Chillers, short for refrigerant dryers, are advanced technology devices in the pneumatic system used for air source treatment. They utilize refrigerant and compressed air for heat exchange, lowering the temperature of compressed air to the dew point temperature within the range of 2~10℃. As customers' demand for air source quality continues to grow, chillers are being used more and more widely. Here, we introduce the selection of chiller equipment for your reference.
What are the categories of commonly used cold dryers?
The cooling methods of the condensers in commonly used cold dryers include air-cooled and water-cooled types; they are categorized by intake temperature into high-temperature models (below 80°C) and normal-temperature models (around 40°C); and by working pressure into standard models (0.7-1.0 MPa), medium and low-pressure models (below 0.6 MPa), and high-pressure models (above 1.0 MPa). Additionally, Linuo's special specification cold dryers can be used to process non-air media.
What technical specifications are required for selecting a refrigerant dryer?
Technical parameters to determine when selecting a cold dryer: processing capacity (Nm3/min), inlet temperature (°C), working pressure (MPa), cooling water temperature (°C) for water-cooled models, and ambient temperature (°C) for air-cooled models. Target parameters of the cold dryer – "Pressure Dew Point" (°C); if "Pressure Dew Point" is specified, relevant conditions (such as inlet temperature, working pressure, ambient temperature, etc.) must also be stated.
What is the "pressure dew point" of the refrigerant dryer actually capable of reaching (°C)?
On product samples from different manufacturers, the "pressure dew point" of the cold dryer is marked with various values: ranging from 0℃ to 10℃, including 0℃, 1℃, 1.6℃, 1.7℃, 2℃, 3℃, 2~10℃, and 10℃. This variation makes it inconvenient for users to select the right model. Therefore, it is of practical significance to realistically determine the maximum temperature (℃) that the cold dryer's "pressure dew point" can reach. We know that there are three conditions that limit the "pressure dew point" of the cold dryer:
There are limitations on the evaporation temperature and bottom line of the freezing point.
There is a limit to how much the heat exchange area of the evaporator can be increased.
③ The separator efficiency of the "air-water separator" does not meet the limitations. It is normal for the cooling temperature of compressed air in the evaporator to be 3-5℃ higher than the refrigerant evaporation temperature; excessively lowering the evaporation temperature does not help; due to the limitations of the air-water separator efficiency, the formation of condensate vapor in the heat exchange of the pre-cooler also increases the water content in the compressed air. All these factors combined make it very difficult to control the "pressure dew point" of the desiccant dryer below 2℃. As for the markings of 0℃、1℃、1.6℃、1.7℃ and so on, they are often more commercial promotional than actual performance, and people should not take them too seriously. However, under good working conditions, achieving a compressed air "pressure dew point" of around 5℃ through the desiccant dryer should be feasible.
Is the "pressure dew point" range of -2 to 10°C for the cold dryer too broad?
Some people may think that the "pressure dew point" range of 2-10℃ on the refrigerant dryer is too wide, with a temperature difference of "5 times." This perception is incorrect:
Firstly, there is no concept of "times" between Celsius degrees (°C). Temperature, as a symbol of the average kinetic energy of the internal motion of a large number of molecules, should truly start from the point where molecular motion ceases completely, which is "absolute zero" (0 K). The Celsius scale sets the melting point of ice as the starting point for temperature, which is 273.15°C higher than "absolute zero". In thermodynamics, the Celsius scale (°C) can be used for calculations related to the concept of temperature, but as a state parameter, calculations should be based on the thermodynamic scale (also known as the absolute scale, starting from absolute zero). 2°C = 275.15 K, 10°C = 283.15 K, this is the true difference between the two.
② From the moisture content of saturated gases, the compressed air at 0.7 MPa has a moisture content of 0.82 g/m³ at a dew point of 2°C, and 1.48 g/m³ at a dew point of 10°C, with no "5" times difference between the two.
③ From the relationship between "pressure dew point" and atmospheric dew point, at 0.7MPa, a dew point of 2℃ is equivalent to an atmospheric dew point of -23℃, and a dew point of 10℃ is equivalent to an atmospheric dew point of -16℃. There is no "5 times" difference between the two, as mentioned above. The "pressure dew point" range of 2-10℃ is not as large as one might imagine.
How to Properly Configure Filters for a Cold Dryer?
The compressed air from the gas source contains a large amount of liquid water, particles of varying sizes, oil, and oil vapor. If these impurities enter the air dryer directly, it will worsen the working condition of the dryer. For instance, oil contamination can pollute the heat exchange copper tubes in the pre-cooler and evaporator, affecting heat exchange; liquid water increases the workload of the air dryer, and solid impurities can easily block the drainage holes. Therefore, it is generally required to install a pre-filter upstream of the air dryer inlet for impurity filtration and oil-water separation to avoid the above issues. The filtration precision of the pre-filter for solid impurities does not need to be very high, usually around 10-25μ is sufficient, but a higher separation efficiency for liquid water and oil contamination is preferable. Post-filter for air dryer: For general power gas use, a high-precision main pipeline filter is needed. When higher gas quality requirements are needed, corresponding oil mist filters or activated carbon filters should be configured.
What should be noted when matching cold dryers with piston air compressors?
Piston-type air compressors are non-continuous in their air supply, generating airflow pulsations during operation. These pulsations exert strong and continuous impacts on the various components of the desiccant dryer, leading to a series of mechanical damages. Therefore, when the desiccant dryer is used in conjunction with a piston-type air compressor, a buffer gas storage tank should be installed downstream of the compressor.
