THERMO ANALYSIS OF COMBINED CYCLE POWER PLANT

Abstract

Combined cycle power plants (CCPPs) are crucial in satisfying the increasing energy needs because of their superior efficiency and flexibility in comparison to single-cycle thermal power plants. However, achieving more improvements in thermal efficiency remains a key challenge. CCPPs are designed to run on specific operating conditions to fetch their maximum efficiency. Ambient temperature is one of those significant operating conditions. As the ambient air temperature rises, the performance of gas turbine power plants decreases. It is essential to mitigate the adverse effects of high ambient air temperature by cooling it before intake to the air compressor. Therefore, this research addresses this challenge by integrating an inlet air cooler based on a double-effect vapour absorption refrigeration system (VARS). The VARS utilizes the waste heat of CCPP exhaust gas as the heat input to cool the air at the compressor’s inlet. The improvements are seen in terms of energy, exergy, and sustainability aspects of an integrated CCPP as compared to the standalone CCPP. The energy analysis reveals the maximum improvements in work output and thermal efficiency of 5.04% and 1.64%, respectively. Furthermore, the results show that as the ambient temperature rises, the work output of the standalone CCPP system decreases faster than that of the integrated CCPP system. Also, the maximum yield in exergetic efficiency and total work output is observed at the degrees of cooling of 8K and 18K, respectively. Therefore, this system can be operated suitably within this range of degrees of cooling. Besides, the exergy-based sustainability indicators are found to be improved. The environmental sustainability index has increased by up to 3.52%, showing improved fuel utilization. This also indicates that, for the same amount of emissions, the integrated CCPP plant generates more power. The performance of CCPP is further investigated as the effect of various input parameters, such as the compressor pressure ratio, and gas turbine inlet temperature. The effect is obtained on the exergetic performance of the CCPP system as a whole and its components. After the most influential operating parameters have been identified, the mathematical model is then subjected to multi-objective optimization using a genetic algorithm. According to the Pareto set of optimal solutions, cooling the inlet air by 16.5K results in the highest net specific work output, but, increased exergy vi destruction. Increased exergy destruction, on the other hand, is undesirable. However, if the cost of power per unit is high, this could be economically advantageous. Exergy analysis is then advanced in a subsequent section by splitting the exergy destruction into avoidable and unavoidable components so that the amount of avoidable exergy destruction in each component can be obtained. Results show that under the standard settings, the avoidable exergy destruction accounts for 25.02% of the overall exergy destruction. Additionally, the heat recovery steam generator exhibits the highest potential to mitigate irreversibility generation, accounting for 91.53% of its overall irreversibility. In contrast, the combustion chamber has the lowest potential, contributing only 6.94% of its total irreversibility. Furthermore, the synergistic combination of advanced exergy and exergy costing methods extends analysis to advanced exergoeconomic analysis, and the resulting optimization is referred to as advanced exergoeconomic optimization. Using auxiliary equations and cost equations for capital costs, the cost functions for each stream are then derived and solved to determine the cost parameters of each component of the CCPP. Investigation subsequently yields the total capital cost and the total cost rate of exergy destruction. Each of these cost factors is also split into avoidable and unavoidable parts. The suggested set of optimal solutions approximates the pressure ratio of 13, 10K degree of cooling, and turbine inlet temperature of 1564K when the operational parameters are optimized to achieve improved modified exergetic efficiency and minimized unavoidable cost per unit of power generation. The outcomes of this research contribute to advancing the state-of-the-art in CCPP technology, offering practical solutions for enhancing energy efficiency and sustainability in power generation.