Scaling in the boiler water treatment system
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The boiler is a horizontal low-pressure double-tube steam boiler; the water used as feedwater is softened with cationic resin, resulting in a water hardness of essentially 0. However, scaling has recently occurred – the scale is white in color, with a small amount of rust as well. Since the manufacturer has already started the furnace, it is not possible to take samples for analysis. With such low hardness, how does scale form? Where does scale in boilers mainly form? After lighting the furnace, the furnace water was taken. The boiler water is cloudy and has a dark yellow color; this is likely caused by rust. There is black sediment at the bottom of the bottle. The pH of the boiler water is 11.5; after filtration, it becomes a yellow, transparent liquid. Salt is added to the boiler water, and acid is used to adjust the pH. Once it becomes acidic, the water starts to become turbid, with a large amount of suspended particles appearing. Initially, it was suspected to be a silicate, but adding an appropriate amount of sodium fluoride did not cause any change. It dissolves in an alkaline environment but precipitates in an acidic one; what is this substance?
I’m here mainly to learn about this. The boiler likely wasn’t cleaned or coated prior to being put into use, so it’s normal for it to be dark yellow – that’s mainly due to rust. I’m not sure if any chemical agents are used in this system; it would be useful to check where the scale accumulates most in the kettles used at home, as it’s likely the same in the boiler as well. I’m also waiting for experts to tell me what the dirt is mainly made of; P
Just now, while testing the hardness, I added sulfuric acid and potassium persulfate to the boiler water and boiled it until it was almost dry. A black, sticky substance appeared at the bottom of the beaker; it was very sticky and could hardly be scraped off with a key. Adding acid and alkali does not cause it to dissolve either, but the viscous substance can be removed more easily. Both acidic and alkaline aqueous solutions change color, turning reddish-brown, with black substances suspended in the water. Furthermore, the filtered boiler water is transparent; it becomes turbid when acid is added, but once an alkaline solution is added to make it alkaline, the precipitate does not dissolve. I’m not sure why I’m really stuck; I don’t know who can help me out. Thank you!
I’m not sure if your scale problem has been resolved; I specialize in dealing with scale issues. If it still hasn’t been fixed, feel free to message me privately!