Demin Water on carbon steel
Demin Water on carbon steel
(OP)
I need advise how to deal with demin water (chemical additive??) so that it will not be too harse on carbon steel piping, without using stainless steel as an option?
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Demin Water on carbon steel
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RE: Demin Water on carbon steel
RE: Demin Water on carbon steel
Demin water is used as make-up for the cooling tower water. What is the process of removing O2 & CO2 from the water and preventing them from being absorbed again by the recirculating water? Thanks again!
RE: Demin Water on carbon steel
You will not be able to prevent the demin water from reabsorbing O2 and CO2 from the air in a cooling tower, sorry.
CO2 removal is the easy part. CO2 is converted into HCO3 and removed by the anion resin inyour demin system. O2 can be removed by vacuum degassing, chemical scavenging using hydrazine or a hydrazine substitute ( I assume that you would not want to add additional TDS, so you couldn't use sulfite), or by using a gas transfer membrane swept with N2.
RE: Demin Water on carbon steel
RE: Demin Water on carbon steel
you can assess the aggresivity of demin. and other waters by means of the Langelier Index. This is a technique for comparing the pH at which Calcium Carbonate begins to precipitate (pHs) with the actual pH. If pHs < pH, water is in a scaling condition, and has a low corrosion capacity. If pHs > pH, water has an aggressive nature. The condition of the water may be determined thus:
pH + TF + CF + AF - 12.1 < 0 implies aggressive water
pH + TF + CF + AF - 12.1 > 0 implies scaling water
where : pH = Measured pH Value
TF = Temperature Factor
CF = Calcium Hardness Factor
AF = Alkalinity Factor
A Table of values of the various factors to assist with this can be seen at point 9 on the following page:
http://www.wastewatertreatmentplantdesign.co.uk/II...
Seán Moran
RE: Demin Water on carbon steel
Something is wrong with the link you provided, would you post a coorected link?
cub3bead
RE: Demin Water on carbon steel
http://www.wastewatertreatmentplantdesign.co.uk/II...
Seán
RE: Demin Water on carbon steel
1. Empirically determined
2. Qualititative, rather than quantitative, representing the probability of the water being corrosive.
Nevertheless, correction of Langelier index is quite widely use in the UK water industry for correcting problems with aggressive waters.
Seán
www.seanmoran.co.uk
RE: Demin Water on carbon steel
The problem with using the simplified calculation method you show on your webpage is that there are cases which do not apply.
The computation method for the Langelier Saturation Index requires six bits of information:
1. Total Alkalinity
2. Calcium Hardness
3. Ionic strength or TDS
4. pH
5. Temperature
6. pH at saturation equilibrium
The first five items can easily be measured but the saturation pH must be calculated and that involves solution of a quadratic equation. In the case of water with low calcium hardness and low alkalinity where it cannot become saturated with respect to calcium carbonate at any pH; the calculated hydrogen ion concentration at saturation equilibrium becomes imaginary. Demineralized water falls into this category of water so the use of LSI to characterize it scaling or corrosive tendencies is meaningless.
Another area where the simplified equations fail is at or above the bicarbonate-carbonate equivalence point (pH ? 10.3 – 10.5) because the negative root of the quadratic equation applies and the definition of LSI must be reversed.
Your method works in most cases involving natural waters, however, you have to be very careful in using it with waters that have been chemically transformed.
cub3bead
RE: Demin Water on carbon steel
the use of indices it is certainly controversial in some quarters, but I still think the simple technique given is useful for all waters. I think it would be a minority opinion that it is totally meaningless. I think it's actually better to use the simple tabular technique for this purpose than the algebra, as the result is quantitatively meaningless. It is however qualitatively useful. DI and RO waters can be remineralised in accordance with the predictions to give reduced corrosivity.
A detailed discussion of the various indices by people far more knowledgeable than me can be seen at:
http://www.corrosion-doctors.org/NaturalWaters/cor...
Hope this helps
Seán
www.expertise-limited.co.uk
RE: Demin Water on carbon steel
In addition, water that contains very little or none of the necessary ions required for the LSI type indices, the results are meaningless.
Gary Schreiber, CWS VI
The Purolite Co.
RE: Demin Water on carbon steel
What we have to remember about forums such as this is that there maybe readers lurking without the training or experience to make informed decisions about the applicability of our discussions.
When I do remineralization calculations I pick a desired hardness and alkalinity level and then calculate the LSI to check whether the blend is corrosive or scaling. I do not start with a desired LSI and use it to calculate the Ca hardness and alkalinity required for a stable water.
I am a believer in going back to the basics and understanding the chemistry involved.
cub3bead