Why is corrosion severe in condensed water returning to the furnace? .
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This post was last edited by avebest on 2015-10-22 at 15:34. Next week I need to give a lecture on water treatment to the boiler operators; I’m in a hurry to prepare the materials… When inspecting boilers of 4t, 6t, and even 20t and 30t capacity, it’s common to find that some factories use condensate water as boiler make-up water. After being used for two or three months, the boiler drums and collectors turn as red as if they had been pickled. The technicians said that in some cases, after two years of use, the collectors even get perforated:funk: So, is corrosion caused by oxygen or acid in condensate water? Is it mainly carbon dioxide corrosion inside? Why does carbon dioxide in soft water not have such a strong effect? Untreated natural water isn’t that scary either……
“2.2 Mechanism of acid corrosion: CO2 enters the steam system; when the steam is condensed into a liquid state, CO2 dissolves in the water to form carbonic acid (H2CO3). H2CO3 is a weak acid; it releases only a small amount of H+ ions when ionizing in water. However, condensed water is relatively pure with low salt content and poor buffering capacity, so even a weak acid like H2CO3 can cause a significant drop in pH (see Table 1). At the same time, as H+ is continuously consumed during corrosion, the ionization equilibrium of 2-2 is disrupted, causing the reaction to proceed in the right direction and continuously producing H+ for use in the corrosion process, until H2CO3 is completely exhausted. ” Reading this passage, I feel it makes some sense, but it lacks a bit of persuasiveness
In the open recycling method, air enters the condensate recovery pipeline, which can easily lead to pipe corrosion. The reasons are as follows: (1) The dissolution of CO2 lowers the pH value of the condensate water system. The boiler make-up water is soft water prepared using sodium ion exchangers; it contains a certain amount of carbonate and bicarbonate ions. When heated, these ions decompose and enter the steam, and upon condensation they dissolve in the condensed water, thereby affecting the pH value of the water system
Our plant recycles condensate to the thermal deaerator; it seems that the deaerator is suffering from significant corrosion, but it’s oxygen-induced corrosion. The boiler drum is in better condition – it’s red in color, but that’s probably due to alkali effects
I’m not sure what the impact will be on our company’s condensate recovery water softening tank