What is the common method of softening hard water?

There are many ways to soften hard water and avoid scale deposits. The methods that are often used are:
1) Ion exchange method: a specific cation exchange resin is used to replace calcium and magnesium ions in water with sodium ions. Since the solubility of the sodium salt is high, scale formation due to an increase in temperature is avoided. This method is currently the most common standard method. The main advantages are: stable and accurate results and mature technology. The hardness can be reduced to zero. The softened water equipment in this manner is also commonly referred to as an "ion exchanger" (usually referred to as a "sodium ion exchanger" because it is mostly a sodium ion exchange resin).
2) Lime method: Lime is added to the water, which is mainly used to treat high-hard water with a large flow rate, and can only reduce the hardness to a certain range.
3) Dosing method: adding a special scale inhibitor to the water can change the characteristics of the combination of calcium and magnesium ions and carbonate ions, so that the scale can not be deposited and deposited. There are many scale inhibitors currently available in the industry. The characteristics of this method are: one-time investment is small, and the adaptability is wide; but when the water volume is soft, the running cost is high. Due to the addition of chemical substances, the application of water is greatly restricted, and generally cannot be applied to drinking, Food processing, industrial production and other aspects. It is rarely used in the civilian sector.
4) Electromagnetic method: The use of a certain electric or magnetic field in water to change the characteristics of ions, thereby changing the deposition rate of calcium carbonate (magnesium carbonate) and physical properties during deposition to prevent the formation of hard scale. Its characteristics are: small equipment investment, easy installation, low operating cost; but the effect is not stable enough, there is no uniform measurement standard, and since the main function is only affecting the physical properties of scale within a certain range, the use of treated water Time and distance have certain limitations. It is mostly used for commercial (such as central air conditioning, etc.) circulating cooling water treatment, can not be applied to industrial production and boiler feed water treatment (and because the mechanism of this equipment has not been truly theoretically confirmed).
5) Membrane separation method: Both nanofiltration membrane (NF) and reverse osmosis membrane (RO) can intercept calcium and magnesium ions in water, thereby fundamentally reducing the hardness of water. The characteristic of this method is that the effect is obvious and stable, and the treated water has a wide application range; however, the inlet water pressure has high requirements, and the equipment investment and operation cost are high. It is generally less used for special softening treatments.
According to actual experience and characteristics, the most common method used in industrial boilers and industrial production is the ion exchange method (currently basically standard equipment). In general, the term "softener" generally refers to such equipment.
In the fields of catering, food, chemical, pharmaceutical, air conditioning, industrial circulating water, etc., the ion exchange method is also used to treat the hydration.
In small water boilers, heat exchangers and other applications, the dosing method is often used.
Central air-conditioning in the commercial field and industrial cooling water with a low temperature (up to a maximum temperature of about 60 degrees) are mostly treated by electromagnetic method, that is, all circulating water treatment, and in most cases, ion exchange is used with supplementary water. The method of treatment or circulating water is medicated to ensure the effect.

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