Using coolant modulation and pre-cooling to avoid turbine blade overheating in a gas turbine combined cycle power plant fired with low calorific value gas

Overheating of turbine blades is one of the major concerns in using low calorific value fuels in gas turbines. In this work, we examined the deviation of operating conditions of a gas turbine fired with a low calorific value gas fuel, with a focus on the turbine blade temperatures. Several measures to suppress blade overheating were compared in terms of the power output and efficiency of the gas turbine combined cycle plant. Blade overheating can be prevented by decreasing the firing temperature without the need for hardware modifications, but the accompanying power reduction is considerable. As a remedy to this large reduction in power, modulation of the coolant supply to each blade row was simulated, and a much lower power penalty was observed. Moreover, pre-cooling of the coolant enhances the power output further by reducing the coolant supply. Pre-cooling recovers 80% of the available maximum augmentation of the combined cycle by simply switching the fuel from natural gas to low calorific value gas. Pre-cooling also provides higher overall combined cycle efficiency compared to under-firing.