The major target of this paper shows effect of selected decision variables in the steam system for optimization of thermal combined cycle power plant.
Material and

Exergoeconomic, and other similar terms used to imply the combined thermodynamic and economic analysis of energy systems, which helps to increase the efficiency of a plant without jeopardizing its economic viability. The optimization accomplished using an iterative exergoeconomic. The design data of an existing plant (Damavand combined cycle power plant in Tehran) used for the present analysis.
Results and Diction: Two different objective functions proposed: one minimizes the total cost of production per unit of output, and the other maximizes the total exergetic efficiency. The analysis shows that the total cost of production per unit of output is 2% lower and exergy efficiency is 4% higher with respect to the base case. It demonstrates that selected decision variables have a good result for the exergy analysis and cost effectiveness

This paper investigates the economic feasibility of installing a turboexpander in parallel with the throttling valve of a city gate station for the purpose of distributed electricity generation through exergy recovery from pressurized natural gas. The preheating requirements for preventing hydrate formation due to pressure reduction are provided by the combustion of a small fraction of the outlet natural gas stream. As a case study, the simulation of Tehran No.2 City Gate Station demonstrates an exergy loss of more than 36.5 million kWh per year for the present throttling valves. Thermoeconomic analyses gives the optimum operating conditions for electricity generation through a turboexpander. Optimization of preheating temperature leads to an exergy recovery of >60%, cost to generate electricity of <$0.04/kWh, and discounted payback period of around ~4 years. Simulation results can be used for designing an automatic preheating temperature control system to optimize exergy recovery via turboexpander under the variable operating conditions of a pressure reduction station.

Nitrogen expansion processes are suitable for mini or small-scale liquefied natural gas plants, due to their simplicity and less equipment. However, they consume a high amount of energy and any attempt to reduce the energy consumption and improve the quality of energy (work potential of energy), leads to enhance the process efficiency and profitability. A mini-scale nitrogen dual expander natural gas liquefaction process is simulated and analyzed by Aspen HYSYS simulator. Then, in order to optimize energy performance of the process, some influencing variables are adjusted using the genetic algorithm approach provided by MATLAB software in two separate optimization cases with different objective functions. Specific energy consumption and total exergy destruction are considered as the objective functions of the optimization cases (namely energy and exergy cases), which represent quantity and quality of energy, respectively. The most important operating variables of the process, refrigerant molar flow, refrigerant temperatures and refrigerant pressures, are selected via a sensitivity analysis. The results indicate that in both of the optimization cases, the specific power consumption of the process is reduced 7.1%. However, the total exergy destruction for exergy case decreases 9.55% which is slightly a more desirable result than the energy case. Also, total exergy efficiency of the process in exergy case is 4.4% higher than the other case which reveals that considering the quality aspect of energy as the objective can improve the performance of the process more appropriately.

Identification of the location of energy loss is the most important step in energy optimization of industrial plants. Exergy analysis specifies the points of irreversibility and the amount of exergy loss. According to the equipment exergy loss، the energy bottlenecks of unit will be specified. Exergy Analysis of Abadan catalytic reforming unit shows heat exchangers، which preheating the feed streams of unifiner and platformer fire heaters (H-E-1 and P-E-1)، have the maximum exergy loss of heat exchangers network. Adding two pairs of heat exchangers to these heat exchangers، the network is retrofitted. Therefore the exergy loss reduces 4. 0769 (MMBtu/hr) in winter and 4. 4563 (MMBtu/hr) in summer. This retrofit needs approximately $215000 investment and will also reduce heat duty of hot and cold utilities to 15 and 9 MMBtu/hr، respectively. This retrofit causes 7% energy saving. The payback period of this investment is 45 months and then will save $57000 annually.

Having calculated the exergy loss for all pieces of process equipment, it is possible to show the thermodynamic irreversibility, which makes certain guidelines for modifying the process industries and improving their performance. In this study the exergy loss is calculated using Omega Composite Curves, which is a novel graphical tool for calculating exergy loss in heat exchanger networks. Unlike other current tools, this graph is linear and calculation of exergy loss using the rectangular shaped area is so easy. The Omega-Enthalpy diagram is used to calculate exergy loss for other unit operations. First, how to achieve this diagram is explained and then the diagrams are used for exergy loss calculation in two case studies. In the first study, each of a PRICO process (LNG production) equipment was investigated especially the multi-stream heat exchanger. The results showed that in the whole process 27.66 MW of exergy is wasted. In the second study, the heat exchanger network of Shazand thermal power plant was investigated and exergy loss of this network was calculated by 8.14 MW.

One of the optimization methods is exergy analysis. It uses the conservation of mass and conservation of energy principles, together with the second law of thermodynamics, for the analysis, design and improvement of energy and other systems. Exergy is defined as the maximum amount of work which can be produced by a system or a flow of matter or energy as it comes to equilibrium with a reference environment. Unlike energy, exergy is not subject to a conservation law (except for ideal, or reversible, processes). Rather, exergy is consumed or destroyed, due to the irreversibility in any real process. The exergy consumption during a process is proportional to the entropy created due to the irreversibilities associated with the process. Exergy is a measure of the quality of energy which, in any real process, is not conserved but, rather, is in part destroyed or lost. Many research studies have been carried out on the exergy analysis of wind energy. The purpose of this paper is to develop an improved approach to the exergy analysis and optimization of a wind turbine and find a way to decrease average Entropy generation and increase exergy in ' Bergey Excel-S ' wind turbine through Cut-in, Rated, Furling speeds optimization, using Particle swarm optimization algorithms. Firstly, we would go for mathematical modeling of wind turbine exergy which results in objective function. Then, by means of nerve web computer code in collecting statistical data of so called turbine, it would be modeled in Matlab program and the output results will be covered in tables and diagrams in this paper. This results shows a relation between inlet air speed, Entropy generation, and the efficiency of second law. By studying optimization results from pso algorithm, we have observed a 24.53 % decrease in Entropy generation and 41.67% increase in exergy efficiency.

This paper focuses on the simulation and exergy analysis of flare gas recovery systems and their consuming resources in a gas processing plant, with the aim of minimizing environmental pollution and maximizing energy utilization. During the extraction and processing of oil and gas, significant amounts of unused gases are typically directed to flares, resulting in both environmental pollution and economic waste. Through simulation, it has been determined that approximately 28,700 kg/hour of flare gases can be recovered from the refinery’s flare network, operating at a pressure of 9 bar and a temperature of 25 degrees Celsius. To optimize the consumption of the recovered gases, exergy analysis has been conducted for different consumption scenarios. Two distinct scenarios for the consumption of flare gases are presented. In the first scenario, the recovered gases are compressed to a pressure of 70 bar and injected into the gas sweetening unit of the refinery. Moreover, the calculated exergy efficiency for this scenario is 69%. In the second scenario, the recovered gases are directed to the compressors available in the gas condensate unit. The calculated exergy efficiency for this scenario exceeds 78%. Ultimatly, based on the simulation and exergy analysis results, it is concluded that injecting the recovered flare gases into the compressors of the gas condensate stabilization unit offers the most optimal utilization of the recovered gases. This finding highlights the potential for reducing environmental pollution, minimizing waste, and maximizing the economic resources available in the gas processing plant.

This research has been carried out with the aim of thermodynamic optimization of Bushehr nuclear power plant with the approach of exergy analysis for the connection of desalination plant and the production of freshwater at the lowest possible cost. After exergy analysis and determination of destruction, gray wolf optimizer and particle swarm algorithms have been used to optimize the system. The performance of these algorithms in solving the Rastrigin function has been evaluated and the main problem has been solved with the superior algorithm to find the optimal temperatures and pressures. Then, a multi-stage distillation desalination unit with a Thermo vapor compressor with a capacity of 24,000 cubic meters per day has been connected to one of the outlet flows of the low-pressure turbine. The results showed that the highest rate of irreversibility and loss with 1510.50 MW belongs first to the reactor and then to 144.50 MW to the steam generator. The cost of producing fresh water in optimal conditions of the power plant is estimated at $ 1.18 per cubic meter.

In this research, a 16-inch pipeline of Ahwaz-Rey oil transmission, 750 km long, was simulated using the Aspen Plus and Pipe Phase software to obtain outgoing flow data and equipment. Exergy analysis of pipelines and pressure boost stations were calculated to determine the exergy degradation. The lowest exergy damping with an approximate value of 34 kilowatts was obtained at Sheshmeh Shoor Station. Thermoeconomic analysis was performed to obtain the price of equipment, material flows, heat and work, as well as the price of feed and product flows, and to calculate the thermoeconomic coefficient in order to optimize the system economically. The highest price level was found at 0.00130 $ per second at the Sabzab pressure station. The highest thermoeconomic coefficient was obtained at 0.8477 at Cheshmeh Shoor station. The maximum value of this coefficient for pipelines was equal to 0.8745 between Astra stations and pole Baba. It was found that the increase in ambient temperature, operating pressure, mass flow rate, pipeline length and diameter increase the final cost.

Biodiesel is viewed as a promising alternative to fossil fuels due to its favorable chemical properties and environmental benefits. Research has shifted towards producing biodiesel from non-edible oils and waste cooking oils to avoid food scarcity issues. The high cost of production is a major challenge, with raw materials accounting for 75% of the total cost. Sustainability depends on low-cost feedstocks like waste cooking oil. Exergy analysis is a useful tool for optimizing biodiesel production by reducing energy and resource consumption and increasing production yield. The study focuses on the exergy flow of transesterification of waste cooking canola oil, with parameters like methanol:oil ratio, catalyst concentration, and temperature being evaluated.

Waste cooking oil (WCO) was used in the present study, with physicochemical properties including density, viscosity, free fatty acid content, and acid value measured. Biodiesel production using a two-step catalyzed method was carried out, with the first step being esterification to remove high water and FFA content in the waste cooking oil. The second step involved transesterification using different methanol:oil ratios, catalyst concentrations, and reaction temperatures. The FAME content of the samples was analyzed using gas chromatography and an equation was provided to calculate the FAME content of the biodiesel samples. In the process of transesterification of WCO, four balance equations were used to analyze exergy. Mass, energy, and entropy input and output must be balanced, with a portion of exergy input being destroyed. The mass exergy component is divided into physical, chemical, potential, and kinetic exergy. The overall exergy of a mixture of substances was calculated by considering physical and chemical exergy. Mixing in the transesterification process is irreversible, with potential work being wasted. Exergy transfer by heat flow and workflow was calculated using specific equations. An exergy conversion coefficient was used to estimate the chemical exergy content of fuels. Dead state conditions were considered for calculating exergy efficiency in the transesterification process.

The GC analysis of transesterification conversion products from a standard sample showed that the main components in WCO-derived biodiesel were methyl salicylate, methyl palmitate, methyl stearate, methyl oleate, methyl linoleate, and methyl oleate. The efficiency of the transesterification process under specific conditions was determined to be 90.23% with an exergy efficiency of 91.73%. Exergy analysis revealed that the exergy embodied in biodiesel was higher than that in WCO, but a portion of WCO's exergy was consumed in the production of biodiesel. The study also highlighted ways to reduce energy loss and material waste in the transesterification process, emphasizing the importance of recycling and reusing waste materials to improve overall resource efficiency. The experiment variables of methanol:oil molar ratio, KOH concentration, and reaction temperature were investigated in the transesterification process for biodiesel production. A higher methanol:oil molar ratio of 6:1 was recommended for maximum yield when using pure oil with low FFA and water content. Increasing the ratio from 4:1 to 8:1 resulted in higher biodiesel yield and exergy efficiency. However, further increasing the ratio to 12:1 led to decreased efficiency. The KOH concentration and reaction temperature also had significant impacts on biodiesel yield and exergy efficiency. Higher catalyst concentration and reaction temperature increased exergy destruction, while a temperature increase from 45℃ to 55℃ improved efficiency and yield. The study suggested that careful optimization of these variables is essential for maximizing biodiesel production and minimizing exergy losses.

Exergy analysis is a valuable tool for assessing the environmental impacts of products, processes, or activities by quantifying energy and material usage and waste generation within a comprehensive framework. It also allows for estimating the resource requirements for processes such as transesterification in the production of renewable resources like biodiesel. In this study, the exergy flow in the transesterification of waste cooking oil was evaluated, with a focus on the impact of variables such as methanol:oil ratio, potassium hydroxide concentration, and reaction temperature on biodiesel yield, exergy efficiency, and exergy destruction. Experimental data was collected and used for exergy calculations, revealing that maximum biodiesel yield and exergy efficiency were achieved at specific conditions. Excess methanol or potassium hydroxide led to decreased efficiency and increased exergy loss in the process. Lower temperatures also resulted in higher exergy loss due to reduced conversion efficiency. Understanding the effects of these variables can help improve exergy efficiency and economic performance in commercial biodiesel production. Exergy analysis can also be used to evaluate environmental performance and aid in the development of environmental policies and resource management strategies.