Vacuum pump elevation 1

[MortenA]

Does A vacuum pump/compressor have any requirements for the elevation of the pump in relation to the source?

Im working on a project where a liquid ring pump shall provide a mild vacuum of 0.8 bara in a large vessel. The vessel is horizontal and half filled with crude oil.

I have now heard that the pump shall be place above the outlet nozzle from the pump in order to avoid liquid entrainment especially during strat up Im quite sure that the guy who says this thinks this must be so in relation to a vacuum destilation tower. How could the vacuum "lift" liquid from the surface and approx. 3 meters in the air (the vessel diameter is 6.7 m)? Condenstation is i believe less likely to occur when the pressure is reduced.

Any experience with (liquid ring) vacuum pumps in this aspect is welcome!

Best regards

Morten

 

[quark]

If your tank is kept under vacuum and the tank bottom valve is opened to atmosphere then there are chances that the liquid may rise in the vessel. But in your case it is not more than 2 meters approximately[(1-0.8)*10]. If your seal fluid is same to that in the tank, then you need not worry whereever you keep the pump.

I faced problems in the past with oil ring vacuum pumps, used to evacuate pharmaceutical vacuum tray dryers and autoclaves, when kept at higher elevation than that of the equipment. We found oil mist carryover and subsequent product contamination during vacuum breaking. My initial idea was that it was better to keep the pumps at higher elevation as air floats up. But this thing put me down.

Regards,

 

[MortenA]

Quark - the first part may be the key. My client only has experience with a full vacuum tower. Here the 10 m makes good sense. My application does not use full vacuum so maybe thats not a problem here.

Anyway - could you avoid this problem just by having a "reverse waterlock" - a 10 m high "pipe loop" instead of lifting the pump itself?

Best regards

Morten

 

[quark]

Just a correction. Actually the formula should be [(Atm.Pre-actual abs.pre)*10/SG]. A liquid of 0.66 specific gravity can easily rise to a height of 3 meters.

Your solution is correct and that will avoid liquid entry into the pump by all means, but why to create some extra pressure drop with more length of piping? Further this looks odd physically. Just check the required height as shown above and add some safety factor.

Regards,

 

[MortenA]

The oil has a density of 0.86 so 3 meter should be sufficient. Further more the vesel itself is actually elevated approx. 5 meters above ground to provide sufficient NPSH for the export pumps.

Best regards
Morten

 

[quark]

Vessel elevation doesn't come into picture. The height to which the liquid rises is considered from liquid vapor interface. Just check if you have any free space in the tank. If so, deduct that height from 3 meters and the rest will be pipeline height.

Regards,