Why is the corrosion of the cathode rods in the two sets of acid coolers used for anodic protection in drying processes different?
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Our company has two sulfuric acid production units. One set is for acid production using \"sulfur,\" and the other is for acid production using \"sulfide concentrate.\" Two sets of acid coolers were used simultaneously. “The acid cooling coil for sulfur-based acid production was put into use in 2002, while the one for sulfur concentrate-based acid production was put into use in 2005. But during this maintenance work, we observed a phenomenon, particularly regarding 93% acid: when we pulled out the cathode rods, it was found that the cathode rods made of \"sulfur\" were practically unaffected by corrosion ； The cathode rods used in “sulfide concentrate” are severely corroded, having reduced in thickness to almost just the size of chopsticks. Our acid concentration remains between 93.7% and 94.5%. Both the current and voltage are within the normal range. Are there any other reasons? This post was last edited by Melody in the Rain on 2007-12-29 22:44.]
Could the excessive impurities in acid production from \"sulfur gold sand\" have an erosive effect on it?
The same equipment from the same manufacturer is being used. But the duration is different, that’s all.
With different durations, corrosion naturally varies
But our acid cooling exchangers for sulfur concentrate acid production were put into use in 2005. The acid cooling coil made of \"sulfur\" was introduced in 2002. However, the cathode rods used with “sulfur” show almost no corrosion over longer periods of time ； Moreover, the cathode rods used for “sulfide concentrate” with shorter durations suffer severe corrosion.
The acidity level, temperature, flow rate, and impurities present in the acid all have an impact; I recall that the acid cooler our company imported from Canada in the 1980s became unusable after just a few years due to excessive flow rates.
The flow rate is too high, causing rapid corrosion of the cathode rod; it is not possible to form a passivation layer, and ultimately the acid cooler gets corroded and becomes unusable
It’s difficult to draw a conclusion on this issue: 1. The material of the cathode rod (including the heat treatment applied to it) may vary, and it would be better to analyze the composition of the material to make a determination； 2. The operating conditions differ; the acid produced from pyrite contains many impurities in its dried form, which also has an impact on corrosion. The question is, which of the two factors above is the main one? In some sulfur-based acid production plants, the anode-protected acid coolers suffer from rapid corrosion; however, in our plant, where acid is produced from smelting flue gas, the conditions are even more severe than those in plants that use pyrite for acid production. Yet, over the past decade or so since these anode-protected acid coolers have been in use in our plant, no major problems have occurred.
Too high a flow rate will definitely have an impact, but its effect should be the same. Moreover, it also has a scouring effect on the shell. Perhaps there is a problem with the material, or it’s possible that different factories use different processing methods.
We tested the casing; the corrosion is mild, so it’s not a serious issue. We need to replace the cathode rod first.