Effect of control modes and turbine cooling on the part load performance in the gas turbine cogeneration system

This work aims to analyse the part load performance in a cogeneration system which consists of a single shaft gas turbine and a heat recovery steam generator. Two distinct part load control modes are considered: the constant air flow and the variable air flow. Meanwhile, the effect of variation in the coolant fraction is evaluated, whose purpose is to maintain the blade temperature as high as possible and thus minimise the coolant consumption. The design point parameters of the heat recovery steam generator are determined by the limiting factors on the part load operation, which are represented by the pinch point temperature difference and the approach temperature difference. It turns out that for both air flow control modes, the variable control of coolant fraction leads to improvement of the gas turbine efficiency, while it reduces the heat recovery potential. On the whole, the variable control of coolant fraction has a favourable effect on the overall fuel economy in the cogeneration system.