อากาศอัดมีการใช้งานอย่างกว้างขวางในภาคอุตสาหกรรม. เราต้องการอากาศที่สะอาดและแห้ง. Because there are many solid, liquid, and gaseous pollutants. They may damage your production system and products. ในหมู่พวกเขา, moisture can lead to pipe corrosion. อีกด้วย, lead to the failure of pneumatic equipment. นอกจาก, water will also spoil the products. ดังนั้น, the dryer is very important to the compressed air system.
นอกจาก, many industries have requirements for air quality. แน่นอน, different industries have different dryness requirements. ในบทความนี้, we will analyze why compressed air requires a dryer.
Lots of Moisture in Compressed Air System
All air compressor systems will generate condensation. ประการแรก, the atmosphere contains many water vapor. During compression, moisture enters the system together. As the pressure rises and cools, they turn into liquid water. These water droplets mix with air. ในที่สุด, they become moist air.
นอกจากนี้, the water vapor content will increase sharply with the increase in pressure. ตัวอย่างเช่น, compress the room air to 8 บาร์. The moisture content will increase approximately 8 ครั้ง. A 37KW air compressor will produce about 90L of water daily (relative humidity is 50%). ดังนั้น, we must discharge the water in the air storage tank daily. มิฉะนั้น, all kinds of problems will arise.
What Problems Does Humid Air Cause?
Moisture is troublesome in the manufacturing process. This could be better for users who use compressed air.
- ประการแรก, moisture tends to corrode pipes. So it will shorten the service life of the pipeline. นอกจากนี้, water will mix with oil and dust. This can easily clog the pipes. นอกจาก, water will also cause corrosion of pneumatic components, เป็นต้น;
- ประการที่สอง, it isn’t good for some special production processes. ตัวอย่างเช่น, water will affect power plant ash spraying, cement transportation, เป็นต้น;
- ประการที่สาม, it may also seriously impact product quality. ตัวอย่างเช่น, it will damage electronic products, medicines, อาหาร, เป็นต้น;
- อีกด้วย, liquid water forms a water hammer at a certain speed. This will damage air-use equipment such as cylinders, เป็นต้น.
- The most terrible thing is that water will breed bacteria. This is very harmful to human health.
So we must dry the compressed air with dryers.
Define Compressed Air Dryness
Air dryness is also known as moisture content. It generally refers to a certain amount of water vapor content in the air. We can define it in relative humidity, ppm of water content, or dew point. The dew point is a more useful term than relative humidity.
The dew point is defined as follows: Water vapor in the air cools under a certain pressure. At a certain time, condensation begins to form. We will call the temperature corresponding to this time the dew point. When the compressed air temperature and dew point are equal, the relative humidity is 100%. There are usually two types of dew points. นั่นคือ, “atmospheric dew point” and “pressure dew point”.
Assume that the relative humidity of the air is 100%. Then the atmospheric dew point refers to the temperature value at standard atmospheric pressure.
เช่นเดียวกัน, assume that the relative humidity of the air is 100%. The pressure dew point refers to the temperature value under a certain pressure. We generally use the PDP to explain the drying performance of air dryers.
The pressure dew point must be greater than the normal pressure dew point. ตัวอย่างเช่น, the dew point value of 7 bar pressure is 3°C. ณ ขณะนี้, the normal pressure dew point value is -20.8°C.
Different dew points, different water content. ตัวอย่างเช่น, assume that the pressure is 0.7MPa. When the pressure dew point is 10°C, the air moisture content is 1.2610g/m³. At a pressure dew point of 0°C, the water content of air is 0.7074g/m³. When the PDP is -20℃, the air-water content is only 0.1438g/m³.
Compressed Air Classes And Requirements For Various Industries
The standard for measuring the moisture content of compressed air is ISO 8573-1:2010. It classifies the pressure dew point (พีดีพี). นั่นคือ, ตั้งแต่ -70°C ถึง 10°C. ยิ่งหมายเลข PDP ต่ำลง, the higher the air quality need.
| ไอเอสโอ 8573-1:2010 ระดับ | PDP Pressure Dew Point Requirement | Application | Compressed Air Dryer Selection Advice |
| 0 | Requirements are stricter than class 1 | Electronic chip, high-tech products | —— |
| 1 | ≤-70C | Food, medical, เครื่องดื่ม, อิเล็กทรอนิกส์ | Desiccant air dryer |
| 2 | ≤-40C | High-end painting, precision pneumatic | Desiccant air dryer |
| 3 | ≤-20C | Packaging, textile, powder conveying | Desiccant or membrane dryer |
| 4 | ≤+3C | Instruments, laser cutting, furniture | Refrigeration air dryer |
| 5 | ≤+7C | Cylinders, motors, pneumatic tools | Refrigeration air dryer |
| 6 | ≤+10C | Factory general air | Refrigeration air dryer |
Different occasions, different pressure dew point requirements. ตัวอย่างเช่น, ordinary conveying lines, instrumentation air sources, and pneumatic tools need lower. The pressure dew point can be above 0℃. Precision spraying and food and beverage production requirements are high. The pressure dew point needed is below 0℃.
We made a comparison chart. This will better visualize the saturated water content of Class4~1 compressed air. Assume that there is 3600m3 compressed air. And the pressure is 7 บาร์. At 3℃ PDP, the water content is 20 liters. At -20℃, มันคือ 4.5 liters. And if PDP is -40℃, water content is less than 500 ml. ในที่สุด, มันคือ 10 ml at -70℃ pressure dew point.
Look at the chart again. For classes 4 ถึง 6, usually use the refrigerated air dryer. And for class 3 and below, we use a desiccant air dryer. นอกจาก, for class 3, it can also use the membrane dryer.
แน่นอน, we must choose the dryer according to the air demand. Do not blindly pursue compressed air high quality.
Function of Refrigerated Compressed Air Dryer
The dryer utilizes the refrigeration principle to reduce compressed air temperature. ในเวลาเดียวกัน, reduce the PDP pressure dew point to 3~10℃. Let the low-temperature refrigerant flow in the evaporator. Then it will exchange heat with the high-temperature air. Water vapor is supersaturated at low temperatures and condenses into liquid. หลังจากนั้น, separate the condensate from the compressed air. ในที่สุด, the water is get out of the dryer system. Refrigerant dryers can also remove some impurities and oil.
Characteristics of Refrigerant Air Dryer
- Does not consume compressed air. So energy consumption is low.
- No need to add or replace regular adsorbent. Operation cost is low.
- The noise is much lower than that of a desiccant dryer. The latter has the noise of pressure relief.
- There is no valve wear. Maintenance is simple, and the cost is low.
- The refrigerated dryer can meet the requirements as long as the dew point is not too high.
Refrigerant Dryer For Compressed Air Applications
- Laser cutting: The pressure dew point should be at least 10°C below. อีกด้วย, avoid low outlet temperatures. Prevent moisture from damaging the laser lens.
- Sandblasting: PDP must be not higher than 10℃. So it can spray the sand evenly on the surface of the object. มิฉะนั้น, moisture will affect the surface quality.
- General machinery and pneumatic tools: the pressure dew point should be between 3 and 10℃. Prevent moisture and impurities from damaging the equipment and pneumatic tools.
The Function of Air Compressor Desiccant Dryer
The working principle of an adsorption dryer is PSA. The desiccant in the working tower will adsorb the water vapor. ดังนั้น, it achieves the purpose of compressed air drying. Desiccant air dryer working is divided into two processes.
หนึ่งคือกระบวนการดูดซับ. Compressed air through the working tower. Due to the role of physical adsorption power, water vapor penetrates the adsorbent. Aluminum oxide/molecular sieve reduces the water vapor content. The dew point of the desiccant dryer is up to -20/-40/-70℃. สามารถถอดประมาณ 98.95%/99.86%/99.99% of water vapor, ตามลำดับ.
Another process is regeneration. นั่นคือ, make the adsorbent above regain the adsorption capacity. So it can be prepared for the cycle work.
Features of Adsorption Dryer For Compressed Air
- It has extremely strong water removal ability. The dew point of the adsorption dryer can be as low as -70℃. It can now remove 99.99% of the water in the system.
- Many options are available. There are many types of desiccant dryers. If the airflow is not high, you can choose a heatless or heated purge dryer. They are also relatively cheap. You can choose the blower purge air dryer if the airflow is high. ตอนนี้, it has an obvious energy-saving effect. อีกด้วย, if you use an oil-free or centrifugal air compressor, you can choose compression of heat air dryer.
Desiccant Air Dryer Applications
- Powder conveying: The pressure dew point should be below -20℃. มิฉะนั้น, the powder product is prone to clumping. In serious cases, it will cause blockage.
- Precision spraying: The pressure dew point must be -40℃. So the paint can be evenly sprayed on the surface of the object. มิฉะนั้น, problems such as paint collapsing will occur.
- Food processing: The PDP must reach -40℃ or -70℃. It needs a dry air source. Prevent bacteria from growing.
- Electronics, semiconductor: the pressure dew point should meet -70℃. Because tiny moisture can cause these products to be scrapped.
สรุป, we need dryer to remove water from compressed air.