After boiling water in a kettle, why is there often limescale in it?

Because tap water is hard water, containing more impurities such as calcium and magnesium, boiling water is actually the process of softening it, and these impurities left after softening are scale.

This phenomenon is caused by too much calcium and magnesium ions in the water. Too much calcium and magnesium ions in water will lead to the formation of calcium carbonate, magnesium carbonate and other substances when heated. It appears as a loose white precipitate, which does not immediately form stubborn scaling, and this phenomenon itself is not harmful to the body, but it is unacceptable to the senses.

The composition of scale is mainly composed of calcium, magnesium, colloids and other substances, and the tap water with high hardness before purification is soluble in water before purification and filtration. For example, calcium and magnesium ions will adhere to the bottom of the pot to form scale; Purified tap water with high hardness.

After purification by the water purifier, the colloids in the water are filtered out, making calcium and magnesium ions insoluble in water. These are not visible in cold water. When boiled, it will float on the surface of the pin of the water.

At high temperature, calcium sulfate containing 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 calcium carbonate and magnesium carbonate that are insoluble in water, that is, water alkali. With the continuous evaporation and concentration of water, the water alkali content continues to increase, and scale is formed after reaching saturation.

Limescale has poor thermal conductivity and can lead to worsening heat transfer on the heating surface, wasting fuel or electricity.

If the scale adheres to the heating surface of the thermal equipment, it will endanger the safe and economical operation of the thermal equipment. Because the thermal conductivity of limescale is very poor, it hinders heat transfer. The heat absorbed by the furnace tube from the flame side cannot be well transferred to the water, and the cooling of the furnace tube is affected, so that the wall temperature rises, causing the furnace tube to bulge and cause a burst pipe.

There are several main ways to remove limescale:

Lemon limescale removal. Put the lemon slices into a kettle (the thinner the better, the purpose is to release the citric acid as much as possible), boil the water for about 5 minutes, and let the lemon source circle soak in water for 2 minutes after boiling.

Vinegar to remove limescale. If the kettle has scale, you can put a few spoonfuls of vinegar into the water and boil for an hour or two to remove the scale. If the main ingredient in the scale is calcium sulfate, the soda ash solution can be poured into the kettle and boiled to remove the scale.

Ion exchange scale removal method. A specific cation exchange resin is used to replace calcium and magnesium ions in the water with sodium ions, and the solubility of the sodium salt stove split chain is high, so the formation of scale caused by the increase of temperature is avoided.