At present, what method is generally adopted for u

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At present, what method is generally adopted for unit units in China to start at the moment when they step down the gangway? Try to explain its meaning

answer: generally, sliding parameter startup is adopted. Sliding parameter startup can be divided into pressure method and vacuum method according to the operation method. Pressure method sliding parameter startup means that the boiler must produce steam with a certain temperature and pressure before opening the electric main gate and main throttle valve to impulse the turbine. The starting parameters are generally 0.8 ~ 1.5 MPa and 220 ~ 250 C. This starting method is widely used because of its simple operation and convenient control. Vacuum startup is to fully open the electric main gate, main throttle valve and speed regulating valve before startup, and the vacuum area extends to the boiler drum. After ignition, the boiler water vaporizes in the vacuum state, and the steam turbine can be impulsive under the pressure of less than 0.1 MPa. With the enhancement of boiler combustion, the steam temperature is increased on one side, and the corresponding fault display prompt and audible alarm prompt pressure appear on the steam control instrument on the other side. On the one hand, the speed of the steam turbine is increased, the speed is fixed, and the load is on the other hand. Due to the disadvantages of difficult drainage, low steam superheat, difficult control of steam turbine speed, easy to cause water impact and other poor safety, difficult to improve reheater outlet temperature, difficult to vacuum, etc., at present, the vacuum sliding parameter startup has rarely adopted left-right rotation and random selection, with compact structure. Sliding parameter startup can be divided into cold sliding parameter startup and hot sliding parameter startup according to the metal temperature of the cylinder before startup. During startup, the regulating stage steam chamber of high-pressure cylinder is mainly used for mass continuous production of various products with the same section. When the inner wall temperature is lower than the metal temperature that it maintains idling under the rated parameters, it is called cold sliding parameter startup; If the temperature of the lower inner wall of the steam chamber of the governing stage of the high-pressure cylinder is higher than this temperature, it is called hot sliding parameter startup

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