Entrained Air / Froth Pumping

[Charlesi]

Hi Gents,

Does anyone have expereince with entrained air / froth pumping. I have a pump (centrifugal) that is seeing alot or air and is surging. The fluid is quite unique, it is about 55% solids and has alot of entrained air and froth in it. Does anyone know of a practicle way to determine if the air is causing a surging in the pump. The pump discharges into a pump box and by looking at the top of the box it is apperent that the amount of air in the fluid is large (I can't quantify this because I have no idea of any test to do so). By the time the fluid is drawn into the pump some of the air could have been removed from the fluid so this presents another problem. The fluid conditions are changing at the pump inlet. A quick and dirty method would be appreciated with any tried and tested methods...

Thanks

 

[Artisi]

Be assured that you have entrained air reaching the pump impeller which is causing the pump to surge.
To be of help I will need more information:
what is the process and what are you pumping?
what type of pump are you using?
pump box configuration
flow / head etc
Froth pumping is not a problem when using the correct equipment ( froth pumps) and is a common occurrence in the mineral dressing industry when taking product from floatation cells.
Depending on the amount of air entrainment it is also possible to make some modifications to centrifugal pumps to handle some air and give reliable performance.

 

[smckennz]

Your situation is not that uncommon.
If you suspect surging, the easiest way to check is to measure the pump current with a clamp-on meter. If the pump current oscillates then you have surging. An oscillation time of around 15 sec is not unusual so you need to watch the meter for a few minutes.
If surging is present, the normal quick fix is to extend a small vent pipe into the pump suction eye. This releases the air bubble that builds up in the impeller. Obviously this fix works only with flooded suction pumping.
Sometimes a lot of mucking around is required before the problem is fixed. Large inlet diameter or double inlet pumps suffer these problems much less.

Cheers

Steve McKenzie

 

[ruble3]

We had a similar problem from flotation cells- froth pumps were deemed too expensive - our centrifugal pumps are on VFD's and combined with sonic level indication we found the best solution was significantly increasing the size of the pumpbox-we increased our size some 400% which gave the froth a chance to 'settle' - other people use additional makeup water ( lots of it) to prevent cavitation- I think Warman pumps has a good froth pump but was expensive- I think it was similar to what smckennz suggested