43. What impact does an excessively high or low steam inlet temperature have on the operation of a turbine?

A steam temperature higher than the design value is advantageous from an economic perspective, but it is not permitted from a safety standpoint. Because at high temperatures, the mechanical properties of metals decline rapidly, which reduces the service life of various components in the turbine, such as throttle valves, nozzles and blades in the speed stages and the first few pressure stages, shaft seals, and bolts. It may also cause the earlier stages of the impeller assembly to become loose. Therefore, an excessively high steam inlet temperature is not allowed. A steam temperature lower than the design value increases the blade reaction degree, thereby increasing the axial thrust. Operating at excessively low steam temperatures increases steam consumption and affects economic efficiency. Furthermore, a decrease in steam temperature will cause water erosion of the blades in the latter stages of a condensing steam turbine, reducing its service life.