Advice on plan 53A installation

[ChocolateHobNob]

I am looking for some advice regarding the installation of an API Plan 53A system. We have a vertical mounted in-line mixer operating at 3 bar. The mixer is blending food flavouring and colourant into a fat and sugar slurry. The original single seals with an atmospheric static oil quench, continually failed due to a build up of sugar on the seal faces. Our supplier is planning to fit Fluiten C2D double mechanical seals with a plan 53A reservoir. The supplier recommends that normal oil level in the reservoir tank is 1 metre above the seal. The problem is, there is limited headroom where the mixers are installed, and the maximum oil level that we can achieve is 60 – 70cm above the seal. What effect is the lower oil level likely to have on the performance of the seals?

 

[JJPellin]

Elevation of the seal pot above the seal is important if you are counting on thermo-syphon for circulation of the barrier fluid. If the seal is equipped with a pumping ring, this is less important. You should have enough elevation to maintain adequate positive pressure on the secondary seal. You should have enough elevation to provide some thermo-syphon, but perhaps not as much as you would otherwise. We require about ½ meter for the elevation of the bottom of the pot above the seal. I don’t see that this is a significant problem.

Johnny Pellin

 

[u0406346]

JJPellin is correct, thermo-syphon is the main reason why the height requirement for the seal pot. Note that your seal pot should be directly above the seal also, cannot be too far away radially, eg. 1 m away.
The concern here is because, circulation of the barrier fuid in the closed-loop system is important to ensure sufficient lubrication and remove heat from the seal face. Typically, seal flush rate of 2~3LPM is required for a 80mm seal, and this flush rate can be calculated using the API 682 formula. I do not think that a pumping ring is applicable for your case, because pumping ring will require speed of 1400rpm min in order to be effective. Since your equipment is in-line mixer, probably the speed will be low. Therefore, you will have to go for a circulation pump for this case. For your case, your circulation pump might have to be FDA approval, subjected to your client's requirement. You may pm me if you require recommendation on the circulation pump. If your Plan 53A system do not meet the height requirement, then this seal may not be operating in an ideal condition. Shall there be seal failure, seal vendor will have to come in and rectify the seal supply system or add in a new circulation pump.

 

[ChocolateHobNob]

Thanks to JJPellin and u0406346 for your advice. The seal is on a 35mm dia shaft, running at 300-400 rev/min. I believe that the seal has a pumping ring, but it will not be very effective below 1000 rev/min. so we are relying on the thermo-syphon for oil circulation. We did consider circulation pumps, but were advised that the size of the seal pot would need to increase from 4 litres to 12 litres and would need an additional cooling coil. We have four of these mixers,two of which run at any one time. I am hoping that the thermo-syphon that is being offered with protect the seal. I can understand that if the elevation is too high, it will impede the thermo-syphon, but I can't figure out what the effect will be on the thermo-syphon will be if the elevation is too low. I am trying to work out how worried I should be if we can only achieve a 60cm elevation against a reccomended elevation of approx. 100cm.

 

[JJPellin]

With the seal pot too high, this would not impede thermo-syphon. Thermo-syphon requires a certain minimum elevation difference between the hot part and the cold part. Heat rises. It is the rise of the heated fluid from the seal and the drop of the cooler fluid from the pot that drives the circulation. If you put the pot on line with the seal, there would be no incentive for the hot fluid to rise of the cool fluid to drop and there would be no circulation.

Johnny Pellin

 

[u0406346]

Sorry for the incorrect statement, the seal pot should not be located directly above the mixer or seal, but should be located as close to the mixer as possible while leaving sufficient room for operation and maintenance. 35mm diameter seal should not be producing much seal heat, estimate 0.3~0.5kW. This is a closed-loop system, 4 liters seal pot can be used with a circulation pump, therefore no need to upgrade to 12 liters seal pot, there are reference and supply record worldwide. Whether the need of additional cooling coil or not, you would have to obtain the exact seal heat and heat soak from the seal vendor, and don't forget that seal pot itself also dissipate heat. There is a reference of 4 liter seal pot with circulation pump has a heat dissipation capability of 2kW. Yes, you are correct, the height of seal pot cannot be too high, otherwise the effect of thermo-syphon might be affected, typically maximum 2 meter. For your case now, you will have to go for a circulation pump for each Plan 53A to ensure proper seal operation. To be exact, 0.9 meter elevation is good enough, 1 meter incorporates the safety factor. Hope the above helps.