Moisture in compressed air, how to filter at the back end

The moisture in the compressed air is filtered mainly through a multi-stage filtration system, which combines the adsorption, condensation and separation of different filter elements to effectively remove liquid water, water vapor and impurities. The following are specific methods and steps:

core objectives of 1. back-end filtering

the core of compressed air back-end filtration is to remove moisture (liquid water and water vapor), oil and solid particles in the compressed air to ensure that the output air meets specific cleanliness standards (such as ISO 8573-1) and meets the air quality requirements of different industries.

Main methods of 2. back-end filtering

1. Multi-stage filtration system

the back-end filtration usually adopts a multi-stage series design, and each stage of the filter element intercepts pollutants of different particle sizes and forms to gradually improve air quality. A typical configuration is:

• pre-filter (coarse filter)
  • role: Intercepts large particles of impurities (such as dust, rust) and some liquid water.
  • Principle: Remove particles with a particle size ≥ 5 μm through the mechanical interception of the filter element.
  • Filter element type: Metal mesh filter element or fiber filter element, can be cleaned or replaced.
• Precision filter (fine filter)
  • role: Further remove small particles of impurities (such as oil mist, fine dust) and residual liquid water.
  • Principle: Using deep filtration technology, the filter element material (such as glass fiber) removes particles with a particle size ≥ 1μm through adsorption and interception.
  • Filter element type: High-efficiency glass fiber filter element, which needs to be replaced regularly.
• Activated carbon filter (deodorization/degreasing)
  • role: Adsorbs gaseous pollutants (such as oil vapor, peculiar smell) to further reduce the water vapor content.
  • Principle: The porous structure of activated carbon removes gaseous molecules through physical adsorption.
  • Filter element type: Activated carbon particles or activated carbon fiber filter element, need to be replaced regularly.
• Dryer (optional)
  • role: Reduce the dew point of compressed air and remove water vapor.
  • Type:
    • freeze dryer: By cooling the compressed air below the dew point, the water vapor is condensed into liquid water and discharged.
    • adsorption dryer: The use of adsorbents (such as silica gel, molecular sieve) physical adsorption, removal of water vapor, can achieve a lower dew point (such as -40 ℃ below).

2. The role of key filter elements

• cohesive filter element
  • role: Condensing small water droplets and oil droplets into large droplets for subsequent separation.
  • Principle: The filter element material (such as hydrophobic glass fiber) causes the droplets to gather and sink to the bottom of the filter through surface tension, and is discharged through the automatic drain valve.
  • Application Scenarios: Commonly used in precision filters, it can remove droplets with particle size ≥ 0.01μm.
• Hydrophobic filter element
  • role: Prevent liquid water from entering downstream equipment through the filter element.
  • Principle: The filter element material is hydrophobic, liquid water cannot penetrate, and can only be discharged from the bottom.
  • Application Scenarios: The drainage section of the pre-filter or precision filter.

Implementation steps for 3. back-end filtering

1. assess needs
   • determine the use of the compressed air (e. g. pneumatic tools, spraying, food processing) and the required air quality class (e. g. ISO 8573-1 Class 1-6).
   • Select the appropriate filter stage and filter element type according to the requirements.
2. Installation of multistage filtration systems
   • install the filters in series according to the order of "coarse filtration & rarr; fine filtration & rarr; deodorization/degreasing" to ensure that there is enough space and pipe connection between each stage of filters.
   • Install an automatic drain valve at the bottom of the filter to drain condensate regularly.
3. Configure dryer (if required)
   • according to the dew point requirements, choose refrigeration or adsorption dryer, installed after the filtration system.
   • Ensure that the inlet air temperature, pressure and flow rate of the dryer match the compressed air system.
4. Regular maintenance
   • replace filter element: Replace the filter element regularly according to the differential pressure indicator or the use time to avoid pressure loss caused by blockage of the filter element.
   • Check the drain valve: Ensure that the automatic drain valve works normally to avoid condensation accumulation.
   • Monitoring air quality: Regularly detect the water content, oil content and particle concentration of compressed air to ensure compliance with standards.

4. application cases in different industries

• food processing industry
  • demand: Compressed air must be sterile, oil-free and water-free (e. g. ISO 8573-1 Class 0).
  • Programme: Adopt the multi-stage filtration system of "pre-filter precision filter activated carbon filter adsorption dryer" to ensure air quality.
• electronic manufacturing industry
  • demand: The compressed air shall be free of dust, oil and low dew point (such as dew point ≤-40 ℃).
  • Programme: The combination of "precision filter adsorption dryer" and high-efficiency filter element are adopted to meet the cleaning requirements of precision components.
• automobile maintenance industry
  • demand: Compressed air should be dry and oil-free to protect pneumatic tools and spraying equipment.
  • Programme: Adopt the simple configuration of "pre-filter freeze dryer" to reduce costs while meeting basic needs.