What are the hazards of a drop in turbine vacuum?

Main hazards of a decrease in vacuum in a condensing steam turbine unit: 1. The shaft power of the steam turbine decreases, while energy consumption increases. 2. It increases the steam humidity at the turbine outlet, accelerating the damage to the blades there.

1. It may cause excessive axial displacement, leading to overload of the thrust bearings and friction between the moving and stationary components. 2. It causes the blades to become overloaded due to the increased steam flow, as the reaction degree of the blades near the last stages increases. 3. The temperature of the exhaust cylinder rises, resulting in increased thermal expansion. 4. It may cause an increase in vibration levels, and even lead to interlock-induced shutdown of the machine. 5. It consumes a large amount of steam, which is uneconomical; it also presents high operational risks and is prone to shutdowns. 6. Apart from the impact on the turbine, a decrease in power generation is inevitable.

Factors that cause a drop in the condenser vacuum include: ① Scaling or fouling of the condenser tubes, which deteriorates heat transfer； ②Air accumulation in the condenser ； ③The circulation water volume is insufficient, or the temperature of the circulating water inlet is too high. An excessively low vacuum in the condenser not only reduces the power output of the turbine and lowers the economic efficiency of the plant, but also affects the safety of operation of the turbine’s exhaust system and the condensation equipment, as the exhaust pressure and temperature are higher than the design values.

During the operation of the turbine, when the vacuum in the condenser decreases and the unit maintains its load unchanged, the steam intake to the turbine necessarily increases, which leads to an increase in axial thrust as well as overload of the blades； Not only that, but the drop in vacuum leads to an increase in the temperature of the exhaust chamber, which in turn causes deformation of the exhaust cylinders and a shift in the center of the unit, resulting in vibration. Additionally, the copper tubes of the condenser expand due to heat, becoming loose, deformed, or even broken. Therefore, when the vacuum level drops during operation, in addition to reducing the load as specified, it is necessary to identify the cause and address it promptly.

This post was last edited by 58958107 on 2011-2-23 at 15:58. Reason: 1. Whether the tube side inside the condenser is fouled and blocked. 2. Problems with the cooling water system (low water pressure or high water temperature). 3. The excessive load on the turbine causes the steam flow to exceed the cooling capacity of the condenser. 4. Is the ejector system functioning properly? (Is there any scaling in the nozzles of the steam-ejector, is the cooler scaled, are the drain pipes blocked, etc.) 5. Air remaining in the condenser. 6 The most terrifying thing is the existence of vulnerabilities in the system. Hazards: 1. Reduced turbine efficiency leads to increased steam consumption. 2. The efficiency of the turbine decreases, causing the main steam valve to stay fully open at lower rotation speeds; as a result, the compressor is unable to meet the production requirements. 3. Excessive turbine load causes fluctuations in the shaft vibration and displacement parameters of the unit, increasing the load on the blades and bearings. Treatment method: 1. If the coolers of the condenser and the extractor are scaled or there are leaks in the system, the plant must be shut down for repairs; scaling on the nozzles of the extractor can be addressed through online cleaning. 2. In northern refineries, winter temperatures are low; therefore, proper insulation within the buildings is necessary. Excessively low temperatures can cause instrument signal failures, leading to false signals and unplanned shutdowns. 3. Auxiliary vacuum pumping can be started when the equipment cannot be stopped for production. 4. Inform the dispatch team to minimize the temperature of the cooling water as much as possible.