Questions about the mechanical seal of the methanol lean liquid pump?

Seal leakage is normal, but frequent leakage is not; it’s possible that the inlet filter is not effective, with too many particles in the methanol. Additionally, it’s necessary to check whether there are any issues with the pump itself, such as vibration. If possible, it is recommended to switch to a dry gas seal. In our plant, the outlet pressure is above 9.0 MPa, and operations proceed normally after switching to a dry gas seal.

The pumps in our factory are imported, so there should be no need for such a complicated dry gas seal. It might still be necessary to purchase imported dry gas seals; it’s quite difficult to use domestically produced ones. In addition, dry gas seal pipelines are required, and there may not be enough space for them. I’m wondering if other types of seals could be used as a solution. Of course, our mechanical seals are also of the FLOWsever type. It is a high-end product.

There are several main reasons for seal leakage: first, the outlet pressure of the pump exceeds the designed pressure for an extended period of time. Second, there is a problem with the shaft at the pump seal (cracks; seal leakage issues). Third, too much methanol-based seal fluid was added. To prevent excessive pressure caused by seal leaks, which could pose a danger to operators, we installed a \"U\"-shaped duct above the seal that leads downward (as leaks in the seal have led to accidents where methanol got into people’s eyes during operation). Or replace the dry gas seal

["1. The outlet pressure of the pump exceeds the design pressure for an extended period of time."] Second, there is a problem with the shaft at the pump seal (cracks; seal leakage issues). Third, too much methanol-based seal fluid was added. To prevent excessive pressure caused by seal leakage, which poses a risk during external operations, we take measures with the seal... May I ask: how can an excess amount of seal fluid lead to seal leakage?

I disagree with the idea of using dry gas seals as mentioned upstairs. The outlet pressure of the methanol-poor pumps in our factory is over 9.0 MPa, so mechanical seals work perfectly well in such conditions. Generally speaking, it’s normal for the circulating methanol to be a bit dirty; deposits will form after it has been in use for some time. If vibrations and alignment issues persist, it means that the level of maintenance work needs to be improved

I believe the vibration level of domestically produced motors does not meet the requirements for imported pumps; excessive pump vibration is one of the reasons for this. The possibility of dirt getting into the mechanical seal is low, as imported seals are usually pre-assembled, and nitrogen is used for purging to prevent external dirt from entering. However, the shaft clearance in the pump is quite small, which makes it easy for dirt to get in and cause problems such as the pump not being able to rotate freely. An appropriate inlet filter must be selected during operation; a higher mesh size is certainly better, but the inlet flow rate also needs to be taken into account. The filtering area of the inlet filter is very important – if the pump is operating properly, the mesh size can be reduced slightly, which will lessen the frequency of filtering and cleaning while preventing damage to the pump.

We import the entire machine. It’s running well. . . . The pressure is 8.8 MPa. . Head 1280m. . Flow rate: 184 m3/h. . . A common cause of leakage in ordinary machine seals is dirty liquid of substandard quality. . Or there might be a problem with the bearing. . If it runs for a long time without any data flow, leakage will definitely occur

Is it because the sealing fluid in the mechanical seal tank is too dirty? Another issue is that the sealing rubber ring used in the machine seal itself is not of the right material

The several methanol pumps in our plant’s low-temperature methanol washing unit are all centrifugal pumps, equipped with double-seal mechanisms as well as tanks and alarm systems. The seal mechanisms of some of these low-temperature methanol pumps also leak frequently; the main signs of this issue are frost forming on the sealing tanks and associated pipelines, and in severe cases, frost even forms on the gearboxes. Additionally, the liquid level in the methanol sealing tanks rises, requiring frequent drainage of the methanol from those tanks. Apart from switching to a dry gas seal, I wonder if there are any other good solutions?

If a dry gas seal is used, is nitrogen used for the primary seal? Can nitrogen entering the pump cause an air pocket? I don’t know much about it; I hope someone can explain how dry gas sealing is used in methanol pumps