Principles and advantages and disadvantages of screw refrigeration compressors in cold storage
Foreword: The cold storage house detailed the classification of cold storage compressors in the article "Introduction to the types of cold storage refrigeration compressors". Among them, screw compressors are mentioned. Now let's talk about the principle and advantages and disadvantages of cold storage screw compressors.
Screw compressors
1. Working principle of screw refrigeration compressor
The screw refrigeration compressor is a new type of high-speed compressor. The gas pressure increase principle of the screw compressor is the same as that of the piston compressor, and both belong to the positive displacement compression. The currently used twin-screw compressors are generally twin-screw compressors. The twin-screw compressors use two mutually meshing screws to perform relative rotation to compress gas. With the rapid development of China’s refrigeration industry and the improvement of processing methods, screw refrigeration compressors have made great progress in recent years. The cold storage is becoming larger and larger, the variety of units is increasing, the scope of use continues to expand, and different applications are Field expansion. It has now developed into one of the main forms of refrigeration compressors.
Driven by the electric motor, the active rotor rotates with the electric motor, and the meshed driven rotors also follow each other to rotate. In the rotor movement, when the pair of meshing grooves of the driving rotor and the driven rotor are connected with the suction pipe, full suction is carried out; when the rotor continues to rotate, the pair of suction grooves leave on the suction end surface After the suction orifice, the gas in the tooth grooves enclosed by the suction and exhaust end seats is isolated from the outside of the casing and begins to be compressed; the driving and driven rotors continue to rotate, and the tooth peaks of the driving rotor continue to the driven rotor In the same way, the tooth peaks of the driven rotor also continuously fill the tooth valleys of the corresponding active rotor. As a result of mutual filling, the groove volume of the respective rotors is gradually reduced. The gas is gradually compressed.
When the gas pressure reaches the specified value, the rotor turns to the position where the groove communicates with the exhaust port to discharge the gas. With such continuous operation, the refrigerant is continuously compressed and then discharged from the screw compressor. The screw refrigeration compressor injects a large amount of oil during the compression process to take away the heat generated during the compression process. At the same time, the oil film is used to seal the gap between the female and male rotors and the gap between the rotor and the cylinder, so that internal leakage The loss is reduced. In addition, the female and male rotors are lubricated and the noise is reduced. The screw type refrigeration compressor has a slide valve type energy adjustment device, which can adjust the load steplessly.
Screw chiller
Second, the advantages and disadvantages of screw refrigeration compressors
The advantages and disadvantages of screw refrigeration compressors compared with piston refrigeration compressors are quite obvious.
1. Main advantages
1) Convenient management. There are no fragile parts such as suction and exhaust valves, pistons, piston rings, cylinder liners, etc. that the piston compressor has, and it is easy to maintain and repair. The operation is stable and reliable, and it is easy to realize remote control and automation.
2) High speed and good economic performance. Screw compressors are rotary machines. Because there are no suction and exhaust valves, the speed can be increased. Usually, the speed is 1500-3000/min, which is generally higher than that of the piston compressor, thus improving the economic index.
3) Small size and light weight. Due to the high speed, when the exhaust volume is the same, the machine is small in size, compact in structure, light in weight, less metal consumption, and small in area.
4) The foundation is small. Because the screw compressor does not have the mass inertia force of the piston compressor, the dynamic balance performance is good, so the foundation can be made small.
5) The single unit has a large cooling capacity. At present, the refrigeration capacity of the domestic screw refrigeration compressor series is 9~2300kW/h, which can meet the different needs of production.
6) Strong operational adaptability. It can be applied to a variety of refrigerants with high volumetric efficiency. Even at low evaporation temperature and high compression ratio, it still has good performance. Since there is no clearance volume, the volumetric efficiency is much higher than that of the piston type.
7) Low exhaust temperature. With oil injection cooling, the exhaust temperature is lower than that of the reciprocating type, so single-stage compression can still be used at a higher compression ratio. When the evaporation temperature is -40℃, the discharge temperature is less than or equal to 90℃, which is beneficial to the operation of the machine.
8) Simple structure. The structure is relatively simple, the number of parts is small, the operation cycle is long, the number of maintenance is small, and the processing time is saved.
9) Continuous stepless adjustment. As the most widely used at present is the use of slide valves for energy adjustment, so the cooling capacity can be steplessly adjusted within the energy range of 10% to 100% to achieve continuous stepless adjustment.
10) Long operating life. Because the machine has few wearing parts and reliable usability, it has a long running cycle. Generally, the machine will be overhauled only once after 3000~50,000h.
11)There is no danger of liquid shock. Due to the structural characteristics, the screw compressor is not sensitive to wet stroke. It can allow wet vapor or a small amount of liquid refrigerant to enter the body without the risk of liquid shock.
Parallel screw machine
2. Main disadvantages
1) The rotor is difficult to process. The machining accuracy of the rotor is required to be high, the machining is relatively difficult, and special equipment is required.
2) The auxiliary equipment is huge. For oil-injected screw compressors, in order to separate the lubricating oil in the exhaust, an oil separator and an oil return device with a large volume, a complex structure, and a high efficiency are required.
3) The noise is large. Because the rotor cogging periodically passes through the suction and exhaust ports at high speed, and leaks through the gap, the noise is relatively high. Generally, if the screw-type refrigeration compressor is installed in the machine room, the machine room should not be close to the main warehouse or other workshops. It is best to leave other buildings and arrange separately. The noise reduction is relatively good. It is best to set up noise isolation between the machine room and the equipment control room to reduce noise interference to the operators.
Screw refrigeration compressors are currently suitable for Freon cold storage and single-stage and two-stage (-40°C) systems. In large and medium-sized (cooling capacity above 350kW/h) occasions, the advantages are more prominent.
