How to improve air quality by using cold dryer?

Through the use of cold dryer to improve air quality, the core lies in efficient removal of water vapor, oil and particulate matter in compressed air so as to prevent equipment corrosion, pneumatic component failure, product pollution and other problems. The following are the specific principles, operation steps, optimization strategies and case studies of the cold dryer to improve air quality:

the principle of 1. cold dryer to improve air quality

cold dryer (freeze dryer) through cooling-Condensation-Drainage three steps, the water vapor in the compressed air is converted into liquid water and discharged, while reducing the concentration of oil and particulate matter:

1. pre-cooling:
   before the compressed air enters the cold dryer, it exchanges heat with the low-temperature dry air through the pre-cooler (or air-air heat exchanger) to initially cool down and recover the cold.
2. Cooling:
   the air enters the evaporator and exchanges heat with the refrigerant (such as R407C), the temperature drops to 2-10°C (dew point temperature), and the water vapor condenses into liquid water.
3. gas-water separation:
   the condensed water flows into the air-water separator and is separated by centrifugation, baffle or filter element. The liquid water is discharged through the automatic drain, and the dry air enters the aftercooler.
4. Rear cooling and discharge:
   the dry air is returned to normal temperature through the aftercooler to avoid condensation in the pipeline and further reduce the water content.

Effect:

• the dew point of compressed air is reduced to 2-10 ℃, and the water content is reduced by more than 90%.
• Indirect reduction of oil (due to condensate to take away part of the lubricating oil) and particulate matter (gas-water separator intercept).

2. operation steps: correct use of cold dryer

1. Installation and commissioning

• location selection:
  • install it behind the air compressor and in front of the air storage tank to ensure that the compressed air temperature is ≤ 45 ℃ (too high will reduce the efficiency of the cold dryer).
  • Avoid direct sunlight or high temperature environment, maintain good ventilation.
• Pipe connection:
  • inlet pipe diameter ≥ outlet pipe diameter of air compressor to reduce pressure drop.
  • The slope of the outlet pipe is ≥ 1/100 to facilitate the condensate to flow to the drainage point.
• Debugging Parameters:
  • set the evaporation pressure (corresponding to dew point temperature). If dew point ≤ 5 ℃ is required, adjust the evaporation pressure to 0.3-0.5MPa.
  • Check the refrigerant charge to avoid insufficient or excessive.

2. Daily operation management

• temperature monitoring:
  • inlet temperature: ≤ 45 ℃ (if it is too high, a pre-cooler shall be installed).
  • Outlet temperature: 10-15 ℃ lower than the inlet temperature (if the inlet is 40 ℃, the outlet should be ≤ 30 ℃).
  • Dew point temperature: regularly detected by dew point meter to ensure the process requirements (such as painting to be ≤ 3 ℃).
• Drainage Management:
  • use an electronic automatic drain and set the drain interval (e. g. 30 seconds every 15 minutes).
  • Manually check whether the drain is blocked every day, and clean up rust or oil.
• Differential pressure monitoring:
  • evaporator pressure difference ≤ 0.02MPa, more than the need to clean the fins or check the refrigerant.

3. Regular maintenance

• monthly maintenance:
  • clean the condenser fins (purge with compressed air or clean with a soft bristle brush).
  • Check the refrigerant pressure and replenish the leaked refrigerant.
• Quarterly Maintenance:
  • clean the filter element of the air-water separator (if removable and washable).
  • Check whether the automatic drain solenoid valve is sensitive.
• Annual maintenance:
  • replace the desiccant (such as molecular sieve, if the cold dryer integrated adsorption function).
  • Check compressor oil level and replace aged seals.

3. optimization strategy: improve the effect of cold dryer

1. Pretreatment optimization

• pre-filter:
  • class C (coarse efficiency) and Class T (precision) filters shall be installed in front of the cold dryer to intercept particles ≥ 5μm and oil mist and reduce the load of the gas-water separator.
  • Example after adding the pre-filter in an electronic factory, the cleaning period of the air-water separator of the cold dryer was extended from 1 month to 3 months.
• Pre-cooler:
  • if the outlet temperature of the air compressor is higher than 45 ℃, install air-cooled or water-cooled pre-cooler to reduce the temperature below 40 ℃ to improve the efficiency of the cold dryer.

2. Parameter adjustment

• evaporation temperature control:
  • adjust the evaporation temperature according to the gas requirements. If the painting industry needs dew point ≤ 3 ℃, the evaporation temperature should be adjusted to 2-5 ℃.
  • Attention: Low evaporation temperature may cause icing (e. g. <0 ℃). Monitor the differential pressure to prevent ice blockage.
• Refrigerant flow optimization:
  • adjust the refrigerant flow through the expansion valve to avoid uneven frosting of the evaporator (such as freezing of some fins).

3. Post-processing strengthening

• post Filter:
  • A grade (activated carbon) and F grade (ultra-precision) filters are installed after the cold dryer to further remove oil (≤ 0.01ppm) and particulate matter (≤ 0.01 μm).
  • Applicable Scenarios the food and pharmaceutical industries have high air quality requirements.
• Pipe insulation:
  • the pipeline from the outlet of the cold dryer to the gas point is equipped with a thermal insulation sleeve to reduce the secondary generation of condensed water caused by temperature rise.

4. common problems and solutions

1. Dew point not up to standard

• reason:
  • insufficient refrigerant, evaporator frosting, high inlet temperature.
• Solve:
  • replenish the refrigerant, clean the evaporator and install the pre-cooler.

2. Poor drainage

• reason:
  • failure of automatic drainer, insufficient pipeline slope, blockage of gas-water separator.
• Solve:
  • replace the drainer, adjust the pipe slope, and clean the separator filter element.

3. Excessive pressure drop

• reason:
  • evaporator fin blockage, filter blockage.
• Solve:
  • clean the fins and replace the filter element.

5. Case Analysis: Application of Cold Dryer in Manufacturing Industry

case 1: Car painting workshop

• question: The high water content of compressed air causes bubbles and orange peel on the painted surface.
• Programme:
  • install cold dryer (dew point ≤ 3 ℃)+ post activated carbon filter.
  • The pipeline shall be equipped with insulation sleeve to avoid condensation.
• Effect: The qualified rate of painting increased from 85% to 98%, and the annual rework cost decreased by 200000 yuan.

Case 2: Electronic Component Production

• question: The compressed air oil content exceeds the standard (>0.1ppm) and pollutes precision components.
• Programme:
  • cold dryer before the installation of T-level precision filter, after the installation of A- level activated carbon filter.
  • Regularly detect the oil concentration and adjust the filter replacement cycle.
• Effect: Component defect rate decreased from 5% to 0.3 and customer complaints decreased by 90%.

6. effect verification and continuous improvement

1. dew point detection:
   • use a portable dew point meter to detect the dew point of the outlet monthly to ensure compliance with process requirements.
2. Oil detection:
   • through the oil concentration detector (such as light scattering method) regular sampling, verify the filter effect.
3. Data logging:
   • record the inlet/outlet temperature, pressure difference, displacement and other parameters, and analyze the operating efficiency of the system.
4. Energy efficiency optimization:
   • adjust the load of the cold dryer according to the fluctuation of gas consumption (such as frequency conversion control) to reduce energy consumption.

Summary

through the correct use of cold dryer, can significantly improve the quality of compressed air, specific needs:

1. reasonable selection: Select the processing capacity of the cold dryer according to the air compressor flow rate and gas consumption requirements (e. g. air compressor 5 Nm & sup3;/min, the cold dryer shall be ≥ 5 Nm & sup3;/min).
2. Pre-treatment + post-treatment: The pre-filter intercepts impurities, and the post-filter is deeply purified.
3. parameter optimization: Adjust the evaporation temperature and refrigerant flow to avoid icing or inefficiency.
4. Regular maintenance: Clean the fins, replace the filter element, and check the refrigerant to ensure long-term stable operation.