First, the preparation work before starting the screw refrigeration unit.
The correct debugging of refrigeration unit is an important link to ensure the normal operation of refrigeration unit, save energy consumption and prolong service life. For large and medium-sized refrigeration systems installed on site, before debugging, you should first be familiar with the layout and connection of the whole system according to the requirements of design drawings, and understand the external structure and component performance of each equipment, as well as the electrical control system and water supply system. 1, preparation before debugging
1) Check whether the installation of the unit meets the technical requirements, whether the foundation of the unit meets the requirements, and whether the size, specifications and materials of the connecting pipes meet the design requirements. 2) Check whether the power supply system of the unit is normal.
3) Carry out water passing test on the cold water and cooling water system separately to flush the sewage in the waterway system. The water pump should work normally, and the circulating water should meet the requirements of working conditions.
4) Check whether the pressure gauge, thermometer and sensor on the pipeline are normal, 5) Check whether the water pressure in the pipeline is normal, and 6) Prepare necessary safety protection articles during operation. 2. Unit debugging
1) Check whether all valves in the refrigeration system are normally open, especially the exhaust stop valve, and do not close it.
2) Open the condenser cooling water valve and evaporator cooling water valve, and the flow of cold water and cooling water shall meet the requirements put forward by the manufacturer.
3) Observe whether the power supply voltage of the unit is normal before starting. 4) Start the unit according to the startup manual provided by the manufacturer.
5) When the unit is started, check whether the parameters of the unit are normal according to the startup manual provided by the manufacturer. 6) According to the unit operation data record table provided by the manufacturer, all data of the unit can be recorded, especially some main parameters must be recorded clearly.
7) During the operation of the unit, pay attention to whether the loading and unloading mechanism of the compressor works normally. 8) Safety protection devices installed in the refrigeration system should be used correctly, such as high and low pressure protection devices, cold water and cooling water cut-off flow switches, safety valves and other equipment. If damaged, they should be replaced in time. 9) If the unit is abnormal, stop the machine immediately for inspection.
Before debugging the refrigeration system, it is necessary to clean and dry the inside of the air conditioning system. If the preliminary work is not carried out seriously, it will increase a lot of workload during debugging and bring many hidden dangers to the future operation of the refrigeration device.
Second, the screw refrigeration unit start operation
After the screw refrigeration compressor is put into trial operation and the problems found are solved, it can enter the normal operation procedure. The operation method is as follows:
(1) Confirm whether the states of all relevant valves of the unit meet the startup requirements.
(2) Power the electrical control device of the unit, turn on the power switch, and the power control indicator light will be on. (3) Start the cooling water pump, cooling tower fan and refrigerant water pump, and you should be able to see the operation indicators of the three. (4) Check whether the oil temperature of lubricating oil reaches 30℃. When the temperature is lower than 30℃, the electric heater should be turned on for heating, and the oil pump can be started at the same time to make the circulating temperature of lubricating oil rise evenly.
(5) After the oil pump starts running, put the energy regulating 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) Turn off the compressor power supply, start the control switch, open the compressor suction valve, start the compressor after a delay, and adjust the lubricating oil pressure after the compressor runs to make it higher than the exhaust pressure by 0. 15 ~ 0.3 MPa.
(8) Close the solenoid valve control circuit in the liquid supply pipeline, start the solenoid valve, supply liquid refrigerant to the evaporator, put the energy regulating device in the loading position, and gradually increase the load with the passage of time. At the same time, the suction pressure was observed, and the suction pressure was stabilized at 0.36 ~ 0.56 MPa by adjusting the expansion valve.
(9) After the compressor is running, when the lubricating oil temperature reaches 45℃, disconnect the power supply of the electric heater and open the inlet and outlet valves of the cooling water of the oil cooler at the same time, so as to control the oil temperature within the range of 40 ~ 55℃ when the compressor is running.
(10) If the cooling water temperature is low, the fan of the cooling tower can be temporarily turned off.
(1 1) Open the fuel injection valve 1/2 ~ 1 circle, and keep the suction valve and liquid outlet valve of the unit in the fully open position. (12) Adjust the energy regulator to the position of 100%, and adjust the expansion valve to keep the suction superheat above 6℃.
(13) Inspection during unit startup. After the unit is started and put into operation, the following contents should be checked to ensure the safe operation of the unit.
(14) Whether the sound and vibration, pump outlet pressure, water temperature and other indicators during operation of chilled water pump, cooling water pump and cooling tower fan are within the normal working parameters.
(15) Whether the oil temperature of lubricating oil is lower than 60℃, whether the oil pressure is higher than the exhaust pressure by 0. 15 ~ 0.3 MPa, and whether the oil level is normal.
(16) Whether the suction pressure is in the range of 0.36 ~ 0.25. The compressor is 56MPa at full load.
(17) Whether the compressor discharge pressure is lower than 1.55MPa and the discharge temperature is lower than 100℃. (18) Whether the running current of the motor is within the specified range when the compressor is running. If the current is too large, it should be adjusted to reduce the load to prevent the motor from burning out due to the excessive current. (19) Whether the sound and vibration of the compressor are normal during operation.
In the above-mentioned projects, if any abnormal situation is found, stop the machine immediately, find out the reason and eliminate the fault before restarting the unit. Never let the unit run with problems, so as not to cause major accidents. Three, screw refrigeration compressor shutdown operation
The shutdown of screw refrigeration compressor can be divided into normal shutdown, emergency shutdown, automatic shutdown and long-term shutdown.
1. Operation method of normal shutdown
(l) 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 diffuser. (3) Stop the compressor and close its suction valve at the same time. (4) When the energy load drops to zero, stop the oil pump. (5) Place the energy regulating device in the "stop" position. (6) Close the cooling water inlet valve of the oil cooler. (7) Stop the operation of cooling water pump and cooling tower fan. (8) Stop the operation of the coolant pump. (9) Turn off the main power supply. 2. Emergency stop of the unit
When the screw refrigeration compressor is running normally, if there is an abnormal pressure gauge; In order to protect the safety of the unit, emergency shutdown should be implemented. Operation method: (1) Stop the compressor. (2) Close the suction valve of the compressor.
(3) Close the solenoid valve on the liquid supply pipeline of the unit 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 coolant pump, cooling water pump and cooling tower fan. (7) cut off the main power supply.
The shutdown method when the unit encounters power failure, water cut-off and other faults during operation can be handled with reference to the relevant contents in Emergency Shutdown of Centrifugal Compressor.
After the emergency stop of the unit, the cause of the failure should be found out in time. After the failure is eliminated, the unit can be restarted according to the normal startup method. 3. The device automatically shuts down
During the operation of screw refrigeration compressor, if the pressure and temperature of the unit exceed the specified range, the protection device in the unit control system will play a role and automatically stop the compressor. This phenomenon is called automatic shutdown of the unit. When the unit stops automatically, the corresponding fault indicator light on the electrical control panel of the unit will light up to indicate the fault location. When this happens, after the main engine stops, other parts of the shutdown operation can be treated as emergency shutdown. After the shutdown operation is completed, the unit should be inspected and restarted according to the normal startup procedure after troubleshooting. 4. Long-term shutdown of the unit
Due to the seasonal operation of the screw refrigeration compressor used as the cold source of central air conditioning, the downtime of the unit is long. In order to ensure the safety of the unit, in case of seasonal shutdown, the following methods can be adopted for shutdown operation. (l) When the unit is in normal operation, close the liquid outlet valve of the unit to reduce the load of the unit, and all the refrigerants in the unit can be pumped into the condenser. To prevent the unit from stopping due to low suction pressure.
(2) After stopping the operation, unload the water in the oil cooler, condenser and evaporator, and discharge the remaining water to prevent the internal heat transfer tubes from freezing in winter.
(3) Close the relevant valves of the unit and check whether there is any leakage.
(4) Start the lubricating oil pump to run 10 ~ 20min every week, so that the lubricating oil can be evenly distributed to all working faces in the compressor for a long time, so as to prevent the machine from being short of oil on the surface of parts due to long-term shutdown and being difficult to restart.
Four, screw chiller maintenance
The main contents of screw chiller maintenance include daily maintenance and regular maintenance. Regular maintenance can ensure the long-term normal operation of the unit, prolong the service life of the unit, and save refrigeration energy consumption. Screw chillers should have operation records, record the operation of the unit, and establish maintenance technical files. Complete technical data is helpful to find hidden dangers and take measures as soon as possible to prevent failures. 1, screw compressor
Screw compressor is the key component of the unit, and the quality of the compressor is directly related to the stability of the unit. If the compressor breaks down, the screw compressor generally needs to be repaired by the manufacturer because of its high installation accuracy.
2. Cleaning of condenser and evaporator
Because the cooling water of water-cooled condenser is an open circulation loop, the tap water commonly used is circulated through the cooling tower.
Use. When the content of calcium salt and magnesium salt in water is large, it is easy to decompose and deposit on the cooling water pipe to form scale, which affects heat transfer. Excessive scaling will also reduce the circulating cross section of cooling water, reduce the water volume and increase the condensation pressure. Therefore, when the quality of the cooling water used is poor, the cooling water pipe should be cleaned at least once a year to remove the scale and other dirt in the pipe. There are usually two ways to clean the condenser water pipe: (1) use a special pig gun to clean the pipe.
(2) Use a special cleaning agent for circular cleaning, or inject cooling water, and replace the solution after 24 hours until it is clean. 3. Replace the lubricating oil
After long-term use of the unit, the quality of lubricating oil becomes worse, and impurities and moisture in the oil increase, so it is necessary to observe and check the oil quality regularly. Once the problem is found, it should be replaced in time, and the replaced lubricating oil brand must meet the technical data.
4. Replacement of dry filter
Drying filter is an important part to ensure the normal circulation of refrigerant. Because water and refrigerant are immiscible with each other, if the system contains water, it will greatly affect the operating efficiency of the unit, so it is very important to keep the system dry, and the filter element inside the drying filter must be replaced regularly. 5, safety valve calibration
The condenser and evaporator on the screw chiller are both pressure vessels. According to the regulations, the high-pressure end of the unit, that is, the condenser body should be equipped with a safety valve. Once the unit is in an abnormal working environment, the safety valve can automatically release pressure to prevent high pressure from causing harm to human body. Therefore, the regular calibration of the safety valve is very important for the safety of the whole unit. 6. Refrigerant filling:
If there are no other special reasons, the general unit will not produce a large number of leaks. If a certain amount of refrigerant leaks due to improper use or maintenance, it is necessary to add refrigerant again. Pay attention to the brand of refrigerant used by the unit when filling refrigerant. V. Matters needing attention in operation management and shutdown 1. Matters needing attention in operation and management of screw chiller
(1) The normal startup and shutdown of the device must be carried out in strict accordance with the steps in the operating instructions provided by the manufacturer.
(2) During the operation of the unit, the parameters shall be recorded timely and correctly.
(3) If there is any alarm shutdown during the operation of the unit, the relevant personnel shall be informed in time to inspect the unit. You can also contact the manufacturer directly.
(4) When the unit is running, it is forbidden to short-circuit the water flow switch to avoid freezing the water pipes.
(5) The computer room shall be staffed by special personnel. Other personnel are prohibited from entering the machine room to operate the unit. (6) The computer room should be equipped with corresponding safety protection equipment and maintenance testing tools, such as pressure gauges and thermometers, and stored in a fixed location. 2. Precautions for stopping the screw chiller (1) The main power switch should be cut off after the unit is stopped.
(2) If the unit is shut down for a long time, all accumulated water in the cold water and cooling water system should be drained to prevent corrosion. The water chamber end cover shall be sealed. (3) When the unit is shut down for a long time, it should be well maintained. (4) During shutdown, all units should be covered to prevent dust accumulation. (5) When the machine is shut down, personnel irrelevant to the unit shall not touch the machine.