Startup and Shutdown Operations of Screw Chiller

2024-09-25

Startup operation of screw chiller unit:
After the screw refrigeration compressor undergoes trial operation and the discovered problems are dealt with, it can enter the normal operation procedure. The operation method is as follows:
(1) Confirm whether the states of the relevant valves in the unit meet the startup requirements.
(2) Supply power to the electrical control device of the unit and turn on the power switch to make the power control indicator light on.
(3) Start the cooling water pump, cooling tower fan and refrigerant water pump. The operation indicator lights of the three should be visible.
(4) Detect whether the oil temperature of lubricating oil reaches 30 °C. If it is not up to 30 °C, turn on the electric heater for heating. At the same time, start the oil pump to make the lubricating oil circulation temperature increase evenly.
(5) After the oil pump starts running, place the energy regulation control valve in the unloading position and ensure that the slide valve is at zero position.
(6) Adjust the oil pressure regulating valve to make the oil pressure reach 0.5-0.6 MPa.
(7) Close the compressor power supply, start the control switch, open the compressor suction valve. After a delay, the compressor starts running. After the compressor runs, adjust the lubricating oil pressure to make it 0.15-0.3 MPa higher than the exhaust pressure.
(8) Close the solenoid valve control circuit in the liquid supply pipeline, start the solenoid valve, supply liquid refrigerant to the evaporator. Place the energy regulation device in the loading position and increase the load step by step over time. At the same time, observe the suction pressure and stabilize the suction pressure at 0.36-0.56 MPa by adjusting the expansion valve.
(9) After the compressor runs, when the lubricating oil temperature reaches 45 °C, disconnect the power supply of the electric heater. At the same time, open the inlet and outlet valves of the cooling water of the oil cooler to control the oil temperature within the range of 40-55 °C during the compressor operation.
(10) If the cooling water temperature is relatively low, the cooling tower fan can be temporarily turned off.
(11) Open the oil injection valve by 1/2 to 1 turn. At the same time, the suction valve and the liquid outlet valve of the unit should be in the fully open position.
(12) Adjust the energy regulation device to 100% position. At the same time, adjust the expansion valve to keep the suction superheat above 6 °C.
(13) Inspection during the startup and operation of the screw chiller unit. After the unit is started and put into operation, attention should be paid to the inspection of the following contents to ensure the safe operation of the unit.

The sound and vibration conditions of the refrigerant water pump, cooling water pump and cooling tower fan during operation, and whether various indicators such as the outlet pressure and water temperature of the pump are within the normal working parameter range.
Whether the oil temperature of lubricating oil is below 60 °C, whether the oil pressure is 0.15-0.3 MPa higher than the exhaust pressure, and whether the oil level is normal.
When the compressor is in full-load operation, whether the suction pressure value is within the range of 0.36-0.56 MPa.
Whether the exhaust pressure of the compressor is below 1.55 MPa and whether the exhaust temperature is below 100 °C.
During the operation of the screw chiller unit compressor, whether the operating current of the motor is within the specified range. If the current is too large, it should be adjusted to run under reduced load to prevent the motor from being burned due to excessive operating current.
Whether the sound and vibration conditions of the compressor during operation are normal.
Among the above items, if any abnormal situation is found, the unit should be shut down immediately. After finding out the cause and troubleshooting, the unit can be restarted. Never let the screw chiller unit run with problems to avoid major accidents.
Shutdown operation of screw refrigeration compressor
The shutdown of screw refrigeration compressor can be divided into shutdown modes such as normal shutdown, emergency shutdown, automatic shutdown and long-term shutdown.

Operation method of normal shutdown
(1) Place the manual unloading control device in the unloading position.
(2) Close the solenoid valve and liquid outlet valve on the liquid supply pipeline between the condenser and the evaporator.
(3) Stop the compressor operation and close its suction valve at the same time.

(4) After the energy is reduced to zero, stop the oil pump.
(5) Place the energy regulation device in the "stop" position.
(6) Close the cooling water inlet valve of the oil cooler.
(7) Stop the operation of the cooling water pump and cooling tower fan.
(8) Stop the operation of the refrigerant water pump.
(9) Turn off the main power supply.
Emergency shutdown of the unit
During the normal operation of the screw refrigeration compressor, if abnormal phenomena are found; in order to protect the safety of the unit, emergency shutdown should be implemented. The operation method is as follows:
(1) Stop the compressor operation.
(2) Close the suction valve of the compressor.
(3) Close the solenoid valve on the unit's liquid supply pipe and the liquid outlet valve of the condenser.
(4) Stop the oil pump.
(5) Close the cooling water inlet valve of the oil cooler.
(6) Stop the refrigerant water pump, cooling water pump and cooling tower fan.
(7) Cut off the main power supply.
When the unit encounters power outages, water outages and other failures during operation, the shutdown method can be handled with reference to the relevant content in the emergency shutdown of centrifugal compressors.
After the unit is emergently shut down, the cause of the failure should be found out in time. After troubleshooting, the unit can be restarted according to the normal startup method.
Automatic shutdown of the unit
During the operation of the screw refrigeration compressor, if the pressure and temperature values of the unit exceed the specified range, the protection device in the unit control system will function and automatically stop the compressor. This phenomenon is called automatic shutdown of the unit. When the unit is automatically shut down, the corresponding fault indicator light on the electrical control panel of the unit will light up to indicate the location of the fault. When this happens, after the main unit is shut down, the shutdown operation of other parts can be handled according to the emergency shutdown method. After completing the shutdown operation, the unit should be inspected. Only after troubleshooting can it be restarted and run according to the normal startup procedure.
Long-term shutdown of the unit
Since the screw refrigeration compressor used as the cold source of central air conditioning operates seasonally, the shutdown time of the unit is relatively long.
To ensure the safety of the unit, during seasonal shutdown, the shutdown operation can be carried out according to the following methods.
(1) When the unit is operating normally, close the liquid outlet valve of the unit to make the unit run under reduced load and pump all the refrigerant in the unit to the condenser. In order to prevent the unit from shutting down due to too low suction pressure, the set value of the low-pressure pressure relay can be adjusted to 0.15 MPa. When the suction pressure drops to about 0.15 MPa, the compressor shuts down. After the compressor shuts down, the low-pressure pressure value can be adjusted back.
(2) Drain the water in the stopped oil cooler, condenser and evaporator and drain the remaining water to prevent the internal heat transfer tubes from being damaged by freezing in winter.
(3) Close the relevant valves in the unit and check for leakage.
(4) The lubricating oil pump should be started to run for 10-20 minutes every week so that the lubricating oil can be evenly distributed to all working surfaces in the compressor for a long time to prevent the unit from causing lack of oil on the surface of parts due to long-term shutdown and causing difficulties in restarting.