Flowrate measurement of gas turbine cooling air at an advanced combined cycle power plant using the heater method for plant operation and maintenance

At a combined cycle power plant, gas turbine cooling air flowrate data is required for operation and maintenance because it is an important for analyzing not only the temperature of both stators and blades but also plant efficiency. However, it is very difficult to measure the data. An ultrasonic flowmeter cannot be used since the measurement position becomes hot, usually exceeding 300 degrees centigrade. An insert type flowmeter is also difficult to use as it requires additional pipe processing for installation and also causes a pressure loss. Accordingly, we tried to use the heater method, which we proposed and validated in our previous papers. In this method, a circumferential heater is attached to the outside of a pipe and then the axial temperature distribution along the outside of the pipe, which is influenced by the fluid velocity in the pipe, is measured by thermocouples. The velocity is analyzed on the basis of the temperature distribution along the pipe. Measurements were conducted for two kinds of cooling air pipe at an advanced combined cycle power plant. In one, cooling air is extracted from the 13th stage of a compressor and supplied to the 2nd stators of the gas turbine; in the other, cooling air is extracted from the 9th stage of the compressor and supplied to the 3rd stators of the gas turbine. As a result, it was clarified that the cooling air flowrate had a positive dependence on atmospheric temperature at the plant. The dependence was also compared to that of a tit 1,600 degrees centigrade-class combined cycle power plant, with a power output of 700 MW.