Water softener technology description and softening principle overview
The softener mainly solves the scale problem caused by hard water, so the domestic water softener is very popular in the United States where the water quality is relatively hard.
Why soften water?
Natural water can be divided into hard water and soft water: water containing a lot of calcium and magnesium ions (inorganic minerals) is called hard water, otherwise it is called soft water. If the hardness of the water is caused by sodium carbonate or magnesium bicarbonate, this water is called temporary hard water. If the hardness of water is caused by sulfates or chlorides containing calcium and magnesium, then this water is called permanent hard water.
In short, water with a calcium carbonate content of less than 10 mg / L is a high standard soft water. In western developed countries, soft water is used as 90% of domestic water (including cooking, washing, bathing, etc.). ). Non-polluting rain, snow and dew are all natural soft water.
1. What is hard water?
Hard water is water containing minerals, mainly calcium and magnesium ions. The higher the calcium and magnesium ions, the harder the water. When you wash your face with hard water, calcium and magnesium ions interact with the soap to form water-insoluble calcium and magnesium soaps. This soap is like a gel-like sticky substance that is difficult to remove on the face. In this way, dirt on the original skin will not be removed and new dirt will increase. These sticky substances formed by dirt and calcium magnesium soap block the openings of the skin glands, not only block the skin’s excretory channels, form embolisms, stimulate the skin, but also affect the skin’s normal metabolism, leading to premature skin shrinkage and aging. Therefore, when washing your face, we should pay attention to choosing soft water with low hardness. In nature, well water and spring water have the highest hardness, lake water and river water have the medium hardness, while rain water, snow water and distilled water have the lowest hardness, so the latter three types of water are more suitable for face washing.
Water hardness is related to taste. Hard water is delicious and refreshing. Most mineral water has a high hardness, which makes people feel fresh and delicious, but the soft level is odorless. However, if you make tea and coffee with hard water, the taste will be affected. Some food processing water is more fussy. Hard water will affect food processing, which will easily cause protein precipitation, inorganic salt precipitation or hard cooking. Soft water is more suitable for beverage water. Boiler water should generally soften hard water, otherwise accidents will occur due to excessive scale. Alkaline water from thermos and showers, hard-to-scrub stains on tiles and sanitary ware in bathrooms, and spots on glassware are all caused by hard water. Hard water gradually blocked household water pipes, wasting energy, and shortening the service life of water heaters. Washing clothes requires more washing supplies, which can damage the cotton fabric and cause waste.
2. Organic pollutants are very harmful to the human body.
At present, organic pollution of water sources in China is very serious, and there are more and more types of organic substances. According to statistics, there are about 70,000 common organics. The presence of organics in the water can protect the colloid and improve its stability. It not only increases the difficulty of water treatment, but also makes it difficult for small toxic organic molecules to degrade and accumulate in the body. It has a strong triple effect (carcinogenic, teratogenic, mutagenic) or chronic toxicity. The harm of organic matter to the human body is often delayed. It can take a long time from discovery to onset, even 20-30 years. In addition, the combination of organic substances and chlorine disinfectants produces halogenated compounds, many of which have been proven to be cancer-causing agents. Among them are volatile trihalomethanes and non-volatile haloacetic acids, the latter being 50-100 times more carcinogenic than the former.
Soft water technology
How does the industry soften water?
At present, our understanding of household water treatment has a wrong consumption concept and consciousness: as long as the “drinking” part meets the standard and other areas use almost no water. In fact, in addition to drinking, domestic drinking water also includes food, bathing, laundry, and toilet flushing. In fact, one third of various substances in water are absorbed into the human body through the skin through bathing and the like. Good water can improve the washing power of water, reduce the amount of washing powder, reduce water environmental pollution, etc. Good water can also reduce the bad smell of flushing and improve the indoor environment. Therefore, in addition to the “drinking” part, people’s water for bathing, washing and washing should also be clean, hygienic and free from pollution. Brown et al. Studied the absorption of volatile organic compounds in water by the skin. According to adult drinking water 2 liters / day, baby drinking 1 liter / day, both bathing time is 15 minutes / day. The oral intake ratios were 63/37 and 40/60 for adults and infants, respectively. Andelaman reports on indoor respiratory intake caused by trichloroethylene in drinking water. Based on drinking 2 liters / person · day and bathing water consumption 40-95 liters / person · day, the respiratory intake of trichloroethylene in the shower is several times the intake of drinking water.
Therefore, the harmful effects of harmful substances in water on human health are not simply caused by drinking. According to foreign reports, the proportion of harmful substances in water absorbed by the human body is roughly: 1/3 is ingested by the oral cavity; 1/3 is absorbed by the skin during washing and bathing; and 1/3 is absorbed by the water vapor through the respiratory tract during bathing.
There are many places where water is used in the industry. Different treatment methods are used to achieve the required standards according to the quality of the water. The industrial method of demineralizing water is the ion exchange method.
Ion-exchanged water treatment refers to the use of ion exchangers to exchange the ions in the exchanger and the aqueous solution to produce a reversible exchange that conforms to the quantity rules of such substances, resulting in improved water quality without substantial (chemical) structure of the exchanger. Changing water treatment. In this water treatment method, only those cations that participate in the exchange reaction are called cation exchange water treatment; those that have only anions in the exchange reaction are called anion exchange water treatment; those that have both cations and anions in the exchange reaction are called cation and anion exchange Water treatment. Because the quality of raw water varies widely, and the quality of the effluent water is diverse, there are many types of ion exchange and a combination of water treatment methods. The use of these water treatment methods to soften, remove alkali and remove salt. When the ion involved in the exchange reaction is sodium ion Na +, this method is called sodium (Na) type ion exchange method, and this exchanger is called sodium (Na) type cation exchanger. Similarly, there is hydrogen (H ) Type ion exchange method and hydrogen (H) type cation exchanger.
Sodium ion exchange method is the most common water treatment method for industrial boiler feed water. When the raw water passes through the sodium ion exchanger, the cations such as Ca2 + and Mg2 + in the water exchange with the Na + in the exchanger, which reduces the hardness of the water and softens the water quality. Therefore, this method is also called the sodium ion exchange softening method.
(1) Exchange process
Carbonate hardness (temporary hardening) softening process:
Ca (HCO3) 2 + 2NaR——CaR2 + 2NaHCO3
Mg (HCO3) 2 + 2NaR——MgR2 + 2NaHCO3
Non-carbonate hardness (permanent hardening) softening process:
CaSO4 + 2NaR——CaR2 + Na2SO4
CaCl2 + 2NaR-CaR2 + 2NaCl
MgSO4 + 2NaR——MgR2 + Na2SO4
MgCl2 + 2NaR——MgR2 + 2NaCl
Can also be expressed by an ionic formula that combines the above reaction formula:
Ca2 + + 2NaR——CaR2 + 2Na +
Mg2 + + 2NaR——MgR2 + + 2Na +
(2) Regeneration process
In the process of sodium ion exchange, when the hardness of soft water appears and the residual hardness exceeds the water quality standard, the sodium ion exchanger is considered to have failed. In order to restore its exchange capacity, it is necessary to regenerate (or reduce) the exchanger. The regeneration process is a process in which a sodium chloride (NaCl) solution containing a large amount of sodium ions is restored to its exchange capacity through a failed exchanger layer. At this time, sodium ions are absorbed by the ion exchanger, and calcium and magnesium ions in the exchanger are replaced into the solution. The regeneration process of sodium ion exchanger can be expressed by the following reaction formula:
CaR2 + 2NaCl-2NaR + CaCl2
MgR2 + 2NaCl-2NaR + MgCl2
In the production of tritium, common salt (NaCl) solution is used as a regenerant. Because common salt is relatively easy to obtain, and the products (CaCl2, MgCl2) formed during the regeneration process are soluble salts, they are easily discharged with the regeneration solution. Most of the salt used for regeneration is industrial salt. The impurity content should not be too much. The salt solution should be used after being clarified and filtered. It is generally believed that the hardness of a 10% table salt solution should not exceed 40 mmol / L, and the suspended solids should not exceed 2%. When regenerating an ion exchanger, a clarified 8-10% salt solution is generally used. The total regeneration contact time varies with the degree of cross-linking of the ion exchange resin. For a strongly acidic styrene-based cation exchange resin with a general cross-linking degree of about 7%, the total contact time of the regenerant and the resin should be at least 45 minutes.
The water softener is equipped with a filter material made of artificial food-grade resin material. The resin looks a bit like grit, but the resin particles are rounder and smoother. The resin can remove hard minerals in water by ion exchange. When the water softener works, most of the calcium and magnesium ions in the source water are replaced. Under a certain pressure flow, the source water flows through the exchangeable sodium contained in the resin of the container (water softener) containing the ion exchange resin, and performs ion exchange with cations (Ca2, Mg2, Fe2, etc.). ), The Ca2 and Mg2 ion content of the effluent of the container is greatly reduced, and the effluent is softened water with extremely low hardness. When an ion resin adsorbs a certain amount of calcium and magnesium ions and then saturates, it must be regenerated-. The resin layer is soaked with saturated concentrated brine to regenerate and replace the calcium and magnesium ions adsorbed by the resin, restore the exchange capacity of the resin, and discharge waste liquid and sewage. Before regeneration, backwash with water from top to bottom. Backwashing serves a dual purpose. One is to loosen the compacted resin during operation by backwashing, which is beneficial for the resin particles to fully contact the backwashing liquid. Second, the suspended matter accumulated on the resin surface during operation is also discharged with the backwash water, so the flow resistance of the exchanger will not increase. The most advanced automatic control system automatically completes the entire process of softening, back washing, salt absorption, slow washing, fast washing, and salt tank water injection.
Introduction to the principle of reverse osmosis
Reverse osmosis is one of the most effective water treatment methods in the prior art. Can effectively treat more than 95% of salts (such as calcium, magnesium and other hardness impurities), heavy metals and chemical residues in water. Reverse osmosis water treatment technology is now everywhere, such as desalination systems, electronic ultra-pure water purification systems, biochemical pharmaceuticals, kidney dialysis, cosmetics manufacturing, beverages, packaging water and even ordinary household filtration.
What are osmotic, osmotic and reverse osmosis
A membrane that is selective for permeable substances is called a semipermeable membrane. In general, a thin film that can penetrate only a solvent but not a solute is considered to be an ideal semi-permeable membrane.
When the same volume of dilute solution (such as fresh water) and concentrated solution (such as seawater or saline) are placed on both sides of the container, the middle is blocked by a semi-permeable membrane, and the solvent in the dilute solution naturally flows to the concentrated solution side through the semi-permeable membrane. The liquid level on the concentrated solution side is higher than the liquid level on the dilute solution by a certain height, and a pressure difference is reached to reach an osmotic equilibrium state. This pressure difference is the osmotic pressure. The osmotic pressure depends on the type of concentrate, and the concentration and temperature have nothing to do with the properties of the semipermeable membrane.
If a pressure greater than the osmotic pressure is applied on the concentrated solution side, the solvent in the concentrated solution will flow to the dilute solution, and the flow direction of the solvent will be opposite to the original infiltration direction. This process is called reverse osmosis.
Rhenium reverse osmosis is a pressure-driven separation method that separates solutes from solvents in a solution by selectively retaining a semi-permeable membrane. At present, it is widely used for the separation and concentration of various liquids. In the water treatment process, inorganic impurities, bacteria, viruses, organic matter, colloids and other impurities are removed from the water to obtain high-quality water.
Penetration phenomenon: the solvent penetrates the semi-permeable membrane from the low concentration solution
Flow to high concentration solution
At present, reverse osmosis membranes are mainly composed of two materials, one is acetate fiber and the other is polyamide.
Reverse osmosis technology is an advanced water treatment technology. In order to produce drinking water that meets the relevant drinking water standards, countries are increasingly applying reverse osmosis technology.
The World Health Organization (WHO) has established drinking water quality standards, which vary from country to country. Its formulation and implementation are often the responsibility of different sectors of the country. For example, in the United States, the Department of Environmental Protection