There are three circulation systems in industrial refrigeration units, and scale problems are prone to occur in different circulation systems, such as refrigeration circulation system, water circulation system, and electronic control circulation system. Different circulation systems require tacit cooperation to achieve the goal of stable work.
Therefore, it is necessary to keep each system within the normal working range. Although the performance of various domestically produced industrial refrigeration equipment is relatively stable, if the necessary maintenance and maintenance are not performed for a long time, it will inevitably lead to a large number of scale problems. It not only leads to blockage of the equipment, but also affects the water flow of the equipment.
It has a serious impact on the overall performance of industrial refrigeration units, and even shortens the overall life of industrial refrigeration units. Therefore, cleaning scale in time is very important for industrial refrigeration units.
1. Why does the refrigerator have scale?
The main components of scaling in the cooling water system are calcium salts and magnesium salts, and their solubility decreases with the increase of temperature; when the cooling water contacts the surface of the heat exchanger, scaling deposits on the surface of the heat exchanger.
There are four situations of refrigerator fouling:
(1) Crystallization of salts in a supersaturated solution with multiple components.
(2) Deposition of organic colloids and mineral colloids.
(3) Bonding of solid particles of certain substances with different degrees of dispersion.
(4) Electrochemical corrosion of certain substances and microbial production, etc. The precipitation of these mixtures is the main factor of scaling, and the conditions for producing solid phase precipitation are: the solubility of certain salts decreases with the increase of temperature. Such as Ca(HCO3)2, CaCO3, Ca(OH)2, CaSO4, MgCO3, Mg(OH)2, etc. Second, as the water evaporates, the concentration of dissolved salts in the water increases, reaching a level of supersaturation. A chemical reaction occurs in the heated water, or certain ions form other insoluble salt ions.
For certain salts that meet the above conditions, the original buds are first deposited on the metal surface, and then gradually become particles. It has an amorphous or latent crystal structure and aggregates to form crystals or clusters. Bicarbonate salts are the main factor causing scaling in cooling water. This is because heavy calcium carbonate loses balance during heating and decomposes into calcium carbonate, carbon dioxide and water. Calcium carbonate, on the other hand, is less soluble and thus deposits on cooling equipment surfaces. Right now:
Ca(HCO3)2=CaCO3↓+H2O+CO2↑.
The formation of scale on the surface of the heat exchanger will corrode the equipment and shorten the service life of the equipment; secondly, it will hinder the heat transfer of the heat exchanger and reduce the efficiency.
2. Removal of scale in the refrigerator
1. Classification of descaling methods
The methods for removing scale on the surface of heat exchangers include manual descaling, mechanical descaling, chemical descaling and physical descaling.
In various descaling methods. Physical descaling and anti-scaling methods are ideal, but due to the working principle of ordinary electronic descaling instruments, there are also situations where the effect is not ideal, such as:
(1). The water hardness varies from place to place.
(2). The water hardness of the unit changes during operation, and the light rain electronic descaling instrument can formulate a more appropriate descaling plan according to the water samples mailed by the manufacturer, so that descaling will no longer worry about other influences;
(3). If the operator ignores the blowdown work, the surface of the heat exchanger will still be scaled.
The chemical descaling method can only be considered when the heat transfer effect of the unit is poor and the scaling is serious, but it will affect the equipment, so it is necessary to prevent damage to the galvanized layer and affect the service life of the equipment.
2. Sludge removal method
Sludge is mainly composed of microbial groups such as bacteria and algae that dissolve and reproduce in water, mixed with mud, sand, dust, etc. to form soft sludge. It causes corrosion in the pipes, reduces efficiency and increases flow resistance, reducing water flow. There are many ways to deal with it. You can add coagulant to make the suspended matter in the circulating water condense into loose alum flowers and settle at the bottom of the sump, which can be removed by sewage discharge; you can add a dispersant to make the suspended particles disperse in the water without sinking; The formation of sludge can be suppressed by adding side filtration or by adding other drugs to inhibit or kill microorganisms.
3. Corrosion descaling method
Corrosion is mainly due to the sludge and corrosion products sticking to the surface of the heat transfer tube to form an oxygen concentration battery and corrosion occurs. Due to the progress of corrosion, the damage of the heat transfer tube will cause serious failure of the unit, and the cooling capacity will drop. The unit may be scrapped, causing users to bear great economic losses. In fact, in the operation of the unit, as long as the water quality is effectively controlled, the water quality management is strengthened, and the formation of dirt is prevented, the impact of corrosion on the water system of the unit can be well controlled.
When the scale increase makes it impossible to use ordinary methods to deal with it, physical descaling equipment can be installed for anti-scaling and descaling operations, such as electronic descaling equipment, magnetic vibration ultrasonic descaling equipment, etc.
After the scale, dust and algae are attached, the heat transfer performance of the heat transfer tube drops sharply, which reduces the overall performance of the unit.
To prevent scaling and freezing of the refrigerant water in the evaporator during operation, there are two types of refrigerant water systems: open cycle and closed cycle. We generally use closed cycle. Because it is a sealed circuit, evaporation and concentration will not occur. At the same time, the atmosphere The sediment, dust, etc. in the water will not be mixed into the water, and the scaling of the refrigerant water is relatively slight, mainly considering the freezing of the refrigerant water. The water in the evaporator freezes because the heat taken away by the refrigerant when it evaporates in the evaporator is greater than the heat that the refrigerant water flowing through the evaporator can provide, so that the temperature of the refrigerant water drops below the freezing point and the water freezes. Operators should pay attention to the following points during operation:
1. Whether the flow rate entering the evaporator is consistent with the rated flow rate of the main engine, especially if multiple refrigeration units are used in parallel, whether the water volume entering each unit is unbalanced, or whether the water volume of the unit and the pump is running one-on-one. A machine group shunt phenomenon. At present, manufacturers of bromine chillers mainly use water flow switches to judge whether there is water inflow. The selection of water flow switches must match the rated flow rate. Conditional units can be equipped with dynamic flow balance valves.
2. The host of the bromine chiller is equipped with a refrigerant water low temperature protection device. When the temperature of the refrigerant water is lower than +4°C, the host will stop running. When the operator runs for the first time in summer every year, he must check whether the low temperature protection of the refrigerant water works and whether the temperature setting value is accurate.
3. During the operation of the bromine chiller air-conditioning system, if the water pump suddenly stops running, the main engine should be stopped immediately. If the water temperature in the evaporator still drops rapidly, measures should be taken, such as closing the refrigerant water outlet valve of the evaporator, opening the drain valve of the evaporator properly, so that the water in the evaporator can flow and prevent the water from freezing.
4. When the bromine chiller unit stops running, it should be carried out according to the operating procedures. First stop the main engine, wait for more than ten minutes, and then stop the refrigerant water pump.
5. The water flow switch in the refrigerating unit and the low-temperature protection of the refrigerant water cannot be removed at will.
Post time: Mar-09-2023