Comprehensive Introduction to Air Compressors and Refrigerated Air Dryers
Air Compressor & Refrigerated Air Dryer System
1 System Overview
Air Compressor No.1
The screw air compressor is a positive displacement gas compression machine with rotary working chambers. Gas compression is realized by the rotary motion of a pair of rotors inside the housing.
Air flows through the intake filter and open intake regulator into the air end. As the male and female rotors rotate, the incoming air is compressed. Lubricating oil is injected into the compression chamber during compression.
Continuous rotation of the rotors increases the pressure of the oil-gas mixture. The mixture flows out through the air end discharge port and enters the oil-gas separator for oil and gas separation.
In this system, closed-circuit cooling water cools the oil first, and then cools the air.
Automatically load when system pressure drops to 0.63 MPa
Unload when system pressure rises to 0.75 MPa
Refrigerated Air Dryer No.2
Compressed air first passes through the oil removal filter to remove most liquid water and oil. Afterwards, the air flows sequentially through the pre-cooler, evaporator,
air-water separator and desiccant air dryer inside the refrigerated air dryer unit, so that the compressed air becomes clean, dry and impurity-free to meet user requirements.
2 System Schematic Diagram
Schematic Diagram of Air Compressor System
Schematic Diagram of Refrigerated Air Dryer System
Operation Instructions
1 Air Compressor Control Panel
Page switching operation: The three display fields on the last line of the display screen correspond to the three function keys on the controller panel.
Press the corresponding keys according to prompts to switch pages or execute functions. Arrow indicators appear at the upper right corner of most pages;
there are three types of indicators: upward arrow, downward arrow and question mark. The arrow indicates that page turning can be performed by pressing the triangular button on the controller.
2 Refrigerated Air Dryer LCD Panel (To Be Completed)
Operating cycle of the refrigerated air dryer system
4 Trip Interlock Logic
1 Interlock Logic of Air Compressors: Auto-start Conditions
Taking Air Compressor A as an example, Air Compressor A will start automatically if any of the following conditions is satisfied:
Air Compressor A is set as the primary standby unit, and either Unit B or C is out of service.
Air Compressor A is set as the primary standby unit, and the pressure of the compressor outlet header drops below 0.65 MPa with a 3-second delay.
Air Compressor A is set as the secondary standby unit; the primary standby compressor fails to start, or the outlet header pressure falls below 0.60 MPa with a 3-second delay.
2 Interlock Logic of Refrigerated Air Dryers
Protective Shutdown Conditions
When Air Compressor A, B and C are all shut down, Refrigerated Air Dryer A will trip for protection after a 60-second delay. (Refrigerated Air Dryer A is taken as an example below.)
Startup Conditions
Auto-start Conditions
Refrigerated Air Dryer A is allowed to start when any one of Air Compressor A/B/C is running.
When interlock function is enabled, Refrigerated Air Dryer A will be automatically started upon trip of Refrigerated Air Dryer B.
5 Operation, Maintenance & Servicing
1 Operation & Maintenance Notes
Air Compressor Section
Faults shall be inspected and handled in accordance with the troubleshooting reference table.
When the intake temperature ≤40°C, discharge temperature shall be lower than 95°C. Replace spare parts timely to avoid severe burnout accidents caused by oil shortage. The unit can be restarted after troubleshooting.
During operation, monitor the oil level frequently. If the oil level drops rapidly or the discharged compressed air carries excessive oil...
Check whether readings of all instruments stay within normal ranges, and confirm air pressure is within the rated range. Monitor compressor intake temperature.
If the pressure difference across the fine oil separator or oil filter exceeds the limit, an alarm will pop up on the controller screen. The compressor can keep running temporarily, but maintenance must be arranged promptly.
If the discharge temperature is excessively high and triggers an alarm on the controller, the main unit will shut down automatically. The unit can only be restarted after root cause identification and troubleshooting.
Listen for abnormal noise during unit operation. If abnormal noise occurs, shut down the unit immediately to eliminate faults.
Compressor maintenance shall be carried out after shutdown, full cooling of the unit and sufficient sedimentation of condensate. Slowly open the ball valve for draining. Close the valve once oil flows out.
Refrigerated Air Dryer Section
Verify the supply air pressure is no less than 0.6 MPa and temperature does not exceed 40°C.
Check condensate drainage of each separator upstream of the oil filter.
Inspect automatic oil drainage performance of the oil filter.
Open the blowdown valve of the dust filter every day during initial operation to discharge dust. Extend the interval appropriately according to actual operating conditions afterwards.
Check the muffler for clogging.
Monitor pressure drop across oil filters and dust filters. Replace filter elements if the pressure drop exceeds 0.05 MPa.
Check the dew point of dried air. If no dew point meter is available, observe the color-changing silica gel inside the filter on the solenoid valve air supply pipeline. Blue-to-red discoloration indicates insufficient air dryness.
Verify the electric heater outlet temperature is maintained between 140°C and 160°C.
Monitor the pressure of the regeneration tower, which is generally required to be lower than 0.010 MPa.
Observe whether switching of adsorption towers is performed according to the set cycle during operation.
2 Key Accident Handling Guidelines
When the alarm of "low instrument air pressure" is triggered in the central control room, operators shall check the HMI of instrument air compressors immediately.
If the running air compressor trips or fails to load, check whether standby compressors start. If the started standby unit also cannot load, report to the shift supervisor immediately.
Each unit shall stabilize load and minimize operation of pneumatic control valves. The shift supervisor shall arrange maintenance personnel to the site rapidly.
If the instrument air compressor system fails completely and all service air compressors fail to load or lose power supply, central control operators shall prepare contingency plans.
The shift supervisor shall contact maintenance staff for on-site treatment and arrange electrical operators to investigate the cause of compressor trips and check for faults on the 380V main plant busbar.
After plant air supply interruption, operators of each unit in the central control room shall maintain unit load and monitor the status of all pneumatic isolating valves and regulating valves.
Boiler side: Monitor status changes of attemperating water isolating valves, attemperating water regulating valves, continuous blowdown regulating valves and other valves; monitor all pneumatic valves and regulating valves of the gas system.
Turbine side: Monitor status changes of main unit and shaft seal attemperating water regulating valves, each heater drain regulating valve, extraction check valves and other valves under loss of instrument air.
For the above valves, switch to local manual adjustment if regulation is required to stabilize operating parameters.
If manual intervention of partial pneumatic valves fails and unit operating parameters reach shutdown criteria, report to the shift supervisor immediately and execute turbine emergency trip.
Restore operation of the instrument compressed air system as soon as possible, and prepare each unit for very hot start-up.
If compressed air loss is caused by complete loss of plant power supply, follow the handling procedure for complete plant power failure.
Restore air compressor operation at the earliest opportunity to prevent misoperation of pneumatic valves. If compressors cannot be restored,
close related valves locally to avoid unintended action of pneumatic valves. Close the manual inlet valve of steam pipeline drainers to prevent massive
drainage from entering the condenser and inducing thermal shock to condenser titanium tubes.
