Location identification and treatment of internal leaks in acid coolers
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Last July, there was a leak in the anode-controlled shell-type acid coolers in my workshop; since there were 11 such coolers on site, it was not possible to determine promptly which one had developed the leak. Not long ago, an internal leakage incident occurred in the acid cooler of Jinlong Copper Sulfuric Acid Project Phase II, and it took several days to locate the source of the leak! It has a significant impact on production. This raises a question: in a site where there are multiple acid coolers, how can one identify the leak location promptly? In fact, most sulfuric acid manufacturers install online pH meters at the water-side outlet of the acid cooler to indicate the pH value of the cooling return water from the acid cooler, thereby enabling the detection of leaks within the acid cooler as soon as they occur. However, the PH monitoring systems of most manufacturers fail to perform as they should. Why is that? In my opinion, there are two main reasons: 1. The pH meter is installed using a water inlet pipe, and this pipe tends to get clogged, causing the pH meter to stop working ； 2. The pH meter is malfunctioning ； 3. The PH monitoring system does not have an alarm function (or a trend chart is not provided); once acid leaks into the circulating water and starts circulating, it becomes difficult to determine the situation.
Ah, our acid coolers used to leak frequently as well, but we managed to detect the leaks in time by using two methods: the first was a pH meter at the outlet of the acid cooler, and the second was using pH test strips. Of course, it’s also necessary to conduct checks every hour at the circulating water station. If a leak goes unnoticed for half a day, it might be difficult to locate the source of the leak, as the pH level throughout the entire system becomes very low, rendering the pH meter and test strips ineffective. As for preventive measures going forward, it’s sufficient to carry out inspections once an hour, or to display the pH readings in the control room; it’s okay if the leak is detected within about an hour, as the circulation rate during that time isn’t enough to completely replace the water in the cooling tank. 1. The water flow connected to the pH meter is visible; if something goes wrong, just clean it. 2. A pH meter is much simpler than an acid concentration meter, right? 3. Isn’t it required to conduct inspections once an hour? This post was last edited by Papua New Guinea on 2008-1-18 at 16:57
Yes! Inspections in many sulfuric acid plants are not proper and are merely a formality.
First, look at the current of the potentiostat; the current in the anode protection shell-type acid cooler with internal leakage will increase significantly.
Our company’s acid cooler was replaced with a new one in December due to a leak. I feel that when there is a slight leak in the acid cooler, it’s not easy to detect, after all, the amount of water circulating is large; by the time the leak becomes more severe, it’s already too late. It is important to detect issues promptly; it is best to use a conductivity meter for monitoring on the water side and to analyze any abnormal data.
In 1988, our company acquired 2 anodic protection shell-type acid coolers from the Canadian company Kemiti. One of these coolers developed leaks after being in use for 3 years; the main cause was excessive flow rates. After several attempts to seal the leaks, it finally became unusable after another 2 years. Kemiti provides specialized tools for sealing leaks, including stainless steel plugs and **guns, and it usually takes 2–3 hours to complete the sealing process. The other absorber is still in use; it has been in service for 20 years now. Later, domestic acid coolers were used, and no leaks have occurred. The domestic unit (used to replace the imported one that became obsolete) is also 15 years old.
Leaks in acid coolers are indeed a very troublesome issue, especially since there are many manufacturers of such coolers, and it’s often difficult to determine which one is leaking. Several friends above have offered some excellent suggestions and insights. I would like to add a few personal opinions for everyone’s reference: 1. Each acid cooler should be equipped with its own inlet and outlet pipes, which should then be combined together ； 2. Methods such as pH testing are not reliable; one can try to determine whether there is acid leakage by measuring conductivity. It is not a viable approach to determine leakage by checking the acid concentration. 3. At present, the vast majority of acid coolers use a pump-after configuration, with the acid pressure being higher than the water pressure; therefore, it is easier to identify and diagnose leaks in the heat exchange tubes ； 4. Manual sampling for testing the pH of circulating water is more effective; in many factories, pH meters are essentially useless. If not properly maintained, they are not repaired even when damaged, and operators rely heavily on them. 5. The sampling point must be at the water outlet of the acid cooler, as this is where it is possible to more accurately determine whether there is a leak. At the inlet, the pH value decreases after passing through the cooling tower and supplementary water, making it impossible to determine whether it is acid leakage from this unit that causes the pH drop or some other factor ； 6. Strengthen the monitoring of water quality, as chloride ions, algae, and dirt can all cause corrosion of the heat exchange tubes. In particular, it is important to monitor the chloride ion content in the water; the concentration in the raw water should generally not exceed 50PPM. With a concentration multiplication factor of up to 2-3, the chloride ion concentration in the water at the outlet after short periods of time is 100-150PPM. Scaling of heat exchange tubes can easily lead to an accumulation of chloride ions beneath the scale; therefore, scaling must be removed regularly, and water treatment chemicals such as scale inhibitors, dispersants, bactericides, and algaecides should be added to the circulating water. 7. The static pressure in the water system piping should be as low as possible compared to that in the acid piping, in order to prevent water from flowing back into the acid cooler in case of a leak in the heat exchange tubes during shutdown, thereby avoiding corrosion. This post was last edited by 30dman on 2008-1-28 10:11]
I agree with the view for Building 7#, especially point 1: each acid cooler should have its own inlet and outlet pipes, which should then be combined together； 2. Methods such as pH testing are not reliable; it is possible to try determining whether acid is leaking by measuring conductivity, but it is not advisable to determine whether there is a leak by checking the acid concentration.
Online pH meters often fail to function properly, mainly due to the fact that the relevant technology is not yet mature or reliable. Numerous sulfuric acid production plants have suffered as a result of this issue. The reason for these failures could be the prolonged use of circulating water without replacement, which leads to a deterioration in water quality. To identify the points where acid is leaking from multiple acid coolers, I have a method that is commonly used in my factory: once acid leakage is detected, all the circulating water pumps are stopped, and all the circulating water is drained (including from the circulation tanks, circulation pipes, and acid coolers). Then fresh water is added, and all the pumps are started again. At the same time, the cooling water from each acid cooler (at the outlet of the acid cooler’s circulation system) is checked manually; this way, it becomes clear which acid cooler is leaking acid. This post was last edited by yangchun646 on 2008-1-27 13:23.]