ABSTRACT

Intercooling between air compressors in gas turbine plants results in reduction not only in net mechanical power requirements but overall thermo economics of such systems. The extent to which intercooler effectiveness affects a robust combined cycle power plant with an improved gas topping and steam bottoming cycles is investigated using exegetics and thermo economic approaches. The system comprises two turbines in the | topping cycle and two feed water heaters in the bottoming cycle. Models which predict the exegetics and thermo economic parameters were obtained in the light ofthe system architecture which allows for selection of optimum operating variables that would reduce cost and environmental impact. The result from detailed modelling shows that increasing the intercooling effectiveness has a number of effects on the overall system performance. An increase in intercooler effectiveness results in reduction in the exergoeconomic cost of the exergy streams in the gas turbine as well as the steam turbine. Increasing the intercooler effectiveness results in reduced exergy destruction, thereby increasing the sustainability index. Between 0.5 and 0.8 effectiveness, the sustainability index increases linearly from 0.365 to 0.4 The limit at which exergetic sustainability ceasep to exist corresponds to a comparatively low intercooler effectiveness of 30 per cent, a point at which the exergy destruction exceeds the overall output. Increasing the intercooler effectiveness results in overall improved system performance with the stated turbine configuration. Since the performance ofthe system was made at varying intercooler effectiveness while the heat exchanger effectiveness was kept constant transient performance ofthe system will aid in determination ofthe interaction ofheat exchanger effectiveness with the intercooler.