What are the causes and hazards of increased temperature in the turbine startup exhaust cylinder?

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(1) When the turbine starts up, steam passes through a throttle valve and then through nozzles to drive the impellers of the speed-regulating 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. Throughout the entire startup process prior to grid connection, very little steam is consumed; at this stage, the work is primarily done by 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 blowing effect. The exhaust temperature rises due to significant blowing loss. As the rotor rotates, friction occurs between the blades (especially the longer blades in the latter stages) and the steam, which is also one of the factors that raise the exhaust steam temperature. When the steam turbine starts, 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 the load increases; 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 also 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 will automatically start to cool it down; the temperature of the exhaust cylinder is not allowed to exceed 120°C.