Working Principle of Refrigerated Air Dryer
Compressed air from the air compressor first exchanges heat in a heat exchanger with dried low-temperature compressed air, lowering its temperature. It then enters the evaporator and is further cooled to approximately 2 degrees Celsius. At this dew point, most of the water in the compressed air has become liquid and is discharged. The compressed air with minimal water content enters the adsorption tower for further drying and water removal. Finally, the low-temperature dried compressed air enters the heat exchanger to cool the high-temperature moist air while its own temperature rises, preventing condensation on the compressed air delivery pipeline exterior.
The refrigerated air dryer uses refrigerant to exchange heat with compressed air, lowering the compressed air temperature to a dew point range of 2 to 10 degrees Celsius, bringing the water content in the compressed air to a supersaturated state, thereby removing moisture (water vapor component) from the compressed air.
Functions of Main Components
Refrigeration Compressor: The heart of the refrigeration system. It raises refrigerant from low pressure to high pressure and causes the refrigerant to continuously circulate, allowing the system to continuously discharge internal heat to the environment above the system temperature.
Condenser: The role of the condenser is to cool the high-pressure, superheated refrigerant vapor discharged from the refrigeration compressor into a liquid refrigerant. Its heat is removed by cooling water, allowing the refrigeration process to proceed continuously.
Evaporator: The evaporator is the main heat exchange component of the refrigerated dryer. Compressed air is forcibly cooled in the evaporator, and most water vapor cools and condenses into liquid water discharged outside the machine, thereby drying the compressed air. Low-pressure refrigerant liquid undergoes a phase change in the evaporator into low-pressure refrigerant vapor, absorbing surrounding heat during the phase change, thereby lowering the compressed air temperature.
Thermostatic Expansion Valve (Capillary Tube): The thermostatic expansion valve is the throttling mechanism of the refrigeration system. In the refrigerated dryer, the supply and regulation of evaporator refrigerant is achieved through the throttling mechanism. The throttling mechanism causes the refrigerant to enter the evaporator from a high-temperature, high-pressure liquid state.
Heat Exchanger: The heat exchanger recovers the cooling capacity carried by the compressed air cooled by the evaporator and uses this cooling capacity to cool the higher-temperature compressed air carrying large amounts of water vapor. This reduces the thermal load on the refrigerated machine refrigeration system, achieving energy savings. Additionally, the low-temperature compressed air temperature rises in the heat exchanger, preventing "condensation" on the compressed air delivery pipeline exterior due to temperature below ambient temperature.
Compressed Air Process Flow
Compressed Air → Mechanical Filter → Heat Exchanger (releases heat) → Evaporator → Gas-Liquid Separator → Heat Exchanger (absorbs heat) → Outlet Mechanical Filter → Air Storage Tank
Pre-Startup Checks
- All valves in the pipeline system should be in normal standby condition.
- Cooling water valve should be open, water pressure should be between 0.15 and 0.4 MPa, water temperature below 31 degrees Celsius.
- The refrigerant high-pressure and low-pressure gauges on the instrument panel should show indication and be approximately equal.
- Check power supply voltage, must not exceed rated value by 10 percent.
Startup Procedure
- Press the start button, the AC contactor delays 3 minutes before starting, refrigerant compressor begins operation.
- Observe the instrument panel, refrigerant high-pressure gauge should slowly rise to approximately 1.4 MPa, refrigerant low-pressure gauge should slowly drop to approximately 0.4 MPa. The machine has now entered normal working condition.
- After the dryer has been running for 3 to 5 minutes, slowly open the inlet air valve, then open the outlet air valve according to the load addition rate until full load.
- Check whether inlet and outlet air pressure are normal (pressure difference of 0.03 MPa between the two gauges should be normal).
- Check whether automatic drainer drainage is normal.
- Periodically check dryer working condition, record air inlet and outlet pressure, refrigerant high and low pressure, etc.
Shutdown Procedure
- Close outlet air valve.
- Close inlet air valve.
- Press the stop button.
Safety Precautions
- Avoid prolonged operation without load.
- Do not start the refrigerant compressor continuously; the number of starts and stops per hour must not exceed 6 times.
- To ensure air supply quality, strictly observe startup and shutdown sequences.
- Startup: Let the dryer run for 3 to 5 minutes before opening the air compressor or inlet air valve.
- Shutdown: First close the air compressor or outlet air valve, then turn off the dryer.
- The bypass valve spanning the dryer inlet and outlet in the pipeline network must be tightly closed during operation to prevent untreated air from entering the downstream air pipeline network.
- Air pressure must not exceed 0.95 MPa.
- Inlet air temperature must not exceed 45 degrees.
- Cooling water temperature must not exceed 31 degrees.
- Do not start the machine when ambient temperature is below 2 degrees Celsius.
- Time relay setting inside the electrical control cabinet must not be less than 3 minutes.
Maintenance and Inspection
Maintain the refrigerated dryer dew point temperature above zero degrees Celsius. Check that the compressed air inlet and outlet pressure difference does not exceed 0.035 MPa. Evaporator pressure gauge should read 0.4 to 0.5 MPa. High-pressure gauge should read 1.2 to 1.6 MPa. Regularly observe the drainage and sewage discharge system.
