In this study, the energy and exergy analysis have been applied to the C¸ atalag˘zı power plant in Zonguldak, Turkey. The fuel used in
this power plant was low calorific value coal middlings with particle size below 0.5 mm. The heat loss of each components were determined
by energy analysis and the irreversibility rates (or exergy destruction rates) of whole plant were obtained for different ambient
temperatures by the exergy analysis. The ambient temperature was selected within the range of 5–35 C. The percentage efficiency defects
of each components (or the ratios of the irreversibility rates to the fuel exergy rate) and the rational efficiency, the exergy efficiencies of
the boiler, the turbine, the pump, the heaters and the condenser were determined for different ambient temperatures.
It was found that the efficiency defect of boiler had strong effects on the total efficiency defect and the rational efficiency of the plant.
The ambient temperature had high effect on the changes of the irreversibility of boiler (or efficiency defect of boiler) but it had low effect
on outer components of the plant.