Total Exergy Destruction Rate Research Articles

Thermodynamic modeling and comparative analysis of a compressed air energy storage system boosted with thermoelectric unit

Current study represents the thermodynamic modeling and exergy analysis of a compressed air energy storage system boosted with thermoelectric generator (CAES/TEG). To evaluate the studied system, a comparative analysis between compressed air energy storage system (CAES) with CAES/TEG has been done. Exergy, a powerful tool for analyzing energy conversion systems, is employed to determine the exergy destruction rate and exergy efficiency of the system as well as different related components. The results of exergy analysis indicates that the wind turbine with 35.28 kW (44.81% of total exergy destruction rate) has the highest exergy destruction rate and after that in the second and third places are combustion chamber and cavern. Findings indicate that with adding thermoelectric modules to the CAES system, the output power of Rankine cycle and organic Rankine cycle increase about 1.16 kW and 0.959 kW in comparison with CAES system, which these changes lead to increasing the net output power of the system in CAES/TEG system from 33.59 kW to 35.71 kW compare with CAES. Moreover, the influences of main parameters such as compressor mass flow rate, compressor pressure ratio, and combustion chamber outlet temperature and wind speed on the CAES/TEG performance are investigated.

Energy and exergy analyses of solid oxide fuel cell-gas turbine hybrid systems fed by different renewable biofuels: A comparative study

In recent years, many studies have been conducted on hybrid solid oxide fuel cell and gas turbine which fed by renewable fuels to reach the high-efficiency power and the low pollution. In this paper, a thermodynamic study based on energy and exergy analyses of a hybrid solid oxide fuel cell and gas turbine hybrid system has been conducted in the presence of reforming with steam, in which the effects of using natural gas and other biofuels including Sewage biogas, Agricultural and Industrial waste biogas, Syngas, Biofuel and Gasified biomass, have been compared to this system. The purpose of this paper is to investigate the effect of each of the mentioned fuels on the performance of individual equipment and the entire system from the thermodynamic perspective. Initially, the modeling and energy balance of all components in the system were carried out in detail. Further, calculating the exergy destruction of all components of the system and the effects of applying different biofuels on the key parameters of the system, including total production power, operating pressure and temperature, compression ratio, the water-to-fuel ratio in the reforming, energy and exergy efficiency, and the amount of irreversibility of each component in the system have been analyzed. To compare more accurately between different fuels, an equal amount of each fuel is considered, and the effect of each fuel system on the hybrid system is analyzed by calculating the operating parameters of the system. By studying the results of modeling, it was determined that natural gas with 879.03 kW produced the highest production capacity and Gasified biomass with 45.44 kW has the least amount of power generation. By studying the thermodynamics of the system, if it is fed with Natural gas, the highest exergy destruction (687.45 kW) occurs and the lowest total exergy destruction rate is related to the system fed by gasified biomass (101.12 kW). Comparing the fuels, it was concluded that the electrical efficiency of the system fed with natural gas has the highest efficiency (72.71%) and Biofuel has the lowest total electrical efficiency (56.6%). Furthermore, by examining the exergy efficiency of the whole system, it was found that Natural gas with the highest efficiency of 61.29% and Gasified biomass with 46.06% the lowest exergy efficiency can be detected. Finally, the effect of the percentage combination of each fuel on the performance of all equipment from the perspective of energy and exergy has been studied.

Evaluation and Optimization of the Annual Performance of a Novel Tri-Generation System Driven by Geothermal Brine in Off-Design Conditions

The difference in heating or cooling to power ratio between required demands for district networks and the proposed tri-generation system is the most challenging issue of the system configuration and design. In this work, an adjustable, novel tri-generation system driven by geothermal resources is proposed to supply the thermal energies of a specific district network depending on ambient temperature in Germany. The tri-generation system is a combination of a modified absorption refrigeration cycle and a Kalina cycle using NH3-H2O mixture as a working fluid for the whole tri-generation system. A sensitive analysis of off-design conditions is carried out to study the effect of operational parameters on the system performances prior to optimizing its performance. The simulation show that the system is able to cover required heating and cooling demands. The optimization is applied considering the maximum exergy efficiency (scenario 1) and minimum total exergy destruction rate (scenario 2). The optimization results show that the maximum mean exergy efficiency in scenario 1 is achieved as 44.67% at the expense of 14.52% increase in the total exergy destruction rate in scenario 2. The minimum mean total exergy destruction rate in scenario 2 is calculated as 2980 kW at the expense of 8.32% decrease in the exergy efficiency in scenario 1.

Comparative analysis and multi-criteria optimization of a supercritical recompression CO2 Brayton cycle integrated with thermoelectric modules

Regarding the high expense of the exploiting energy from energy resources, each innovation or modification on the energy systems with the aim of enhancing the efficiency and affordability is so valuable. Along with this fact, in the present work, the effects of employing thermoelectric (TEG) unit in a recompression Brayton cycle ( $${\text{sCO}}_{2}$$ -reB/TEG) are examined. The results of thermodynamic modeling represents that adding the thermoelectric to the system in the s $${\text{CO}}_{2}$$ -reB can improve the net output power about 2.41 kW and increase the first and second law efficiency of s $${\text{CO}}_{2}$$ -reB/TEG system about 1.09% and 1.12% in comparison with s $${\text{CO}}_{2}$$ -reB system. Additionally the exergo-economic analysis for s $${\text{CO}}_{2}$$ -reB/TEG revealed that the reactor and turbine II should be considered more than other elements from exergo-economic point of view since the highest values of $$\dot{Z}_{\rm k} + \dot{C}_{\rm D,k}$$ belong to these components. After identifying the important parameters as well as evaluating system from thermodynamic and economic aspects, a multi-objective optimization is implemented on the $${\text{sCO}}_{2}$$ -reB-TEG system for determining the optimum conditions. Two optimization scenarios are defined using the results of parametric analysis. Multi-objective optimization with first scenario results in total cost rate of 1.6 $ h−1 and total exergy efficiency of 0.5 in minimum temperature, maximum temperature and compression ratio of 36.17 °C, 577.15 °C and 1.6. Furthermore, for optimization based on second scenario results in total exergy destruction cost and exergy destruction rate of 3.04 $ h−1 and 435.85 kW in 48.75 °C, 569.77 °C and 3.44 for minimum temperature, maximum temperature and compression ratio.

Waste heat recovery in an intercooled gas turbine system: Exergo-economic analysis, triple objective optimization, and optimum state selection

The development of heat and power generation systems has a major step towards sustainable development, reducing fossil energy consumption and reducing environmental pollution. Integrated energy systems are considered widely due to their high efficiency. In the present paper, an intercooled gas turbine system is developed to achieve a system with high thermal efficiency as well as better economic performance and cleaner production. The main goals of the suggested system is improvement of thermodynamic and exergo-economic performance beside multi-criteria optimization, which lead to improve the system sustainability. The intercooled gas turbine in the current work integrated with hot water system and thermoelectric generator unit to develop an advanced combined heat and power system. A comprehensive energy, exergy, and exergo-economic analyses are employed to price assessment of the new introduced system. A comparative analysis with conventional intercooled gas turbine system is presented. The results of thermodynamic modeling indicate that an improvement about 613.3 kW, 8.21 kW, and 12.3 kW can be obtained in the gas turbine, Kalina cycle, and regenerative organic Rankine cycle subsystems. The results of energy and exergy analysis show that the values of both energy and exergy efficiencies for all subsystems experience increment in the new introduced. Parametric analysis based on thermodynamic and exergo-economic criteria is done and a triple objective optimization conducted to determine the best system configurations. The Technique for Order of Preference by Similarity to Ideal Solution is employed to choose the final optimal state of the system. The result of optimum selection among non-dominant solutions suggested by Pareto points indicates that the energy efficiency, total exergy destruction rate and electricity cost rate are 53.91%, 2392.01 kW, and 52.29 $/h.

Using waste heat of high capacity wind turbines in a novel combined heating, cooling, and power system

In this paper, a new combined cooling, heating and power system was proposed to investigate the utilization of the waste heat of 12 high capacity wind turbines, each has a capacity of 7500 kW. This system includes a modified organic Rankine cycle consisting of a regenerator and feedwater heater, an absorption refrigeration cycle, and heat exchangers. It is investigated theoretically to assess power, cooling, and hot water production. There is a large number of wind data during a year in the location of these high capacity wind turbines (Noordoostpolder; Netherlands); therefore, to follow a logical procedure for each month and reduce calculations, the hourly average wind speed of 2 days of each season are selected. For the 15th day of the first and last months of each season, the hourly average wind speeds at 12 p.m. are considered. Energy analysis was performed for all chosen hourly average wind speeds; however, to reduce exergy calculations, the average wind speed of 12.25 m/s was selected. At this average wind speed, results indicated that the hourly produced net power, hot water at 65 °C, and cooling at −10 °C are 196.2 kWh, 35.5 m3/h, and 147.7 kWh, respectively. The highest exergy destruction rate belongs to the heat exchanger applied for recovering waste heat from high capacity wind turbine and equals to 74.82% of the total exergy destruction rate. The energy and exergy efficiencies of the proposed system were obtained as 45.32% and 38.61%, respectively. Finally, a simple economic analysis was carried out, accordingly, the payback period was calculated as 1.9 years and it resulted that the proposed system is cost-efficient.

Experimental energy and exergy performance of an automotive heat pump using R1234yf

Various energy and exergy performance parameters of an automotive heat pump (AHP) with R1234yf have been investigated and compared with those of the baseline system with R134a. For this aim, an AHP system was set up from the components of an air-conditioning system employed in a compact car and equipped with instruments for mechanical measurements. It was tested with R1234yf and R134a by changing the compressor speed and air stream temperatures incoming the outdoor and indoor units. Using test data, energy and exergy analyses of the AHP were performed, and its performance parameters were evaluated. The R1234yf system provided conditioned air temperatures in the range of 29.9–59.3 °C, heating capacities in the range of 1.96–3.14 kW and coefficient of performance (COP) values in the range of 2.44–4.56. It yielded 3.3–10.8 °C lower conditioned air temperature, 9.2–15.4% lower heating capacity, 1.6–7.1% lower COP, 13.8–21.6 °C lower compressor discharge temperature, 3.1–19.2% higher total exergy destruction rate per unit heating capacity but significantly less TEWI in comparison with the system with R134a. Moreover, the R1234yf system yielded larger exergy destructions in the outdoor unit, compressor and expansion device but lower exergy destruction in the indoor unit. These findings reveal that R1234yf can be used in AHP systems in expense of less heating capacity, lower COP and higher exergy destruction rate per unit heating capacity in comparison with R134a.

Energy and exergy investigation of two modified single mixed refrigerant processes for natural gas liquefaction

Liquefaction processes consume a high amount of energy, and any attempt to achieve lower energy consumption and higher exergy efficiency would lead to a remarkable enhancement in the process efficiency. In the present study, two mini-scale modified single mixed refrigerant processes for natural gas liquefaction are simulated. The specific power consumption and total exergy destruction rate are optimized using the genetic algorithm tool. As a result of the energy optimization of the base case process, the specific energy consumption and the total exergy destruction rate are reduced by 19.4% and 25.4%, respectively. On the other hand, the maximum total exergy efficiency of 47.51 % is obtained through the exergy optimization of the process. The results related to the process configuration with a pump shows a higher exergy efficiency. Moreover, the minimum specific power consumption of 0.221 kWh/kg LNG is obtained through the optimization of the exergy destruction rate function.

Development, evaluation, and multi-objective optimization of a multi-effect desalination unit integrated with a gas turbine plant

In this research study, a 40 MW gas turbine power plant, which is coupled with a multi-effect desalination system with thermal vapor compression, is investigated. The energy, exergy and exergoeconomic analyses of the integrated plant are presented. As the number of effects in a desalination system is a key parameter, the effect of number of effects on the system performance is investigated. The genetic algorithm-based multi-objective optimization is applied to determine the best decision variables.To achieve the best optimization states, different scenarios of multi objective optimization based on the total exergy destruction rate, unit electricity price, total cost rate, gain output ratio, distilled water cost, and total exergy efficiency are examined. Additionally, seven decision variables are compressor pressure ratio (rp), combustion temperature (T3), compressor isentropic efficiency (ηc), gas turbine isentropic efficiency (ηGT), top brain temperature (TBT), last effect temperature (LET), and ejector compression ratio (Cr). The parametric analysis results indicated that although increasing the number of effect enhance the distilled water production rate, it increases the total cost rate of the system. With motive steam flow rate of 14 kg/s, results showed that distilled water production rate is 12294m3/day. Additionally, with three different scenarios the optimal states of integrated system are introduced. The results of optimization scenarios suggested different optimal states that are best guide for designer to select the best system configuration.

Technoeconomic and environmental optimization of a solar tower integrated energy system for freshwater production

A novel energy system consisting of a Brayton cycle, a heliostat field, an organic Rankine cycle and a multi-effect desalination-thermal vapor compression unit is proposed and investigated. Freshwater and electricity are the products of the proposed energy system. The present study proposes a sustainable renewable-based energy unit for freshwater production, and introduces a new concept of a pair plot, which can provide useful insights into the behavior of an energy system. A multi-objective optimization is conducted using NSGA-II with two objective functions (total cost and total exergy destruction rate) and ten decision variables. The point on the Pareto optimal solution nearest to the ideal point has a total exergy destruction rate of 4.7 MW and a total unit cost of 0.045 $/kWh. The scatter distribution and pair plot of the decision variables are illustrated and trends for each decision variable are discussed. The NSGA-II and NSGA-III performances are contrasted and compared by employing the hypervolume indicator technique. An NSGA-II genetic algorithm optimization with three objective functions is conducted and the results are discussed. The three objectives are total exergy destruction rate, total unit cost and gain output ratio. Also, the impact on CO2 emissions of the heliostat field is discussed, and a thermodynamic description of each model is developed and validated with numerical and experimental data.

Working fluid selection for regenerative supercritical Brayton cycle combined with bottoming ORC driven by molten salt solar power tower using energy–exergy analysis

The objective of the present work is the investigation of a regenerative supercritical Brayton cycle (SBC) and its combination with an organic Rankine cycle (ORC). The study includes assessment, comparison, and single-objective optimization of these systems which are driven by molten salt solar power tower (SPT). First, the performances of 13 different working fluids from 18 introduced gases in the supercritical regions are studied in SBC and 6 working fluids are selected for further analysis. Then, a parametric analysis is performed to assess the effects of the compressor pressure ratio (CPR) and the Brayton turbine inlet temperature (BTIT) variations on net power output, exergy efficiency and total exergy destruction rate. After that, the optimum operating points of system performance are reported. The results show that using ORC causes all three output parameters to be improved. The highest net power output is 177321 kW and the highest exergy efficiency is 21.23% which are obtained by Helium as the working fluid. Moreover, the minimum exergy destruction is found to be 70576 kW allocating Oxygen. Finally, by comparing the examined gases in SBC, it can be concluded that using Helium leads to the best thermodynamic performance of the system.

Exergoeconomic optimization of a new double-flash geothermal-based combined cooling and power (CCP) system at two different cooling temperatures assisted by boosters

A new cooling/power cogeneration system applicable to double-flash geothermal power plants is devised which provides cooling load at two different adjustable cooling temperatures. To further increase efficiency of the set-up, two boosters are employed to boost pressure of the secondary flow of each ejector due to the considerable drop of pressure of the geofluid through the steam turbines as well as the throttling valves. A comprehensive modeling of the proposed system is achieved from thermodynamics laws as well as economic perspectives and the results are elaborated with more details. In comparison with the previous integrated systems based on the flash geothermal power plants, the present system produces around 47.8% more cooling load and 38.9% more electricity. Also, the results of multi-objective optimization revealed that the net electrical power and exergetic efficiency can be increased approximately 20.59% and 68.11%, respectively. However, the unit cost of power and cooling (UCPC) is decreased around 36.3%. Meantime, the total exergy destruction rate is decreased after optimization. Among all elements, the highest exergy destruction occurred in the condenser by 2570 kW out of 7609 kW (in base mode) and 2333 kW out of 6836 kW (in optimum mode). Also, it is found that the energy efficiency of the proposed system can be increased by increasing turbines outlet pressure, boosters pressure ratio, and separator 1 pressure or decreasing separator 2 pressure.

Energetic and exergetic performance analysis of a solar driven power, desalination and cooling poly-generation system

This paper presents a thermodynamic analysis of a poly-generation system powered by solar thermal energy using parabolic trough collectors. The proposed system consists of an organic Rankine cycle, a multiple effect distillation and an absorption cooling unit. The performance analysis of the solar system is conducted for different configurations: power generation only, cogeneration power and cooling, cogeneration power and desalination, and poly-generation. The effects of turbine inlet temperature and pump inlet temperature on the energetic and exergetic system performance as well as the net power output and total exergy loss of the system are examined. In addition, exergetic parameters, including system total exergy loss, fuel depletion ratio and improvement potential were analyzed. The study reveals that increasing the turbine inlet temperature increases the performance while it reduces the total exergy destruction rate of the system. The result of the study also shows that the two main sources of exergy destruction are the solar thermal collector and desalination unit; with 49.3% of the input exergy (76% of the total exergy loss) destructed in the collector while 9.6% of the inlet exergy (14.9% of the total exergy loss) is destroyed in the desalination system. The overall improvement potential of the system was found to be 64.8%.

Exergoenvironmental Analysis of Tetrahydrofuran/Ethanol Separation through Extractive and Pressure-Swing Distillation

Abstract Extractive distillation uses a high-boiling point solvent for changing the relative volatility of the azeotropic mixture, whereas pressure-swing distillation is based on the difference of operating pressures for such a purpose. In this paper, said separation technologies were applied to a tetrahydrofuran/ethanol mixture and compared with regard to their thermodynamic and environmental performances. The former was assessed by determining the total exergy destruction rate and rational efficiency of each configuration, while the latter was evaluated by estimating their respective indirect carbon emissions. The results showed that the pressure-swing process has not only the lowest exergy destruction rate (383.1 kW) but also the lowest CO2 emission rate (678.7 kg/h), which is mainly due to its lower thermal energy requirements. A sensitivity analysis was then carried out in order to determine how the carbon emissions respond to both the efficiency and the fuel type of the utility boiler.

Enhanced exergy-based malfunction diagnosis of an integrated solar combined cycle system: parametric study and multi-objective optimisation

In this research, a malfunction diagnosis method based on the enhanced exergy concept is applied to quantify the anomalies' sources in a real integrated solar combined cycle system (ISCCS). A comprehensive parametric study is performed to evaluate the malfunction indicators and the overall performance of the power plant by varying the substantial operating parameters under single and multi-malfunction conditions. Then, the fast and elitist non-dominated sorting genetic algorithm (NSGA-II) is applied to maximise the net power and minimise the total exergy destruction rate of the system under a multi-malfunction condition.

Exergy and exergoeconimic analysis and multi-criteria optimisation of 1 MW installed CCHP system (a case study in Kashan University)

The present study deals with exergy and exergo-economic evaluation of a 1 MW combined cooling, heat and power (CCHP) system, composed of a natural gas prime mover internal combustion engine located in the main campus of the University of Kashan, Kashan, Iran. Using appropriate linking between engineering equation solver (EES) and MATLAB software, thermal and economic modelling and multi-criteria optimisation (MCO) have been performed. The optimisation results showed that the minimum total exergy destruction rate occurs for the exhaust gas extraction factor of 0.68, which causes $33.52/h total cost rate. For this case, among all of the system components the highest exergy destruction rate of 1,700 kW belongs to the engine. In addition, the results of the genetic algorithm-based multi-objective optimisation represented that the optimisation causes $2.68/h decrease in total cost rate and reduction of 4,512 kW in exergy destruction rate.

Energy and exergy analyses of dual refrigerant system for liquefaction of natural gas

Present study proceeds thermodynamic modelling, and analysis of dual refrigerant system for liquefaction of natural gas (LNG) that is one of the most important technologies in producing LNG. Using energy equations pressure, quality, enthalpy, entropy of natural gas and two refrigerants, i.e., methane and propane are specified. The effects of different cycle variables on the thermodynamic performance especially the coefficient of performance (COP) is studied. Using the second law of thermodynamic for the system components, the exergy destruction rates has been found. The exergy analysis results show that heat exchanger I (HX I), heat exchanger II (HX II) and turbine have the highest exergy destruction rate. Furthermore, results indicate that the total exergy destruction rate of studied cycle for generation of 1 kg/s LNG is 2,996 kW. Moreover, energy and exergy analysis show that important parameters such as propane mass flow rate has different effects on the COP and exergy destruction rate.

Energy and exergy analyses of dual refrigerant system for liquefaction of natural gas

Present study proceeds thermodynamic modelling, and analysis of dual refrigerant system for liquefaction of natural gas (LNG) that is one of the most important technologies in producing LNG. Using energy equations pressure, quality, enthalpy, entropy of natural gas and two refrigerants, i.e., methane and propane are specified. The effects of different cycle variables on the thermodynamic performance especially the coefficient of performance (COP) is studied. Using the second law of thermodynamic for the system components, the exergy destruction rates has been found. The exergy analysis results show that heat exchanger I (HX I), heat exchanger II (HX II) and turbine have the highest exergy destruction rate. Furthermore, results indicate that the total exergy destruction rate of studied cycle for generation of 1 kg/s LNG is 2,996 kW. Moreover, energy and exergy analysis show that important parameters such as propane mass flow rate has different effects on the COP and exergy destruction rate.

Enhanced exergy-based malfunction diagnosis of an integrated solar combined cycle system: parametric study and multi-objective optimisation

In this research, a malfunction diagnosis method based on the enhanced exergy concept is applied to quantify the anomalies' sources in a real integrated solar combined cycle system (ISCCS). A comprehensive parametric study is performed to evaluate the malfunction indicators and the overall performance of the power plant by varying the substantial operating parameters under single and multi-malfunction conditions. Then, the fast and elitist non-dominated sorting genetic algorithm (NSGA-II) is applied to maximise the net power and minimise the total exergy destruction rate of the system under a multi-malfunction condition.

A new approach for optimization of combined cycle system based on first level of exergy destruction splitting

A multi-objective optimization of a combined air cooled gas turbine and steam turbine system is carried out using non-dominated sorting genetic algorithm II (NSGA-II). In the optimization process, performance and environmental aspects of the system are considered, and the first level of exergy destruction splitting is incorporated. Such parameters as second law efficiency, ratio of total avoidable exergy destruction rate to total exergy destruction rate, and CO2 emission in exhaust gases, are considered as the objective functions. Once the model of the system is constructed in engineering equation solver (EES) software and validated, the gas turbine inlet temperature and compressor pressure ratio are considered as the decision variables based on the performed sensitivity analysis. Then, EES is coupled with MATLAB and the multi-objective optimization is performed for various values of gas turbine blade cooling air fractions. By comparing the obtained Pareto optimal points with those of the base case, considerable improvements in the values of the objective functions are observed.