Deionised Water

What's your flow rate? If it's more than 4m³/hour, you may need to install a reverse osmosis system for it. Likewise, you will need to install a polishing mixed bed unit to further reduce the water conductivity.

As for regeneration, check with your resin supplier on the quantity of reagent required for each type of resin. As for how frequently to do it, that should be done whenever your water resistivity drops by 1MΩ.

Flow rate is very low around 300 ltrs/hr (0.3m3/hr). If I use a polishing mixed bed how could I regenerate the resin in it when needed. If I use HCl then rinse the mixed bed and then use NaOH and rinse again will it be acceptable.

Another question I have not seen Stainless Steel vessels used as cation or anion columns. Is there any technical reason for above. The reason why I ask is for me it is cheaper to make a SS vessel than to buy a fiber vessel!

demin water is highly corrosive and the SS is not exempted.

Adding just one of the links

http://www.finishing.com/521/30.shtml

(BTW the oxide forming that prevents the corrossion/growth of it, in the steels is no more valid in case of pure demin waters)

Stainless steel becomes less suitable as the conductivity drops, as the water becomes more aggressive, and any species that might leach an ion into the water, like steels, will increase the conductivity markedly. Further, some grades of stainless, particularly in the region of the heat-affected zone for the welds, will show a marked decrease in resistance to corrosion, the products of which will manifest themselves as in increase in the conductivity of the product water, which is not what is wanted.

So despite the economic advantage locally of stainless steel, it is not really suitable for vessel manufacture for high purity water.

There are a number of plastic/fibreglass vessel manufacturers on the web, specialising in vessels for industrial and domestic water treatment, and the original poster needs to perform this research early in the design process. Further, the flanges and fittings needed for various grades of plastic pipework are readily available.

thanks a lot for your advice. Now onto the plastic & fiber vessels. I know one manufacturer from china WaveCyber which offers fiber vessels at cheap prices unfortunately they are tied up with my competitor. I tried some Indian HDPE vessels but quality was no where near Wavecyber fiber vessels which are rated at 10 bar.

Unlike in Europe or US in my country Sri Lanka we need to find very cost effective solutions as the income level of general public is comparatively low.

Try Enpress tanks, great durability and pressure tested at high temperature where other tank manufactureres do not make this claim.

email me and we can discuss options.

Regards,

Seth

srock@resintech.com

Reverse Osmosis is the next process step. Discuss the problem with a reputable water treatment company, or even several companies.

You mentioned a few things that caught my eye in the discussion.

If columms are not fully filled I'm presuming the void is air. If not it could also be CO2 (to get good deionization need to remoive it, If as you describe it is composing the 405 void the that is extra duty on the Anion. If air, that too induces Cationic loading on the Anion.

having said that much you will have to add a mixed bed after the anion of well mixed 50/50 anion/cation resin. This should take you to less than 1uS/cm. As also mentioned RO would work also.

So far as regneration watch for "conductivity Breaks down stream of each resin bed but primarily the anion and Mixed bed. Also how is the Cation to Anion volume sized? Typical the cation is ~2X the Anion so the Anion breaks first on conductivity to prevent anion breaks prematurily exhausting the anion resins and Mixed bed.

Resin supplier give both contact time, and weight of regenerant per volume of resin and required concentration during the injection period, typically 5% for most resins to allow good regeneration and avoid damage to resins and vessel internals.

Best of Luck!

Been There...

Your solution is probably a lot simpler than you might imagine. First, it would be useful if you posted the water analysis of your source water.

Secondly, your treated water quality target is not too strict.

My suggestion is for you to add a second cation column to follow your anion column, eg., pretreatment; cation (1); anion; cation (2). You will be surprised how much better your conductance will be after cation (2).

I am a little suspicious about your conductivity after cation exchange. Acid is formed in the cation exchange that would usually form a solution that would have a higher conductivity than the feed. You may have very high alkalinity, however. As mentioned previously, an analysis would better serve to scope your problem accurately.

BTW, if you use the secondary cation bed, you can regenerate the cation in both tanks in a thoroughfare fashion passing the acid through cation (2) in series with cation (1) and then to waste. This gives you an essentially "free ride" for the secondary cation treatment.

Flow rate and resin volume posting would enable calculation of resin capacity assuming standard gel resin exchangers.

In my opinion, you do not require anything as elaborate as addition of a reverse osmosis system or mixed bed to meet your quality needs.

Please email me at srock@resintech.com and include raw water analysis. I can place your data into my new process water simulator program and it will tell you how long your columns will work or if you should change your design. As for stainless steel, if there is free chlorides, it could attack the steel, it all depends on pH and concentrations of contaminents in the water. Also include where you are located. My network is world wide. Also depending on total amount of water needed it might be easier to switch to mixed bed cartridge application.

hope to be able to help,

Seth Rockmacher

ResinTech Incorporated

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