Thermal Efficiency of Combined Cycle Power Plant

  • R. Rajesh
  • Dr. P.S. Kishore
Keywords: Brayton Cycle, Rankine Cycle, Heat Supplied, Work Output, Efficiency


Now a day’s power generation is most important for every country. This power is generated by some thermal cycles. But single cycle cannot be attain complete power requirements and its efficiency also very low so that to fulfill this requirements to combine  two or more cycles in a single power plant then we can increase the efficiency of the power plant. Its increased efficiency is more than that of if the plant operated on single cycle. In which we are using two different cycles and these two cycles are operated by means of different working mediums. These type of power plants we can called them like combined cycle power plants. In combined cycle power plants above cycle is known as topping cycle and below cycle is known as bottoming cycle. The above cycle generally brayton cycle which uses air as a working medium. When the power generation was completed the exhaust gas will passes in to the waste heat recovery boiler. Another cycle also involved in bottoming cycle. This cycle works on the basis on rankine cycle. In which steam is used as working medium. The main component in bottoming cycle is waste heat recovery boiler. It will receive exhaust heat from the gas turbine and converts water in to steam. The steam used for generating power by expansion on steam turbine. Combined cycle power plants are mostly used in commercial power plants.

In this paper we are analyzing one practical combined cycle power plant. In practical conditions due to some losses it can not be generates complete power. So that we are invistigated why it is not give that much of power and the effect of various operating parameters such as maximum temperature and pressure of rankine cycle, gas turbine inlet temperature and pressure ratio of Brayton cycle on the net output work and thermal efficiency of the combine cycle power plant.

 The outcome of this work can be utilized in order to facilitate the design of a combined cycle with higher efficiency and output work. Mathematical calculations and simple graphs in ms excel, and auto cad has been carried out to study the effects and influences of the above mentioned parameters on the efficiency and work output.


Download data is not yet available.


Thamir K. Ibrahim & M.M. Rahman. (2012). Effect of compression ratio on performance of combined cycle gas turbine. International Journal of Energy Engineering, 2(1), 9-14.

Ashley De Sa & Sarim Al Zubaidy. (2011). Gas turbine performance at varying ambient temperature. Applied Thermal Engineering, 31, 2735–2739.

Carniere H., Willocx A., Dick E., & Paepe M De., (2006). Raising cycle efficiency by inter cooling in air cooled gas turbine. Applied Thermal Engineering, 26(16), 1780–1787.

AlHazmy M.M. & Najjar Y.S.H. (2004). Augmentation of gas turbine performance using air coolers. Applied Thermal Engineering, 24(2-3), 415-429.

P.k. Sarma, K.Hari Babu , T.Subrahmanyam, V.Dharma Rao, & P.S.Kishore. (2006, March). Augmentation of convective condensation of steam in a horizontal tube with twisted tape inserts. (World scientific and engineering academy and society) Transations on Heat and Mass Transfer, 1(3), 222-228.

Thamir K. Ibrahim & Rahman M.M. (2012). Thermal impact of operating conditions on the performance of a combined cycle gas turbine. Journal of Applied Research and Technology, 10(4), 567–577.

Firdaus B., Takanobu Y., Kimio N., & Soe N. (2011). Effect of ambient temperature on the performance of micro gas turbine with cogeneration system in cold region. Applied Thermal Engineering, 31, 1058–1067.

P.K.Sarma, C.P.Ramanayanan, K.V.Sharma, P.S.Kishore, & V.Dharma Rao. (2009, June). A method to predict turbulent convective heat transfer coefficients of condensation of steam-air mixture in a horizontal tube. International Journal of Heat and Technology, 27(1), 45-56.

Kaushika S.C., Reddya V.S., & Tyagi S.K. (2011). Energy and exergy analyses of thermal power plants: A review. Renewable Sustainable Energy Review, 15, 1857–1872.

Khaliq A. & Kaushik S.C. (2004). Thermodynamic performance evaluation of combustion gas turbine cogeneration system with reheat. Applied Thermal Engineering, 24(13), 1785–1795.

How to Cite
R. Rajesh, & Dr. P.S. Kishore. (2018). Thermal Efficiency of Combined Cycle Power Plant. International Journal of Engineering and Management Research, 8(3), 229-234.