Exergy Method Research Articles

Comparative exergy analysis of the processes of heating reserve liquid fuel using various coolants at thermal power plants

In this paper the technologies for heating reserve liquid fuel at a thermal power plants are proposed. Provision is made to implement a transition from fuel oil to another reserve fuel that does not require high-temperature heating at thermal power plants. A comparative analysis of the traditional scheme of heating reserve fuel with industrial steam and other coolants was carried out. The analysis was carried out using the exergy method, which allows taking into account different types of power. Exergy flows, exergy losses and exergy coefficient of efficiency are calculated for traditional and proposed technologies of reserve fuel heating.

Exergoeconomic analysis of a new integrated copper-chlorine cycle for hydrogen production

In this study, an exergoeconomic analysis is performed on an integrated four-step thermochemical copper-chlorine cycle developed at the Ontario Tech. University through exergy, cost, energy, and mass (EXCEM) method. A thermodynamic model is first constructed in Aspen-plus (a process simulation software) to simulate and investigate the integrated cycle through exergy and energy analyses. The capital costs, thermodynamic loss rates, and the ratio of the thermodynamic loss rate to the capital cost of various system's components are also determined. Moreover, the average unit cost of hydrogen is evaluated and the influence of several system's parameters on the unit cost of hydrogen is analyzed. The results show that the cost of hydrogen is strongly dependent on the production capacity of the plant. Based on the analysis, our system generates hydrogen at an average unit cost of 5.54 $/kg with a plant capacity of 1619.3 kg/h considering both internal (operating and maintenance costs, etc.) and external (costs of various inputs, etc.) parameters.

A novel enhanced exergy method in analyzing HVAC system using soft computing approaches: A case study on mushroom growing hall

A novel enhanced exergy method in analyzing HVAC system using soft computing approaches: A case study on mushroom growing hall

Velocity Decomposition Method for Exergy-Based Drag Prediction

The exergy method is a powerful tool for aerodynamic analysis and drag prediction. However, its formulation still requires further improvements in order to obtain a useful drag breakdown for the analysis of wind-tunnel data (like the far-field methods). The far-field drag breakdown is achieved by using a velocity decomposition technique, but the related formulation is not well suited for the exergy method. Thus, the main objective of this work is to develop a new velocity decomposition suited for the exergy analysis and to propose a related exergy-based drag breakdown formulation for wind-tunnel applications.

Dynamic exergy analysis of a novel LNG cold energy utilization system combined with cold, heat and power

Plenty of cold energy is released through the regasification process of liquified natural gas (LNG). Thus, the LNG cold energy utilization has become a hot issue of research in both academic and engineering area. In this study, a novel LNG cold energy utilization system integrating a gas turbine, four Rankine cycles and a NG directly expander is proposed and analyzed by the dynamic exergy method. Moreover, LNG regasification pressure and air inlet temperature are selected for the parameter sensitive analysis. At last, a typical hotel located in South China is chosen as the study case. The results show that comparing with the traditional CCHP system, the novel system has higher Power/Cold ratio and Heat/Cold ratio which can reach to 5.55 and 3.65, respectively. Besides, the system exergy efficiency can reach to 48.97% at specific conditions. Furthermore, it has a variation section in where the system exergy efficiency decreases sharply due to the influence of the regasification pressure of LNG. Moreover, the proposed system has higher exergy efficiency when it is working at lower atmospheric temperature.

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.

Performance evaluation of external fired hybrid solar gas-turbine power plant in Colombia using energy and exergy methods

Hydro and thermal generation power systems dominate the Colombian electricity sector. In 2017, Colombia installed electrical generation capacity was 16.8 GW. Renewable energy sources represent at least 85% of the total generation, being hydro the principal source. Several alternatives had been evaluated through the years to improve the Colombian energy matrix and capacity, including solar photovoltaic and wind plants; despite that, no consensus about the appropriate solution in terms of the available resource, energy demand, and energy mix has been attained. Thermosolar power plants arise as an alternative to produce energy in sites where nearly constant solar irradiance throughout the year is available, which is the case for most Colombian cities. This work concerned the evaluation of a single-stage hybrid Central Solar Power (CSP) plant at a location on the Caribbean Colombian coast. The study is focused on establishing the effect of local environmental conditions (ambient temperature and solar resource availability), as well as some operational cycle parameters (heat exchanger effectiveness and the system pressure ratio) on the CSP plant performance. Additionally, site emplacement conditions, i.e., proximity to the power grid, presence of conventional thermal power plants, proximity to principal cities, and availability of natural gas), are also considered to attain the factors that might constrain the plant optimal operating conditions. The CSP plant and the Direct Normal Irradiance (DNI) model results obtained fitted in good agreement the experimental data from the literature used for validation. Results have shown a global plant efficiency of 35% without solar resource which is reduced to 30% when solar contribution attains its maximum value at midday. Additionally, fuel-saving per day varies between 9.21% and 6.3% during the months of maximum and minimum global radiation, respectively. Finally, that the combustion chamber, its associated heat exchanger and the one that is in direct exchange with the surroundings, are the components with the most exergy destruction, as expected. From the above, it is sensible to explore alternatives regarding different working fluids that could be used in lower temperature cycles and other applications for heat recovery.

Non-equilibrium thermodynamic analysis of adsorption carbon capture: Contributors, mechanisms and verification of entropy generation

Emissions of greenhouse gases should be reduced for the slowing of global warming. Carbon capture by adsorption, which is available to retrofit of existing power plants and to integration with renewable energy, is an effective technology to reduce CO2 emissions. However, the heavy energy consumption has already become a limitation to scale-up applications. Thermodynamic research, especially entropy analysis, could quantitatively clarify the irreversible loss and provide a guidance to the energy-saving design. Considering that classical thermodynamics is powerless in the description of significant kinetic characteristics of adsorption carbon capture, non-equilibrium thermodynamics is thus required, as it could provide a detailed analysis on the contributors and mechanisms of entropy sources. In this paper, the entropy source contributors of adsorption systems, which are composed of entropy generation of 9 irreversible factors for different adsorption cycles, were derived. An entropy research framework was proposed and illustrated through a case study of vacuum temperature swing adsorption (VTSA). The results are also compared with the classical exergy method, and the difference between the results of the two methods for entropy generation is 1.97%. This paper provides a thorough research framework for detailed thermodynamic analyses of adsorption carbon capture.

Thermodynamic Analysis of a Hybrid Trigenerative Compressed Air Energy Storage System with Solar Thermal Energy.

The comprehensive utilization technology of combined cooling, heating and power (CCHP) systems is the leading edge of renewable and sustainable energy research. In this paper, we propose a novel CCHP system based on a hybrid trigenerative compressed air energy storage system (HT-CAES), which can meet various forms of energy demand. A comprehensive thermodynamic model of the HT-CAES has been carried out, and a thermodynamic performance analysis with energy and exergy methods has been done. Furthermore, a sensitivity analysis and assessment capacity for CHP is investigated by the critical parameters effected on the performance of the HT-CAES. The results indicate that round-trip efficiency, electricity storage efficiency, and exergy efficiency can reach 73%, 53.6%, and 50.6%, respectively. Therefore, the system proposed in this paper has high efficiency and flexibility to jointly supply multiple energy to meet demands, so it has broad prospects in regions with abundant solar energy resource.

Finite time thermodynamic analysis of water cooled multi-spilit heat pipe system

Energy saving in data centers is increasingly important along with the rapidly developing IT industry. A integrated heat pipe air conditioning (AC) system which used chilled water unit and heat pipe heat exchanger (HPHE) was proposed.With the meteorological parameter of Changde city (31°53′N and 117°15′E) as the reference. The thermodynamic simulation software SIMULINK was employed in build the simulation model of the combined system. And it is compared with the traditional air-conditional system. The system include heat pipe evaporator cooling deliver unit (CDU) and the cold source. A time integral model for heat transfer of heat pipe evaporator is proposed. A heat pipe evaporator of a 12KW in the company was taking as an example. The results show that the time period of working fluid passing through the heat exchanger is about 6 seconds. When the dry degree is greater than 0.72, the heat transfer efficiency is low. When arranging the IT server, we should concentrate on the location below 1.3 meters. The CDU was treated as a condenser. Then, the cooling source is vapor compressor. The finite time thermodynamic and the exergy method were employed to analysis the heat exchanger and the compress processes.The results show that the former one has saved 26% of the energy. Then the using time and energy saving potential in major cities of China were investigated and studied.

Thermodynamic analysis of the thermal-technological complex of sugar production: the energy and entropy characteristics of an enterprise

This paper reports the approbation of a procedure of thermodynamic analysis of the thermal-technological complex of sugar production using the analysis of an enterprise of typical configuration as an example. Currently, the thermodynamic analysis of sugar production systems is mainly performed on the basis of a classical energy method. Minor attempts to exploit the potential of the second law of thermodynamics in the form of the adaptation of an exergy method are not systemic. Underlying the applied procedure is a joint analysis of general synthetic and analytical balances of mass, energy, and entropy. Such a procedure makes it possible to quantify the level of perfection of the existing and proposed thermal circuits, as well as the impact exerted on their perfection by energy efficiency measures, and it could be applied both to optimize the energy characteristics of the existing ones and in designing new enterprises of the sugar industry. It has been shown that the thermodynamic analysis of the thermal-technological complex of sugar production as a single system makes it possible to analyze the main factors of influence on the energy efficiency of the complex disregarding the course of the processes implemented therein. Such an approach can also be effectively used for the quick evaluation of the thermodynamic perfection of an enterprise and for determining its «energy-saving potential». Based on the results of energy analysis, the relationship has been established between the fuel and energy resources, supplied to the system, and the sources of their losses; a set of measures has been proposed to reduce the impact of each of these factors on resource consumption. Entropy analysis has revealed the internal and external causes of the irreversibility of processes; the principle of «energy irreversibility compensation» has made it possible to compile a rating of major imperfections and determine the optimal sequence of resource-saving measures. The results of the analysis have confirmed the efficiency of the procedure, which allows a comprehensive study, while operating only with the fundamental laws and the principles of classical thermodynamics, as opposed to procedures, based on energy-exergy characteristics

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.

Application of Thermoeconomics in HVAC Systems

In order to achieve a sustainable society, the energy consumption in buildings must be reduced. The first step toward achieving this goal is to detect their weak points and analyze the energy-saving potential. to detect the units with higher consumption and cost. Exergy is very useful for analyzing pieces of equipment, systems or entire buildings. It measures not only the quantity of energy but also its quality. If the exergy is combined with economic analysis, this gives rise to thermoeconomics, and the system can be checked systematically and optimized from the perspective of economics. In this work, exergy methods and thermoeconomic analysis were applied to a building thermal system. Due to its complexity, it is necessary to adapt some concepts to translate the exergy application from industry to buildings. The purpose of this work is to overcome these shortcomings and to deal with energy-saving actions for buildings. To this end, a thermoeconomic study of a facility that covers the heating and domestic hot water (DHW) demands of 176 dwellings in Vitoria-Gasteiz (Basque Country) using two boilers and two cogeneration engines was analyzed. The irreversibility associated with each piece of equipment was quantified, and the costs associated with resources, investment and maintenance were calculated for each flow and, consequently, for the final flows, that is, electricity (11.37 c€/kWh), heating (7.42 c€/kWh) and DHW (7.25 c€/kWh). The results prove that the boilers are the lesser efficient components (with an exergy efficiency of 15%). Moreover, it is demonstrated that micro-cogeneration engines not only save energy because they have higher exergy efficiency (36%), but they are also economically attractive, even if they require a relatively high investment. Additionally, thermoeconomic costs provide very interesting information and underscore the necessity to adapt the energy quality in between the generation and demand.

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.

Exergoeconomic and exergoenvironmental analyses and optimization of different ejector based two stage expander-organic flash cycles fuelled by solar energy

In this work, four new architectures of two-stage expander organic flash cycles (EOFCs) based on ejector namely, ejector based EOFC (E-EOFC), ejector based high-pressure evaporation EOFC (EF1-EOFC), ejector based low-pressure evaporation EOFC (EF2-EOFC), and double ejectors based EOFC (DE-EOFC) are proposed and analyzed using exergy, exergoeconomic and exergoenvironmental methods. The thermodynamic, cost and environmental impact indicators of the suggested EOFCs are compared with those of the base EOFC. A performance comparison exhibits that the net power, energy, and exergy efficiencies are improved by 16.83%, 13.05%, and 10.99%, receptively in EF1-EOFC, E-EOFC and DE-EOFC relative to the base EOFC. EF2-EOFC gives the highest reduction in the total cost rate by 7.26% relative to the base EOFC and DE-EOFC with minimum increment in cost rate by 0.66% and a 0.95% improvement in the environmental impact rate relative to the base EOFC is recognized as the appropriate layout from the thermodynamic, economic and environmental impact aspects. In addition, non-dominated sorting genetic algorithm II (NSGA-II) and three decision-making methods are implemented to ascertain the maximum net power and minimum total cost and environmental impact rates of proposed cycles.

Comparative assessment of advanced power generation and carbon sequestration plants on offshore petroleum platforms

On conventional offshore petroleum platforms, the combined heat and power production (CHP) currently depends on simple cycle gas turbine systems (SCGT) that operate at lower efficiency and increased environmental impact compared to modern onshore thermoelectric plants. Additionally, the reduced space and the limited weight budget on offshore platforms have discouraged operators from integrating more efficient, but also bulkier cogeneration cycles (e.g. combined cycles). In spite of these circumstances, more stringent environmental regulations of offshore oil and gas activities have progressively led to a renewed interest in the integration of advanced cogeneration systems, together with either customary or unconventional carbon capture approaches, to maintain both higher power generation efficiencies and reduced CO2 emissions. Thus, in this paper, it is evidenced how advanced gas turbine concepts are promising technologies for maintaining or even increasing efficiency, while facilitating the capture rate of CO2 produced, either for geological storage or enhanced oil recovery. Despite the profuse research works on onshore applications, advanced cogeneration and carbon capture systems have been barely studied in the context of supplying power to offshore petroleum platforms. Accordingly, the performance of a conventional offshore petroleum production platform (without carbon capture system) is compared to other configurations, based on either an amine-based chemical absorption system or oxyfuel combustion concepts ( S-Graz and Allam cycles) for CO2 capture purposes. Since the original power and heat requirements of the processing platform must remain satisfied, an energy integration analysis is performed to determine the waste heat recovery opportunities. Additionally, the exergy method helps quantifying the most critical components that lead to the largest irreversibility and identifying the thermodynamic potential for enhanced cogeneration plants. As a result, oxyfuel equipped platforms provide a diversified set of advantages, while keeping competitive efficiencies. For instance, advanced systems allow for cutting down ostensibly the atmospheric CO2 emissions compared to the conventional and amine-based power plant configurations of the FPSO.

Natural gas as a transitional solution for railway powering systems: Environmental and economic assessment of a fuel cell based powering system

This study presents a comprehensive environmental impact and economic assessment of the use of natural gas in potentially cleaner locomotives. An integrated direct methane-solid oxide fuel cell powering system is proposed and analyzed using energy and exergy methods. The system reaches the optimum energy and exergy efficiencies of 85.8% and 83.3%, respectively. Comparing the operation of this integrated system to a currently used diesel-electric engine for an intercity passenger locomotive duty cycle, the use of methane in a solid oxide fuel cell powering system reduces CO2 emissions by 58.4%, and fuel costs drop by a factor of 3.4. In general, a total of 10.6% increase in power production by the cascaded Rankine cycles helps reduce the CO2 emissions by 4.4%. As a result, the use of natural gas in rail transportation has clear and significant environmental and economic advantages over diesel. Also, the implementation of solid oxide fuel cell-based powering systems is justified environmentally and economically, and future researchers should build prototypes for demonstration purposes of future clean locomotives.

Proposal and assessment of a novel carbon dioxide energy storage system with electrical thermal storage and ejector condensing cycle: Energy and exergy analysis

The intermittent nature of renewable energy leads to significant issues when increasing the penetration level of renewable power. Energy storage system is generally considered to be an efficient measure for stabilizing the fluctuations of renewable power. A creative liquid carbon dioxide energy storage system integrating with transcritical Brayton cycle, electrical thermal energy storage and ejector condensing cycle is kindly proposed in this paper. To evaluate the feasibility of the developed system, the system thermodynamic model is clearly established and verified. The parametric analysis is performed based on energy and exergy methods to assess the relationships between key functioning variables and the system performance. The analysis results indicate that the ejector condensing cycle can be introduced as a green solution to the dilemma of carbon dioxide condensation during discharging stage. A higher turbine inlet pressure and temperature both bring about a promotion of the system net power output as well as the round trip efficiency. The ejector entrainment ratio gives a decrease with the rise in ejector back pressure, and the decreasing trend is first steep until the ejector back pressure being at 8.2 MPa in the considered conditions and then becomes distinctly moderate. Meanwhile, the optimal system efficiency is always located at the constant ejector back pressure (8.9 MPa in the considered conditions). The exergy destruction within the ejector condensing cycle decreases substantially with the low pressure storage temperature, increases monotonically with turbine inlet pressure, keeps unchanged with turbine inlet temperature and decreases with ejector back pressure.

Novel integrated helium extraction and natural gas liquefaction process configurations using absorption refrigeration and waste heat

Conceptual design and modeling of novel-integrated process configurations for helium extraction and natural gas liquefaction is investigated. Mixed fluid cascade (MFC) refrigeration system is considered for providing the needed refrigeration in the natural liquefaction section. Using an absorption refrigeration system as the precooling cycle is investigated in one of the introduced processes. Integrated flash and distillation method is used for helium extraction. Purity of the extracted crude helium is 50% (mole). Process streams operational condition and specifications of the devices are presented and explained. Composite curves of the heat exchangers demonstrate that thermal design has been done properly. Ratio of the power consumption to the produced liquefied natural gas (LNG) of the MFC process is 0.265 kWh per kg LNG and applying absorption refrigeration system instead of the pre-cooling cycle decreases it to 0.1849 kWh per kg LNG. For the modified process with absorption refrigeration system helium extraction rate and power consumption ratio are 0.951 and 132.9 (kWh/[kgmole Helium]) respectively. Exergy method is applied on the under consideration processes. The results show that the compressors have the highest rate of exergy destruction among the other process equipment. An extensive economic analysis is done on the proposed processes. The results show that prime cost of the product (US$/kg LNG) for MFC and modified MFC processes are 0.1939 and 0.2069, respectively. Finally, a sensitivity analysis is done based on the economic factors such as electrical energy price and prime cost of the product.

Thermodynamic comparison of small liquid nitrogen generators driven by mixed-refrigerant J-T refrigerators and gas expansion cycles

The thermodynamic comparison of small mixed-refrigerant J-T (MRJT) and gas expansion (Kapitza cycle) LN2 generators are conducted by the exergy method in this paper. Both of two types are employed for low pressure N2 liquefaction and air separation (< 9.0 bar). Pure N2, PSA units or cryogenic air separation columns are used for LN2 production. The MRJT type is driven by single-stage compressors. It is indicated that the efficiency of MRJT type is higher than Kapitza type. With pure N2 at 8.0 bar, the figures of merit (FOM) of MRJT and Kapitza types are 26.86% and 12.79%, respectively. With mini air separation columns, the FOM of MRJT and Kapitza types are 21.42% and 11.34%, respectively. The large exergy losses in the compressor unit and non-isentropic expansion are the main reasons of the inferior efficiency of the Kapitza type. In addition, the Kapitza type requires larger total compressor displacement than the MRJT type. The MRJT type is recommended to be used in small LN2 generators.