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Causes of mechanical seal leakage of desulfurization pumps in power plants

13 Jan 2021Email

One of the important equipment in power plants is the desulfurization pump. The use of desulfurization pumps in power plants often has serious impacts on the use of the equipment due to problems in the mechanical seal process, making the equipment unable to work safely under normal operating conditions. , In severe cases, it may cause safety problems and threaten the lives of workers. Therefore, in the face of use and time failures, it is necessary to accurately analyze the reasons for inspection and formulate reasonable maintenance methods.

 

  Power plant desulfurization pump mechanical seal leakage point

   Although there are many types and models of mechanical seals for pumps, there are mainly 5 leakage points

  (1) The seal between the shaft sleeve and the shaft;

  (2) The seal between the moving ring and the sleeve;

  (3) Seal between dynamic and static rings;

   (4) The seal between the static ring and the static ring seat;

  (5) The seal between the end cover and the pump body.

Generally speaking, it is easier to find and solve the leakage between the shaft sleeve, the sealing end cover and the pump body, but it needs careful observation, especially when the working medium is liquefied gas or high pressure, toxic and harmful gas, it is relatively difficult some. The rest of the leakage is difficult to distinguish and judge intuitively. It is necessary to observe, analyze, and judge the leakage symptoms on the basis of long-term management and maintenance practices in order to draw a correct conclusion.

 

   Analysis and Judgment of Leakage of Mechanical Seal of Desulfurization Pump in Power Plant

   (1) Leakage during installation of static pressure test.

   After the mechanical seal is installed and debugged, a static pressure test is generally carried out to observe the leakage. If the leakage is small, it is mostly a problem with the moving or static ring seals; when the leakage is large, it indicates that there is a problem between the moving and static ring friction pairs. On the basis of preliminary observation of the leakage and judgment of the leakage location, the manual cranking observation is performed. If there is no obvious change in the leakage, the static and dynamic ring seals are defective; if the leakage changes significantly during cranking, it can be concluded that the leakage is dynamic or dynamic. There is a problem with the static ring friction pair; if the leaking medium is sprayed along the axial direction, there are mostly problems with the moving ring seal. If the leaking medium is sprayed around or leaks from the water cooling hole, most of the static ring seal fails.

  (2) Leaks that occurred during trial operation.

  The centrifugal force generated by the high-speed rotation of the mechanical seal for the desulfurization pump of the power plant after undergoing a static pressure test will inhibit the leakage of the medium. Therefore, the mechanical seal leakage during trial operation is basically caused by the damage of the dynamic and static ring friction after the failure of the shaft and the end cover seal is eliminated. The main factors that cause the failure of the friction pair seal are: 1) During operation, due to abnormal phenomena such as evacuation, cavitation, holding pressure, etc., a large axial force is caused, which separates the contact surface of the dynamic and static rings; 2) Compression when installing the mechanical seal If the amount is too large, the end face of the friction pair will be severely worn and scratched; 3) The moving ring sealing ring is too tight, and the spring cannot adjust the axial floating amount of the moving ring; 4) The static ring sealing ring is too loose, when the moving ring is floating axially , The static ring is separated from the static ring seat; 5) There are particulate matter in the working medium, which enters the friction pair during operation, and damages the sealing end face of the moving and slap ring; 6) The design and selection are wrong, the sealing end face is lower than the pressure or the sealing material is cold More shrinkage and so on. The above phenomenon often occurs during trial operation. Sometimes it can be eliminated by adjusting the static ring seat, but most of them need to be disassembled and replaced, and the seal is replaced.

  (3) Sudden leakage during normal operation.

The sudden leakage of desulfurization pumps in power plants during operation is due to normal wear or has reached the service life, and most of them are caused by large changes in working conditions or improper operation or maintenance: 1) Evacuation, cavitation or holding pressure for a long time, Cause the seal to be damaged; 2) The return flow is too large, causing the sediment at the bottom of the suction pipe side container (tower, tank, pool) to appear and damage the seal; 3) For a long period of time, there is no manual cranking when restarting. The sealing surface is torn due to adhesion; 4) The corrosive, polymerizable, and gelling substances in the medium increase; 5) The ambient temperature changes sharply; 6) Frequent changes or adjustments in working conditions; 7) Sudden power failure will cause shutdowns, etc.

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