In Pakistan, escalating electricity demand driven by industrial expansion and population growth has caused a notable supply-demand gap, resulting in a socio-economic crisis. This shortage primarily stems from pricey fuel, transmission inefficiencies, and suboptimal power plant performance. Policymakers must address these challenges by exploring energy-efficient solutions, such as tri-generation, regeneration, and energy recovery. CCPP, integrating gas and steam turbines, offers high efficiency and operational flexibility, garnering considerable attention in the electricity generation sector. Numerous experts advocate for various modifications to maintain production levels while curbing fuel consumption, environmental impact, and costs [1]. Gas turbine power plants are optimized for efficiency under ideal conditions (1 atm pressure, 15°C temperature, and 60% humidity). However, real-world variations, especially in ambient temperature, significantly affect performance. To cool air for the gas turbine compressor inlet at 15°C, vapor absorption refrigeration cycles are the optimal choice. These cycles rely on moderate-temperature thermal energy instead of mechanical power. By increasing refrigerant pressure during absorption, the cycle reduces required work input, as liquid pumping is less demanding than vapor compression due to smaller specific volumes. This method leverages temperature-dependent gas solubility in liquid [2]. Gas engines, despite their lower environmental impact, typically have an efficiency of only 30%–40%, resulting in significant energy loss through exhaust and cooling. To improve efficiency, Waste Heat Recovery (WHR) systems like the steam Rankine Cycle (RC) and Organic Rankine Cycle (ORC) are commonly used. Each method has its advantages and limitations. This study focuses on comparing RC and ORC for a 1000 kW gas engine, evaluating their effectiveness in power recovery, thermal efficiency, and economic feasibility [3].

Thanganadar et al. [4] analyzed the maximum performance and cost of electricity for five sCO₂ cascaded cycles, emphasizing the importance of the GT pressure ratio as a design variable for optimizing plant performance. Results show that each sCO₂ Brayton cycle achieves maximum efficiency at different GT pressure ratios, with an optimal ratio higher than the equivalent steam Rankine cycle. A novel sCO₂ cycle configuration is proposed to enhance efficiency. Ehsan et al. [5] presented a comprehensive review of heat transfer and pressure drop characteristics with supercritical CO₂ in heating and cooling applications. The study evaluates convective heat transfer behavior, pressure drop, and factors affecting heat transfer deterioration in supercritical CO₂. Insights gained from this review help in efficient thermal design and optimization of heat exchangers, which are crucial for applications in thermal power plants.

Erdem et al. [6] devised a dual-gas turbine concept tailored for seven distinct climate regions in Turkey. Compared with typical annual production in hot regions, power generation losses range from approximately 2.88% to 0.71%. When temperatures surpass 15 degrees Celsius, all regions experience power production declines, ranging from 1.67% to 7.22%, contingent on the region. Their analysis revealed that lowering the inlet temperature by up to 10 degrees Celsius could enhance power generation by 0.27% to 10.28%. Santos et al. [7] introduced a gas turbine thermodynamic model to analyze power output, heat rate, and thermal efficiency across different inlet air temperatures. They explored various intake conditions, incorporating evaporative and absorption chillers based on relative humidity and inlet temperature. Their findings indicate that, for extremely high temperatures with low relative humidity, where substantial temperature reduction is needed, the chiller emerges as the preferred cooling method. Porumb et al. [8] conducted a numerical analysis investigating the impact of operating conditions on the performance of a LiBr-H₂O solar absorption chiller. Their study revealed the correlation between the coefficient of performance and crystallization conditions of the chiller with the temperatures of the solar hot water, cold water, and cooling water.

Darwish Ahmad et al. [9] utilized an engineering equation solver to simulate a plant, comparing the results with real-world data from a power plant. They incorporated input air cooling methods including absorption and mechanical chillers of the cascade type, along with a CSP system. This approach led to a 22.8% increase in power, a 4.3% improvement in efficiency, and an 8.4% reduction in specific fuel consumption (SFC) compared to the real power plant. Ridha et al. [10] performed a thermodynamic assessment of a combined heat and power system integrating a gas turbine (GT), a heat exchanger (HX1), and an ORC. By comparing two models using ASPEN Plus software, they demonstrated that the combined system achieves notably higher thermal efficiency (51.55%) in contrast to standalone GT efficiency (21%). Elevating the GT pressure ratio enhances net power output and efficiency while decreasing thermal energy rejected to the environment. Khan et al. [11] conducted a parametric analysis to optimize combined cycle performance, focusing on the bypass valve. Their findings show substantial improvements in network output and net efficiency with increasing turbine inlet temperature. Moreover, the study recommends optimizing bypass valve operation based on compression ratio values. Njoku et al. [12] conducted studies that highlight the benefits of integrating ORC and absorption refrigeration cycles (ARC) with CCPP using flue gas exhaust heat. This integration improved net power output by 9.1%, thermal efficiency by 8.7%, exergy efficiency by 8.8%, and sustainability by 8.4%, while reducing exergy destruction and fuel consumption by 13.3% and 8.4%. These enhancements demonstrate significant efficiency and environmental sustainability improvements over traditional CCPPs. The novelty of this study lies in its innovative approach to integrating an ORC and a VAC with a CCPP in Kotri, Pakistan, to address the country’s power outages. Unlike previous studies, this research also utilizes ψ for the ORC and VAC integration, effectively catering to higher ambient conditions and increased demand. Additionally, this study incorporates an economic analysis to evaluate the feasibility of this integration in Pakistan’s context, providing a comprehensive assessment of both the technical and economic benefits.

The concept of a modified system of an original CCPP at Kotri, Pakistan is shown in Fig. 1. The original plant has a total installed capacity of 144 MW, with four 25 MW GT units and HSRG units topping a 44 MW ST cycle with four HSRG units. The primary CCPP, VAC, and ORC are all part of the modified system. Waste heat from the stack is used to provide heating for the ORC and cooling for the VAC. To improve the heating and cooling abilities when the demand is high and the outside air is warm, ψ from the GT units is diverted to join the stack gas flow.

The heating system and the cooling system are supplied by two separate streams of hot gas. The mass flow rate of hot gas is controlled by dampers to achieve the required mass fractions and to meet the changing needs of heating and cooling. The ORC receives some of the warm gases (1−ξ), which heat the organic fluid and vaporize it to drive the turbine to generate electric power. A portion of the hot gases ξ is delivered to the VARC’s generator, which runs the refrigeration cycle, which cools the humidifier and cools the air compressor’s incoming air to 15 degrees Celsius.

The cooled air is non-isentropically compressed to greater pressure in the GT cycle and T-S diagram of GT is shown in Fig. 2. The combustion chamber uses high-pressure, high-temperature air to burn the fuel. The combustors of the power plant have a can-annular design, which allows the gases from combustion to leave with a pressure drop of around 5% (power plant officials said the drop was between 2% and 8%). The hot gases from combustion then go to the turbine, where they are non-isentropically expanded and generate power for the turbine. A part of the turbine’s output runs the compressor. The GT units’ exhaust gases are sent to the HRSG for the generation of the mainstream, which is then expanded in ST to provide extra W_ ST. ST works on the principle of Rankine cycle and the T-S diagram of Rankine cycle is shown in Fig. 3. The steam goes to a CND after expanding, where it becomes liquid and is sent to a DE by a CP for deaeration and preheating with low-pressure economizer combustion gases. The FWP then pumps the feedwater to a high-pressure storage tank. HPE is used before the EV and SH generate saturated and superheated steam [13]. The system is cooled by a single-effect VAR cycle with a LiBr-H₂O working solution and a regenerator. The cooling cycle has high pressure in the generator and condenser, and low pressure in the evaporator and absorber. The rich solution is heated by hot gas in the generator, which makes the refrigerant (H₂O) vapors rise. The hot gas is then released into the air, while the refrigerant cools down in the condenser before taking heat from the chilled water in the evaporator. The refrigerant goes to the absorber, where it mixes with the absorbent LiBr, creating a refrigerant-rich LiBr-H₂O solution. The absorber is cooled to increase H₂O absorption in the LiBr because the temperature and the amount of H₂O that can dissolve in LiBr are inversely proportional. The rich solution is moved to the generator (regenerator) by a heat exchanger. The generator separates most of the refrigerant, and the hot weak solution goes through a regenerator, which heats the cold, rich solution that comes from the pump to the regenerator. The weak solution is then reduced to absorber conditions. Organic fluid, heating system, steam turbine, condenser, and solution pump comprise the ORC. The hot gas fraction enters the heating system, where it transfers heat to the organic fluid before being liberated into the atmosphere. The organic fluid expands at high pressures and temperatures in the steam turbine, causing rotational motion. The shaft is attached to the generator, which generates electricity. The low-pressure fluid passes through the condenser, transferring its heat to the cooling water and leaving it at a low temperature and pressure, which then passes through the pump, increasing the pressure [14]. Tozer et al. [15] emphasized the significance of temperature-entropy (T-S) diagrams in quantifying thermodynamic processes. While generalized T-S diagrams have been applied to various absorption cycles, specific diagrams tailored for LiBr/water systems are lacking. Their paper addresses this gap by extending the T-S diagram of water to include curves representing real and ideal LiBr/water absorption cycles. T-S diagram of LiBr/water VAC is shown in Fig. 4 [16].

Mathematical modeling plays a very important role in designing and controlling new systems and existing systems, respectively, it helps us to estimate the outcomes of the systems working on different conditions and helps us to figure out the optimum design parameters and conditions.

This paper presents a detailed discussion of the thermodynamic and economic models of each component of the proposed system, based on the first and second laws of thermodynamics and the investment and operating costs.

The scope of this research is to modify an existing CCPP to utilize its maximum potential to meet the high electrical demands in the summer which should be economic at the same time. In doing so, we will operate the gas turbine under standard conditions and evaluate its performance on different parameters. The objectives of the study are as follows:

1) To develop energy and economic models of modified combined cycles.

2) To conduct parametric-based energy and economic analysis of the modified combined cycle under varying ambient conditions (Temperature, Relative Humidity) and ψ.

The thermodynamic and economic model of the system will be formulated within the Energy Equation Solver (EES) software, leveraging foundational thermodynamic principles such as the First Law of Thermodynamics, energy equation, and mass balance equations. Additionally, essential economic equations, including the total cost function and payback period equations, will be integrated into the model.

Following model development, parametric analysis will be executed utilizing the EES software to assess the system’s performance, energy parameters, and economic indicators under varying ambient conditions. This analytical approach will provide detailed insights into how fluctuations in ambient conditions impact the system’s thermodynamic efficiency, operational robustness, and economic feasibility.

This section presents a detailed discussion of the study’s results. The performance, energy outputs, and PBP of the proposed system at various ambient conditions and the mass fraction of the exhaust gases from the gas turbine exit have been evaluated.

The modified system’s operational parameters are constrained to analyze the consequences and are given in Table A8. Also, thermodynamics parameters of main components are given in Table A9.

This paper discusses the energy, economic, and performance analysis of a modified CCPP with ORC and VAC to cool the ambient air to meet the design conditions of the gas turbine and generate additional power. Parametric studies have been carried out on varying ambient conditions and fractions of exhaust gases from the outlet of the gas turbine. An engineering equation solver (EES) is used to model the system. Results are validated and a comparison is carried out between energy outputs and performance of the original system with the modified system. Moreover, the effects on PBP are also disused on varying ambient conditions and with different values ψ. The important findings are summarized as follows:

Through the modification, there is an overall increase in the system’s efficiency which depends on the operating conditions.

After conducting a comprehensive analysis, it has been determined that the system shows promise for areas with environmental conditions akin to Kotri, Pakistan. However, regions facing extreme weather patterns may require alterations in the system’s design, a consideration that was not explored in the current study.

Furthermore, it has been noted that during periods of high temperatures, the system’s performance heavily relies on the parameter ψ, which directly influences the power generation of the CCPP. In light of this, employing artificial intelligence (AI) to design an artificial neural network for the system could prove beneficial. By training the system on various ambient conditions and values of ψ, optimal operating conditions can be achieved. A technically sound approach involves implementing an adaptive design capable of adjusting to ambient conditions. For instance, when the ambient temperature drops to or below 15°C, the system should deactivate the VAC and prioritize directing maximum exhaust energy towards operating ORC to enhance power output and meet demand requirements.

As for prospects, it is recommended to conduct an environmental analysis of the system to ascertain the energy content in the exhaust emissions. This analysis could reveal opportunities for integrating additional equipment to enhance the overall output of the system and improve its environmental impact.

For future endeavors, particularly in industrial applications, it’s advisable to undertake the design and analysis of the proposed system tailored to specific cities, taking into account their unique ambient conditions. The objective would be to determine optimal operating conditions under various circumstances to economically fulfill energy demands. Such a design should encompass crucial aspects including working parameters, equipment costs, payback periods, environmental impacts, and more. By conducting comprehensive analyses tailored to specific locations, it becomes possible to devise systems that are not only efficient but also economically viable and environmentally sustainable.