What is the purpose of using spray desalinated water in the turbine exhaust cylinder?

Reasons and hazards for the increase in temperature of the exhaust cylinder during turbine startup: (1) During turbine startup, steam passes through a throttle valve before reaching the nozzles that drive the impellers of the speed control stage; after throttling, the entropy of the steam increases while its enthalpy drop decreases, resulting in a higher temperature of the exhaust steam after work is done. During the entire startup process prior to grid connection, very little steam is consumed; at this stage, power generation relies mainly on the regulation stages. The waste steam, as it flows toward the exhaust cylinder, has a low flow rate and low velocity, as well as a large cross-sectional area, which results in a significant draft effect. The exhaust temperature rises due to significant blowdown losses. As the rotor rotates, the blades (especially the longer ones in the latter stages) come into friction with the steam, which is also one of the factors that raise the exhaust steam temperature. When the turbine starts up, the vacuum level is low, and accordingly the saturation temperature rises, which means that the exhaust temperature increases. An excessively long startup time for the turbine can also cause the exhaust cylinder temperature to become too high. (2) When the load on the grid-connected power generation system increases, the main steam flow rises as well with the increase in load; the turbine gradually enters its normal operating condition, and the proportion of power consumed due to friction and aerodynamic losses becomes smaller and smaller. As the vacuum in the turbine exhaust cylinder gradually increases, the exhaust temperature decreases accordingly. (3) An increase in the exhaust cylinder temperature leads to greater thermal deformation of the low-pressure cylinder shaft seal, which can cause the center of the turbine’s pit to shift, resulting in increased vibration and greater friction between the moving and stationary parts; in severe cases, this can damage the low-pressure cylinder shaft seal. (4) When the temperature of the exhaust cylinder exceeds 80°C, water injection into the exhaust cylinder is initiated to cool it down; the temperature of the exhaust cylinder must not exceed 120°C.

The explanation on the 2nd floor is very thorough~~~~ So, safety nozzles for water exist only in the exhaust cylinder of condensing steam turbines； This problem does not exist with backpressure machines~~~~