What is the impact of nozzle erosion on a steam turbine's efficiency and output?

Nozzle erosion in a steam turbine has a significant negative impact on both its efficiency and output. Steam turbine nozzles are carefully designed to direct and accelerate the steam flow onto the turbine blades at the optimal angle and velocity. This precise control of steam flow is essential for maximizing energy transfer to the rotor. Erosion of the nozzles alters their shape and dimensions, disrupting the designed steam flow pattern. As the nozzles erode, their throat area typically increases. This increased area allows more steam to pass through the nozzles, which can increase the turbine's steam consumption. However, the steam is no longer accelerated to the optimal velocity or directed at the correct angle. This misalignment and reduced velocity decrease the amount of energy transferred to the turbine blades, resulting in a lower turbine output. Furthermore, the eroded surfaces create turbulence and increased friction losses, further reducing efficiency. The eroded nozzles also lead to uneven steam distribution across the turbine stages, causing imbalances and vibrations. The overall effect is a reduction in both the turbine's power output and its thermal efficiency, leading to higher fuel consumption for the same power generation.