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Increased differential pressure at Ion Exchangers

We are facing problem of increased differential pressure across the cation and anion ion exchanger when we are running our demineralizing train with cold river water i.e. about 7 °C. Due to these increased differential pressures we have to decrease our flow. My question is that the density of water does not change a lot from 20 degrees to 7 °C then why we are facing this problem and what can be the solution?

Shazia Butt
- Toronto, Ontario, Canada
2003

Could it be your resin bed? It if contracts in cold water, the individual beads would be come smaller, allowing to the bed to pack more densely. This would help restrict flow and drive your dp up. I suggest you call your resin manufacturer and ask them about it.

Christian M. Restifo
- Pittsburgh, Pennsylvania
2003

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2003

It is not the density that causes the higher pressure drop, it is more likely that it is the increase in viscosity.

If it doesn't go away when the water gets warmer, other causes may be a partial plugging of the screens in the resin vessels or particulate matter in the resin bed.

Lyle Kirman
consultant - Cleveland Heights, Ohio

Hi Shazia,

What Christian said sure seems to make some sense ... but another thing.... surely, surely, surely after some time doesn't the i.e. resin get depleted? After all, surely it wouldn't 'last' for ever, would it, eh?

If that's the case, then the resin particles will get smaller and you'll get compacting, ergo the density increases as does the pressure drop.

Freeman Newton [deceased]
(It is our sad duty to advise that Freeman passed away
April 21, 2012. R.I.P. old friend).
2003

 

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2003

Do you pre-heat or warm your beds before you regenerate them? I'm not certain that I buy the smaller denser argument, as we are talking about very little expansion/contraction coefficients for resins, especially divinylbenzene styrene based resins. On the other hand, if you subject a resin bed that has been operated at 7 degrees C to regeneration chemicals that are going to be on the order of magnitude at 50-60 degrees C or higher due to heat of formation from the dilution of the acids and caustics that can cause significant breakage of resin beads due to thermal shock. This makes very small pieces, that can be a cause of excessive pressure drops.

You state that you are treating river water. What grade of prefiltration are you using? IX is an excellent 2-4 micron filter - even smaller with deeper bed depth. Is your system co-flow or counterflow regeneration?

Tom Baker
wastewater treatment specialist - Warminster, Pennsylvania