How to dehumidify the refrigeration system of industrial refrigerators

How to dehumidify the refrigeration system of industrial refrigerators

The water content in the industrial refrigerator system comes from two aspects. One is that the vacuum is not in place, so that air and water vapor remain in the system. The other is that the industrial refrigerator refrigerant and lubricating oil have a certain water content. Controlling the moisture in the refrigeration system of an industrial refrigeration unit within the allowable range is the goal of dehumidifying the refrigeration system of an industrial refrigeration unit.

　　1. Water content control of industrial refrigerator refrigerant

　　The water content of Freon refrigerants commonly used should be controlled below 25PPm:

　　 Freon gas has very good chemical stability, generally it does not directly react with water. But when in contact with metal, it reacts slowly with water. This reaction is called the water addition reaction. The acid (such as HCI) generated in the reaction reacts with the oil to degrade the quality of the lubricating oil and generate precipitates. Corrosion occurs at the same time, damaging the insulation of the enclosed motor, or copper plating on compressor parts (that is, on high-temperature steel surfaces) such as the inner surface of the cylinder, pistons, connecting rods, crankshafts, etc., appearing "copper plating" precipitation). In severe cases, "carbon deposits" may even have adverse effects on the performance of the machine. Not only that, industrial refrigerator refrigerants affect (except pure lead) magnesium, magnesium alloys and aluminum alloys containing more than 1% magnesium. There will only be a little water, which will corrode these metals. However, if the industrial refrigerator refrigeration system is properly dried, copper plating will not occur. Therefore, the mixing of water into the refrigerant or the refrigeration system must be avoided as much as possible.

　　The reason why moisture enters the refrigeration system:

　　 1. The purity water content of the refrigerant itself exceeds the standard;

　　2, the water content of lubricating oil exceeds the standard;

　　3. During the pressure test of the refrigeration system, the vacuum degree of the vacuum test is not high or the system leaks, so that the air outside the system enters the system and brings moisture;

　　4. When charging the refrigerant, improper operation will bring air into the system.

　　 2. Dehumidification measures for industrial refrigerator refrigeration systems

　　 1. Vacuum carefully before charging refrigerant. The higher the vacuum, the better. Vacuuming is one of the means of dehumidification and drying of the system. The length of the system drying time is related to the size of the system container, the working capacity and efficiency of the vacuum pump, the indoor temperature and the amount of moisture in the system. Generally, when the temperature and pressure of the system reach 1.7°C and 5mmHg column, it can be considered that all the air in the system has been pumped out. Then a certain amount of nitrogen is added, and the industrial refrigerator system is evacuated again to reach the above temperature and pressure. It can be considered that the drying and vacuum requirements of the system have reached the required limit.

2. When the industrial refrigerator system is charged with refrigerant, the refrigeration is dried outside the machine, that is, a drying filter is installed in the charging pipeline. The drying agent includes calcium fluoride, silica gel, molecular sieve (artificial zeolite), etc. . Reduce the water content of the refrigerant entering the system to a certain extent.

　　3. Install a filter drier on the pipe before the high-pressure liquid pipe of the industrial refrigerator refrigeration system enters the thermal expansion valve to further remove the moisture and the deposits produced by the chemical reaction during operation. The desiccant generally uses 4A0 molecular sieve, and its saturated water absorption rate can reach 21-25% (mass). To prevent the desiccant powder from harming the system, currently most of the whole-core desiccants are used. When the desiccant filter is selected, the flow rate in the cylinder is generally selected 0.03m/s.

　　The desiccant used for the R134a system is XH7 (carbide) or 3×10-10M molecular sieve. The reason is that compared to R12, the solubility of water in R134a is lower. Therefore, in the R134a system, especially in the low temperature system, a desiccant with better water absorption performance is required, so the desiccant generally used in the R12 refrigeration system is obviously not suitable of.

　　 3. The refrigeration system of the desiccant dryer is composed of expansion valve, refrigeration compressor, water-cooled condenser, plate evaporator, etc.

The main engine of dehumidification dryer adopts imported single-machine two-stage semi-hermetic compressor. Each main engine constitutes an independent refrigeration cycle system. The plate layer and cold trap are respectively cooled by plate heat exchanger or condenser. The cold trap of the refrigeration system is a device that captures sublimation water vapor and is integrated with the drying box, separated by a mushroom valve/butterfly valve, which can make the feeding and discharging and defrosting at the same time. After entering the freeze-drying end judgment program, the pressure test is automatically performed to find the end point of freeze-drying. In the event of a short-term power failure (10min), in order to protect the safety of the product, the small butterfly valve will automatically close, using the pressure difference between the cold trap and the drying box to maintain the sublimation state.

　　The system is also equipped with many functions such as motor overload thermal protection, high pressure protection, low pressure protection, medium pressure protection, oil pressure difference protection, automatic liquid collection, and cooling water shortage protection. The compressor is also equipped with a CPCE pressure regulator to prevent the compressor from operating under extreme conditions and to balance the secondary compression ratio. The refrigeration system is designed with sufficient cooling capacity to cope with the water vapor load generated by sublimation.