Why must the steam seal extractor (steam seal cooler) be turned on first before starting a back-pressure turbine?
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Why must the steam seal extractor (steam seal cooler) be turned on first before starting a back-pressure turbine?
Before starting the turbine, there is air inside it, and the pressure inside the turbine is roughly equal to the atmospheric pressure. If vacuuming is not performed, the air cannot be removed, and as a result the exhaust pressure increases. In such a situation, to get the turbine to rotate, the amount of steam supplied to it must be increased significantly in order to overcome the friction and inertial forces of the compressor bearings; this results in large forces being exerted on the blades. After the turbine starts rotating, the heat transfer rate decreases due to the presence of air, the exhaust pressure rises, which may cause damage to the internal components. Therefore, the steam seal extractor must be turned on before starting the back-pressure turbine. The above is for reference only
What does a steam seal extractor look like? Could you provide the process flow and equipment diagrams?
Steam seal extractor – a brief explanation: it is a three-way pipe with a varying diameter; one path is for steam to flow through, another path leads to the discharge of gases from the machine, and the third path uses steam to carry away the gases discharged from the machine. In foreign systems, the exhaust gases are directed to a water seal tank, after which they are incorporated into the condensate drainage network.
⑴Due to the high exhaust pressure in back-pressure turbines, if the steam seal extractor is not activated first before startup, a large amount of steam will leak out of the turbine through the shaft ends. ⑵Additionally, some steam entered the bearing lubricant, causing the lubricant to become water-contaminated and emulsified. ⑶Therefore, the steam seal extractor must be turned on first to create a certain level of vacuum and draw the steam out.
I think it mainly serves to remove air.
The steam extraction from the shaft seal of the backpressure unit is primarily intended to prevent high-pressure, high-temperature steam from leaking out of the shaft seal, which could cause the components outside the shaft seal to become overheated and lead to adverse consequences, such as oil emulsification; therefore, it is necessary to start the steam extraction first. The others are not major problems.
The back-pressure turbine operates under a constant back pressure; therefore, the shaft seal is primarily used to prevent steam from leaking out, and it is the extractor that performs this function.
Reply to 1# jiaohuadsy: Mainly, when the exhaust pump is not in use, high-pressure steam leaks from the shaft seal into the bearing box, causing the lubricating oil to emulsify. This leads to deterioration of the lubricating oil, a reduction in its lubricating efficiency, an increase in bearing temperature, and potential hazards
The shaft sealing type for steam turbines is mainly comb seal: (1) In back-pressure steam turbines, due to the high exhaust pressure, if the shaft seal extractor is not activated first before startup, a large amount of steam will leak out of the turbine through the shaft end. ⑵Additionally, some steam entered the bearing lubricant, causing the lubricant to become water-contaminated and emulsified. ⑶Therefore, the steam seal extractor must be turned on first to create a certain level of vacuum and draw the steam out.