Let's first understand what is demineralized water
In daily life, we often see scales on the inner wall of the kettle after long use. What is the reason for this? It turned out that the water we used contained many inorganic salts, such as calcium and magnesium salts. These salts cannot be found with the naked eye in water at normal temperature. Once they are heated and boiled, a lot of calcium and magnesium salts are precipitated as carbonates, and they form scales close to the wall of the pot. We usually express the content of calcium and magnesium ions in water as an index of "hardness". A hardness of 1 degree is equivalent to 10 mg of calcium oxide per liter of water. Water below 8 degrees is called soft water, those above 17 degrees are called hard water, and those between 8 and 17 degrees are called moderate hard water. Rain, snow, rivers, rivers, and lakes are all soft water, spring water, deep well water, and sea water are all hard water.
Let's look at the difference between demineralized water and other waters.
Raw water refers to untreated water. In a broad sense, water before entering the water treatment process is also referred to as raw water for the water treatment. For example, water sent from a water source to a clarifier for treatment is called raw water.
Demineralized water refers to water whose hardness (mainly calcium and magnesium ions in water) removes or reduces to a certain degree. In the process of water softening, only the hardness decreases, while the total salt content does not change.
Demineralized water refers to water that is removed or reduced to a certain extent by salts (mainly strong electrolytes dissolved in water) in the water. Its electrical conductivity is generally 1.0 to 10.0 μS / cm, resistivity (25 ¡ã C) (0.1 to 1.0) ¡Á 106Ω ¡¤ cm, and salt content is 1 to 5 mg / L.
Pure water refers to the strong electrolytes and weak electrolytes in water (such as SiO2, CO2, etc.), water that is removed or reduced to a certain degree. Its electrical conductivity is generally 1.0 to 0.1 μS / cm, and the electrical conductivity (1.01.0 to 10.0) ¡Á 106Ω ¡¤ cm. The salt content is <1mg / L.
Ultrapure water refers to water that is almost completely removed from the conductive medium in the water, and at the same time non-dissociated gases, colloids, and organic substances (including bacteria) are also removed to a very low level. Its electrical conductivity is generally 0.1 to 0.055 μS / cm, the resistivity (25 ¡ã C) ﹥ 10 ¡Á 106Ω ¡¤ cm, and the salt content ﹤ 0.1 mg / L. The ideal pure water (theoretically) has a conductivity of 0.05 μS / cm and a resistivity (25 ¡ã C) of 18.3 ¡Á 106Ω ¡¤ cm.
What is demineralized water treatment?
The strongly acidic cationic resin is used to replace the calcium and magnesium ions in the raw water, and the boiler inlet water filtered by the water softening device becomes the softened water for boilers with extremely low hardness.
Ion exchange method: using a specific cation exchange resin to replace the calcium and magnesium ions in the water with sodium ions. Due to the high solubility of sodium salts, the occurrence of scale formation with increasing temperature is avoided.
Features and effects: The effect is stable and accurate, and the technology is mature. Can reduce the hardness to 0.
Scope of application: in the fields of catering, food, chemicals, medicine, etc., in applications such as air conditioning and industrial circulating water. The most commonly used standard way.
Electromagnetic method: Add a certain electric or magnetic field to the water to change the characteristics of the ions, thereby changing the deposition rate of calcium carbonate (magnesium carbonate) and the physical characteristics during deposition to prevent the formation of hard scale.
Features and effects: Small equipment investment, easy installation and low operating costs. The effect is not stable enough, there is no uniform measurement standard, and because the main function is only to affect the physical properties of scale within a certain range, the use time and distance of the treated water have certain limitations.
Scope of application: It is mostly used for the treatment of circulating cooling water in commercial (such as central air-conditioning, etc.), and cannot be used in the treatment of industrial production and boiler make-up water.
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 hardness can only be reduced to a certain range.
Features and effects: The effect is obvious and stable, and the treated water has a wide application range. There are higher requirements for water inlet pressure, and equipment investment and operating costs are higher.
Scope of application: Generally less used for special softening treatment.
Lime method: Add lime to the water.
Characteristic effect: The hardness can only be reduced to a certain range.
Scope of application: high-hard water with a large flow rate.
Dosing method: Adding a special scale inhibitor to the water can change the combination of calcium and magnesium ions and carbonate ions, so that scale cannot be precipitated and deposited.
Features and effects: Less one-time investment and wide adaptability. When the amount of water is soft, the running cost is partial.
Scope of application: Due to the addition of chemical substances, the application of water is greatly restricted. Generally, it cannot be used in drinking, food processing, industrial production and other aspects. It is also rarely used in civil applications.