The precooler is an air heat exchanger. It is not only the cold recovery equipment of refrigeration system, but also the regenerator of low temperature air after dehydration. It is the main component of the cold dryer, and it is also the characteristic condition that distinguishes the chiller from other refrigeration equipment.
Generally speaking, the precooler is not a necessary part of the dryer, but it plays an important role in the operation of the dryer. The main function of the precooler in the dryer is to recover the cooling capacity carried by the compressed air cooled by the evaporator (this part of the cooling capacity belongs to "waste cooling" for most users), and use this part of the cooling capacity to cool the compressed air with high temperature carrying a large amount of water vapor, so as to reduce the heat load of the cooling system of the cold dryer and achieve the purpose of energy saving. On the other hand, the temperature of the low-temperature compressed air in the precooler rises, so that the outer wall of the exhaust pipe will not be exposed due to the low temperature. In addition, when the temperature of compressed air increases, the relative humidity of the air in the pipeline is reduced (up to 5-10%). According to the theory of metal corrosion, when the relative humidity of the environment is lower than the zero point (40%), the metal pipe rust will stop. Therefore, a precooler is installed in the dryer.
In the precooler, the same amount of cold and hot fluids (compressed air) exchange heat with each other depending on the difference in temperature
1. To reduce the temperature and water content of the saturated inlet air, the heat load of the evaporator can be reduced to a certain extent, and then the energy consumption of the whole machine can be reduced;
2. The temperature of compressed air with low temperature and saturated moisture content can be recovered, so as to reduce the relative humidity when the compressed air is discharged, so that the inner wall of the gas transmission pipeline will not be rusted due to the high relative humidity of the gas transmission pipeline. At the same time, the "dew" phenomenon outside the pipeline caused by the low temperature of the outer wall of the gas transmission pipeline is avoided, and the workshop environment is improved.
It is easier to drain the condensate attached to the outer wall of the heat exchange pipe, so the saturated compressed air with higher temperature is usually arranged to go through the shell side of the precooler, while the dry cold air with lower temperature is arranged to go through the tube side of the precooler.
The existence of the precooler makes the compressed air flow through the passage and forms its own system in the cold dryer. The air system and the refrigerant system cross meet in the evaporator, so that the saturated compressed air entering the dryer is cooled twice and heated once, and then the dry compressed air with low absolute moisture content (dew point) and low relative humidity (%) is obtained at the exhaust port.
If there is no precooler or the precooler is not designed properly, the output of the dryer is only humid cold air with low dew point and high relative humidity. Its function is equivalent to a cooler with good refrigeration effect and great energy consumption, so it has no great application value in industry.
Can the dryer without precooler be used?
Some users need compressed air with low water content and low temperature, so the pre cooler can be no longer set in the cold dryer. Because there is no precooler, the cooling capacity of cold air can not be recycled, and the heat load of evaporator will increase a lot. In this case, it is not only necessary to increase the power of the refrigeration compressor for energy compensation, but also for other parts of the whole refrigeration system (evaporator, condenser and throttling components).
What is the significance of the exhaust temperature of the cold dryer?
The exhaust temperature of the cold dryer is the exhaust temperature of the precooler.
Generally speaking, the exhaust temperature of the chiller can reflect the regeneration and utilization degree of the cooling capacity produced by the precooler to the refrigeration system. If the exhaust temperature is high, the cold capacity utilization rate will be high; if the exhaust temperature is low, the cold capacity utilization rate will be low.
Due to the restriction of heat exchange conditions, especially the condition that the internal dew point can not be lower than freezing point, the difference between the exhaust temperature and the inlet temperature of the dryer is limited, that is, the ability of the precooler to raise the temperature of the finished gas is limited.