Dirt is an extremely common phenomenon that is widespread in various heat transfer processes. According to Steinhagen's survey of 3,000 different types of heat exchangers in 1100 companies in New Zealand, more than 90% of the heat exchangers have different degrees of fouling problems, and the waste and loss caused by scaling is very serious. Therefore, the research on anti-scaling technology has attracted the attention of the scientific community and engineering and technical personnel, and it is an urgent problem to be solved in many industries and departments of the national economy.

At present, the anti-scaling methods used in the industry can be divided into chemical methods and physical methods.

1 chemical anti-scaling

The chemical methods mainly include softening method, acid treatment method, carbonization stabilization method and application of scale inhibitor. The first three methods have a narrow application range due to high cost or corrosion of equipment. The scale inhibitor is widely used at home and abroad. The scale inhibitor is a general term for a class of chemicals, and the addition of it can prevent or prevent the formation of scale.

1.1 Natural Dispersant
In the early 1960s, natural organic substances such as tannins, sulfonated tannins, lignin, starch, modified starch and carboxymethyl cellulose were mainly used. These natural scale inhibitors are widely available, inexpensive, non-toxic and biodegradable. However, the content of impurities is high and the amount is large. Currently, only a small amount of commercial compound formula is still used.

1.2 Homopolymer
Polyacrylic acid (PAA), polymethyl endoic acid (PMAA), polyacrylamide (PAM), polymaleic acid (anhydride) (PMA and HPMA) and other homopolymers were in the late 1960s and 1970s. Initially developed, they are all anionic polyelectrolytes.
Polyaspartic acid (PASP) is a new type of scale inhibitor developed by Donlar in the United States in the early 1990s. It contains no phosphorus in the molecule and is biodegradable. It is a green water treatment agent with excellent scale inhibition. performance. PASP has good biodegradability and is similar to glucose degradation performance. The degradation rate is over 73% within 28 days, and it has no harmful effects on the environment.
Polyepoxysuccinic acid (PESA) has no P in the molecular structure, no N, and is easily biodegradable. It is a green water treatment agent. It has good synergistic effect and certain corrosion inhibition performance when combined with various agents such as phosphate and 2-phosphinobutane-1,2,4 tricarboxylic acid.

1.3 Copolymer
Since the homopolymer has a single species and can only inhibit CaCO3 scale, since the 1980s, two-dimensional, ternary and multi-component water-soluble copolymers with excellent performance have been developed at home and abroad. They are characterized by not only inhibiting CaCO3 scale, but also inhibiting the dispersion of calcium phosphate scale, zinc phosphate, iron oxide, and mud, and some have special effects, such as inhibiting silicon scale and even participating in slowing down. Etc.
Acrylic copolymers are a class of polymers in which acrylic acid is used as a main monomer and one or more monomers are copolymerized. The main role of such scale inhibitors is the -COO- group in the polymer, which has strong chelating ability to Ca2+, Mg2+, Fe2+, etc., not only dispersing, but also interfering in the inorganic scale crystallization process. The crystals are normally aligned to achieve scale inhibition and flocculation at higher molecular weights.
Maleic acid (anhydride) copolymer is a kind of scale inhibitor which is copolymerized with maleic acid (anhydride) or hydrolyzed maleic anhydride as monomer and has better resistance to CaCO3, CaSO4 and BaSO4. Effect. The terpolymer has maleic acid/vinyl acetate/styrene copolymer, maleic anhydride/acrylic acid/acrylamide copolymer, maleic acid/ethylene glycol ester/acrylic acid copolymer, etc., all of which have good scale inhibition. Performance has its own characteristics.
The outstanding advantage of the sulfonic acid copolymer is that it is not affected by the presence of metal ions in the water in terms of scale inhibition, and has good inhibition to phosphate scale, sulfate scale, magnesium hydroxide scale, CaCO3 scale, etc., especially for calcium phosphate scale. It can effectively disperse the particles, stabilize the metal ions and the organic phosphonic acid, has a long-lasting drug, is easy to gel, and has a certain corrosion inhibition effect.

1.4 phosphorus and scale inhibitor
Inorganic polyphosphate is a scale inhibitor with good corrosion inhibition properties and was widely used in water treatment in the 1960s. A disadvantage of polyphosphates is that they hydrolyze, especially at high temperatures. After hydrolysis, the scale inhibition and corrosion inhibition performance is lowered, and the orthophosphate formed by hydrolysis is easy to form Ca3(PO4)2 scale with a higher solubility product of Ca2+ in water.
Organic phosphonic acid was developed in the late 1960s and was widely used in circulating cooling water treatment in the 1970s. It forms a chelate with calcium and many metal cations, stabilizes water containing iron and manganese, forms a protective film on the surface of the metal, acts as a corrosion inhibitor, and also has a critical value effect and synergistic effect. It is non-toxic. Or low toxicity agents. It has good chemical stability, is not easy to hydrolyze, and is resistant to high temperature. It does not form calcium phosphate scale due to the formation of orthophosphate during use.
The molecular structure of the organic phosphine carboxylic acid contains a phosphonic acid group and a carboxylic acid group. Therefore, it has both scale inhibition and corrosion inhibition properties, and is compounded with other water treatment agents, and has good synergistic performance.
Phosphonocarboxylic acid (PCA) is formed by copolymerization of an inorganic monomer hypophosphorous acid with other organic monomers. It is characterized by the combination of a carboxyl group and a phosphate group on the same molecule. It has good scale inhibition performance and plays a certain role in corrosion inhibition.

2 physical anti-scaling

In 1945, Belgium's Vemelang successfully applied magnetic processing technology for the first time to prevent boiler scale formation and remove the previously deposited scale, creating a precedent for physical treatment. For half a century, various physical treatment techniques for water have emerged, such as electrostatic treatment, high-energy electron irradiation, electromagnetic treatment, and ultrasonic treatment. The physical processing equipment is relatively simple, the maintenance operation is simple, the service life is long, the running cost is low, no pollution problem, the formation of scale of the heat exchange equipment is reduced, and the original deposit can be removed, and therefore, in building materials, chemical industry, metallurgy, mine The fields of agriculture, medicine and medicine have been widely used.

2.1 Magnetic field anti-scaling
After the introduction of the "CEPI" magnetic field anti-scaling device in 1945, a large number of CEPI anti-scaling devices were used in Europe. In addition to domestic hot water boilers, there are more than 100 sea-going vessels installed in Norway. More than 500 such anti-scale devices have been installed in the enterprise. China's very early magnetic treatment anti-scaler appeared in 1959. In the 1970s, the former Soviet Union, the United States, and Japan successively set off the heat of magnetic processing research. The academic and business circles invested a large amount of manpower and funds to study magnetic processing, and obtained a large number of achievements and invention patents, and built large magnetic Processing equipment. After the 1980s, scientists conducted more in-depth research on magnetic processing and accumulated a large amount of experimental data. The industrial water treatment method recommended by the US Department of Energy in 1998, including magnetic field technology.
At present, the widely used electromagnetic anti-scaler CALC-TECH series products are designed based on the principle of alternating pulse electromagnetic field. They are installed outside the pipeline and do not change the structure of the pipeline system or disconnect the pipeline during installation. Its operating cost is very low, and the operating cost is only 65W of installed capacity, which is equivalent to 1/10 of the ion exchange method. The "super-sleeve internal magnetic processor" manufactured by Shanghai Puqiang Magnetic Equipment Factory uses the rare magnet material and has excellent magnetic properties. Its coercive force, large magnetic product energy and anti-aging demagnetization performance are significant. Improvement.
The magnetic field anti-scaling device is suitable for anti-scaling of the heat exchanger. According to reports, hundreds of thousands of small CFPI units in Europe are used in domestic heat exchangers. Also suitable for hot water boilers without evaporation and concentration. There are 400,000 boilers in China, the vast majority of which are heating boilers, and the heat exchangers of hot water boilers and thermal networks are mostly. Therefore, magnetic field processing has considerable potential for use.

2.2 Electric field anti-scaling
Electrostatic water treatment technology is one of the new technologies in the modern industrial field. In the late 1960s, the United States Niigata Washington Company successfully developed the first static electricity scale controller. Since then, in just a few years, hundreds of units have been used in the United States. Adopted by leading companies, it has a high evaluation of its practical effects and is widely used in water systems such as cooling cycle, heat exchange, refrigeration, and boilers. In the late 1970s, Japan developed another way. The electrostatic descaler was combined with a water tank and a degassing device for the feed water treatment of a steam boiler and a hot water boiler. The addition of the drug in the furnace was completely eliminated, and the purpose of preventing scale and corrosion was achieved. The US National Aviation Administration also introduced an electronic water processor. China is one of the earliest countries to study electrostatic anti-scaling methods. In 1975, it successfully developed the head static anti-scaler. Later, an electronic water processor and a high-frequency electric water processor were introduced. In the early 1990s, China's second-generation electrostatic cleaner series products were developed and mass-produced.
Electric field treatment is divided into two types: high voltage electrostatic method and high frequency electronic method. These two types of devices have the same function and the same advantages, but the applicable conditions are different. The electronic anti-scaler uses DC low voltage, and the electrostatic anti-scaler uses current high voltage. Although it is high voltage, but the current is very small, and the curing insulation measures are adopted, there is no safety problem. The anode of the electrostatic anti-scaler is made of tetrafluoroethylene. It is resistant to abrasion, corrosion, aging and non-adhesion. It can be used continuously for 20 years. There is basically no cleaning during use. The anode of the electronic anti-scaler is made of titanium alloy, and the surface is covered with a protective film so that it does not corrode, does not age, and has high strength.

2.3 Ultrasonic anti-scaling
An acoustic wave that is higher than the upper threshold of the human ear, called ultrasound. Power ultrasound, also known as "active application" of ultrasound, is a technique that uses higher power ultrasound to act on matter to alter or accelerate the physical, chemical, and biological properties or state of matter. Ultrasonic anti-scaling and enhanced heat transfer technology is an energy-saving and environmentally-friendly technology. Foreign countries such as South Korea and Russia have related products. At present, there are some ultrasonic anti-scaling devices on the market, but the application is not widespread. The research on ultrasonic anti-scaling mechanism is still not deep, and there is still a certain gap compared with other physical anti-scaling methods such as electric field, magnetic field or electromagnetic field, which affects the promotion of this technology.

2.4 Physical methods synergistic anti-scaling
The above physical anti-scaling method is widely used in the fields of chemistry, metallurgy, mining agriculture and medicine. However, most physical treatment technologies have little influence on some basic physical and chemical properties of water, and it is difficult to induce fundamental changes in the physical and chemical properties of water. Therefore, the effects of some physical treatment techniques in practical applications are limited by many factors. The application is not very extensive. In order to get better processing results, the physical anti-scaling technology began to turn to the combination technology of several processes coupled to each other.
2.4.1 Photon and magnetic field synergistic anti-scaling
Zheng Shaobo of Northeastern University proposed a new technique that uses photons to strengthen and stabilize the magnetic treatment effect of water. The physicochemical action of photons on the cooler under magnetic field is theoretically analyzed. It is concluded that the synergistic treatment of magneto-magnetism can reduce the formation of hard scale during cooling. Reduce the corrosiveness of water and kill bacteria in the water. The synergistic test of light waves and magnetic fields at different frequencies shows that the synergistic magnetic field treatment of infrared light is excellent.
2.4.2 Laser and electric field synergistic anti-scaling
Xia Mao et al. use "laser electric field to control active oxygen" as the theoretical basis, using laser and high-frequency electric field and single-chip control technology, which has many functions such as descaling, anti-scaling, sterilization, algae-proof, anti-corrosion and water purification. The specific electric field can change the crystal form of CaCO3, inhibit the production of calcite crystal salts (hard scale), and provide energy for producing aragonite crystal salts (soft scale) to achieve anti-scaling purposes.
2.4.3 Electromagnetic field combined with filtration
Prof. YICho from Drexel University in the United States used an electromagnetic field combined with filtration to conduct anti-scaling experiments. Studies have shown that after electromagnetic field treatment, the crystals aggregate and the particles become larger, and then intercepted by the filter device. Only a small amount of crystals enter the heat exchanger, reducing the scale. Formation.
2.4.4 Combination of electromagnetic field and membrane technology
Chen Jinhui from the School of Environmental and Energy Engineering of Beijing University of Technology combines membrane technology with electromagnetic technology to conduct experimental research on anti-scaling and scale-reducing heat transfer technology under cold conditions under the action of low-frequency electromagnetic fields. The results show that under the action of electromagnetic field, the fouling crystal changes from dense to loose. After filtration through the membrane, the amount of crystal is reduced, which plays a role in anti-scaling.
2.4.5 Ultrasound field cooperates with O3
Liu Tianqing of Dalian University of Technology studied ultrasound and O3 to control the growth of bioscale. The treated biofouling thickness was significantly lower than the biofouling in the untreated control tube. He also performed a bioscale removal test. After the bioscale was treated with O3 and then treated with ultrasound, more than 90% of the biofouling could be removed, which was much more effective than the addition of O3 and ultrasound alone.

3 Outlook
Heat exchange is an important chemical unit. The scaling of heat exchanger equipment on the wall is very common, causing huge losses to the industries of various countries. It is an urgent problem to be solved in many industries and sectors of the national economy. Especially in the evaporation of NaCl, KCl, NaOH and other salts, alkali solution evaporators and evaporation equipment such as sugar, food, paper, seawater desalination, wastewater treatment, and reboilers in petroleum and chemical rectification towers, due to the liquid The precipitation of dissolved solid matter is more serious. For half a century, people have paid great attention to the study of dirt problems, and proposed many techniques and methods to prevent fouling and enhance heat transfer.
With the increasing awareness of human environmental protection, the environmental protection requirements for anti-scaling are also increasing. The international advanced anti-scaling technology is tending to develop green industry with high efficiency, low toxicity, no harm, multi-function and compounding.