On the use of liquid chlorine for disinfection in circulating water
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Our company produces ammonia and urea as by-products of the synthesis process. The water used for replenishing the circulating water comes from surface rivers and streams. Liquid chlorine is used as a disinfectant. Over time, the alkalinity of the circulating water decreases significantly; the concentration ratio is around 3, with the alkalinity of the water used for replenishment being 120, while that of the circulating water is only 100. The pH value is 7.5 for both the water used for replenishment and the circulating water. It seems that the system is continuously consuming alkalinity – I’m not sure why. Are there any users who have encountered a similar situation? ?
How are the fungicides applied, continuously or in pulses? Under normal circumstances, it should not be caused by liquid chlorine; rather, there must have been a leak in your company’s system, resulting in an ammonia leak. This leads to the growth of nitrifying and denitrifying bacteria, which convert ammonia into nitric acid and nitrous acid; both of these acids are moderately strong acids, resulting in a decrease in the pH of the recirculating water system.
I agree with the person above; there must be an ammonia leak in the system, which allows nitration bacteria and nitrosation bacteria to grow and convert ammonia into nitric acid and nitrous acid. However, if a large amount of chlorine is added, hypochlorous acid is generated, which also has a slight effect on the alkalinity of the circulating water.
When we were still using liquid chlorine, it was necessary to add liquid sodium carbonate to adjust the total alkalinity. It is not necessarily related to system leakage.
Alkalinity refers to the total amount of substances in a unit volume of water that can undergo neutralization reactions with strong acids. When liquid chlorine is added to water, chloride ions, chlorate ions, and hypochlorite ions are formed. The latter two ions also turn into chloride ions after being neutralized by sodium carbonate. As a result, the alkali in the system reacts with the chloride ions in the water, so it is normal for the alkalinity to decrease.
In other words, liquid chlorine consumes the alkali in water
When using liquid chlorine for disinfection and algae control, it consumes the alkalinity in water; this depends mainly on the amount of liquid chlorine added and the frequency of its application. Liquid chlorine is most effective at a pH level of 6.5–7.5; its effectiveness decreases when the pH is higher than this range. Therefore, in many cases, sulfuric acid must be added to adjust the pH in order to achieve the best results with liquid chlorine. The alkalinity consumed by liquid chlorine can be calculated.
We add liquid chlorine in a shock manner; we have a water storage capacity of 8,000 cubic meters, and about 30 kilograms of liquid chlorine are added per day. Meanwhile, there is indeed an ammonia leak in our system – severe corrosion of the heat exchangers was detected during a recent overhaul
It is recommended to promptly identify and address any issues, as well as replace the circulating water. Also, do you apply the fungicide every day? Generally, we adjust the frequency of addition according to the season. Once a month in winter, once every two weeks in spring and autumn, and once a week in summer. The addition should be done in a shock manner, but the concentration must be maintained at a consistent level; for oxidizing disinfectants, the residual chlorine level is generally kept between 0.3–0.5 ppm. It is also advisable to alternate between oxidizing and non-oxidizing agents to prevent bacteria and algae from developing resistance. If the water retention capacity is 8,000, and 30 KG of chemical is added per day, the dosage concentration is too low. Moreover, continuously adding such bacteria and algae can easily lead to the development of resistance, making it harder to control them. If there has been ammonia leakage recently, it is best not to use oxidizing disinfectants, as the ammonia in the water will also consume some of the liquid chlorine, resulting in a much poorer effect. It is recommended to use non-oxidizing bactericides in the near future, such as isothiazolinones and quaternary ammonium salts
We add 30 kilograms of liquid chlorine per day. Due to the fact that our chlorination system is relatively small, it takes about 4 hours to complete the addition process. In addition, we also apply non-oxidizing disinfectants twice a month, at a concentration of 70 PPM. Someone upstairs said that 30 kilograms of liquid chlorine is too little; so, based on your situation, how much should be used? ?