Exergy and Energy Analysis of Combined Cycle systems with Different Bottoming Cycle Configurations Sanjay * ,† Department of Mechanical Engineering, National Institute of Technology, Jamshedpur Pin 831 014, India SUMMARY The paper deals with thermodynamic analysis of cooled gas turbine-based gas-steam combined cycle with single, dual, or triple pressure bottoming cycle configuration. The cooled gas turbine analyzed here uses air as blade coolant. Component- wise non-dimensionalized exergy destruction of the bottoming cycle has been quantified with the objective to identify the major sources of exergy destruction. The mass of steam generated in different configurations of heat recovery steam gen- erator (HRSG) depends upon the number of steam pressure drums, desired pressure level, and steam temperature. For the selected set of operating parameters, maximum steam has been observed to be generated in the case of triple pressure HRSG ¼ 19 kg/kg and minimum in single pressure HRSG ¼ 17.25 kg/kg. Plant-efficiency and plant-specific works are both highest for triple-pressure bottoming cycle combined cycle. Non-dimensionalized exergy destruction in HRSG is least at 0.9% for B3P, whereas 1.23% for B2P, and highest at 3.2% for B1P illustrating that process irreversibility is least in the case of B3P and highest in B1P. Copyright © 2012 John Wiley & Sons, Ltd. KEY WORDS rational efficiency; combined cycle; exergy; multipressure bottoming cycle; parametric analysis Correspondence *Department of Mechanical Engineering, National Institute of Technology, Jamshedpur, Pin 831 014, India. † E-mail: ritsanjay@yahoo.com Received 25 May 2011; Revised 22 October 2011; Accepted 27 December 2011 1. INTRODUCTION Global warming is being considered as the greatest threat to planet earth, and efforts are being made by global leaders and scientists to address this issue most effectively. One of the methods under consideration involves the best possible utilization of fossil fuel energy sources and increasing energy conversion efficiency by improved cycle design and reduction of exergy destruction associated with cycle the components. Most effective utilization of gas turbine (GT) exhaust heat is the key to this improvement. Selection of proper bottoming cycle configuration plays a major role in GT exhaust heat utilization. The steam generated in the heat recovery steam generator (HRSG) is generally used to drive steam turbine (ST), usually coupled to a single shaft with the GT. The arrangement is popularly known as combined cycle, and these GT-based combined cycle power plants have become the mainstay in providing power worldwide. Most of these combined cycle plants burn natural gas as fuel, and the output of such GTs for power generation has been projected [1] to increase from around 570 GW in 1999 to 2035 GW in 2020, an increase of over 6% per year. This necessitates for studying the thermodynamics of these workhorses, and especially, a parametric analysis of bottoming cycle is necessary. Analysis of thermodynamic systems based on the first law of thermodynamics is the traditional method of asses- sing how energy is consumed in a thermodynamic system involving the physical or chemical processing of materials and the transfer and/or conversion of energy. This usually involves performing energy balances, which are based on the first law of thermodynamics, and evaluating energy efficiencies of the processes. Second law analysis of thermodynamic systems involves identifying the sources of irreversibility existing in the system and can help design, optimize, and assess such systems and identifying the locations of exergy destruction and thereby highlight- ing directions for potential improvement. The lesser the irreversibility associated with a process taking place, the lower is the exergy destruction during the process. Work in the area of parametric analysis of GT-based cycles has been reported by Louis et al. [2,3] in which they have carried out a comparative analysis of the effect of various blade cooling means on combined cycle perfor- mance and have reported the sensitivity of key cycle parameters on overall cycle efficiency. El-Masri [4,5] in his articles has discussed cooled GT model and a computer code ‘GASCAN’ to predict the performance of the same INTERNATIONAL JOURNAL OF ENERGY RESEARCH Int. J. Energy Res. 2013; 37:899–912 Published online 15 February 2012 in Wiley Online Library (wileyonlinelibrary.com). DOI: 10.1002/er.2892 Copyright © 2012 John Wiley & Sons, Ltd. 899