Get out of the Soup

Readers clarify a consistency complication.

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Glen Oswald, engineer advisor
Mosaic Phosphates, Plymouth, Minn.

SWITCH THE PUMP
The centrifugal pump is putting too much shear in the additive and causing a viscosity change. Try using a metering pump of some kind with low shear capability.
Ron Strybos, salt cavern storage specialist
Air Liquide Large Industries U.S. LP, Houston

LOOK AT OTHER INDUSTRIES
If you are adding a coagulant through a pump, you are both under-mixing and
over-mixing. Under-mixing in that mixing with a pump is very inefficient, perhaps only 10%, especially in a large tank. Over-mixing produces intense mixing in the pump, tearing the coagulated particles apart again — hence the soup. It is best to gently mix with an impeller, something like the milk industry uses for cottage cheese, etc. You should talk to the coagulant supplier.
Cliff Gaddis, senior project engineer
NOV-Brandt, Conroe, Texas

REDESIGN THE SYSTEM
You are shearing the polymer with the centrifugal pump. Invest in a polymer make-down system.
Jon Robson, general manager
Wellons Water Technology, Vancouver, Wash.

TAKE A SAMPLE
Consider the possibility that the shear from the pump is reducing the molecular weight of polymeric coagulating agent. Reducing the molecular weight could very well reduce the viscosity of the solution. Testing a sample of the solution from before the centrifugal pump for susceptibility to shear thinning could point to the source of the lowered viscosity. If the centrifugal pump is the source of the problem, a lower shear pump could be the answer.
Rob Vermeulen, technologist
Applied Materials, Santa Clara, Calif.

SCALE-UP POSES ISSUES
Too much shear due to the use of a centrifugal pump is breaking down the polymer. Use a diaphragm pump for the polymer addition.
Many times when going from pilot plant to fullscale production, things that are least expected will jump up and bite you. While working for a major food manufacturer, one of these little guys bit me and my team.
The fullscale plant operation was designed to add all ingredients using load cells and pneumatic conveying. After the first batch, the product was not acting or tasting right. Several minor ingredients were trapped in the conveying system! They were hand fed after that and no more batches were ruined.
Donald Phillips, engineer
Phillips Engineering, Melbourne, Fla.

GO WITH PREMIX
Probably the addition pump is breaking down the polymer structure preventing a rise in viscosity. Try adding the premixed polymer solution or change the centrifugal pump for a pneumatic pump.
Emilio Malaguti, technical director
Chemtron, Davie, Fla.

SWITCH THE PUMP
Depending on the chain length of the polymer being used, the centrifugal pump may have sheered the polymer. I recommend switching to a diaphragm pump to dose the polymer into the mixing tank.
Scott Patrick, process engineer
DuBois Chemicals, Inc., Cincinnati, Ohio

 

In the experiment above, polymer was added to
clay to floculate it.  Further tests were done to find
out whether shearing the clay and polymer mixture
would change the settling time of the clay. 
Source: Alison Springer-Wilson, Mosaic Phosphates


VERIFY IN THE LAB

My guess would be that the centrifugal pump is shearing the polymer before it gets to the stuff being treated in the cosmetic tank, limiting the polymer’s effectiveness. To test this, you could obtain samples of polymer and material being coagulated and shear the polymer at different levels before you add it to the cosmetic tank, to see if you get a consistency similar to the runny soup or tapioca pudding. If shear is what causes the change in consistency, I would improve consistency by installing a positive displacement pump with low shear instead of the centrifugal pump.

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