zeotropic mixture R290/R170 is feasible and there are obvious improvements in terms of the COP, volumetric refrigeration capacity and exergy efficiency. It is found that compared to the ARC, the COP improvement of MARC can reach up to 16.1%. The exergy efficiency of MARC is increased by 10.23% and the overall cost rate of MARC is decreased by 2.51% under a typical operating condition. In addition, the COP of MARC has a maximum value at given conditions when the mass fraction of R290 at the compressor inlet is around 0.3. In general, the performance characteristics of the proposed cycle demonstrate its potential applications in low-temperature freezers.

Ексерго-економічна оптимізація комплексних систем енергопостачання

The optimization of energy supply system becomes especially important problem in those cases where there are several different energy sources, including, e.g., renewable energy sources, and several energy sinks of different power. This problems can be solved with the use of a graph of exergy and economic expenditures for the pairwise interaction of flows. The purpose of the study is to specify the concept of exergy schedule and economic costs applied to energy supply systems (ESS). We shall interpret a graph of the exergy and economic expenditures of an ESS, having an arbitrary structure, as a bipartite graph Z such that the set of its nodes C corresponds to the heating H and heated C flows, and the set of its arcs D to a possible distribution of the exergy and economic expenditures in the corresponding elements of this ESS in the course of interaction between the heating and heated flows. A symmetric graph represents an oriented graph, whose arcs can be grouped into pairs of parallel but oppositely directed arcs. Such graphs, having no isolated nodes, are convenient for studying complex interrelated systems. If we have determined the optimal pair of elements (аі, aj), corresponding to the sequence of nodes, beginning from the root of the foretree and finishing by a suspended node, giving a matrix of unit dimension, then the obtained sequence of elements forms a single-contour system with the minimum level of exergy and economic expenditure. For finding the optimal solution it is advisable to use the method of branches and boundaries, which enables one to improve the solution simpler than with the application of different methods of exergy analysis.

Exergy analysis of updraft and downdraft fixed bed gasification of village-level solid waste

The most commonly used for gasification of village-level solid waste is the fixed-bed gasifier, but there is no reasonable method to evaluate the gasification process. This paper attempts to find a gasifier that is most suitable for gasification of village-level solid wastes through exergy analysis method. Based on experimental data from literature, the exergy efficiencies and LHV(Low Heat Value) of product gas from updraft and downdraft fixed bed gasifier are studied in this paper. The results show that the updraft fixed bed gasifier has higher exergy efficiency, and the gas produced by the downdraft fixed bed gasifier has a higher heating value. Air gasification has higher exergy efficiency than steam gasification and pure oxygen gasification. The highest exergy efficiency at a gasification temperature of about 1000 °C and ER (Equivalence Ratio) value in the range of 0.33–0.36. The volatile content of gasification raw materials is higher, and the gasification efficiency is higher. Through the research of this paper, a new path to reasonably evaluate the gasification process is obtained.

ЭКСЕРГЕТИЧЕСКИЙ ПИНЧ-АНАЛИЗ ВСЕХ ЭЛЕМЕНТОВ КОТЕЛЬНОГО АГРЕГАТА И КОТЕЛЬНОГО АГРЕГАТА В ЦЕЛОМ

The relevance of the research is caused by the need to improve the energy efficiency of heating systems, since all types of fuel are becoming more expensive. In this regard, there is a need to create a method of thermodynamic improvement of heat engineering systems. The main aim of the research is the creation of a method for improving heating systems, the application of this method on the example of a boiler unit PP-2650-255 GM. Objects: a direct-flow boiler PP-2650-255 GM, for which a thermodynamic analysis of the processes occurring in individual elements of the boiler – an air heater, economizer, firebox, and superheater – is performed. The article analyzes all heat fluxes on each element of the boiler. Methods. An exergy method of thermodynamic analysis is used as a research tool. It allows taking into account the energy potential of thermal processes. To date, the most effective method of parametric optimization of heat and power processes is the method of integration of heat flows (pinch method). However, the pinch method is based on a change in flow enthalpy, which does not take into account the qualitative characteristics of energy. In the article, the development of the pinch method continues; flow exergy is used instead of flow enthalpy. Optimization of heat engineering parameters is carried out using an exergy pinch method. Results. Exergy pinch analysis allows you to identify unused exergy and determine in which part the loss occurs. According to the calculations and the graph, it can be seen that hot flows lost 1503,57 MW of exergy, cold flows took 1295,57 MW of exergy, taking into account cooling of the working fluid by bypass. Thus, 47,9 MW of unused exergy was detected in this boiler unit. The results of the exergy pinch analysis allow us to formulate and justify specific design measures to improve the energy efficiency of the boiler unit. This analysis allows you to effectively use the energy and resources of heating equipment.

Study on Energy Saving of Epichlorohydrin Unit Based on Entransy Theory

The mathematical models for calculating the energy utilization efficiency of heat exchanger networks (HENs) based on entransy analysis method was built. The energy utilization efficiency of HENs for epichlorohydrin unit were calculated by exergy analysis and entransy analysis. Aiming at the maximum energy recovery, the entransy analysis of epichlorohydrin unit’s HENs was done. By taking three different ?Tmin, 10 K, 15 K and 20 K, the results show that the exergy efficiencies are 61.01 %, 59.28 % and 57.27 %. The entransy transfer efficiency is 42.81 %, 42.13 % and 41.00 %. Using the entransy analysis method, utilities were saved by 19.41 %, 18.01 % and 15.70 %. Using the exergy analysis method, utilities were saved by 16.59 %, 14.86 % and 12.02 %.The results of different methods were analysed and compared. Exergy is more complicated than entransy in the calculation process. The exergy analysis method can not complete HENs Synthesis. But the entransy analysis method not only can complete HENs synthesis, but also can calculate the energy utilization efficiency of HENs. The entransy analysis method is more suitable for analyzing the energy utilization of epichlorohydrin unit.

Exergy efficiency of the air-conditioning system with adsorption drying and regeneration of the adsorbent by heat of condensation for the premises of arbitration storage of drugs

Engineering systems of microclimate provisionin buildings and structures are significant consumers of electrical and heat energy at different temperature levels. Among them, air conditioning systems for various purposes in terms of energy consumption are the most energy-intensive. When developing them, the enough attention is not always paid to assessing the degree of their energy efficiency, and variant design is carried out by comparing the non-relevant indicators. The exergy method of analysis for technical systems provides the correct numerical assessment of energy efficiency and the possibility of a comparative analysis of circuit solutions at different stages. The existing engineering methods are not enough for this application. Adsorption is more energy efficient method for dehumidifying than condensation with re-heating, especially using the secondary energy source – heat of a condenser of a chiller. This article provides an example of an exergy analysis when developing an air conditioning system for pharmaceutical production in order to select the best heat source in terms of energy efficiency for adsorbent regeneration. The results of analytical studies are presented in the form of relative values of exergy efficiency and specific values of air exergy during its processing, which are convenient for proper comparison and subsequent analysis. The article shows how exergetic destruction and the most energy-intensive processes in the system are determined using an exergetic flow diagram of exergetic components of moist air. Sequential numerical exergy analysis is an effective and useful tool for determining energy-efficiency indicators of air conditioning systems in their design. The method allows significant decrease of energy consumption in air treatment of air conditioning in buildings and structures.

Локалізація ексергетичних втрат в утилізаторі теплоти відхідних газів газоспоживальних теплових установок

The problem of increasing the thermodynamic efficiency of power plants can be solved only by using a complex approach using methods based on modern methods of exergy analysis in combination with methods of heat transfer theory, theory of linear systems, structural-variant methods, multi-level optimization methods, etc. The analysis of the possibility of applying the discrete-modular principle and the corresponding complex method for analyzing the efficiency of the exhaust gases heat-recovery exchanger of a cogeneration unit heat engine is performed in the paper. The aim of the work is to analyze the localization of exergy losses, their differentiation, and the establishment of the relative contribution of various types of losses to the general exergy losses in the exhaust gases heat-recovery exchanger of a cogeneration unit heat engine. The structural features of the heat-recovery exchanger and the exergy properties that reflect the essence of exergy methods: universality and additivity, made it possible to use the discrete-modular principle and a complex method based on exergy-dissipative functions for efficiency analysis. The advantage of this method is the ability to analyze the localization of exergy losses in separate modules of the heat-recovery exchanger and to differentiate the exergy losses associated with nonequilibrium heat transfer between the heat-transfer agents and the wall, heat conduction and the movement of heat-transfer agents. Using the chosen complex method, the analysis of the localization of exergy losses in the heat-recovery exchanger was carried out and the exergy-dissipative functions of each of the eight modules of the heat-recovery exchanger were calculated. Differentiation of exergy losses was carried out and the relative contribution of exergy losses associated with the processes of heat transfer from flue gases to the wall, from wall to water, in heat conduction processes, as well as exergy losses associated with the movement of heat-transfer agents, in the general exergy losses was analyzed. To determine the exergy losses due to nonequilibrium heat transfer between the heat-transfer agents and the motion of the heat-transfer agents, the differential exergy equations, the equations for the heat flow densities between the heat-transfer agents and the wall, the equation for the heat flow density due to heat conduction through the wall and the equations of motion are used. It has been established that the localization of maximum exergy losses in all modules of the heat-recovery exchanger is associated with losses due to heat transfer from flue gases to the wall.

Performance optimization of a heat pump driven liquid desiccant dehumidification system using exergy analysis

Liquid desiccant dehumidification system driven by heat pump is recognized as an efficient approach for humidity control in the air-conditioning system. The liquid desiccant dehumidification system is optimized by exergy destruction analysis method in the present research. According to the exergy destruction theory, the exergy destruction of a liquid desiccant dehumidification system is divided into exergy destructions arising from heat pump cycle, evaporators, condensers, heat and mass transfer modules and various mixing processes, respectively. The heat and mass transfer process uniformity coefficients γt and γω are proposed to describe the uniformity of the heat and mass transfer driving forces along the whole system. It’s indicated γt and γω of the basic cross-flow system are as high as 1.4 and 1.2. Then reducing the exergy destruction is chosen as the guideline to optimize the system. On the basis of the basic cross-flow system, the improved cross-flow system and the improved counter-flow system are further proposed. γt (γω) of the improved systems are reduced to 1.12(1.12) and 1.04(1.01), respectively. Owing to the system optimization, the exergy efficiency increases from 20.1% of the basic cross-flow system to 21% and 25% respectively, COPsys increases from 5.7 to 6.0 and 7.4 respectively. The exergy analysis method is effective for an optimized scenario of a heat-pump driven liquid desiccant process.

Порівняльний аналіз ексергетичної ефективності теплоутилізаційних систем різного призначення

To assess the exergy efficiency of heat recovery systems, a complex approach was used, which allows us to evaluate the operation of heat recovery systems simultaneously from several positions: thermodynamic, heat engineering, and technological. In this work, within the framework of this approach, the heat-exergy efficiency criterion and exergy efficiency were used. Four types of heat recovery systems for various purposes for boiler plants were investigated. For the systems under consideration, structural schemes have been developed in which exergy flows between individual discrete elements of a simple structure are identified. The calculation of exergy characteristics was carried out using the balance methods of exergy analysis and a technique combining the methods of exergy analysis with the RP method of representing the thermodynamic balances of the system in matrix form. Based on the calculated exergy characteristics, a comparative analysis of the exergy efficiency of heat recovery systems for various purposes is carried out. According to the research results, one of the possible ways to reduce the total exergy losses in heat recovery systems is to reduce losses in the pump system and piping system. This reduction is achieved by aggregating the maximum number of functional elements of the heat recovery system in one device. It is shown that for a heat recovery scheme in which the three main elements are structurally combined in one housing, the heat-exergy criterion is reduced by 6.7 %, and the exergy efficiency is increased by 4.0 % compared to the non-aggregated heat recovery scheme. Thus, heat recovery systems with complex use of recover heat for heating various heat-transfer agents and with aggregation of the main system elements in one housing are characterized by the best exergetic indicators. Key words: boiler plants; waste gas heat recovery, exergy losses, complex techniques; efficiency

Performance Improvement of a Gas Turbine Power Plant in Nigeria by Exergy Analysis: A Case of Geregu 1

This paper presents the performance improvement study of gas turbine power plant in Nigeria by exergy analysis method using Geregu 1 gas turbine power plant as a case study. The study analyzed the system’s components separately in order to identify the sites where the largest exergy losses occur and to quantify the amount. Results of the component efficiencies based on their thermodynamic models of energy and exergy analyses at design and operating years of the power plant revealed that the maximumexergy destruction efficiency occurred in the combustion chamber. Improvement approaches made on the performance of the combustion chamber included: 1) Increasing turbine inlet temperature at constant pressure ratio; 2) Increasing combustion chamber pressure ratio at constant turbine inlet temperature; and 3) Increasing both turbine inlet temperature and pressure ratio. Results of improvement conditions show that the first condition produced progressive decrease in exergy efficiency for the design and operating years when temperature was increased from 1060?C - 1080?C at 11 bar pressure. Second condition resulted to increase in exergy efficiency when pressure increased from 11 bar to 15 bar. Similarly, increasing turbine inlet temperature and pressure by 20?C and 4 bar respectively increased the exergy efficiency by 0.22% on design condition. In addition the exergy efficiency of the operating years increased with increase in both temperature and pressure at the amount. Hence, pressure variation affects exergy efficiency of combustion chamber.

Mathematical Model for Optimization of Heat Exchange Systems of a Refinery

The article is devoted to the issue of thermodynamic optimization of heat transfer systems. Optimization is carried out by an exergy pinch method. This method includes the advantages of exergy analysis and pinch method. Exergy analysis takes into account the quantitative and qualitative characteristics of thermal processes, the pinch method allows structural and parametric optimization of heat transfer systems. The article presents a mathematical model for optimization by exergy pinch analysis. This model allows automated system optimization. Exergy pinch analysis allows more efficient use of energy and resources at the enterprise, which is relevant today.

Mathematical model for optimization of heat exchange systems

The article is devoted to the issue of thermodynamic optimization of heat transfer systems. Optimization is carried out by an exergy pinch method. This method includes the advantages of exergy analysis and pinch method. Exergy analysis takes into account the quantitative and qualitative characteristics of thermal processes, the pinch method allows structural and parametric optimization of heat transfer systems. The article presents a mathematical model for optimization by exergy pinch analysis. This model allows automated system optimization. Exergy pinch analysis allows more efficient use of energy and resources at the enterprise, which is relevant today.

Optimal Operation of Integrated Energy System Based on Exergy Analysis and Adaptive Genetic Algorithm

Due to the rising tensions surrounding the energy industry in response to the depletion of non-renewable energy sources and pollution of the environment, it is especially important to improve the energy utilization rate of integrated energy systems (IESs). Exergy is an important index to measure energy quality. Therefore, this paper proposes an IES operation optimization method based on exergy analysis and an adaptive genetic algorithm. First, based on the energy network theory, a unified expression of the exergy transfer process is given, and the energy level factor is introduced to evaluate the energy quality. Second, the steady-state expression of different forms of exergy in the energy transfer line is given. Third, the exergy economic model of the IES is established by combining exergy analysis, and the solution process of the adaptive genetic algorithm is given. Finally, the operation optimization simulation and analysis of an IES in Bali are carried out to verify the effectiveness of the exergy analysis method and feasibility of the simulation method.

Exergy analysis, optimization approach and transient mode operation study of non-flammable biomethane liquefaction process

Since the advent of the industrial age, the planetary energy demand has substantially increased to improve daily comfort. In a view to counterbalance the growing energy consumption of fossil fuels, such as natural gas, various strategies have been deployed for increasing the share of renewable energy (i.e., solar, wind, biogas...) in the global energy mix. A particular interest is paid to the use of biogas as natural gas substitute. For producers geographically located far from natural gas grid infrastructures, biogas shall be liquefied to facilitate its transport. Existing mixed refrigerant liquefaction units, operate with flammable hydrocarbons. However, increasingly stringent safety requirements impel to predict the inherent risks of handling hydrocarbons, in particular in biogas units close to farms. The use of non flammable alternative refrigerants is a potential solution currently barely considered. In this paper, a novel mixed refrigerant cycle for biogas micro-liquefaction process using a non flammable mixed refrigerant is proposed. The proposed cycle is first simulated in Aspen HYSYS® and further assessed by the exergy analysis method in order to evaluate process performance, to locate exergy destruction and to define key parameters for optimization approach. In attempt to improve the energy efficiency of the cycle, a link between Aspen HYSYS®, PIKAIA genetic algorithm tools (Charbonneau, 2002) and Microsoft Visual Basic was developed. In the proposed methodology the objective function consists on the maximization of the amount of the liquefied biomethane per unit of the required compressor work. The combination of exergy analysis and genetic algorithm optimization improved the proposed architecture performance leading to higher energy efficiency. Actually the operating parameters optimization contributed, in comparison to the reference case, to a 27 % reduction in electric power consumption and 26 % in exergy destruction. As a second step and with the aim of studying the transient-mode operation of liquefaction units, results obtained for a steady state operation are considered in order to assess the suitability of optimized solutions and robustness of systems against quick start-and-stop or partial load operating mode.

Energetic optimization and exergetic performance investigation of an ejector refrigeration system using HCFO-1233zd(E) as a refrigerant

In this study, the performance of an ejector refrigeration system using HCFO-1233zd(E) as the working fluid is investigated and presented. A novel improved modeling approach that considers ejector loss coefficients as functions of the ejector pressure lift and area ratio has been used. The resulting mathematical model developed using the first and second laws of thermodynamics and gas dynamics is solved using Engineering Equation Solver. Different ejector geometries with area ratios of 6.44, 7.04, 7.51, 7.73, 8.28, 8.62, 9.13, 9.41 and 10.64 were used in this study. The evaporator temperatures were between 0 °C and 16 °C, the generator temperatures were between 75 °C and 120 °C and the condensing temperatures varied between 20 °C and 40 °C. For the range of parameters used, the optimal coefficient of performance (COP) is in the range 0.11 and 0.88 for evaporator temperatures between 4 °C and 16 °C. At the optimal working conditions, the COP improves with higher area ratios, lower condensing temperatures and requires increased generator temperatures. In the critical mode of operation, both the energetic and exegetic performance of the ejector are shown to decline as generator temperatures increase, evaporator temperatures reduce and as the area ratios decrease. Thermodynamic investigation using the exergy analysis method indicates that most of the exergetic losses come from the ejector (46–56%) followed by the condenser (18–29%), the generator (21–26%), the evaporator (0.8–3%), and the throttle valve (1–1.6%), with the pump having a very small contribution. Moreover, correlations for the optimal generator and optimal COP were derived and presented.

Thermodynamic cycle analysis and optimization to improve efficiency in a 700 °C ultra-supercritical double reheat system

When increasing steam parameters, the incomplete thermodynamic cycle and large irreversible system losses are bottlenecks in improving thermal efficiency in ultra-supercritical power plants. In this study, a comprehensive analysis of both parameter optimization and system cycle analysis is carried out for a 1000-MW double reheat ultra-supercritical thermal power plant. First, the genetic algorithm is used to optimize the primary and double thermal pressure, as well as the steam extraction parameters of the steam turbine. Then, a thermodynamic optimization model is proposed to analyze performance. Moreover, the exergy analysis method is applied to reveal the irreversibility mechanism in the thermodynamic cycle. In order to further solve the energy-grade mismatch problem, the performance of a regenerative steam turbine thermal system is improved based on the optimized system. The results indicate that the power generation efficiency of the optimized system is 0.31% higher than that of the prototype system, and the heat consumption rate is decreased by 43.67 kJ (kW h)−1. The power generation efficiency in the regenerative steam turbine system is up to 52.42%, which is 1.44% higher than that of the optimized system. Therefore, an effective method to improve the thermal efficiency is obtained through the thermodynamic cycle analysis and optimization for 700 °C ultra-supercritical double reheats systems.