Nowadays, the heat exchanger has been applied in various industries, and the effect is very obvious. The so-called favorable and flawed, the heat exchanger is also disadvantageous. For example, the heat exchanger is easy to scale, which is a common problem of the heat exchanger. It is also very troublesome. Today, we will analyze why the heat exchanger is fouled and how it is treated after scaling.

First look at why the heat exchanger will scale, the reason is very simple, the first point, when the heat exchanger equipment is running, the environment is a big reason for the formation of scale. For example, some heat exchangers are installed in the workshop. There is a lot of dust in the workshop. When the time is long, it becomes scale. Some heat exchangers are installed in the water. It takes a long time, and the suspended solids in the water are also easy to scale. The situation will produce scale. Look at the common types of scale.

1) Particulate soil: The accumulation of solid particles suspended in a fluid on a heat exchange surface. Such fouling also includes deposits of large solid particles formed by gravity on the horizontal heat transfer surface, so-called deposition of precipitated dirt and other colloidal particles.
2) Crystalline fouling: A deposit formed by crystallization of an inorganic salt dissolved in a fluid on a heat exchange surface, usually occurring during supersaturation or cooling. Typical soils are calcium carbonate, calcium sulfate and silica fouling layers on the cooling water side.
3) Chemical reaction fouling: dirt generated by chemical reaction on the heat transfer surface, the heat transfer surface material does not participate in the reaction, but can be used as a catalyst for the chemical reaction.
4) Corrosive soil: Corrosive fluid or fluid containing corrosive impurities that corrode the heat exchange surface. Generally, the degree of corrosion depends on the composition of the fluid, the temperature, and the pH of the fluid being treated.
5) Biofouling: In addition to seawater cooling devices, general biofouling refers to microbial fouling. It may produce slime, which in turn provides conditions for the propagation of biofouling, which is sensitive to temperature, and under suitable temperature conditions, biofouling can produce a layer of dirt of considerable thickness.
6) Solidified dirt: The dirt formed by the solidification of the fluid on the supercooled heat exchange surface. For example, when the water is below the freezing point, it solidifies into ice on the heat exchange surface. The uniformity of the temperature distribution has a great influence on this type of fouling.

Techniques to prevent scaling should consider the following:
1) Prevent the formation of scale;
2) preventing adhesion between the materials after fouling and deposition on the heat transfer surface;
3) Remove deposits from the heat transfer surface.

The measures taken to prevent scaling include the following:

I. Measures to be taken during the design phase In the design phase of the plate heat exchanger, considering the design of potential fouling, the following six aspects should be considered:
1) The heat exchanger is easy to clean and repair (such as plate heat exchanger);
2) After the heat exchange equipment is installed, it is not necessary to disassemble the equipment when cleaning the dirt, that is, it can be cleaned at the work site;
3) should take less dead zone and low flow rate zone;
4) The flow velocity distribution in the heat exchanger should be uniform to avoid a large velocity gradient and ensure uniform temperature distribution (such as baffle zone);
5) Under the premise of ensuring reasonable pressure drop and no corrosion, increasing the flow rate helps to reduce dirt;
6) The effect of heat transfer surface temperature on fouling formation should be considered.

2. Control of dirt in the operation phase
1) Maintaining the design conditions Because the excess heat exchange area is used when designing the heat exchanger, in order to meet the process requirements during operation, the flow rate and temperature should be adjusted, which is different from the design conditions, but should be bypassed by the bypass system. Maintain design conditions (flow rate and temperature) to extend run time and delay fouling.
2) Operation parameter control When the heat exchanger is running, the inlet material conditions may change. Therefore, the content of the fouling substance in the fluid, the particle size and the pH of the liquid should be tested periodically.
3) Maintenance measures Good solder joints, scratches, etc. generated during the maintenance process of the heat exchange equipment may accelerate the formation of the fouling process. Uneven distribution of the flow rate may accelerate the corrosion. The fluid leaks into the cooling water and provides nutrients for the microorganisms. The lack of precautions for dust in the surrounding air accelerates the formation of particulate deposits and chemical reaction scales in the heat exchanger. Hydrostatic testing with unclean water can cause accelerated formation of corrosive dirt.
4) Use of additives Different additives can be used to reduce or eliminate scale formation for different types of fouling mechanisms. Such as biocides and inhibitors, crystal modifiers, dispersants, flocculants, corrosion inhibitors, chemical reaction inhibitors and additives suitable for preventing fouling in combustion systems.
5) Reducing the concentration of fouling substances in the fluid Generally, the scaling increases with the concentration of the fouling substance in the fluid, and the particulate dirt can be removed by filtration, coagulation and precipitation; for the crucible, it can be ion exchanged or Chemical treatment to remove; ultraviolet, ultrasonic, magnetic, electric and radiation treatment of ultraviolet light is very effective in killing bacteria, ultra-strong ultrasound can effectively inhibit biofouling, and now the research also has magnetic field, electric field and radiation treatment device, the conclusion needs further study.

Chemical or mechanical cleaning technology Chemical cleaning technology is a widely used method. Sometimes it can be cleaned while the equipment is running, but its main disadvantage is that the chemical cleaning fluid is unstable and corrodes the heat exchanger and the connecting pipe. . Mechanical cleaning techniques are commonly used to remove dirt from the shell side, first removing the tube bundle, immersing it in a different liquid, so that the dirt is soaked and loosened, and then the scale layer is mechanically removed.

Mechanical online descaling technology

1) Using abrasive particles Solid particles are added to the fluid to rub the surface of the heat exchanger to remove dirt, but it is prone to corrosion on the surface of the heat exchanger.
2) Continuous descaling of sponge rubber ball is mainly applied to the removal of dirt on the cooling water side of the condenser of the power station. The sponge rubber ball is circulated through the pump in the heat exchanger tube. The rubber ball is slightly larger than the diameter of the pipe, and each glue passing through the pipe The ball slightly compresses the tube wall and erases the deposit during exercise.
3) Automatic brushing The heat exchanger pipe scrubbing facility consists of 2 outer covers and 1 nylon brush. The outer cover is installed at both ends of each pipe. Changing the direction of water flow allows the brush to be brushed along the pipe. The water flow is reversed to allow the brush to be brushed along the pipe. The water flow commutation is accomplished by compressed air and timing control of a four-way valve coupled to the pipe.