Impact of changes to the balance pipe of DG-type boiler feed water pumps
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Our company’s power plant desulfurization system uses DG-type boiler feed pumps with a flow rate of 15 m3/h and a head of 400 m. During operation, the flow rate is controlled by a return valve. Over time, seal failures have occurred at the non-driving end (the outlet side) of these pumps. Later, due to production requirements, the medium transported changed from process water to brine, which is more corrosive; as a result, the axial movement of the pumps increased, leading to a decrease in head, with the outlet pressure reaching only 2.5 Mpa at most. In addition, several of these pumps experienced overflow when the outlet valves were opened during startup, as well as during operation. Since new pumps are being prepared for replacement, temporary measures have been taken for these existing pumps by thickening the original balance tubes to increase the flow back into the balance chamber – could this help reduce some of the axial force?
Adjust the clearance between the balance disc and the balance ring so that the shaft’s play returns to normal levels; this will make a significant difference
It turns out that the frequent failure of mechanical seals might be due to design issues or problems with the quality of those seals. However, when the medium changed to high-salinity superfluid, the decrease in head pressure seems to be related to changes in the density and concentration of the medium. Since there is a change in the medium, it constitutes a change in parameters, and it is necessary to select new seals in accordance with the relevant specifications.
The sealing surface of the mechanical seal is severely worn; this issue can be resolved by adjusting the compression amount of the seal. High-salinity water has a high density, so it’s certain that the head pressure will not meet the required levels. High-salinity water is corrosive and causes scaling; corrosion leads to an increase in the sealing gaps, which again can result in the head pressure not meeting the requirements. It is recommended to use clean water for flushing after shutting down the high-salt water pump, in order to prevent corrosion or scaling of the pump body and impeller; scaling can lead to an excessively high starting current. The outlet pressure has reached 2.5 MPa, so the axial force should be lower.