What is limescale?
Limescale, commonly known as "water scale, water rust, water alkali", refers to the white block or powdery substance gradually formed in the container (such as pots, kettles, etc.) after the hard water is boiled. The main components are calcium carbonate, magnesium hydroxide, magnesium carbonate, calcium sulfate, magnesium sulfate, calcium chloride, magnesium chloride, etc. The thermal conductivity of limescale is very poor. If the limescale formed in the boiler is too thick, it will lead to reduced boiler efficiency, and in severe cases, it will cause the boiler tube to burst and cause a boiler accident.
| Name | limescale | Common name | water scale, rust, water alkali |
| Properties | white or yellowish white solid | Characteristics | poor thermal conductivity |
| Main ingredients | calcium carbonate, magnesium hydroxide, magnesium carbonate, calcium sulfate, etc | ||
Formation process
Under high-temperature conditions, calcium sulfate that is slightly soluble in water will precipitate due to the evaporation of water, and the carbonate in the water will combine with calcium and magnesium ions to form water-insoluble calcium carbonate and magnesium carbonate, also known as limescale. As the water continues to evaporate and concentrate, the limescale content continues to increase, and when it reaches saturation, limescale is formed.
limescale classification
(1) According to chemical composition, it can be divided into carbonate limescale, sulfate limescale, silicate limescale, and mixed limescale. The main components of carbonate limescale are calcium carbonate and magnesium carbonate; the main components of sulfate limescale and silicate limescale are calcium sulfate and silicate compounds respectively; mixed limescale is mostly a mixture of the above three types of limescale.
(2) According to physical properties, there are two types of limescale: limescale that is firmly bonded to the wall of the boiler drum and the wall of the tube, and sludge that is loose and easy to fall off.
Hazards of limescale
(1) Limescale has poor thermal conductivity, which will lead to worse heat transfer on the heating surface, thus wasting fuel or electricity.
(2) If limescale adheres to the heating surface of thermal equipment, it will endanger the safe and economical operation of thermal equipment. Because limescale has poor thermal conductivity, it hinders heat transfer. The heat absorbed by the furnace tube from the flame side cannot be transferred to the water well, and the cooling of the furnace tube is affected. In this way, the wall temperature rises, causing the furnace tube to bulge and cause the tube to burst.
Removal method
There are several ways to remove limescale:
(1) Descaling with lemon. Put lemon slices into a kettle (the thinner the better, the purpose is to release as much citric acid as possible) and boil the water for about 5 minutes. After boiling, soak the lemon in the water for 2 minutes to remove it.
(2) Descaling with vinegar. If there is limescale in the kettle, put a few spoons of vinegar in the water and boil it for one or two hours to remove the limescale. If the main component of the limescale is calcium sulfate, pour a soda solution into the kettle and boil it to remove the limescale.
(3) Descaling with ion exchange. Using a specific cation exchange resin, the calcium and magnesium ions in the water are replaced by sodium ions. Since the solubility of sodium salt is very high, the formation of scale with the increase of temperature is avoided.
(4) Descaling with membrane separation. Nanofiltration membrane (NF) and reverse osmosis membrane (RO) can intercept calcium and magnesium ions in water, thereby fundamentally reducing the hardness of water. The characteristics of the membrane separation descaling method are that the effect is obvious and stable, and the treated water has a wide range of applications; however, it has high requirements for the water inlet pressure, and the equipment investment and operating costs are high.
(5) Descaling agent removes limescale. The main ingredient of a descaling agent is hydroxytris(hydroxypropionic acid), and the raw material is safe, non-toxic and environmentally friendly. This descaling agent is easy to use and has good effects. It has a suitable dosage and relatively detailed instructions, and is very suitable for home users.
