Daily Question: Methanol and Purification Technology Forum Edition 20191109

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The reason for creating a certain vacuum before starting a condensing steam turbine is as follows: 1. There is air inside the turbine, and the pressure there is equivalent to atmospheric pressure. If a vacuum is not created, a large amount of steam is required during startup to overcome the resistance of the air surrounding the turbine rotor, as well as the frictional forces and inertial forces in the bearings of the turbine and generator, in order to rotate the rotor; this results in increased steam impact forces on the blades. 2. After the rotor is started up, the presence of a large amount of air in the condenser affects the heat exchange between the exhaust steam and the cooling water, resulting in excessively high exhaust steam temperatures, which may cause deformation of the rear cylinder and its internal components. 3. An increase in the back pressure of the condenser can also cause the safety diaphragm to activate. Therefore, a certain vacuum must be established before starting a condensing steam turbine.