Problems with the acidity and iron ion content in circulating water
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Some time ago, I sought help on forums to find out the reasons behind the increase in the acidity of the circulating water; it was later discovered that there was a leak in a heat exchanger containing acidic media. That problematic heat exchanger was removed a long time ago, and all parameters of the circulating water are now within the required ranges, yet the iron ion concentration still remains above the acceptable level. What’s the problem?
I’m not sure about the dissolved oxygen level; if it hasn’t been measured, it’s worth considering whether dissolved oxygen corrosion is the cause.
Under acidic conditions, corrosion of the condenser leads to an increase in the iron ion concentration in the circulating water. I’m not sure what length of time you mean by ‘removal’. It is recommended that you monitor the changes in the concentration of iron ions in the water; if it is showing a downward trend, it is likely still caused by corrosion that occurred when the circulating water was acidic some time ago. There can only be two reasons for excessive iron ions in circulating water: corrosion or those brought in by the make-up water.
Increase the amount of replacement fluid and then monitor the iron ion level; if it remains high despite no leaks in other heat exchangers, it is recommended to flush the system. This post was last edited by Welcome on 2009-2-10 23:05.]
Be alert that other heat exchangers may also be corroded and on the verge of leaking. Especially with water of high acidity, it takes a long time; the plant must be shut down to test and leak-check each heat exchanger.
Is the turbidity high in your system? If the turbidity of the system is high, then iron ions will not decrease in a short period of time. Since many sludges contain iron ions, the original poster can analyze the iron content at different times. Does a high turbidity level also lead to an increase in iron ions?
Excess iron ions indicate that corrosion may still be present in the system.
In fact, an excess level of iron ions indicates that corrosion in the system is quite severe. There are various reasons for this corrosion; one of them is related to the system itself. If corrosion caused by such factors is ruled out, then what other possibilities could there be? II. Whether it is caused by the addition of oxidizing biocides; check the amount added and the frequency of addition, etc. III. What is the quality of the water used for supplementation? If it is purified water, or if its total hardness and total alkalinity are high, it can easily cause corrosion ； IV. Is the concentration ratio too low, or is corrosion caused by too low an alkalinity in the circulating water? ； V. Whether too much scale inhibitor has been added; scale inhibitors are generally acidic, and excessive amounts can lead to corrosion.
Generally, the water quality appears clear to the naked eye, with a low turbidity level as well. The iron ion content has remained around 2.6. The pH value is around 8.5, and all other indicators seem to be normal. However, the turbidity increased after adding biocides and algaecides, and the iron ion concentration rose to around 6; after replacing the water, the iron ion concentration was around 2.6.
Corrosion may still be ongoing; cleaning and pre-coating treatments could help improve the situation
Let me point out one issue: the corrosion in your system is caused by the biocides and algaecides. Current methods that can be used to make corrections: one is to change the type of biocides and algaecides currently in use ； Secondly, it is possible to reduce the amount used or increase the frequency of application, but the amount for the first application can be reduced. Third, the system can be re-cleaned and pre-coated before being put back into operation.
There are roughly four types of opinions: 1. The circulating water system is corroded； 2. The biocides and algaecides used have their own issues; there are problems with the type of agents, the dosage, and the frequency of application. 3. The fresh water added during replacement also has problems. 4. The high turbidity is caused by a large amount of iron ions in the sludge within the circulating water system, and the high turbidity itself is resulting from the use of biocides and algaecides. Please provide more relevant data so that we can analyze the situation together. Find the root cause.