Technical and economic comparison should be made for the refrigeration scheme according to the cooling requirements (cooling capacity, cooling mode, frozen water temperature, etc.), the water source situation (water temperature, water quality, water quantity, etc.) of the project construction area, and the party preparing the power source and heat source. Both good economic indicators and local possibilities are required.
The selection of refrigeration device is the central link in the process of refrigeration scheme determination. The main types of refrigeration device are as follows.
1, compression refrigeration device
Compression refrigeration device includes piston (reciprocating), centrifugal and screw type three.
Piston (reciprocating) compression refrigeration device is the main equipment of piston refrigeration compressor, commonly used working medium ammonia (NH3), freon - 12, 22(F - 12, 22). This kind of equipment driven by electric motor, easy to use, variety, product complete, can meet the requirements of all kinds of air conditioning cooling, is widely used. However, a large investment, high equipment cost, power consumption, maintenance and management is more complex.
The main equipment of centrifugal compression refrigeration device is centrifugal refrigeration compressor, the commonly used working medium is Freon -11, 113, 114(F-11, 113, 114). The machine and piston refrigeration compressor of the same principle, but it only rotary movement, than the piston type smooth operation, small vibration, less parts, often combined with evaporator, condenser, compact equipment covers a small area. The refrigeration capacity of centrifugal refrigeration compressor is large, so only when the cooling consumption of air conditioning is large, this kind of equipment is selected.
Screw type compression refrigeration device is the main equipment of screw refrigeration compressor, commonly used working medium is freon -12, 22, ammonia (F-12, 22, R717). Current production of screw refrigeration compressor compared with piston, although slightly lower efficiency, but because of its simple structure, small volume, high suction coefficient, low exhaust temperature, single stage compression ratio is big, is not sensitive to wet stroke, the exhaust fluctuation is small, less wearing parts, column repair cycle is long, the advantages of refrigerating capacity can be adjusted, so get more extensive application in all kinds of refrigeration unit. Generally in (120-800)x105kJ h capacity refrigeration equipment used this machine has better technical and economic indicators.
2, absorption refrigeration device
Absorption refrigeration devices use thermal energy to refrigerate. Common ammonia - water absorption refrigeration device and water - lithium bromide aqueous solution absorption refrigeration device. The former is suitable for cryogenic freezing; The latter is suitable for air conditioning cooling, making more than 4℃ air conditioning or process cold water. In lithium bromide absorption refrigeration, water is the working medium and lithium bromide aqueous solution is the absorbent. Its advantages are as follows.
It has great adaptability to the pressure of steam heat source. When the steam pressure is 0.02 -- 0.1MPa, single lithium bromide absorption chiller can be used. When the steam pressure is 6.0 -- 1.0MPa, double effect lithium bromide chiller can be used.
Secondly, the equipment is simple, basically a combination of heat exchanger, easy to manufacture, in addition to the small power shield pump, vacuum pump, no moving parts, so small vibration, smooth operation; The equipment works under vacuum, the working medium is odorless, non-toxic, harmless to people, safe to use, simple to operate and manage; Easy to realize automatic equipment operation, refrigeration capacity can be adjusted automatically in the range of 10% ~ 100%; Strong adaptability to the water temperature of cooling water, the equipment can still operate normally even when it reaches 37 ~ 38℃; The power consumption of the lithium bromide refrigerator is only about 5% of that of the compression refrigerator under the same conditions. It is suitable for the areas with tight power supply and sufficient heat source. However, disadvantages as well as lithium bromide absorption refrigeration and use limitations, mainly is the lithium bromide aqueous solution in the case of contact with air, with strong corrosive to metal, once corrosion, not only affect the heat transfer effect, reduce the service life, and will cause equipment damage, so the equipment must be strict sealing, also very attention should be paid on the operation and management.
3, steam jet refrigeration device
Steam jet refrigeration device is also a kind of refrigeration equipment using heat energy, with water as refrigerant and steam as refrigeration power. Steam pressure requirements of 0.2-0.8mpa, its main advantages are: equipment under vacuum work, in addition to the pump, no rotating parts; The refrigerant is water, harmless to people, safe to use, simple to operate; Simple equipment, easy to manufacture, general machinery factory or machine repair shop can be processed and manufactured; Equipment a small investment, and can be installed in the outdoor, save civil construction costs; Can use waste heat in industrial enterprises or industrial enterprises in the heating boiler, heating in winter, summer for steam refrigeration.
The main disadvantage of steam jet refrigeration is its low efficiency, and it is uneconomical to set up special boilers and use small heating boilers for steam supply. It can be used when the frozen water temperature is above 5℃, and it is more economical when the frozen water temperature is above 100℃. Its efficiency varies with the temperature of chilled water. The lower the temperature of chilled water is, the more steam is consumed and the lower the efficiency is. In addition, the cooling water is very large. Under the same single-machine cooling capacity, the cooling water required by steam jet refrigerator is about 1.5 times that of compression type or brominated precession type, which is not suitable for water shortage areas.