Causes of scale formation in kettle
Water containing minerals such as calcium (Ca) and magnesium (Mg) salts is called? Hard water? . Rivers, lakes, wells and springs are all hard water. Tap water is obtained from rivers, lakes or well water after precipitation, sediment removal and disinfection. Hard water, too. It has just rained and snowed. Does the water contain minerals? Soft water? . After the water is boiled, part of the water evaporates, and insoluble calcium sulfate (CaSO4, gypsum is calcium sulfate containing crystal water) is precipitated. The original dissolved calcium bicarbonate (Ca(HCO3)2) and magnesium bicarbonate (Mg(HCO3)2) are decomposed in boiling water, releasing carbon dioxide (CO2), which becomes insoluble calcium carbonate (CaCO3) and magnesium hydroxide (Mg(OH)2) and precipitates, and sometimes MgCO3 is generated. This forms a scale. When washing clothes with hard water, calcium and magnesium ions in the water combine with soap to form flocculent precipitation of calcium fatty acid and magnesium fatty acid, which is? Bean curd residue? The origin of. Washing clothes in hard water wastes soap. Scale grows in the kettle, which is not easy to transfer heat and wastes fuel. For a family, these wastes are not serious. For the factory, the problem is big. Some large boilers used for heating and steam supply in factories emit several tons of steam per hour, which is equivalent to burning several tons of water. According to the test, one ton of river water contains about 1.6 kg of minerals; The minerals in a ton of well water are as high as 30 kilograms. How amazing is the amount of scale deposited on the inner wall of boiler by hard water when transporting dozens of tons of steam a day! Scale is formed in a large boiler, just like building a thermal insulation stone wall between the steel plate and water on the boiler wall. The steel plate of the boiler can't touch the water, and the fire in the furnace keeps burning the steel plate red.
At this time, if the scale cracks, water will immediately leak to the high-temperature steel plate and evaporate quickly, resulting in the pressure in the boiler soaring and explosion. The power of boiler explosion is no less than a blockbuster! It can be seen that the harm of scale must not be taken lightly! Therefore, in factories, a proper amount of sodium carbonate (commonly known as soda ash) is often added to water, so that calcium and magnesium salts in water are precipitated and removed, and water becomes soft water. Passing hard water through ion exchange resin can also remove minerals and get soft water. The kettle and thermos bottle at home have grown scales. How to remove it? Carefully boil the kettle until it is just dry, and then soak it in cold water immediately. When it is hot, it is hot, and when it is dirty, it is cold. Because of the different degrees of expansion and contraction of aluminum and scale, the scale will break off from the boiler wall. The main components of scale are calcium carbonate and magnesium hydroxide, which can change chemically with acid. According to this principle, pour some vinegar (mainly CH3COOH, organic acid-acetic acid) into the kettle and heat it on the fire, only to see the dense small bubbles released on the scale, and the scale will be crushed. Using dilute hydrochloric acid (HCl, a strong acid) can also remove scale. Dilute hydrochloric acid? Digestion? Calcium carbonate is stronger than vinegar. But be very careful when handling it, and don't let hydrochloric acid corrode the handle. You know, hydrochloric acid and aluminum (Al) react easily. If it's an enamel kettle, the enamel hasn't fallen off yet, so it's good to use dilute hydrochloric acid to remove the scale. It is no problem to remove the scale from the thermos bottle like this.
What about the scale?
(1) Boil sweet potatoes (sweet potatoes, sweet potatoes) in a kettle, put more than half a pot of sweet potatoes, fill them with water, cook them, and then boil the water, so that scale will not accumulate. However, it should be noted that do not scrub the inner wall of the kettle after cooking the sweet potato, otherwise it will lose the descaling effect. For the old kettle that has been covered with scale, after being boiled once or twice by the above method, not only the original scale will gradually fall off, but also it can prevent the scale from accumulating again.
(2) Baking soda descaling When boiling water in an aluminum pot with scale, add 1 teaspoon baking soda and boil for a few minutes, and the scale will be removed.
3 Boil the eggs and scale the boiling pot. After a long time, it will be difficult to scale. If you use it to cook eggs twice, you will get the ideal effect.
(4) Scale removal of potato skin After being used in aluminum pot or aluminum pot for a period of time, there will be a thin layer of scale. Put the potato skin into it, add appropriate amount of water, boil it, and take it out for about 10 minutes.
⑤ Thermal expansion and cold contraction remove scale. Put the empty kettle on the stove to dry the water in the scale until there is a crack at the bottom of the kettle or a crack at the bottom of the kettle. Bang? When it rings, remove the kettle and quickly fill it with cold water, or wrap the handle and spout with a rag, hold it with both hands and quickly sit the boiled kettle in cold water (don't let water fill the kettle). Repeat for 2 to 3 times, and the scale at the bottom of the pot will fall off due to thermal expansion and cold contraction.
6 vinegar descaling If the kettle has scale, you can put a few spoonfuls of vinegar in the water and burn it for an hour or two, and the scale will be removed. If the main component of the scale is calcium sulfate, the soda solution can be poured into the kettle for cooking to remove the scale.
⑦ Mask In order to prevent scaling, put a clean mask in the kettle. When boiling water, the scale will be absorbed by the mask.
⑧ Magnetization Put a magnet in the pot, which not only does not scale, but also magnetizes boiled water, and has the function of preventing constipation and pharyngitis.
⑨ ion exchange descaling method: using specific cation exchange resin, calcium and magnesium ions in water are replaced by sodium ions. Due to the high solubility of sodium salt, scaling with the increase of temperature is avoided.
⑩ Method of membrane separation and scale removal: Both nanofiltration membrane (NF) and reverse osmosis membrane (RO) can intercept calcium and magnesium ions in water, which fundamentally reduces the hardness of water. The characteristics of membrane separation scale removal method are obvious and stable effect, and the treated water has a wide range of applications; However, the requirement for water inlet pressure is high, and the equipment investment and operation cost are high.
Anti-scaling method
An ion exchange method
There are two kinds of ion exchange resins. One is used to reduce the hardness of water to soft water for cleaning and bathing. This ion exchange resin is called sodium ion exchange resin. The second type is hydrogen ion exchange resin, which is used to appropriately reduce the hardness in water, so that drinking water will not form scale after boiling.
1) cleaning, bathing, etc. Sodium ion resin reacts with calcium and magnesium ions in water, quickly exchanging sodium ions into water and adsorbing calcium and magnesium ions in water, thus completely softening hard water and turning it into water without calcium and magnesium ions. Suitable for washing clothes, bathing, etc. Products using this resin are water softeners or water softeners.
2) Drinking: The hydrogen ion exchange resin reacts with some calcium and magnesium ions in water to reduce the hardness appropriately, so that the boiled water will retain a proper amount of calcium and magnesium ions in the water without remaining scale. Products using this resin, such as baby-specific water purification equipment, baby love the water baby-specific filter kettle, etc.
Physical filtration method
A membrane separation process of extracting fresh water from water by using the selective permeability of a selective membrane that can only penetrate water but not solute as the driving force. Reverse osmosis is also called reverse osmosis. It is commonly known as the pure water machine.
Three chemical treatment methods
A chemical agent that can prevent the formation of scale or inhibit its deposition and growth. Such as silicon phosphate crystal and trisodium (sodium hydroxide, trisodium phosphate and sodium humate) of water softener. It can be selected according to different usage situations.
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