Tadeh Avanessian - School of Mechanical Engineering, Shiraz University, Shiraz, Iran;
Omid Abouali - School of Mechanical Engineering, Shiraz University, Shiraz, Iran

In this study, energy and exergy analysis of a combined gas and steam unit (containing two gas units and a steam unit) in Kazeroon power plant is presented. The primary objective of this paper is to analyze the unit components separately to specify the ones with the largest quantities ofenergy and exergy losses. Also the effect of fuel type(natural gas or gas oil) on the exergy destruction in the gas units is investigated. In addition, the performance of steam unit is compared when either one or two boilers are in operation. Furthermore the second law efficiency of gas and steam units in two points of view is computed. The results show that in gas units the highest exergy destruction occurs in the combustion chamber (87.0%) followed by the turbine (7.4%) and then the compressor (5.6%). The performance of gas units is better when natural gas is burnt in their combustion chambers. In the steam unit, when both boilers are in operation, the boilers and the turbine have nearly the same exergy destruction (about 30%), while the condenser has a small part in the total exergy destruction of the unit (about 10%). When only one boiler is in operation the highest exergy destruction occurs in the boiler (57%) followed by the turbine (40%) and then the condenser (3%). Exergetic efficiencies of gas units, the steam unit, and the whole combined unit are 29.6%, 54.1%, and 43.3% respectively.

Combined cycle power plant, Exergy analysis, Exergetic efficiency, Second law analysis