Exergy Efficiency Values Research Articles

Energy integration of light hydrocarbon separation, LNG cold energy power generation, and BOG combustion: Thermo-economic optimization and analysis

To recover boil-off gas (BOG) and liquefied natural gas (LNG) cold energy, this paper proposes three systems integrating light hydrocarbon separation (LHS), BOG combustion, organic Rankine cycle (ORC) with different structures and natural gas (NG) direct expansion. Both single and multi-objective optimizations are implemented to find the best system performance. Meanwhile, two multi-objective decision methods are also used to refine this work. Single objective optimization depicts that the system with parallel ORC has the highest net electric power (NEP), exergy efficiency, and net present value (NPV) of 6.85 MW, 29.07%, and 31.08 × 107 $ respectively. Multi-objective optimization results indicate the NEP, exergy efficiency, and NPV of the system with parallel ORC still outperform the other two systems. From the energy analysis, it is found that the system with parallel ORC achieves 81.07% utilization of LNG cold energy, which is the highest among the three systems. The exergy analysis indicates that the combustion chamber and heat exchanger (HX) with the highest exergy destruction in any system. Moreover, economic analysis demonstrates that the three systems are more sensitive to fluctuations in interest rates than in electricity prices.

Effect of hydrogen addition in a diesel engine fuelled with diesel and canola biodiesel fuel: Energetic-exergetic, sustainability analyses

In this study, the influence of diesel and biodiesel fuels with various flow rate of hydrogen (3 L per minute and 6 L per minute) addition through the intake manifold of a diesel engine was investigated at three different engine speed (1500 rpm, 1800 rpm, and 2100 rpm) by considering second law of thermodynamic as a different perspective. Energy, exergy, and sustainability analysis were evaluated by utilizing the data from the experiments. According to the results, it is enlightened that useful work energy ascends with the hydrogen addition in all engine speeds and the net work rates of all test fuels were found as highest at 1800 rpm engine speed while the rate of energy heat loss decreased with hydrogen addition. Furthermore, exergy input is also increased with the hydrogen addition to the engine whereas exergy destruction and exergy heat lost decreased with the increment of the hydrogen. The highest values of energy efficiency and exergy efficiency obtained at 1800 rpm engine speed by using diesel fuel with 6 L per minute hydrogen addition as 38.67 % and 35.09 %, respectively. The highest entropy generation occurred at 2100 rpm as 0.288 kW/K for the biodiesel fuel and the lowest value was observed as 0.201 kW/K for DH6 fuel at 1800 rpm. The analyses showed that the sustainability index values determined to be in the range of 1.437–1.541 and the increase in hydrogen ratio enhanced the sustainability index at all engine speeds and the DH6 and BH6 fuels are more sustainable fuels than the other experimental fuels.

Thermodynamic performance of a cryogenic energy storage system based on natural gas liquefaction

Cryogenic energy storage (CES) is a viable method for grid-scale electrical energy storage. Considering the high energy density and mature application of liquefied natural gas (LNG), we proposed an LNG cryogenic energy storage (LNGES) system. A steady-state process model of the LNGES system was established using Aspen HYSYS. The effects of the natural gas composition and key operating parameters such as the charging pressure, discharging pressure, throttling temperature, and liquid storage pressure on the system performance were investigated. A multi-parameter genetic algorithm model built using the MATLAB software was used to optimize the LNGES system to optimize the round-trip efficiency (RTE). Then, an exergy analysis of the optimal configuration was conducted. The results suggested that the LNGES system could achieve optimal RTE and exergy efficiency values of 60.14% and 71.64%, respectively. Exergy destruction mainly occurred during the compression, throttling, expansion, and heat exchange. The proposed LNGES system could be a promising candidate for the large-scale application of CES technology in power grids and gas networks.

Ocean thermal energy conversion (OTEC) system driven with solar-wind energy and thermoelectric based on thermo-economic analysis using multi-objective optimization technique

In the present study, we investigated a multiple energy generation system based on the use of solar, wind and ocean thermal energy for the study area with high renewable energy potential. In this study, all existing capacities in coastal areas (wind, sun, ocean temperature difference) are used to design a renewable system. The present system consists of subsystems including organic Rankin cycle (ORC), wind turbine, thermoelectric, heat exchanger and flat panel solar collector. EES thermodynamic software has been used to model the system and obtain thermodynamic results. The system designed for the city of Bushehr, which has good ocean thermal energy, wind energy and solar radiation potential, has been studied. The most important effective and practical parameters in the proposed system are collector area, solar radiation, and wind turbine speed. The results of the investigation of the system in Bushehr City showed that the production power of the system is 4,840,913.8 and 1,138,957.02 kWh compared to the climate changes. Also, the amount of freshwater produced by the system is 103,495.99 and 429,080.51 m3/h compared to the climate changes. Finally, in order to optimize the designed system, the response level multi-objective optimization method has been used to find the best set of objective functions and decision variables. The two objective functions of this optimization included the exergy efficiency of the whole system and the system cost rate. The most optimal value of exergy efficiency was 13.25% and the cost rate was 72.17 $/hour.

Comparison between two LiBr–H2O absorption-compression chillers and a simple absorption chiller driven by various solar collectors: Exergy-economic performance and optimization

Although some studies have been conducted on various types of compressor-based absorption chillers (ACH), a comprehensive comparison of the performances of these configurations has not been made. In addition, selecting a proper solar collector in combination with the best compressor-based ACH is worthwhile as solar energy is widely available during the summer season. For this purpose, the exergy-economic performances of 12 LiBr–H2O chiller configurations are compared in the present study to produce 100 kW of cooling. The configurations are a single-effect ACH and two absorption-compression chillers (ACCH) driven by 4 collector types, namely, a flat plate collector (FPC), an evacuated tube collector (ETC), a parabolic trough collector (PTC), and a compound parabolic collector (CPC). In ACCH 1, a compressor is embedded between the evaporator and the absorber of the ACH. In ACCH 2, a compressor is employed between the generator and the condenser of the ACH. The outcomes of the research indicate the superiority of the PTC and ETC over the two other collector types in terms of exergy efficiency and economic performance, respectively. The highest exergy efficiency and lowest total cost rate are calculated as 4.8% and 23.58 $h−1, which are obtained by the PTC-driven ACCH 1 and ETC-driven ACCH 1, respectively. Nevertheless, the unit cost of cooling produced by these two layouts is too high compared to the other configurations. Hence, they cannot be selected as the best configuration. Instead, the ETC-driven ACCH 2 is selected as the best configuration since it brings about the lowest unit cost of cooling (20.45 $GJ−1), and it has acceptable values of exergy efficiency (4.11%) and total cost rate (29.3 $h−1).

Direct waste heat recovery from a solid oxide fuel cell through Kalina cycle, two-bed adsorption chiller, thermoelectric generator, reverse osmosis, and PEM electrolyzer: 4E analysis and ANN-assisted optimization

The present study investigates an innovative model for the utilization of redundant heat from a solid oxide fuel cell (SOFC). The proposed system comprises a Kalina cycle (KC), a two-bed adsorption chiller (AC), a thermoelectric generator (TEG), reverse osmosis (RO), and a proton exchange membrane electrolyzer (PEME). A parametric analysis is conducted to evaluate the impact of key variables on the performance of the system. Various metrics are employed, including energy, exergy, economic, and environmental (4E). The environmental analysis reveals that waste heat recovery from SOFC decreases CO2 emissions by 36.41 kg per megawatt output at the base condition. At a fuel (methane) consumption rate of 0.0743 kg/s, the system produces 2206.49 kW of power, 166.09 kW of cooling load, 404.68 m3/day of fresh water, and 18.04 kg/day of hydrogen with reported energy efficiency and exergy efficiency values of 63.91% and 51%, respectively. Besides around 60.55% of the overall exergy destruction in the entire system is attributed to the air preheater, afterburner, and water preheater of the SOFC. The system is optimized using a genetic algorithm (GA) in three separate optimization issues, aiming to minimize the total cost rate while maximizing other objective functions, such as exergy efficiency, freshwater production, and cooling load. A modern optimization model using artificial neural networks (ANNs) is employed to reduce optimization time. By considering the overall cost rate and exergy efficiency as the objective functions, the optimal point is achieved at 58.03 $/h and 59.92%, respectively. The optimum values of 120.99 $/h and 1346.30 m3/day for the objective functions of total cost rate and freshwater production, respectively, are obtained in the second issue. In the third optimization problem, the evaluated values at the optimal point are 272.6 kW and 70.69 $/h for cooling load and total cost rate, respectively. Sensitivity analysis indicates that the changes in current density significantly affect the exergy efficiency, cost rate, net power, and cooling load, while variations in the fuel utilization factor coefficient considerably influence freshwater production.

Waste heat recovery assessment of triple heat-exchanger usage for ship main engine pre-heating and fresh water generation systems

In this study, the applicability, fuel saving and CO2 emission reducing potential of the triple heat-exchanger fed by the diesel generator exhaust gas with and without water steam have been studied for ship’s one and two main engines pre-heating and freshwater generation (FWG) cycles under port conditions with conducting energy and exergy analysis. The performance criteria (PC) and exergy efficiency (ε) values of the main engine pre-heating and freshwater generator systems of the Ro-Ro ship selected for the case study were determined by written Matlab 2021a codes merging CoolProp 6.4.2 database with Python. It was determined that even at the lowest operating load of the diesel generator (25%), the exhaust heat energy would be sufficient to preheat the main engine and generating fresh water with also saving fuel consumption. As a result, during the 12-h port period, each 1 kW heat energy reduction on steam will provide 0.0853 kg/h fuel saving in the boiler. Thus, 273 kg CO2 emission will be reduced for each kW of heat energy to be obtained. Considering the comparatively increased PC and ε values of whole system cycle containing common triple heat-exchanger for two main engines, it can be used conveniently and reliably on ships.

Investigation of the performance parameters for a PEMFC by thermodynamic analyses: Effects of operating temperature and pressure

In the present study, thermodynamic performance characteristics of the proton exchange membrane fuel cell (PEMFC) at ranging operating temperatures and pressures were examined through energy and exergy analyses. The energy and exergy figures of the reactants and products were taken into account by thermodynamic analysis. In addition, the significant parameters such as destroyed exergy, entropy generation, thermal efficiency, and exergy efficiency were calculated at the aforementioned conditions to give more knowledge regarding the PEMFC. In conclusion, the power density and exergy efficiency improved as the operating temperature of the FC boosted. When the current density was 1, the exergy efficiency increased by 13.17% as the operating temperature ascended from 303 K to 363 K. At all operating temperatures, the augmentation in current density caused irreversibility, so entropy generation ascended. Since the increase in operating temperature led to an increase in power density, amount of exergy that was destroyed declined. Augmentation of the working pressure at constant temperature did not remarkably enhance the exergy efficiency. In the case of a current density of 1, the exergy efficiency values at the operating pressures of 3 atm and 12 atm were found to be 54.42% and 53.79%, respectively.

Thermodynamic and feasibility analysis of using diesel generator exhaust gases for ship main engine preheating at port periods

In this study, the feasibility and potential impact on fuel consumption of the proposed preheating system driven by diesel generator exhaust gas instead of steam to satisfy main engine pre-heating demands especially under port operation conditions have been analyzed according to the 1st and 2nd laws of thermodynamics. The proposed novel term named performance criteria (PC) and exergy efficiency (ε) values of the main engine preheating and cooling water systems of the Ro-Ro ship selected for the case study under the existing voyage and port operating conditions have been determined by written Matlab-2021a codes merging CoolProp-6.4.2 database with Python. It was determined that even at the lowest operating load of the diesel generator (25%), the exhaust heat energy would be sufficient to preheat the main engine with also reducing the fuel consumption. As a result, during the 12-hour port period, 22% of the boiler fuel consumption and 8% of the ship's fuel consumption can be saved. Accordingly, if a shipping company uses Mine Gas Oil as fuel, it will be able to achieve fuel savings of approximately US$ 32.000 on annual basis. Considering the fuel saving values, it has been determined that 1.016 tons of CO2 emissions for per port operation and 106 tons of annual CO2 emissions can be reduced. It was determined that, the PC and Ɛ values of the system decrease as the ambient temperature increases. In this context, there is a 7% decrease in the PC and a 5% decrease in the Ɛ for existing system and 8% decrease in the PC and a 2.5% decrease in the Ɛ for proposed system. It was also determined that the proposed new system is both physically and economically feasible and that the investment cost, which was determined to be in the range of US$ 30.000-US$ 35.000, can pay for itself after 1 year.

Comparative study of compound parabolic concentrator - photovoltaic thermal – thermoelectric generator (CPC-PVT-TEG) collector integrated with vapour absorption refrigeration (VAR) system

ABSTRACT In this communication, a hybrid CPC-PVT-TEG collector integrated with the VAR system has been analyzed, taking into consideration 3 different types of PV modules based on their back cover material, namely Tedlar (Case 1), Aluminium (Case 2) and semi-transparent (glass to glass) (Case 3). The simulation of the whole system, including the hybrid collector and VARS, has been done for a clear day in May in New Delhi using MATLAB 2021b. A comparative study has been conducted between the three cases and based on the results obtained from the analysis, the overall exergy (EEX), overall exergy efficiency (ηEX), daily electrical energy and overall exergy attained their highest values for Case 2 [Aluminum based] with their values being 289.33 Wh, 28.92%, 2.37 kWh and 2.55 kWh, respectively. The coefficient of performance (COP), which is a measure of the refrigeration effect of the VAR system, attained its highest value for Case 3 [glass to glass based] at 1.28 and lowest value for Case 1 [Tedlar based] at 0.28. Also, from a purely overall exergy aspect, the aluminum-based hybrid CPC-PVT-TEG collector integrated with the VAR system (Case 2) is found to be the most suitable with exergy and exergy efficiency values and from the refrigeration as well as from a thermal exergy aspect, the semitransparent-based or glass to glass-based hybrid CPC-PVT-TEG collector integrated with a VAR system (Case 3) is found to be the most suitable.

Experimental performance evaluation of solar still with zig-zag shape air cooled condenser: An energy–exergy analysis approach

In the present experimental effort is made to increase the performance of a solar still (SS) by including a novel design of a zig-zag-shaped air-cooled condenser (ZZACC) and cuprous oxide (CuO) as a nanomaterial. Research work is conducted in the climatic conditions of Gandhinagar, Gujarat, India, from September to November 2020. A comparison was made to assess the performance of a conventional solar still (CSS) and a solar still equipped with a zig-zag shape air-cooled condenser (SSWZZACC) with CuO. The experiments’ findings showed that adding CuO to SSWZZACC increases the distillate production by 46.83% and the daily energy efficiency by 45.98%, respectively, compared to CSS. Also, SSWZZACC demonstrates a better efficiency of exergy and latent heat of vaporization than CSS because CuO causes an increase in the evaporative heat transfer coefficient of water. In life cycle cost analysis study discovered that SSWZZACC has a 27.77% lower cost per litre of water (CPL) than CSS. The obtained maximum energy and exergy efficiency values for CSS and SSWZZACC were 2.36% & 25.75% and 3.9% & 37.59%, respectively. In economic and environmental aspects, it was found that SSWZZACC with CuO showed a cost-effective desalination unit and was highly effective from a carbon credit point of view (CCP) by CO2 mitigation.

Energetic, exergetic, exergoeconomic, environmental and sustainability analyses of a solar, geothermal and biomass based novel multi-generation system for production of power, hydrogen, heating, cooling and fresh water

The present study proposes and investigates a novel solar, geothermal and biomass based multi-generation system producing multiple outputs to generate power, hydrogen, heating, cooling, and fresh water. Parabolic trough solar collectors, a two stages Rankine cycle, two organic Rankine cycles, two absorption cooling systems, a gas turbine system, a once-through (OT) multi stage flash (MSF) desalination unit, a geothermal unit, a heat pump, an electrolyser and a thermal energy storage are used as sub-systems. The novelty of the system is to focus on novel sub-system design pattern for the proposed multi-generation system by using multiple energy inputs as there is a gap about those studies in the literature. The overall system performance is evaluated from energetic, exergetic, exergo-economic, environmental (4E) and sustainability points of view by using the EES software package. The total installed power and hydrogen mass flow rates are 7.76 MW and 3.52 kg/h, respectively. The energy and exergy efficiency values of the overall system are found to be 65.55% and 27.09%. Fresh water flow rate is calculated to be 6.16 kg/s with 10 stages. The overall unit product cost is determined to be 21,79 $/GJ and the overall social ecologic factor is calculated to be 1.37.

Multi-objective optimization and evaluation of a water-saving scenario to produce hydrogen and freshwater in an innovative biomass-assisted plant

With global communities being susceptible to adverse impacts of greenhouse gases, hydrogen has substantially drawn the attention of scientists to investigate it as a promising fuel. Hence, the present investigation aims to conduct an exhaustive thermodynamic analysis of an innovative biomass-assisted system driven by the Brayton cycle through multi-objective optimization to detect the different optimal scenarios for generating and storing hydrogen. This system contains a Brayton cycle as a prime mover, steam gasification of biomass and three-stage compressors to generate and store hydrogen, and multi-effect distillation to produce freshwater. The ultimate goal of this study is to use the generated steam through the produced freshwater as a steam agent of the gasifier to conclude a water-efficient scenario in producing hydrogen. To discern the impact of the chosen design parameters on the performance of the system, an exhaustive parametric study has been carried out. Afterward, multi-objective optimization via the non-dominated sorting genetic algorithm has been undertaken to find the optimal values by regarding the financial constraints. Tri-objective optimization results demonstrated that optimum values of total cost rate, exergy efficiency, and hydrogen production rate are 1.43 $/s, 47.56%. , and 0.12 kg/s. Besides, by regarding the consumption of water as an additional objective function, the results demonstrate that by reducing consumed water up to 47.5%, the generated hydrogen only decreases by 8%.

Investigations on energy efficiency enhancement under knock threshold limit conditions for a turbocharged direct-injection spark-ignition engine fueled with wet ethanol

Wet ethanol is a promising biofuel whose properties fit with turbocharged direct-injection spark-ignition (DISI) engines for countries with yearly production capacity. Even though it has a higher life-cycle efficiency than regular ethanol, which reduces significantly the energy required on ethanol production, wet ethanol’s potential is wasted by the continuous dehydration process. In order to highlight such potential as a fuel for engines, this study investigates the early injection of different blends of wet ethanol (E100W0, E95W5, E90W10, and E80W20, respectively) via an in-house engine simulator to improve engine operating conditions — enhancing engine and ethanol’s life-cycle efficiencies. This study searched for the highest sustainable values of engine energy and exergy efficiencies based on the threshold value of the knock index number. The combustion phasing model used correlations obtained from a machine learning algorithm fed with experimental data for a DISI engine. This investigation provided 120 different cases under different compression ratios (r), engine speeds, relative air-fuel ratios, and wet ethanol blends. Results showed that E80W20 can operate with a turbocharger at r = 18. The highest efficiencies (43% and 40%, respectively) were found for E90W10 and E80W20 — values 30% higher than regular Brazilian FFV. Lastly, cases involving the best conditions for torque, lean air-fuel conditions at high compression ratios and water content, and downspeeding are presented as interesting alternatives to either stationary engines or hybrid vehicles, therefore highlighting the potential of wet ethanol for DI engines.

A simplified opto-thermal assessment and economic study of parabolic dish solar concentrator pondering on the receiver position induced uncertainties

This paper investigates the opto-thermal and economic assessment of low-cost solar parabolic dish concentrators (PDC), focusing on the receiver position-induced uncertainties. An optical model of the proposed PDC system is developed in Tonatiuh optical simulation tool. The optical analysis is conducted by the Monte Carlo Ray Tracing method for different vertical and horizontal positions of the PDC’s receiver. In addition, An experimental test rig based on a locally manufactured PDC with a low-cost reflecting surface made of aluminium reflector foil is developed to achieve the purpose of this work. A cavity receiver made of a cylindrical-cone brass tube is used and tested under different positions of the focal point of the PDC. The impact of the uncertainties on the performance of the proposed PDC is experimentally estimated. A relatively simple mathematical model is utilized to evaluate the thermal and exergy performance for the different positions of the cavity receiver. The results showed that the proposed PDC could generate hot water at temperatures 77 °C, 64 °C, and 55 °C for the three focal point positions, respectively. The collector efficiency of the PDC-cavity receiver system in the receiver position 1, 2, and 3 were 70.2%, 53.2%, and 24 % while the average values of exergy efficiency for the PDC at the receiver positions were 4.7%, 2.3%, and 0.93% respectively. This clearly shows the effect of the receiver positions on the performance of the parabolic dish solar concentrator and justifies the requirement of appropriate positioning of the receiver for the parabolic dishes.

Thermal performance optimization of rectangular cavity receiver for cross linear concentrating solar power system

ABSTRACT A thermodynamic analysis was performed on a newly developed concentrated solar power (CSP) technology known as the Cross-Linear (CL), which addresses the issue of cosine loss in conventional CSP technology. The analytical model has been developed and validated using experimental data collected at the experimental site situated in Bhopal, India. The analysis was performed under direct normal irradiance of 775 W/m2 with the key objective to determine the optimum inlet condition of the heat transfer fluid (HTF) considering three optimization parameters: HTF outlet temperature, energy, and exergy efficiency of the receiver. Also, the exergy of the solar field is investigated depending on the available solar irradiation throughout the day for three different configurations of the heliostat field. After a comprehensive analysis of the results, the optimal air inlet temperature range was observed to be between 373 and 423 K, and the optimal air mass flow rate was overserved to be 0.0925 kg/s (333 kg/h), which provides energy and exergy efficiency values within 50% to 60% and 28% to 34%, respectively. The maximum electrical exergy efficiency for 30 kW plant capacity is observed to be around 70% at solar noon with a cosine factor of around 0.9 for 4-hour duration.

Thermo-economic performance enhancement of the hemispherical solar still integrated with various numbers of evacuated tubes

Experimental investigations of the hemispherical solar still (HSS) augmentation with various numbers of evacuated tubes (EVT) were performed and evaluated. The modified hemispherical solar still (HSS-EVT) performance was illustrated with two categories of EVT distributions and compared with the traditional HSS (THSS) design. In the first category, the EVT was distributed on the water basin perimeter in all directions (Dis-ɸ), and in the second category, the EVT was distributed in the south direction (Dis-So). The impact of various water heights (Hw) from 1 to 4 cm was also studied. Results revealed that the integration of EVT had a significant influence on distillate performance. The highest daily production rate at 1 cm water height of HSS-EVT was 5860 mL with an increment of 551, 316, 156, and 91% compared to THSS at NEVT = (16, 8, 4, and 2 tubes), respectively. The productivity increment by 7.2%, when compared EVT distribution (Dis-ɸ) with (Dis-So) effect. The reduction of water level to 1 cm increases the yield by about 5.96, 11.61, and 18.74% with HW (2, 3, and 4 cm), respectively. The proposed system's peak energy and exergy efficiency value was 42.29 and 5.57%, with an increment of 47.30 and 124%, respectively, related to the traditional one. The maximum daily production related to the exposed surface area was 6.69 L/m2 at NEVT = 8 tubes. The estimated cost varied between 0.00237, and 0.0101 USD/L.

Parametric optimization of a VCR diesel engine run on diesel-bioethanol-Al2O3 nanoparticles blend using Taguchi-Grey and RSM method: a comparative study

PurposeThe study aims to verify and establish the result of the most suitable optimization approach for higher performance and lower emission of a variable compression ratio (VCR) diesel engine. In this study, three types of test fuels are taken and tested in a variable compression ratio diesel engine (compression ignition). The fuels used are conventional diesel fuel, e-diesel (85% diesel-15% bioethanol) and nano-fuel (85% diesel-15% bioethanol-25 ppm Al2O3). The effect of bioethanol and nano-particles on performance, emission and cost-effectiveness is investigated at different load and compression ratios (CRs). The optimum performance and lower emission of the engine are evaluated and compared with other optimization methods.Design/methodology/approachThe test engine is run by diesel, e-diesel (85% diesel-15% bioethanol) and nano-fuel (85% diesel-15% bioethanol-25 ppm Al2O3) in three different loadings (4 kg, 8 kg and 12 kg) and CR of 14, 16 and 18, respectively. The optimum value of energy efficiency, exergy efficiency, NOX emission and relative cost variation are determined against the input parameters using Taguchi-Grey method and confirmed by response surface methodology (RSM) technique.FindingsUsing Taguchi-Grey method, the maximum energy and exergy efficiency, minimum % relative cost variation and NOX emission are 24.64%, 59.52%, 0 and 184 ppm, respectively, at 4 kg load, 18 CR and fuel type of nano-fuel. Using RSM technique, maximum energy and exergy efficiency are 24.8% and 62.9%, and minimum NOX emission and % cost variation are 208.4 ppm and –6.5, respectively, at 5.2 kg load, 18 CR and nano-fuel. The RSM is suggested as the most appropriate technique for obtaining maximum energy and exergy efficiency, and minimum % relative cost; however, for lowest possible NOX emission, the Taguchi-Grey method is the most appropriate.Originality/valueWaste rice straw is used to produce bioethanol. 4-E analysis, i.e. energy, exergy, emission and economic analysis, has been carried out, optimized and compared.

Design and multi-objective optimization of a multi-generation system based on PEM electrolyzer, RO unit, absorption cooling system, and ORC utilizing machine learning approaches; a case study of Australia

The geothermal systems' capability to produce various products persuades the design of a novel hybrid system, including power, cooling, freshwater, and hydrogen. Australia, with numerous geothermal sources and the tendency of hydrogen utilization as fuel, is considered a case study. The designed system is analyzed from energy, exergy, and economic viewpoints. Also, the artificial neural network is implemented to optimize the system's operation. Hence, the accuracy of four artificial neural networks in optimizing and predicting systems' performance is compared. Furthermore, four double-objective and four triple-objective optimization scenarios are considered to achieve the best optimum state from different viewpoints. The mean absolute Error value of 2.28×10−14 to predict the exergetic efficiency in the testing procedure is the best algorithm. The system provides 1263 kW net power with 39.89% exergy efficiency and 2.13 years of payback period at the base condition. The exergy efficiency-net present value scenario represents the best performance in which the net power, hydrogen, and freshwater production rates reach 3946 kW, 8.73 kg/h, and 152 kg/h, respectively. Subsequently, the exergy efficiency, payback period, and net present value are estimated at 46.27%, 1.84 years, and 19.52 M$.

Exergy Analysis of Thermal Power Plant for Three Different Loads

This paper presents the energy and exergy analysis of thermal power plant Tuzla in Tuzla, Bosnia and Herzegovina. The main aim of this paper is to analyze the components of a 200 MW steam power plant unit in order to identify and quantify the sites with the highest exergy losses and to calculate exergy efficiency values of all components when operating at nominal load. The influence of the change in ambient temperature and block load on the value of exergy losses and exergy efficiency was taken into analysis. The analysis further includes the impact of steam block operation without high-pressure and low-pressure heaters on the exergy efficiency of the steam block. The goal of the analysis is to determine the functional state of individual steam block components after a long period of exploitation and maintenance in order to take appropriate measures to improve their technical performance. Exergy losses during nominal operation of the steam power plant unit are the largest in boiler and amount to 313.42 MW, followed by a turbine with 205.60 MW, condenser 1 with 6.03 MW, condenser 2 with 5.75 MW, while other components of the steam power plant have exergy losses in the range of 0.03 to 2.15 MW. Operation of the unit at nominal load without HPH results in an exergy efficiency decrease from 5.60 to 9.80 %, while in case of operation without HPH and LPH it results in a decrease in exergy efficiency from 9.86 to 16.40 % depending on the pattern used to calculate. The conclusion after the analysis indicates that the biggest exergy losses are in the boiler and turbine and consequently these components have the lowest exergy efficiency values. The increase in ambient temperature has different effects on individual components of the thermal power plant, increasing exergy losses of the boiler while reducing the turbine exergy losses and condensers.