Demin regen problem 2

[bethw]

Our plant has two demin trains, anion and cation type. Beads are 1 year old in one unit and 2 months old in the other. When we regen our units, we measure the SiO2 in the effluent to determine if the regen has been successful. Recently, we have had trouble with our regens in regards to getting the SiO2 readings down after doing one. I am not a chemist, but do have a basic understanding of what is happening here. My question, for lack of further understanding, is: From which unit does the SiO2 come from? (We may be working on the wrong unit) Is it "flushed" from the cation, thru the anion and out? Or does it come directly from the anion, or both, as in sodium leakage?

 

[quark]

ABB

http://www.hungerfordterry.com/condensate.htm

These two links may be helpful to you.

 

[bimr]

Silica passes through the cation unit and is removed with the anion units.

 

[sbush]

As Bimr mentions, silica is removed by the anion resin. The trouble with silica is it is both difficult to remove from the feedwater during service and to elute from the resin during regeneration. In service mode, silica is more efficiently removed at colder water temperatures. In regeneration mode, elevating the caustic-in and slow rinse water temperature to 95-degrees F will greatly enhance the elution of silca from the resin. The resin selection is also important. When water contains organic matter, a macroporous anion resin is beneficial. Using higher caustic dosages (8 lbs per cubic foot) may be helpful too.

Silica levels in feed water can vary quite a bit. You should monitor the incoming silica levels too.

S. Bush

http://www.water-eg.com

 

[cub3bead]

A minor correction, reactive silica is removed by the strong base anion resins, however, colloidal silica passes through the beds.

Is your anion resin type I or II? Type II resins are damaged irreversibly if the water or regenerant temperature exceeds 95 degrees F. Type I are damaged above 120 degrees F.

What is the pH of the anion rinse water at the end of your normal rinse time? If it is still high, then Na leakage from the cation could be part of the problem.

If you are operating packed beds or one of the counter-current designs you could be disrupting the bed during regeneration. These units depend on having 3" - 6" of fully regenerated resin at the bed outlet. You shouldn't over run your beds either because it will take a 2X or 3X regenration to restore the polishing section.

And the obvious problem is: are you getting sufficient regenerant into the bed to regenerate the resin?

 

[Karbone]

I need some advice on resin selection for Mixed Bed Polishers. What are the resin selection criteria based on your water quality report?

I also have a question on what is the best way to deal with RO membrane biofouling? I have a chemical softening/coagualtion/flocculation system followed by Sand Filters, AC filters and cartridge filters.

Best regards to all

rami cremesti