Examining the issues from the water quality parameters of circulating water
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The high level of iron ions in the water of the circulating water system is always a problem. The relevant values are as follows: pH 8.81, total hardness 412.68 mg/L, calcium ions 115.35 mg/L, phenolphthalein alkalinity 10.62 mg/L, total alkalinity 254.76 mg/L, turbidity 50 NTU, chloride ions 40.55 mg/L, total iron 5.55 mg/L, total phosphorus 16.91 mg/L, and concentration factor 3.1. Could it be determined from these values what is causing the high level of iron ions?
May I ask, LZ, does your circulating water system have an acid addition system? Based on the data, the system corrosion is severe, with high total iron levels. According to the data, the alkalinity is too low, which leads to increased corrosion in the system. Another possibility is that the amount of scale inhibitor added is excessive; since scale inhibitors are generally acidic substances, adding too much of them will consume a large amount of alkalinity, leading to corrosion in the system.
We maintain the total alkalinity in the water at around 110 mg/L, and the amount of scale inhibitor added is 25 KG per day. Based on the pH value, the conditions seem to be normal; I’m wondering whether the active components of the scale inhibitor are insufficient, resulting in it no longer being able to provide corrosion and scale inhibition effects. Moreover, the water quality here is currently turbid, appearing earthy yellow.
If the solid content of the scale inhibitor is fine, then it means too much of the inhibitor has been added; the total P value is a bit high, and it’s generally recommended to keep this value between 4 and 8. Additionally, the amount of scale inhibitor used is calculated based on the water volume to be replenished, rather than being fixed
The content of new ferrous ions can be analyzed, and due to the low calcium ion level, zinc-based corrosion inhibitors can be considered to enhance corrosion resistance.
Friend upstairs, do you think it’s a problem with the medication? Can the issue with the device be resolved?
It should be a problem with the dosage of the slow-release scale inhibitor
What could be the reason for the water to be earthy yellow? Our water plant was shut down on January 24 and restarted on February 9, but the water was still green before it was shut down, and has remained earthy yellow ever since it was restarted. The calcium ion content in the water is not high either; it doesn’t seem like there is deep well water mixing in. Although two new heat exchangers have been installed, this should not be sufficient to cause any issues, right?
What was your turbidity level before? Is the side filtration system operating properly?
Replying to the original poster, I suspect it’s a problem with the make-up water; since operations were halted, the make-up water line hasn’t been in use for a long time, and there might be too much rust in the make-up water.
It has been running for a fairly long time now; if the problem lies in the water supply pipes, things should gradually improve. However, it seems that’s not the case. It was previously assumed that water from deep wells might have seeped into the supply pipes, but the calcium content in the water isn’t high.
Stop talking about it – the corrosion inhibition effect is just not good enough; replace the corrosion inhibitor
The heat exchange temperature is too low, causing the water to stay in the system for too long; as a result, iron accumulates, and sometimes its level becomes high. When the turbidity is too high, spectrophotometers used to measure iron are prone to measurement errors. The scale and corrosion inhibitors are fine; the dosage added is sufficient ； The alkalinity is fine; it’s not low, so there’s no need to worry.
The circulating water tank requires regular chemical dosing, periodic analysis and testing, as well as timely water replenishment.
The scale-inhibition dosage in the system is high enough; it is recommended to reduce it slightly to save costs. Spectrophotometers are prone to measurement errors when determining iron, and I agree with this view. The main reason is that high turbidity affects the accuracy of iron ion measurement. The high turbidity is due to the sediment at the bottom of the pipes and heat exchangers being carried up by the water once the system starts operating. It is recommended to increase the water replacement rate. I believe it won’t take long for the system to return to normal.
We have been changing the water these past few days; starting from noon on the 25th, a sample was taken at 2 p.m., and the turbidity was found to be 96 NTU, with a total iron concentration of 8.16 mg/L； On the morning of the 27th, water samples were taken from the recirculation tank and left to stand for one day and night; earthy-yellow flocculent sediment appeared at the bottom. The clearer liquid from the upper layer was used for turbidity and total iron analysis, which yielded values of 94 NTU and 7.43 mg/L respectively. It seems there hasn’t been much change in the displaced water over the past two days; what’s going on here?
The cause cannot be determined from the water quality data; a thorough investigation is needed
May I ask the original poster whether water added for analysis has been tested? First, we need to look at the analysis data of that added water in order to rule out possibilities one by one.
Excess turbidity can also increase the iron ion content in water. Therefore, under such circumstances, I believe replacement should be increased to reduce water turbidity. Keep it under 20.
The turbidity at the inlet and outlet of the cooler was analyzed: it was 80 NTU at the inlet and 85–90 NTU at the outlet. I would like to ask whether this difference in turbidity between the inlet and outlet is normal?
The supplementary water has been added; it’s normal.