1. Introduction
Considering that the global need for energy is increasing, researchers are seeking strategies to utilize less energy and prevent the negative effects of burning fossil fuels such as environmental pollution and global warming. It is desired that options provide energy conversion with improved efficiency and lower carbon emissions. Fossil fuels, due to their availability and convenience in utilization compared to other energy sources, are receiving a great deal of attention [
1]. Fossil fuels have a key disadvantage. By using the fossil fuels, the environmental consequences such as global warming, subsequent climate changes, and air pollution increase [
2]. In order to limit these impacts, two approaches can be considered: utilizing renewable and/or sustainable energy sources (e.g., hydro, biomass, solar, geothermal, and wind energies) and the waste heat recovery (WHR) of exhaust gases from the topping cycles, along with other efficiency improvement measures. Renewable and sustainable energy sources usually provide energy services with practically no air pollution and greenhouse gas emissions [
3]. However, these energy sources have some limitations, such as cost concerns for hydropower and solar energies and location dependence for geothermal energy [
4]. The use of WHR not only lowers the use of fossil fuels but additionally boosts the overall efficiency of the system and lessens environmental problems [
5].
The WHR approach forms the foundation of the combined plant proposed in the current study. The system comprises two integrated cycles operating at various temperatures. After converting a portion of high-temperature thermal energy to electricity, the topping cycle transforms the rest of the high-temperature energy to the low-temperature cycle. In the bottoming cycle, a share of this thermal energy is transformed into electricity, while the remainder is discharged to the atmosphere [
6,
7]. Since electricity is produced by two components in the combined cycle, applying WHR can boost the efficiency of the overall system [
8].
Among various systems, the gas turbine (GT) system is potentially suitable as a topping cycle due to being cost-effective, efficient, and being able to use a wide range of hydrocarbon fuels [
9,
10]. However, without WHR, about 60% of the energy in a typical GT is rejected into the atmosphere at high temperature [
11,
12]. Using the advanced gas turbine in the hybrid system results in an enhanced energy efficiency of 50–58% [
13]. As a result, the efficiency of the entire plant can be improved by integrating the bottoming cycle with the GT system. Much effort has been committed to boost the efficiencies of the conventional GT cycles. Among these is CGAM cogeneration system, which integrates a gas turbine with a heat recovery steam generator (HRSG) and an air preheater [
14,
15,
16]. The utilization of air preheater boosts the efficiencies based on exergy and energy of the system, as the air passing into the combustion chamber absorbs heat from the hot gases leaving the turbine, which lowers fuel consumption. It is potentially advantageous to use this type of heat exchanger when the temperature of the air entering the combustion chamber is less than the temperature of the gases exiting the turbine; otherwise, the efficiency of the system can drop. The GT cycle is most extensively employed in the aviation [
17,
18,
19] and maritime industries [
20].
Exergo-economic and exergy evaluations of the GT cycle have been performed by Ameri and Enadi [
21]. They concluded that the combustion chamber has the highest exergy destruction rate, and this variable is reduced by raising the chamber’s entrance temperature. In addition, as the intake temperature of the gas turbine climbs from 1100 K to about 1450 K, the cost of destroyed exergy is lowered by 22%. To increase the efficiency of the GT cycle, Pirkandi et al. [
22] employed solar energy in the cycle. This procedure increased the temperature of the air passing into the chamber, decreasing the amount of fuel used. Overall, 10% more power is generated by the solar GT cycle than the traditional system. Avval et al. [
23] investigated the GT cycle with a preheater from economic, energy, exergy, and environmental perspectives. By utilizing an evolutionary method, the system was subjected to a multi-objective optimization (MOO). The authors also evaluated the impacts of pressure ratio in the compressor and gas turbine isentropic efficiencies, and combustion chamber intake temperature on the environmental, economic, and thermodynamic performances of the plant.
Altinkaynak and Ozturk [
24] analyzed an integrated cycle including gas turbine, as well as supercritical carbon dioxide (S-CO
2), trans-critical carbon dioxide, and ORC systems, to generate thermal energy, cooling, electricity, and hydrogen. The exergy and energy efficiencies of the multi-generation plant have been found to be 42.0% and 44.7%, respectively. Maroufi et al. [
25] compared the performances of direct combination systems, including GT and pressurized fuel cell and GT and atmospheric fuel cell, and indirect combination systems, from energy and economic standpoints. The direct combined GT cycle and pressurized fuel cell were found to offer the best thermodynamic and economic characteristics. An innovative water and electricity generation system that utilized the waste heat of the GT cycle was examined thermodynamically, economically, and environmentally by Liu et al. [
26]. This system included a Kalina cycle, a GT cycle, and a desalination unit. Under basic design conditions, the overall products’ cost, the capacity of freshwater generation, the levelized total emission (LTE), and the exergy efficiency were found to be 20.2
$/GJ, 10.8 kg/s, 63.7 kg/W, and 43.1%, respectively. Also, the combustion chamber had the greatest exergy destruction rate among the components of the proposed system. Du et al. [
27] investigated the economic, exergy, and energy performances of supercritical and trans-critical carbon dioxide cycles driven by a GT system. The plant’s exergy and energy efficiencies were found to be 46.1% and 24.9%, respectively. Additionally, the total cost rate of investment and the products unit exergy cost were 126.1
$/h and 6.31
$/GJ, respectively.
Several systems have been suggested for their use as a low-temperature cycle in hybrid gas turbine-based plants. A steam Rankine cycle has been often used as the low-temperature cycle for a GT system. However, steam Rankine cycle has some significant disadvantages. This cycle utilizes water as the working fluid, and it is necessary to superheat water before inputting it to the turbine. Otherwise, there is the potential for erosion of turbine blades, and utilization of expensive and complex turbines [
28]. To overcome these challenges, organic working fluids are proposed as alternatives. An organic fluid typically has a critical pressure and temperature and molecular mass higher than water [
1,
28]. One of the main cycles in the WHR field is the ORC. This system utilizes an organic working fluid and avoids many of the issues of the steam Rankine cycle. Due to the simplicity, reliability, and adaptability of the ORC, it has recently attracted a great deal of research interest [
29,
30]. The major drawback with this cycle is that the evaporation process occurs at an unchanged temperature, which leads to a pinch point problem. This difficulty is caused by the lack of sufficient temperature compatibility between the two fluid flows during heat transfer, which lowers the exergy efficiency and causes notable exergy destruction in heat exchangers.
Khaljani et al. [
31] investigated a combined plant with ORC and GT sub-systems from environmental, economic, and thermodynamic perspectives. They concluded that in the combustion chamber, exergy was destroyed at the greatest rate. They also highlighted how the exergy and energy efficiencies of the plant rise with the compressor pressure ratio and isentropic efficiencies of the compressor and turbine. Nevertheless, the rise in these parameters increased the overall cost rate. Therefore, there should be an optimal value for these three specified parameters, where the efficiencies are at the highest values and the overall cost rate is at the lowest value. The desired values for the compressor and the turbine isentropic efficiencies and compressor pressure ratio were 87%, 89%, and 13.8, respectively. Ahmadi et al. [
1] examined the integration of a GT cycle and an ORC from energy and exergy viewpoints. In this research, six working fluids were employed in the ORC to determine which is the most suitable. Based on the exergy and energy efficiencies, dimethyl carbonate and o-xylene were seen to exhibit the best and the worst performances, respectively. The authors also investigated the impacts of operating pressure of the ORC on the exergy and energy efficiencies. The outcomes showed that the best optimal value for this variable to maximize the energy and exergy efficiencies is the highest accessible pressure reported in this research for each working fluid. Mohammadi et al. [
32] thermodynamically analyzed an absorption refrigeration cycle, ORC, and combined GT cycle. This integrated system was capable of providing 8 kW of cooling and 30 kW of power under specified conditions. Parametric investigation revealed that the pressure ratio and inlet temperature of the turbine are the two variables that most affect the performance of the system. Cao et al. [
33] comprehensively evaluated the integration of a GT system and an ORC from thermodynamic perspective. They compared the GT-Rankine integrated system and the GT-ORC integrated plant, and the findings demonstrated that the GT-ORC integrated plant possesses superior thermodynamic performance. Three distinct ORC working fluids were employed, and the optimum performance of the GT-ORC was obtained when toluene was utilized. A trigeneration system combining the GT cycle, single-effect chiller, water heater, and ORC was evaluated by Ahmadi et al. [
34] based on exergo-environmental analysis. With regard to the exergy efficiency and carbon dioxide emission, this system exhibited superior performance over the GT combined cycles for the specified input data. The authors also clearly highlighted that the environmental and thermodynamic performances of this system are notably affected by the isentropic efficiency of the gas turbine, the gas turbine inlet temperature, and the compressor pressure ratio.
Hemdari and Subbarao [
35] analyzed a combined GT and reheat ORC from energy and exergy perspectives. In this research, they investigated hexane, benzene, and cyclopentane as viable working fluids for the ORC. They reported that the maximum output power of cycle is obtained when benzene is employed. Sun et al. [
36] investigated the combined S-CO
2 cycle and ORCs for WHR application of a GT from exergo-economic and thermodynamic standpoints. The combined plant consisted of two S-CO
2 cycles and one ORC. The exergy and energy efficiencies and the exergo-economic factor of the proposed plant were found to be 51.9%, 48.6%, and 28.3%, respectively. The performances of the S-CO
2 cycle and the ORC were compared for waste recovery of a GT-sub system by Ancona et. al. [
37]. They observed that when the same installed topping GT cycle is utilized for both S-CO
2 and ORC sub-systems, the S-CO
2 cycle exhibits greater energy efficiency than the ORC. Pan et al. [
38] considered recompression, reheat, and pressurized intercooling supercritical CO
2-ORC for WHR from a GT. They assessed and optimized the suggested system from economic, energy, exergy, and environmental viewpoints. They reported values for the system of 84.5%, 66.9%, and 41.2%, respectively, for its environmental, exergy, and energy efficiencies.
Another significant system in the field of WHR is the Kalina cycle, which, due to utilizing zeotropic mixtures, can address the temperature mismatch problem between high- and low-temperature working fluids. As indicated before, temperature profile mismatching is one of the major challenges for ORCs. However, the Kalina cycle’s configuration complexity has motivated researchers to focus on the thermodynamic analysis of this system [
39]. A new cogeneration cycle made up of a GT cycle, the Kalina cycle, and a freshwater production unit was proposed by Ding et al. [
40]. They evaluated this system from environmental, economic, and thermodynamic viewpoints. They also employed MOO to obtain the most effective operational variables. The greatest exergy efficiency and the lowest levelized total emission were observed to be 43.8% and 62.6 kg/W, respectively. Zhang et al. [
41] considered the Kalina cycle as the low-temperature source to reuse the waste heat of a GT system, and assessed the plant from thermodynamic and environmental perspectives. Referring to the thermodynamic optimization findings, the exergy and energy efficiencies of the system were found to be 47.2% and 46.1%, respectively, and LTE was 60.1 kg/W. The combustion chamber was observed to be responsible for the greatest rate of exergy destruction in the system. Ebrahimi-Moghadam et al. [
42] comprehensively studied a combined plant containing GT system and Kalina cycle considering environmental, economic, exergy, and energy assessments. The system’s main operational performance parameters, including the exergy and energy efficiencies, LTE, and levelized total cost (LTC), were treated as the objective functions. Based on design parameters, energy and exergy efficiencies, LTE and LTC were found to be 69.4%, 37.9%, 88.0 kg/W, and 8.96
$/W, respectively. Köse et al. [
2] considered the Rankine and Kalina sub-systems as the low-temperature cycles to utilize waste heat from a GT plant. They conducted energy, exergy, economic, and environmental evaluations for the suggested system. Considering the GT and Rankine cycle (RC), the first law efficiency was 41.7%, but the energy efficiency of the GT-RC-Kalina system was 46.4%.
Ji-chao and Sobhani [
43] thermodynamically and exergo-economically evaluated a cogeneration system including GT, supercritical CO
2, and Kalina cycles. This system exhibited exergy and energy efficiencies of 41.0% and 78.2%, respectively. The net present value and the payback period were calculated as
$ and 6.9 years, respectively. Ebrahimi-Moghadam [
44] investigated a trigeneration system, including GT, Kalina, and ejector cycles, from exergo-environmental and exergo-economic perspectives. Based on the optimization results, the exergo-economic criterion, the exergo-environmental criterion, and the exergy efficiency were observed as 58.4
$/GJ, 42.7 kg/GJ, and 30.8%, respectively. Environmental, economic, exergy, and energy performances of an integrated micro-GT cycle and a superheated Kalina cycle were analyzed and optimized by Liu and Ehyaei [
45]. This system exhibited exergy and energy efficiencies of 50.8% and 51.7%, respectively. Moreover, the greatest exergy destruction was attributable to the gasifier. Employing the superheated Kalina cycle as the bottoming cycle decreased the payback period from 9.07 years to 4.6 years.
As indicated previously, an important disadvantage of the ORC is the temperature mismatch between the working fluid and heat source throughout the process of heat transfer, resulting in a rise in irreversibility and a drop in exergy efficiency. To tackle this difficulty, researchers have presented several promising approaches, one of which is the trilateral flash cycle (TFC). Yari et al. [
46] compared the thermo-economics of the Kalina cycle, ORC, and TFC utilizing a low-temperature heat source. The expander isentropic efficiency had a notable impact on the production cost of the TFC, even though TFC had greater net output power than the Kalina cycle and ORC. Based on references [
47,
48], the manufacturing of a highly efficient two-phase expander poses a substantial challenge for the TFC. The organic flash cycle (OFC) is well known as a developed version of the TFC. In addition to the fact that this cycle does not require a two-phase expander and can address the mentioned disadvantage of the TFC, it can also address the temperature profiles mismatch in the ORC. The above advantages suggest that the OFC is potentially one of the best options for utilizing GT cycles’ waste heat.
Ho et al. [
49] demonstrated that the energy efficiencies of the OFC and the optimized ORC for low-grade heat sources are the same. Moreover, aromatic hydrocarbons were reported as the most suitable working fluids to be utilized in OFCs and ORCs. Mondal and De [
50] utilized R600-R245fa mixture as the OFC working fluid to reuse the waste heat of the flue gas devoid of SO
2. The GWP of this mixture is less than 800 kg of CO
2 per kg of fluid. This mixture can provide a higher output power for the OFC than that of the OFC utilizing pure working fluids. The thermodynamic and thermo-economic characteristics of four OFC systems using five distinct working fluids were compared by Nemati et al. [
51]. A simple OFC was seen to have the highest and the lowest cost per unit of produced electricity and exergy efficiency, respectively. The exergy investigation demonstrated that the enhanced expander-OFC has the greatest performance. However, the dual flash OFC attained the greatest economic performance out of the three proposed configurations. The best exergo-economic and exergy performances of systems were obtained when toluene was utilized as the working fluid. An organic Rankine flash cycle (ORFC) integrates the trilateral cycle with the ORC. De Campos et al. [
52] compared the ORFC with the OFC, demonstrating that the greatest exergy efficiency is attained for the ORFC at lower volume flow ratio of the two-phase expansion than the OFC. Moreover, the exergy and energy efficiencies of the ORFC were higher than those of the OFC when utilizing pentane as the working fluid. Economic, exergy, and energy assessments of an ORFC were evaluated by Wang et al. [
53]. They determined that utilizing working fluids with higher critical temperatures offer improved energy efficiencies and lower power costs. Based on the optimization findings, the ORFC was able to perform thermodynamically better than the ORC and the OFC. Wu et al. [
54] evaluated an OFC integrated with a S-CO
2 recompression Brayton cycle (SCRBC) thermodynamically and thermo-economically. In this system, the OFC was utilized as the bottoming cycle to reuse the SCRBC waste heat. The findings revealed that the product overall unit cost and the exergy efficiency of the SCRBC integrated with the OFC were, respectively, 3.75% lower than and 6.57% higher than those of the standalone SCRBC. Moreover, the SCRBC combined with the OFC exhibited better thermo-economic and thermodynamic performances compared to the SCRBC integrated with the ORC. The authors considered seven different OFC working fluids, and the findings illustrated that the best thermo-economic and thermodynamic performances were obtained with n-nonane. For enhancing the performance of the SCRBC, three distinct bottoming systems, including Kalina cycle, OFC, and ORC, were considered to reuse the SCRBC waste heat and evaluated from the viewpoints of thermo-economics and thermodynamics by Mahmoudi et al. [
55]. The SCRBC/ORC and SCRB/Kalina cycles showed the greatest and the lowest exergy efficiencies, respectively, while the SCRBC/ORC exhibited the best thermo-economic performance. Ten distinct working fluids were employed for the OFC and the ORC. The best thermodynamic and economic performances were achieved with n-nonane and R134a for the OFC and ORC, respectively.
A S-CO
2 cycle combined with an OFC driven by hybrid geothermal and solar energies was introduced by Que et al. [
56]. In this system, a solar tower provided thermal energy to the S-CO
2 cycle, while the OFC was powered by the S-CO
2 system’s waste heat and geothermal energy. The authors investigated four different OFC working fluids and discovered that R245ca is the best choice from exergy and energy viewpoints. The system efficiencies of exergy and energy were found to be 33.4% and 26.0%, respectively. Ai et al. [
57] compared thermodynamically a new combined cooling, heating, and power (CCHP) system comprising the solar system and the regenerative OFC to a CCHP-ST-ORC system. The ratio of primary energy, which was defined as the ratio of useful energy output to the primary energy input, and the exergy efficiency were found to be 53.1% and 38.7%, respectively. Moreover, the consumption of natural gas for the CCHP-ST-OFC system was 9% lower than that for the CCHP-ST-ORC system.
The integration of the GT cycle with the OFC can have several practical implications, offering potential benefits in terms of efficiency, flexibility, and environmental impact. Practical implications of this integration are:
Enhanced efficiency: The integration of a GT cycle with an OFC allows for the recovery of waste heat from the GT exhaust gases. This waste heat can be utilized to generate additional power through the OFC. By effectively capturing and utilizing this waste heat, the overall system efficiency can be significantly improved compared with standalone GT cycles.
Flexible power generation: The combined GT-OFC system offers increased flexibility in power generation. The GT cycle provides a reliable and responsive power generation option, while the OFC can be utilized during periods of lower power demand or as a peaking power source. This flexibility allows for better matching of power generation with varying demand patterns, improving system reliability and grid stability.
Fuel diversity and decentralized energy generation: The integration of GT and OFC technologies allows for the utilization of a wider range of fuels. Gas turbines are known for their fuel flexibility, being able to operate on natural gas, liquid fuels, or even alternative fuels such as biofuels. By integrating an OFC, the system can also utilize low-grade waste heat sources, such as geothermal or industrial waste heat, further diversifying the fuel sources and enabling decentralized energy generation.
Environmental benefits: The integration of an OFC with a GT cycle can contribute to lower greenhouse gas emissions. The increased efficiency of the combined cycle reduces the amount of fuel required per unit of electricity generated, leading to lower CO2 emissions. Additionally, by utilizing waste heat that would otherwise be discharged into the environment, the system helps to reduce thermal pollution.
Combined heat and power (CHP) applications: The integrated GT-OFC system is well-suited for combined heat and power applications. The waste heat recovered from the GT cycle can be utilized for combined electricity and thermal energy generation, providing simultaneous power and heat for industrial purposes, commercial buildings, or district heating systems. This CHP configuration improves overall energy efficiency and reduces primary energy consumption.
To our best knowledge, a complete examination via environmental, exergy, energy, and economic evaluations of a novel combined GT cycle with the OFC has not yet been conducted, which is the novelty of the current work. Moreover, another novelty of the paper is carrying out genetic algorithm-based multi-objective optimization. In addition, one of the most important aspects of this study is applying environmental analysis to the combined GT-OFC system. The present study aims to enhance the environmental, economic, and thermodynamic performances of the GT cycle by using an OFC to utilize GT waste heat. Parametric investigations are applied to evaluate the impacts of several factors on the LTE, total cost rate, and the exergy efficiency of the system. Single- and multi-objective optimizations were carried out to the GT cycle combined with the OFC to determine the lowest total cost rate and LTE of the system and the highest exergy efficiency. In addition, six organic working fluids are examined, and the most appropriate working fluid is selected from environmental, economic, and thermodynamic viewpoints.