The desalinated water has become acidic
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Recently, a strange phenomenon has occurred in our demineralized water system: the water coming from the water treatment station has a pH of 9.0, but once it reaches our system, its pH drops to 5.7. This happens every time we test it. There is no problem with the sodium hydroxide used, nor are there any issues with the dosing pumps. The problem is more noticeable at night, when it’s cold, as the pH becomes even lower. We have three ammonia synthesis units, and all of them receive their demineralized water from the same source; the pH level in all three systems is below 7. Is there anyone with expertise in this area? Thank you
After the metal ions are removed, the carbonate ions turn into carbon dioxide which dissolves in water, resulting in a weakly acidic environment. In engineering applications, stainless steel is required to be used in the desalinated water pipelines; furthermore, a fan must be installed during the desalination process to blow away the dissolved carbon dioxide
What did the original poster use for testing? An acidity meter, or general-purpose test strips, or precision test strips? When using both general-purpose and precision test strips to measure pH, a value within the range of 7–9 indicates weak acidity; only values above 9 indicate a normal pH level
Our factory encountered the same problem some time ago; later, a tank was added to it, with disodium phosphate placed inside to neutralize its alkalinity.
We do the same here; generally, sodium diphosphate and similar substances are used to neutralize the alkalinity
I wonder if your demineralization plant uses ammonia to adjust the pH value? This situation occurs when the pH value is adjusted using ammonia, and the system does not have a device for removing carbon dioxide. Do you mean the boiler as the system in question? Adjusting the pH value using ammonia will result in some loss in the deaerator. If your system consists of reverse osmosis followed by anion and cation exchange resins, the higher the pH of the water coming out of the desalination station, the lower the pH of the steam condensate – we have encountered this situation as well.