High pressure and leakage in the mechanical seal tank
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We have a feed pump for a distillation tower; the inlet pressure is 0.35 MPa and the outlet pressure is 1.3 MPa. The feed temperature is 265°C. A Plan32+53B mechanical seal is used, and the pressure in the seal chamber during operation reaches 2.2 MPa, which results in damage to the mechanical seal on the non-driving side. The flushing oil used is mixed diesel at 60°C. Could anyone help analyze the reasons for this?
I don’t know what the pressure is for the flushing fluid at 32 It seems that the high pressure in the sealing tank is caused by a leak of sealed diesel.
The outlet pressure is 1.3 MPa; the pressure in plan32 won’t be that high either, while the pressure in 53B is 2.2 MPa. It is recommended to check the accumulator; if the bladder is damaged or the pressure is lost, the accumulator will be filled entirely with a sealing fluid. Since liquids are incompressible, temperature changes may cause the pressure to rise.
The pressure you’re using for rinsing is too high! To create backpressure, the pressure of the isolation fluid generally needs to be 0.5–1 MPa higher than that of the flushing oil; otherwise, backpressure will cause the flushing oil to enter the isolation fluid system. Your flushing oil pressure might be too high – check whether the pressure gauge is damaged
The pressure of the flushing fluid should be 0.1–0.5 MPa higher than the pressure in the sealing chamber; your flushing fluid has a pressure of only 0.3 MPa, the pump inlet pressure is 0.35 MPa and the outlet pressure is 1.3 MPa, so the pressure in the sealing chamber must be at least 0.6 MPa. The pressure of the flushing fluid is too low; I suspect that it isn’t effective at flushing, as it doesn’t flow within the sealed chamber. Additionally, the high temperature causes it to vaporize.
The 53B pressure can be appropriately reduced; it needs to be 2 bar higher than the pressure in the sealing chamber. This way, the service life of the seal will be longer. Send the detailed operating condition information to the seal supplier, and they will provide a reasonable pressure setting.
What is the flushing oil pressure for PLAN13? It is generally 0.1-0.2 MPA higher than the sealed chamber. If the fluid pumped contains fractions that are prone to vaporization, damage to the mechanical seal on the fluid side can allow these fractions to enter the external sealed chamber, from where they circulate back to the isolation fluid tank. The vaporization of these fractions due to changes in temperature and pressure leads to an increase in pressure inside the tank