[bold]Help!!![/bold]demin water unit

[rizky123]

Do anybody know why does my demin water unit cannot reach pH 7? cause it only reach 5.
please i need a sugestion on how to increase pH in demin unit with an ion exchanger bed

 

[cub3bead]

If you are collecting a sample and then taking it to the lab to measure the pH then absorption of atmospheric CO2 could be depressing the pH.

If the pH is measured by a pH probe do you have one specifically designed for low conductivity operation?

When does the low pH occur in the service cycle?

What type of anion resin are you using in your beds?

What is the demin water's condcutivity?

 

[bimr]

Your question is impossible to answer without further information. For example:

1.Type of demin. unit, cation, anion, or mixed bed?
2.Age of demin. unit and resins?
3.Regenerant chemicals used and consumptions?
4.Is this a new problem or has the pH been trending off?
5.Are you following the manufacturer's instructions?
6.What is the conductivity of the effluent?

 

[rizky123]

yes i've been following the manufacture's instruction. for information the conductivity from mixed bed is 0.9, from anion bed is 6.8 and cation conduc. is 172. the resins that i use are amberlite IRA 420 and IR 120. the pH been trending off since the plant was built and start and i don't know where exactly the problem is

 

[rizky123]

oh yeah one thing i forgot to tell u. we've tried to add amine to the BFW stream before it enters the boiler and the pH is rising up to 10. but after that the steam and condensate pH drop again to 5 so its a weird thing....
oh yeah and the raw water we use are rain water that we collect from a dam so it's an acid water

 

[cub3bead]

The anion effluent conductivity indicates you are leaking about 0.6 mg/L of Na from the cation. If this a packed bed DI design you should be seeing about 0.25 mg/L of Na leakage which would give you an anion effluent of < 3 uS/cm.

Are you using HCl or H2SO4? Have you made sure that you are getting sufficient acid into the cation vessel? If you are then you need to make sure that you are getting good flow distribution during service and regenration.

Is there a break tank between the anion and MB. If there is you are likely getting enough CO2 absorption to shorten your MB runs unless you have a great excess of anion resin in the MB vessel.

The MB should be doing much better than 0.9 uS/cm, you should be seeing <0.1 uS/cm for most of the service run. Make sure that you are getting good resin bed separation before introduction of regenerants. Also, make sure you are getting the right quantity of regenerant in the vessel. starvation diets don't work on IX resins for long.

 

[GarySCWSVI]

cub3bead's suggestions are correct. I would only remind that you should not attempt a pH test on water produced by a Mixed Bed DI unit unless, as also mentioned previously by cub3bead, &quot;If the pH is measured by a pH probe do you have one specifically designed for low conductivity operation?&quot;. Normal run of the mill pH test kits, monitors or litmus paper are useless for that.

Gary Schreiber, CWS VI
The Purolite Co.

 

[rizky123]

i'm using H2SO4 for regeneration and the regeneration time is 15 min longer than it supposed to be. any thoughts?

 

[cub3bead]

While contact time is certainly important, have you verified that you have the corrent concentration of acid? The easiest way to do that is to measure the specific gravity of the dilute acid with a hydrometer. Make sure that you follow safety precautins for handling acid (i.e. chemical safety suit, safety glasses and face shield, etc.).

Your primary cation likely uses a 2 or 3 step dilution cycle to avoid CaSO4 precipitation. Your mixed bed likely requires 4% acid.

 

[bimr]

It is obvious from your posts that the demineralizer is not operating properly. There is no way that you should have a pH of 5 after the mixed bed unit.

How long have you been operating?

Did you have the manufacturer's service engineer onsite during startup?

As a start, you should call the equipment manufacturer and have them out for a service call. The equipment (demin or instrumentation) is definitely not working properly and something like this is difficult to diagnose with short email messages.

 

[rizky123]

this unit has been working for 24 years. about the acid concentration yes it is 4%. now i'm doing a jar test to simulate the demin unit. and my guess is the mixed bed is not right. i think i should review the regeneration SOP for the mixed bed.
oh yeah we've tried to inject TSP to this demin water for BFW but after the water became steam the pH is back to 5.4.
and one thing did i mention that the raw water we use? it's rain water that we collect by using dams.

thanks for your tips guys. i really appreciate a lot

 

[bimr]

If you are using rainwater, then it unlikely that you need a cation and anion. Rainwater has minimal dissolved contaminants compared to other waters. You probably only need mixed bed demineralization to get the water quality that you need.

Anion resin degrades over time and if you have not replaced the anion resin in the last 5 years, you need replacement of the resin. The cation resin has a longer life.

I still think that you should get a qualified service engineer from an equipment manufacturer to check your system out.