Knowledge about the cold dryer! 1. What are the characteristics of domestic cold dryers compared with imported ones? At present, the hardware configuration of domestic cold-drying machines is not much different from that of foreign imported machines, and international famous brands are widely used in refrigeration compressors, refrigeration accessories and refrigerants. However, the user applicability of the cold dryer generally exceeds that of imported machines, because domestic manufacturers have fully considered the characteristics of domestic users, especially the climatic conditions and daily maintenance characteristics, when designing and manufacturing the cold dryer. For example, the refrigeration compressor power of domestic cold dryer is generally higher than that of imported machines of the same specification, which fully adapts to the characteristics of China’s vast territory and great temperature difference in different places/seasons. In addition, domestic machines are also quite competitive in price and have incomparable advantages in after-sales service. Therefore, the domestic cold dryer is very popular in the domestic market. 2. What are the characteristics of the cold dryer compared with the adsorption dryer? Compared with adsorption drying, freeze dryer has the following characteristics: ① There is no gas consumption, and for most gas users, using cold dryer saves energy than using adsorption dryer; ② No valve parts are worn; ③ There is no need to add or replace adsorbents regularly; ④ Low operation noise; ⑤ Daily maintenance is relatively simple, as long as the filter screen of automatic drainer is cleaned on time; ⑥ There is no special requirement for the pre-treatment of air source and supporting air compressor, and the general oil-water separator can meet the requirements of air inlet quality of cold dryer; ⑦ The air dryer has a “self-cleaning” effect on the exhaust gas, that is, the content of solid impurities in the exhaust gas is less; ⑧ While discharging condensate, part of oil vapor can be condensed into liquid oil mist and discharged with condensate. Compared with the adsorption dryer, the “pressure dew point” of the cold dryer for compressed air treatment can only reach about 10℃, so the drying depth of the gas is far less than that of the adsorption dryer. In quite a few application fields, the cold dryer can not meet the requirements of the process for the dryness of the gas source. In the technical field, a selection convention has been formed: when the “pressure dew point” is above zero, the cold dryer is the first, and when the “pressure dew point” is below zero, the adsorption dryer is the only choice. 3. How to obtain compressed air with extremely low dew point? The dew point of compressed air can be about -20℃ (normal pressure) after being treated by a cold dryer, and the dew point can reach above -60℃ after being treated by an adsorption dryer. However, some industries that require extremely high air dryness (such as microelectronics, which requires dew point to reach -80℃) are obviously not enough. At present, the method promoted by the technical field is that the cold dryer is connected in series with the adsorption dryer, and the cold dryer is used as the pre-treatment equipment of the adsorption dryer, so that the moisture content of compressed air is greatly reduced before entering the adsorption dryer, and compressed air with extremely low dew point can be obtained. Moreover, the lower the temperature of compressed air entering the adsorption dryer, the lower the dew point of compressed air finally obtained. According to foreign data, when the inlet temperature of adsorption dryer is 2℃, the dew point of compressed air can reach below -100℃ by using molecular sieve as adsorbent. This method has also been widely used in China.
4. What should be paid attention to when the cold dryer is matched with the piston air compressor? The piston air compressor does not supply gas continuously, and there are air pulses when it works. The air pulse has a strong and lasting impact on all parts of the cold dryer, which will lead to a series of mechanical damage to the cold dryer. Therefore, when the cold dryer is used with a piston air compressor, a buffer air tank should be set at the downstream side of the air compressor. 5. What should I pay attention to when using a cold dryer? Attention should be paid to the following matters when using the cold dryer: ① The flow, pressure and temperature of compressed air should be within the allowable range of the nameplate; ② The installation site should be ventilated with little dust, and there is enough space for heat dissipation and maintenance around the machine, and it cannot be installed outdoors to avoid direct rain and sunlight; (3) cold dryer generally allows installation without foundation, but the ground must be leveled; (4) should be as close as possible to the user point, to avoid the pipeline is too long; ⑤ There should be no detectable corrosive gas in the surrounding environment, and special attention should be paid to not being in the same room with ammonia refrigeration equipment; ⑥ The filtration accuracy of the pre-filter of the cold dryer should be appropriate, and too high accuracy is not necessary for the cold dryer; ⑦ The inlet and outlet pipes of cooling water should be set independently, especially the outlet pipe should not be shared with other water-cooling equipment to avoid drainage obstruction caused by pressure difference; ⑧ Keep the automatic drainer unblocked at all times; Pet-name ruby don’t start the cold dryer continuously; Attending the parameter indexes of compressed air actually treated by the cold dryer, especially when the inlet temperature and working pressure are inconsistent with the rated value, they should be corrected according to the “correction coefficient” provided by the sample to avoid overload operation. 6. What is the influence of high oil mist content in compressed air on the operation of the cold dryer? The exhaust oil content of air compressor is different, for example, the exhaust oil content of domestic piston oil-lubricated air compressor is 65-220 mg/m3; , less oil lubrication air compressor exhaust oil content is 30 ~ 40 mg/m3; The so-called oil-free lubrication air compressor made in China (actually semi-oil-free lubrication) also has an oil content of 6 ~ 15mg/m3; ; Sometimes, due to the damage and failure of the oil-gas separator in the air compressor, the oil content in the exhaust of the air compressor will be greatly increased. After the compressed air with high oil content enters the cold dryer, a thick oil film will be covered on the surface of the copper tube of the heat exchanger. Because the heat transfer resistance of the oil film is 40~70 times greater than that of the copper tube, the heat transfer performance of the precooler and evaporator will be greatly reduced, and in serious cases, the cold dryer will not work normally. Specifically, the evaporation pressure drops while the dew point rises, the oil content in the exhaust of the air dryer increases abnormally, and the automatic drainer is often blocked by oil pollution. In this case, even if the oil removal filter is constantly replaced in the pipeline system of the cold dryer, it will not help, and the filter element of the precision oil removal filter will soon be blocked by oil pollution. The best way is to repair the air compressor and replace the filter element of the oil-gas separator, so that the oil content of the exhaust gas can reach the normal factory index. 7. How to correctly configure the filter in the cold dryer? Compressed air from air source contains a lot of liquid water, solid dust with different particle sizes, oil pollution, oil vapor and so on. If these impurities directly enter the cold dryer, the working condition of the cold dryer will deteriorate. For example, oil pollution will pollute the heat exchange copper tubes in the precooler and evaporator, which will affect the heat exchange; Liquid water increases the workload of the cold dryer, and solid impurities are easy to block the drainage hole. Therefore, it is generally required to install a pre-filter upstream of the air inlet of the cold dryer for impurity filtration and oil-water separation to avoid the above situation. The filtration accuracy of the pre-filter for solid impurities need not be very high, generally it is 10~25μ m, but it is better to have a higher separation efficiency for liquid water and oil pollution. Whether the post filter of the cold dryer is installed or not should be determined by the user’s quality requirements for compressed air. For general power gas, a high-precision main pipeline filter is enough. When the gas demand is higher, the corresponding oil mist filter or activated carbon filter should be configured. 8. What should I do to make the exhaust temperature of the air dryer very low? In some special industries, not only compressed air with low pressure dew point (i.e. water content) but also the temperature of compressed air is required to be very low, that is, the air dryer should be used as a “dehydration air cooler”. At this time, the measures taken are: ① cancel the precooler (air-air heat exchanger), so that the compressed air forcibly cooled by the evaporator can not be warmed up; ② at the same time, check the refrigeration system, and if necessary, increase the power of the compressor and the heat exchange area of the evaporator and condenser. The simple method commonly used in practice is to use a large-scale cold dryer without precooler to deal with the gas with small flow. 9. What measures should be taken by the air dryer when the inlet temperature is too high? The inlet air temperature is an important technical parameter of the cold dryer, and all manufacturers have obvious restrictions on the upper limit of the inlet air temperature of the cold dryer, because the high inlet air temperature not only means the increase of sensible heat, but also the increase of water vapor content in compressed air. JB/JQ209010-88 stipulates that the inlet temperature of the cold dryer should not exceed 38℃, and many famous foreign manufacturers of cold dryers have similar regulations. It stands to reason that when the exhaust temperature of the air compressor exceeds 38℃, a rear cooler must be added downstream of the air compressor to reduce the temperature of compressed air to a specified value before entering the post-treatment equipment. The present situation of domestic cold dryers is that the allowable value of air inlet temperature of cold dryers is constantly increasing. For example, ordinary cold dryers without pre-cooler started to increase from 40℃ in the early 1990s, and now there have been ordinary cold dryers with air inlet temperature of 50℃. Regardless of whether there is commercial speculation component or not, from a technical point of view, the increase of inlet temperature is not only reflected in the increase of gas “apparent temperature”, but also reflected in the increase of water content, which is not a simple linear relationship with the increase of load of cold dryer. If the increase of load is compensated by increasing the power of the refrigeration compressor, it is far from cost-effective, because it is the most economical and effective way to use the rear cooler to reduce the temperature of compressed air within the normal temperature range. The high-temperature air-intake type cold dryer is to assemble the rear cooling on the cold dryer without changing the refrigeration system, and the effect is very obvious. 10. What other requirements does the cold dryer have for environmental conditions besides temperature? The influence of ambient temperature on the work of the cold dryer is very great. In addition, the cold dryer has the following requirements for its surrounding environment: ① ventilation: it is especially necessary for air-cooled cold dryers; ② Dust should not be too much; ③ There should be no direct radiant heat source at the use site of the cold dryer; ④ There should be no corrosive gas in the air, especially ammonia can’t be detected. Because ammonia is in an environment with water. It has a strong corrosive effect on copper. Therefore, the cold dryer should not be installed with ammonia refrigeration equipment.
11. What influence does the ambient temperature have on the operation of the air dryer? The high ambient temperature is very unfavorable to the heat dissipation of the refrigeration system of the air dryer. When the ambient temperature is higher than the normal refrigerant condensation temperature, it will force the refrigerant condensation pressure to increase, which will reduce the refrigeration capacity of the compressor and eventually lead to the increase of the “pressure dew point” of compressed air. Generally speaking, a lower ambient temperature is beneficial to the operation of the cold dryer. However, at too low ambient temperature (for example, below zero degrees Celsius), the dew point of compressed air will not change greatly even though the temperature of compressed air entering the air dryer is not low. However, when the condensed water is drained through the automatic drainer, it is likely to freeze at the drain, which must be prevented. In addition, when the machine is stopped, the condensed water originally gathered in the evaporator of the cold dryer or stored in the water storage cup of the automatic drainer may freeze, and the cooling water stored in the condenser may also freeze, all of which will cause damage to the related parts of the cold dryer. It is more important to remind users that: When the ambient temperature is lower than 2℃, the compressed air pipeline itself is equivalent to a well-functioning cold dryer. At this time, attention should be paid to the treatment of condensed water in the pipeline itself. Therefore, many manufacturers clearly stipulate in the manual of the cold dryer that when the temperature is below 2℃, do not use the cold dryer. 12, cold dryer load depends on what factors? The load of the cold dryer depends on the water content of the compressed air to be treated. The more water content, the higher the load. Therefore, the working load of the cold dryer is not only directly related to the flow of compressed air (Nm⊃3; /min), the parameters that have the most influence on the load of the cold dryer are: ① Inlet air temperature: the higher the temperature, the more water content in the air and the higher the load of the cold dryer; ② Working pressure: At the same temperature, the lower the saturated air pressure, the more the water content and the higher the load of the cold dryer. In addition, the relative humidity in the suction environment of the air compressor also has a relationship with the saturated water content of compressed air, so it also has an impact on the work load of the cold dryer: the greater the relative humidity, the more water contained in the saturated compressed gas and the higher the load of the cold dryer. 13. Is the “pressure dew point” range of 2-10℃ for the cold dryer a little too large? Some people think that the “pressure dew point” range of 2-10℃ is marked by the cold dryer, and the temperature difference is “5 times”, isn’t it too big? This understanding is incorrect: ① First of all, there is no concept of “times” between the temperature of Celsius and Celsius. As a sign of the average kinetic energy of a large number of molecules moving inside an object, the real starting point of temperature should be “absolute zero” (OK) when the molecular movement stops completely. Centigrade scale takes the melting point of ice as the starting point of temperature, which is 273.16℃ higher than “absolute zero”. In thermodynamics, except centigrade scale℃ can be used in the calculation related to the concept of temperature change, when it is used as a state parameter, it should be calculated on the basis of thermodynamic temperature scale (also called absolute temperature scale, the starting point is absolute zero). 2℃=275.16K and 10℃=283.16K, which is the real difference between them. ② According to the water content of saturated gas, the moisture content of 0.7MPa compressed air at 2℃ dew point is 0.82 g/m3; The moisture content at 10℃ dew point is 1.48g/m⊃3; There is no difference of “5″ times between them; ③ From the relationship between “pressure dew point” and atmospheric dew point, the 2℃ dew point of compressed air is equivalent to -23℃ atmospheric dew point at 0.7MPa, and the 10℃ dew point is equivalent to -16℃ atmospheric dew point, and there is also no “five times” difference between them. According to the above, the “pressure dew point” range of 2-10℃ is not as big as expected. 14. What is the “pressure dew point” of the cold dryer (℃)? On the product samples of different manufacturers, the “pressure dew point” of the cold dryer has many different labels: 0℃, 1℃, 1.6℃, 1.7℃, 2℃, 3℃, 2~10℃, 10℃, etc. (of which 10℃ is only found in foreign product samples). This brings inconvenience to the user’s selection. Therefore, it is of great practical significance to discuss realistically how much℃ the “pressure dew point” of the cold dryer can reach. We know that the “pressure dew point” of the cold dryer is limited by three conditions, namely: ① by the freezing point bottom line of evaporation temperature; (2) Limited by the fact that the heat exchange area of evaporator cannot be increased indefinitely; ③ Limited by the fact that the separation efficiency of “gas-water separator” can’t reach 100%. It is normal that the final cooling temperature of compressed air in the evaporator is 3-5℃ higher than the evaporation temperature of refrigerant. Excessive reduction of evaporation temperature will not help; Due to the limitation of the efficiency of gas-water separator, a small amount of condensed water will be reduced to steam in the heat exchange of precooler, which will also increase the water content of compressed air. All these factors together, it is very difficult to control the “pressure dew point” of the cold dryer below 2℃. As for the labeling of 0℃, 1℃, 1.6℃, 1.7℃, it is often that the commercial propaganda component is more than the actual effect, so people don’t have to take it too seriously. In fact, it is not a low standard requirement for manufacturers to set the “pressure dew point” of the cold dryer below 10℃. The standard JB/JQ209010-88 “Technical Conditions of Compressed Air Freeze Dryer” of the Ministry of Machinery stipulates that the “pressure dew point” of the cold dryer is 10℃ (and the corresponding conditions are given); However, the national recommended standard GB/T12919-91 “Marine Controlled Air Source Purification Device” requires the atmospheric pressure dew point of the air dryer to be -17~-25℃, which is equivalent to 2~10℃ at 0.7MPa. Most domestic manufacturers give a range limit (for example, 2-10℃) to the “pressure dew point” of the cold dryer. According to its lower limit, even under the lowest load condition, there will be no freezing phenomenon inside the cold dryer. The upper limit specifies the water content index that the cold dryer should reach under rated working conditions. Under good working conditions, it should be possible to obtain compressed air with a “pressure dew point” of about 5℃ through a cold dryer. So this is a rigorous labeling method. 15. What are the technical parameters of the cold dryer? The technical parameters of the cold dryer mainly include: throughput (Nm⊃3; /min), inlet temperature (℃), working pressure (MPa), pressure drop (MPa), compressor power (kW) and cooling water consumption (t/h). The target parameter of the cold dryer-”pressure dew point” (℃) is generally not marked as an independent parameter on the “performance specification table” in the product catalogs of foreign manufacturers. The reason is that “pressure dew point” is related to many parameters of compressed air to be treated. If “pressure dew point” is marked, relevant conditions (such as inlet air temperature, working pressure, ambient temperature, etc.) must also be attached. 16, commonly used cold dryer is divided into several categories? According to the cooling mode of condenser, commonly used cold dryers are divided into air-cooled type and water-cooled type. According to the high and low intake temperature, there are high temperature intake type (below 80℃) and normal temperature intake type (about 40℃); According to the working pressure, it can be divided into ordinary type (0.3-1.0 MPa) and medium and high pressure type (above 1.2MPa). In addition, many special cold dryers can be used to treat non-air media, such as carbon dioxide, hydrogen, natural gas, blast furnace gas, nitrogen and so on. 17. How to determine the number and position of automatic drainers in the cold dryer? The primary displacement of automatic drainer is limited. If at the same time, the amount of condensed water generated by the cold dryer is greater than the automatic displacement, then there will be condensed water accumulation in the machine. Over time, the condensed water will gather more and more. Therefore, in large and medium-sized cold dryers, more than two automatic drains are often installed to ensure that condensed water does not accumulate in the machine. The automatic drainer should be installed downstream of the precooler and evaporator, most commonly directly below the gas-water separator.
18. What should I pay attention to when using the automatic drainer? In the cold dryer, the automatic drainer can be said to be the most prone to failure. The reason is that the condensed water discharged by the cold dryer is not clean water, but thick liquid mixed with solid impurities (dust, rust mud, etc.) and oil pollution (so the automatic drainer is also called “automatic blowdown”), which easily blocks the drainage holes. Therefore, a filter screen is installed at the entrance of the automatic drainer. However, if the filter screen is used for a long time, it will be blocked by oily impurities. If it is not cleaned in time, the automatic drainer will lose its function. So it is very important to clean the filter screen in the drainer at regular intervals. In addition, the automatic drainer must have a certain pressure to work. For example, the minimum working pressure of the commonly used RAD-404 automatic drainer is 0.15MPa, and air leakage will occur if the pressure is too low. But the pressure should not exceed the rated value to prevent the water storage cup from bursting. When the ambient temperature is below zero, the condensed water in the water storage cup should be drained to prevent freezing and frost cracking. 19. How does the automatic drainer work? When the water level in the water storage cup of the drainer reaches a certain height, the pressure of compressed air will close the drain hole under the pressure of the floating ball, which will not cause air leakage. As the water level in the water storage cup rises (there is no water in the cold dryer at this time), the floating ball rises to a certain height, which will open the drain hole, and the condensed water in the cup will be discharged out of the machine quickly under the action of air pressure. After the condensed water is exhausted, the floating ball closes the drainage hole under the action of air pressure. Therefore, the automatic drainer is an energy saver. It is not only used in cold dryers, but also widely used in gas storage tanks, aftercoolers and filtration devices. In addition to the commonly used floating ball automatic drainer, electronic automatic timing drainer is often used, which can adjust the drainage time and the interval between two drains, and can withstand high pressure and be widely used. 20. Why should an automatic drainer be used in the cold dryer? In order to discharge the condensed water in the cold dryer out of the machine in time and thoroughly, the simplest way is to open a drain hole at the end of the evaporator, so that the condensed water generated in the machine can be continuously discharged. But its disadvantages are also obvious. Because the compressed air will be continuously discharged while draining water, the pressure of compressed air will drop rapidly. This is not allowed for the air supply system. Although it is feasible to drain water manually and regularly by hand valve, it needs to increase manpower and bring a series of management troubles. Using the automatic drainer, the accumulated water in the machine can be automatically removed regularly (quantitatively). 21. What is the significance of discharging condensate in time for the operation of the air dryer? When the cold dryer works, a large amount of condensed water will accumulate in the volume of the precooler and evaporator. If the condensed water is not discharged in time and completely, the cold dryer will become a water reservoir. The results are as follows: ① A large amount of liquid water is entrained in the exhaust gas, which makes the work of the cold dryer meaningless; (2) the liquid water in the machine should absorb a lot of cold energy, which will increase the load of the cold dryer; ③ Reduce the circulation area of compressed air and increase the air pressure drop. Therefore, it is an important guarantee for the normal operation of the cold dryer to discharge the condensed water from the machine in time and thoroughly. 22, air dryer exhaust with water must be caused by insufficient dew point? The dryness of compressed air refers to the amount of mixed water vapor in dry compressed air. If the water vapor content is small, the air will be dry, and vice versa. The dryness of compressed air is measured by the “pressure dew point”. If the “pressure dew point” is low, the compressed air will be dry. Sometimes the compressed air discharged from the cold dryer will be mixed with a small amount of liquid water droplets, but this is not necessarily caused by insufficient dew point of the compressed air. The existence of liquid water droplets in the exhaust may be caused by water accumulation, poor drainage or incomplete separation in the machine, especially the failure caused by the blockage of the automatic drainer. The exhaust of air dryer with water is worse than the dew point, which can bring worse adverse effects to downstream gas equipment, so the reasons should be found out and eliminated. 23. What is the relationship between the efficiency of gas-water separator and pressure drop? In baffle gas-water separator (whether flat baffle, V-baffle or spiral baffle), increasing the number of baffles and reducing the spacing (pitch) of baffles can improve the separation efficiency of steam and water. But at the same time, it also brings about an increase in the pressure drop of compressed air. Moreover, too close baffle spacing will produce airflow howling, so this contradiction should be taken into account when designing baffles. 24, how to evaluate the role of gas-water separator in the cold dryer? In the cold dryer, the separation of steam and water takes place in the whole process of compressed air. A plurality of baffle plates arranged in the precooler and evaporator can intercept, gather and separate the condensed water in the gas. As long as the separated condensate can be discharged from the machine in time and thoroughly, compressed air with a certain dew point can also be obtained. For example, the measured results of a certain type of cold dryer show that more than 70% of the condensed water is discharged from the machine by the automatic drainer before the gas-water separator, and the remaining water droplets (most of which are very fine in particle size) are finally effectively captured by the gas-water separator between the evaporator and the precooler. Although the number of these water droplets is small, it has a great impact on the “pressure dew point”; Once they enter the precooler and are reduced to steam by secondary evaporation, the water content of compressed air will be greatly increased. Therefore, an efficient and dedicated gas-water separator plays a very important role in improving the working performance of the cold dryer. 25. What are the limitations of the filter gas-water separator in use? It is very effective to use the filter as the gas-water separator of the cold dryer, because the filtering efficiency of the filter for water droplets with a certain particle size can reach 100%, but in fact, there are few filters used in the cold dryer for steam-water separation. The reasons are as follows: ① When used in high-concentration water mist, the filter element is easily blocked, and it is very troublesome to replace it; ② There is nothing to do with condensed water droplets smaller than a certain particle size; ③ It is expensive. 26. What is the working reason of cyclone gas-water separator? Cyclone separator is also an inertial separator, which is mostly used for gas-solid separation. After the compressed air enters the separator along the tangential direction of the wall, the water droplets mixed in the gas also rotate together and generate centrifugal force. The water droplets with large mass generate large centrifugal force, and under the action of centrifugal force, the large water droplets move to the outer wall, and then gather and grow up after hitting the outer wall (also the baffle) and separate from the gas; However, the water droplets with smaller particle size migrate to the central axis with negative pressure under the action of gas pressure. Manufacturers often add spiral baffles in the cyclone separator to enhance the separation effect (and also increase the pressure drop). However, due to the existence of negative pressure zone in the center of rotating airflow, small water droplets with less centrifugal force are easily sucked into the precooler by negative pressure, resulting in an increase in dew point. This separator is also an inefficient device in the solid-gas separation of dust removal, and has been gradually replaced by more efficient dust collectors (such as electrostatic precipitator and bag pulse dust collector). If it is used as a steam-water separator in a cold dryer without modification, the separation efficiency will not be very high. And because of the complex structure, what kind of huge “cyclone separator” without spiral baffle is not widely used in cold dryer. 27. How does the baffle gas-water separator work in the cold dryer? Baffle separator is a kind of inertial separator. This kind of separator, especially the “louver” baffle separator composed of multiple baffles, has been widely used in the cold dryer. They have good steam-water separation effect on water droplets with wide particle size distribution. Because the baffle material has a good wetting effect on liquid water droplets, after water droplets with different particle sizes collide with the baffle, a thin layer of water will be generated on the surface of the baffle to flow down along the baffle, and the water droplets will gather into larger particles at the edge of the baffle, and the water droplets will be separated from the air under their own gravity. The capture efficiency of baffle separator depends on airflow speed, baffle shape and baffle spacing. Some people have studied that the water droplet capture rate of V-shaped baffle is about twice that of plane baffle. Baffle gas-water separator can be divided into guide baffle and spiral baffle according to baffle switch and arrangement. (The latter is the commonly used “cyclone separator”); The baffle of baffle separator has a low capture rate of solid particles, but in the cold dryer, the solid particles in compressed air are almost completely surrounded by water film, so the baffle can also separate the solid particles together while catching water droplets. 28. How much does the efficiency of gas-water separator affect the dew point? Although setting a certain number of water baffles in the compressed air flow path can really separate most condensed water droplets from gas, those water droplets with finer particle size, especially the condensed water generated after the last baffle, may still enter the exhaust passage. If it is not stopped, this part of condensed water will evaporate into water vapor when it is heated in the precooler, which will increase the dew point of compressed air. For example, 1 nm3 of 0.7MPa; The temperature of compressed air in the cold dryer is reduced from 40℃ (water content is 7.26g) to 2℃ (water content is 0.82g), and the water produced by cold condensation is 6.44 g. If 70%(4.51g) of the condensate water is “spontaneously” separated and discharged from the machine during the gas flow, there is still 1.93g of condensate water to be captured and separated by the “gas-water separator”; If the separation efficiency of the “gas-water separator” is 80%, 0.39g of liquid water will eventually enter the precooler with the air, where the water vapor will be reduced by secondary evaporation, so that the water vapor content of compressed air will increase from 0.82g to 1.21g, and the “pressure dew point” of compressed air will rise to 8℃. Thus, it is of great significance to improve the separation efficiency of the air-water separator of the cold dryer to reduce the pressure dew point of compressed air. 29, compressed air and condensate is how to separate? The process of condensate generation and steam-water separation in the cold dryer begins with compressed air entering the cold dryer. After baffle plates are installed in the precooler and evaporator, this steam-water separation process becomes more intense. Condensed water droplets gather and grow up due to the comprehensive effects of motion change direction and inertial gravity after the baffle collision, and finally realize the separation of steam and water under their own gravity. It can be said that a considerable part of condensate water in the cold dryer is separated from steam water by “spontaneous” intake during the flow. In order to catch some small water droplets remaining in the air, a more efficient special gas-water separator is also set in the cold dryer to minimize the liquid water entering the exhaust pipe, thus reducing the “dew point” of compressed air as much as possible. 30. How is the condensed water of the cold dryer generated? After the normally saturated high-temperature compressed air enters the cold dryer, the water vapor contained in it condenses into liquid water in two ways, namely, ① the water vapor directly contacting with the cold surface condenses and frosts with the low-temperature surface of the precooler and evaporator (such as the outer surface of the heat exchange copper tube, the radiating fins, the baffle plate and the inner surface of the container shell) as the carrier (like the dew condensation process on the natural surface); (2) The water vapor that is not in direct contact with the cold surface takes the solid impurities carried by the airflow itself as the “condensation core” of cold condensation dew (like the formation process of clouds and rain in nature). The initial particle size of condensed water droplets depends on the size of “condensation nucleus”. If the particle size distribution of solid impurities mixed in the compressed air entering the cold dryer is usually between 0.1 and 25 μ, then the initial particle size of condensed water is at least the same order of magnitude. Moreover, in the process of following the compressed air flow, water droplets collide and gather constantly, and their particle size will continue to increase, and after increasing to a certain extent, they will be separated from the gas by their own weight. Because the solid dust particles carried by compressed air play the role of “condensation nucleus” in the process of condensate formation, it also inspires us to think that the process of condensate formation in cold dryer is a “self-purification” process of compressed air.