How to select cold drying machine


Cold drying machine is short for frozen dryer, cold drying machine is a new technology, belongs to the air source treatment equipment in the pneumatic system. The refrigerant is used for heat exchange with the compressed air, and the temperature of the compressed air is reduced to the dew point temperature in the range of 2~10℃. With the continuous development of customer demand for air quality, cold drying machines are more and more widely used. Here we introduce the equipment selection of the cold and dry machine for reference.

1, commonly used cold drying machine divided into several categories?

Commonly used cold and dry machine condenser cooling methods are divided into: air-cooled type, water-cooled type two; From the high and low intake temperature, there are: high temperature type (below 80℃) and normal temperature type (about 40℃); The working pressure is divided into: ordinary type (0.7-1.0mpa) and medium and low pressure type (less than 0.6MPa) and high pressure type (above 1.0MPa). In addition, Linuo special specifications can be used to deal with non-air media, such as: biogas, hydrogen, natural gas, carbon dioxide, coal bed methane, nitrogen, flue gas, etc.

2. What technical parameters do you need to provide for the selection of cold and dry machine?

Cold and dry machine selection needs to determine the technical parameters: processing capacity (Nm3/min), intake air temperature (℃), working pressure (MPa), water-cooled type needs cooling water temperature (℃), air-cooled type needs ambient temperature (℃). The target parameter of the cold and dry machine - "pressure dew point" (℃), if marked "pressure dew point", must also be accompanied by relevant conditions (such as intake temperature, working pressure, ambient temperature, etc.).

3, the "pressure dew point" of the cold and dry machine can reach how much (° C)?

On the product samples of different manufacturers, the "pressure dew point" of the cold and dry machine has a variety of different labels: 0 ° C, 1 ° C, 1.6 ° C, 1.7 ° C, 2 ° C, 3 ° C, 2~10 ° C, 10 ° C, etc. This brings inconvenience to the user's selection. Therefore, it is of great practical significance to actually find out how much ° C the "pressure dew point" of the cold dryer can reach. We know that the "pressure dew point" of the cold dryer has three conditions, namely:

(1) There is a limit of the bottom line of evaporation temperature freezing point;

(2) There is a limit that the heat transfer area of the evaporator can not be increased indefinitely;

③ The separation efficiency of the "gas-water separator" can not reach . It is normal that the final cooling temperature of compressed air in the evaporator is 3-5 ℃ higher than the refrigerant evaporation temperature; Reducing the evaporation temperature too much will not help; Due to the limitation of the efficiency of the gas-water separator, a small amount of condensed water forms water vapor in the heat exchange of the precooler, which will also increase the water content of the compressed air. All these factors together, it is very difficult to control the "pressure dew point" of the cold dryer below 2 ° C. As for 0 ° C, 1 ° C, 1.6 ° C, 1.7 ° C and other labels, it is often the commercial propaganda ingredients more than the actual effect, people do not have to take it too seriously. However, under good working conditions, it should be possible to obtain compressed air with a "pressure dew point" of about 5 ° C through the cold dryer.

4. Is the "pressure dew point" range of 2-10 ° C for the cold dryer a little larger?

Some people think that the "pressure dew point" range of 2-10 ° C marked by the cold dryer, the temperature difference of "5 times" is not too large? This perception is incorrect:

First of all, there is no concept of "times" between the Celsius temperature. Temperature is the mark of the average kinetic energy of a large number of molecules inside the body, and its real starting point should be calculated from the complete stop of molecular motion, that is, absolute zero (0 K). The Celsius scale uses the melting point of ice as the starting point for temperature, which is 273.15 ° C above absolute zero. In thermodynamics, in addition to the Celsius temperature scale used in the calculation of the temperature concept, when used as a state parameter, it should be calculated on the basis of the thermodynamic temperature scale (also known as the absolute temperature scale, the starting point is absolute zero). 2 ° C =275.15K, 10 ° C =283.15K, this is the real difference between the two.

② From the point of view of the water content of saturated gas, the moisture content of 0.7MPa compressed air at the dew point of 2℃ is 0.82g/m3, and the moisture content at the dew point of 10℃ is 1.48g/m3, and there is no "5" times difference between the two.

③ From the relationship between the "pressure dew point" and the atmospheric pressure dew point, the compressed air at 0.7MPa at 2 ° C dew point is equivalent to atmospheric pressure dew point -23 ° C, at 10 ° C dew point is equivalent to atmospheric pressure dew point -16 ° C, and there is also no "5 times" difference between the two, according to the above, the "pressure dew point" range of 2-10 ° C is not as large as imagined.

5, how to correctly configure the filter of the cold dryer?

The compressed air from the air source contains a lot of liquid water, solid dust with different particle sizes, oil, oil vapor and so on. If these impurities enter the dry machine directly, it will worsen the working condition of the dry machine. For example, oil pollution will pollute the heat exchange copper tube in the precooler and evaporator, affecting the heat exchange; Liquid water increases the working load of the cold and dry machine, and solid impurities are easy to block the drainage hole. Therefore, it is generally required to install a pre-filter upstream of the air intake of the cold and dry machine to filter impurities and separate oil and water to avoid the occurrence of the above situation. The filtration accuracy of the pre-filter for solid impurities is not very high, generally in the range of 10 to 25 μs, but the separation efficiency of liquid water and oil is higher. The rear filter of the cold and dry machine: such as the general power gas, need to be equipped with a high precision main filter. When the gas requirements are higher, the corresponding oil mist filter or activated carbon filter should be configured.

6. What should we pay attention to when matching the cold and dry machine with the piston air compressor?

The piston type air compressor is not continuous gas supply, and the air pulse is generated when working. The air pulse forms a strong and continuous impact on the parts of the cold and dry machine, which will lead to a series of mechanical damage to the cold and dry machine, so when the cold and dry machine is used with the piston air compressor, the buffer storage tank should be set on the downstream side of the air compressor.




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