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Sizing an ion exchange pump

Sizing an ion exchange pump

(OP)
I have a small water treatment plant (15 m3/h) and part of the treatment process is softening (Ca/Mg removal by ion exchange). There is about 400L of resin in a 1000L tank. The water to the resin tank is supplied by a centrifugal pump (5-30 m3/h @ 2-5 bar total head). The resin tank is fitted with a Fleck 2850 control valve that can do service/backwash/regeneration/rinse functions. The pump is not fitted with any controls, only a throttling valve.

The problem is the following:
The flow requirements are dramatically different between operation and regeneration steps. As per resin specs, service flow is max 60 m3/h, so no problem there. But regeneration flow is 1-4 m3/h/m3, meaning that in my case it is 0.4-1.6 m3/h.

Can a centrifugal pump be operated so far off the low end of the pump curve?
Or maybe I am misreading the resin specs?
If not, what is the usual way of achieving this miserly flow rate?

Thank you all in advance!

RE: Sizing an ion exchange pump

Since 0.4 m3/h is probably less than the minimum continuous flow requirement for this pump, you'll need to operate at a higher flowrate and divert the excess fluid somewhere else (back to the supply tank or to a plant drain. The alternative is to install a separate (smaller) pump for the regeneration step.

RE: Sizing an ion exchange pump

Do you have a pump curve? This will be the starting point for the discussion.
Obviously the softener system manufacturer thinks it can, and whilst its not perfect it may be okay.

Regards
Ashtree
"Any water can be made potable if you filter it through enough money"

RE: Sizing an ion exchange pump

(OP)

Quote (don1980)

Since 0.4 m3/h is probably less than the minimum continuous flow requirement for this pump, you'll need to operate at a higher flowrate and divert the excess fluid somewhere else (back to the supply tank or to a plant drain. The alternative is to install a separate (smaller) pump for the regeneration step.

That's what I was afraid of. I've done my reading about ion exchange plant design, and while resin volume, service flow rate, rinse volume, etc, are discussed, I have yet to read anything about supplying the water to the system. Because the difference between service and regeneration flows is so dramatic I would expect this to be a common problem.

Would constant pressure control on the supply pump help solve this problem?

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