At what levels of hardness and alkalinity in the make-up water for circulating water is acid treatment necessary?
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Our factory uses groundwater as make-up water for the circulating water system; the alkalinity of this water is around 200 mg/L, while the methyl orange hardness is approximately 250 mg/L. One supplier has proposed a treatment plan for the circulating water that involves the use of no acids, only corrosion and scale inhibitors, with a concentration ratio that can only reach 2.5. To achieve a ratio of 4.0, acid treatment is necessary. I would like to know whether it is really necessary to use acids in this case. I hope experienced experts can give me some advice
With a low concentration ratio, the amount of water that needs to be added is large. There is a lack of water resources; there isn’t enough water to replenish them.
With a lower concentration ratio, do you still add water?
With a low concentration ratio, the amount of water that needs to be added is large. A high concentration ratio and low waste discharge can easily lead to scaling in surface-type heat exchangers
What’s the pH? The alkalinity and hardness aren’t high either, right?
The manufacturer is right. If the concentration ratio reaches 4, the circulating water will definitely be severely scaled. According to your parameters, the water is classified as high-alkaline and high-hardness water. The 2.5 times figure mentioned by the manufacturer refers to the national standard, which stipulates that the hardness and alkalinity of circulating water should be <1100 mg/l. In fact, this 1100 is only a guideline value; the actual value should be determined through corresponding simulation experiments carried out by the manufacturer. Rotation hanging test and limit carbonate test are necessary to be conducted.
pH 7.5 – these values are all measured for the supplementary water
Acid treatment is required; the higher the concentration factor, the greater the alkalinity and hardness will be； PH will also increase accordingly.
If the alkalinity and pH are too high, acid needs to be added; otherwise scaling is likely to occur. Most factories do this, especially power plants, by using sulfuric acid. Physical technologies are now also used to control alkalinity and hardness, thereby increasing the concentration factor