Overview
When the solubility limitations of the constituents of water constituents are surpassed, a scale forms on the heat transfer surface. Impurities in the water precipitate directly on heat transfer surfaces, causing boiler scale. In other ways, suspended in the water settles out on the metal, hardening and adhering to it, causing boiler scale. Impurities concentrate during the evaporation process in a boiler. This can generate hot areas by interfering with heat transfer. As a result, overheating occurs in the local area. The solubility limitations of mineral substances are exceeded. Scaling occurs as a result of higher temperatures and solids concentrations at the tube/water interface.
The formation of crystalline precipitates on the boiler’s walls obstructs heat transfer. This can lead to hot spots, which can lead to localized overheating. They’re more harmful if they don’t conduct much heat. When the solubility limitations of the elements of water are surpassed, resulting in the precipitation of compounds across the heat transfer surface, scale is created. Scales are calcium and magnesium compounds that are highly insoluble in water.
What is the Process of Scale Formation in Boilers?
Scale forms when contaminants from the feed water precipitate on the heat transfer or metal surface of the boiler.
The deposits harden and concentrate during evaporation, obstructing heat transport and causing hot patches, which finally leads to local overheating. Impurities mainly cause deposit formation in the feedwater, such as calcium, magnesium, iron, silica, and aluminium. Salts that aren’t totally insoluble in boiler water cause scale to form. As a result, the salts are soluble and precipitate on the surface. Deposit formation is mainly causing sue to impurities in the feedwater such as calcium, magnesium, iron, silica, and aluminium. Scales forms when ions in the boiler water are not totally insoluble. As a result, soluble salts reach the surface and precipitate.
Scaling in boilers mainly by the presence of calcium and magnesium salts, as well as a high concentration of silica in the boiler’s water alkalinity. Scaling in boilers is mostly by the presence of calcium and magnesium salts, as well as a high concentration of silica in the boiler’s water alkalinity. Granular or porous carbonate deposits are common. Large and tangled calcium carbonate crystals generate dense scales in boilers. Suspending carbonate deposits in an acid solution causes carbon dioxide bubbles to effervesce from the scale, which we will be using to identify them.
As the crystals are more minor and link together, the sulphate deposit is denser than the carbonate deposit. When exposed to acid, the sulphate deposit becomes brittle and does not easily pulverize. High-silica deposits are rigid and have incredibly tiny crystals, resulting in a dense scale buildup in boilers. The scale is brittle and pale in color, making pulverisation difficult. Hydrochloric acid renders it insoluble.
Drawbacks:
Scaling has several major disadvantages, including:
- In comparison to a boiler without scales, the amount of fuel required for the same boiler output would be more.
- Because the conductivity of the sodium sulphate scale is around a hundredth that of steel, it significantly slows down heat flow. A tiny layer of scale on the metallic surfaces of the boiler can diminish its efficiency by 20%.
- Due to the restriction in heat flow, the metal becomes increasingly hot, making it more susceptible to deformation and breakage.
- Scale layers operate as an insulator, slowing heat transfer from heated zones to the water.
How is scaling caused?
Because calcium and magnesium salts (carbonates or sulphates) are less soluble in hot water than cold water, they induce scaling. It can also be due to silica concentration that is excessively high in comparison to the alkalinity of the boiler water.
A carbonate deposit is typically granular, but it can sometimes be quite porous. Calcium carbonate crystals are huge, but they are generally matted together with finely divided particles of other materials to make the scale appear solid and homogeneous. It’s easy to spot a carbonate deposit by dipping it in an acid solution. The scale will emit carbon dioxide bubbles.
A sulphate deposit is substantially tougher and denser than a carbonate deposit because the crystals are smaller and cement together more securely. When placed into acid, a Sulphate deposit is brittle, difficult to pulverize, and does not effervesce.
A high silica deposit is extremely hard, almost porcelain-like. Silica crystals are exceedingly tiny, resulting in a dense and impermeable scale. This scale is incredibly hard to pulverize since it is so fragile. It is a very light-color substance that is not soluble in hydrochloric acid. Iron deposits are quite dark in color, either because of corrosion or because of iron contamination in the water. Magnetism is ordinary in iron deposits in boilers. In heated acid, they dissolve and produce a dark brown solution.
Causes of Scale Build-up
If left unchecked, scaling reduces the boiler’s efficiency by serving as an insulator and retarding heat flow. In addition, scale buildup will eventually cause the tube to overheat and burst. Corrosive attack beneath boiler deposits can also produce clogging or partial obstruction. Boiler deposits, in general, can reduce operational efficiency, cause boiler damage, result in unplanned boiler outages, and raise cleaning costs.
Silica Scaling in Boilers
Silica can evaporate into steam at operating pressures of as low as 28 bars. The solubility of silica increases as steam temperature rises, making it more soluble. The factors that generate vaporous silica carryover have been studied and documented extensively. Silica is mainly distributing in a specific ratio, according to research. Under any set of boiler settings utilizing demineralized or evaporated grade make-up water, it is distributed between the boiler water and the steam. This ratio is affected by two factors: boiler pressure and boiler water pH. The ratio’s value climbs virtually logarithmically as pressure rises but declines as pH rises.
Bottom Line
The following are some methods for preventing scale formation in boilers:
- Scaling is mainly due to the presence of insoluble salts, calcium, and magnesium in the feed water of a boiler. Before us ing boiler water for activities, it’s critical to make sure we have treat them appropriately.
- Water softeners: Installing water softeners in the steam boiler might assist avoid limescale buildup.
- Cooling Water Inhibitors: Cooling water inhibitors are helpful in increasing salt solubility and preventing boiler scaling.
- Scale Removal: A wire brush or a scraper can be used to remove loosely formed scales on a boiler surface.
Scaling can be hazardous to a steam boiler because it increases the amount of fuel required, raises the cost of energy, and diminishes heat transmission and efficiency. If we ignore scaling, then it can result in a loss in heat efficiency by acting as an insulator, slowing down heat transfer. If scaling is ignored, it can result in a loss in heat efficiency by acting as an insulator, slowing down heat transfer.
You can reach out to us for additional information about our approaches in removing the scales in boilers or to learn more about Jateen Trading Co. We’ll get back to you as soon as possible! Do you find this article interesting? Then please check out the rest of the blogs too. We’re sure that you’ll find them fascinating and valuable as well.
