Maintenance and maintenance methods of screw chiller
With the development of China's economy and the improvement of production process requirements, screw chillers have become an important aspect of the refrigeration demand of most enterprises, so the application of screw chillers in enterprises is more and more extensive. However, the follow-up maintenance of screw chillers has also become an important aspect for business owners with screw chillers. This paper briefly introduces some maintenance methods of screw chiller:
(1) Preparation before starting the screw chiller The correct debugging of the screw chiller is an important link to ensure the normal operation of the refrigeration device, save energy consumption and prolong the 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. Therefore, engineers such as refrigeration, water and electricity should participate in the debugging. Before debugging, users should carefully read the instruction manual provided by the manufacturer and proceed step by step according to the operation requirements. Operators must receive special training from the factory and obtain the operation certificate of the unit before taking up their posts, so as to avoid fatal injury to the unit due to misoperation. 1. Preparation before debugging
(1) As the screw chiller belongs to medium and large refrigerators, it needs close cooperation in design, installation and use during debugging. In order to ensure the debugging work in an orderly way, it is necessary to form a temporary debugging team by relevant personnel to fully command the debugging work.
(2) The personnel in charge of debugging should be fully familiar with the structure and performance of screw chillers, the safety technology of refrigerators, the methods, steps and technical requirements to be achieved in debugging, and make detailed and specific debugging plans so that the debugging personnel in each position can clearly understand their tasks and requirements.
(3) Check whether the installation of the screw chiller meets the technical requirements, whether the foundation of the screw chiller meets the requirements, and whether the size, specifications and materials of the connecting pipes meet the design requirements. (4) The power supply system of the unit shall be installed and passed the debugging.
(5) The cold water and cooling water systems were tested 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.
(6) Clean up the debugging environment and site to be neat, bright and smooth. (7) Prepare all kinds of general tools and special tools needed for debugging.
(8) Prepare various measuring instruments and meters such as pressure, temperature, flow, quality and time required for debugging. (9) Prepare necessary safety protection equipment during commissioning. 2. Debugging of screw chiller
(1) Fill the refrigerant. At present, refrigeration units are usually filled with refrigerant before leaving the factory. After site installation, if no accidental damage is found by visual inspection, you can directly open the relevant valves (you should read the manufacturer's instruction manual first, and the valves on the unit are generally closed during transportation). If it is found that the refrigerant has completely leaked or is insufficient, first find out the leakage point and eliminate the leakage phenomenon, and then add the refrigerant of the specified brand according to the requirements of the product instruction manual. Pay attention to the refrigerant filling quantity should meet the technical requirements. (2) Some screw chillers need to be filled with refrigerant at the user's place, and the filling amount and brand of refrigerant must comply with the regulations. Insufficient refrigerant charge will lead to insufficient refrigeration capacity. Excessive refrigerant charge will not only increase the cost, but also adversely affect the energy consumption of operation.
(3) Before filling refrigerant, sufficient refrigerant should be prepared in advance. When filling, it can be filled directly from the special filling valve. Because the system is in a vacuum state, the pressure difference between the refrigerant in the steel cylinder and the system is large. When the valve is opened (the air in the connecting pipe should be blown out with the refrigerant first to avoid air entering the unit and affecting the performance of the unit), the refrigerant will quickly flow into the system from the cylinder. After filling, close the filling valve first, and then remove the connecting pipe.
(4) Commissioning of refrigeration system. After refrigerant filling is completed (if it is necessary to fill refrigerant), load debugging can be carried out. In recent years, screw chillers have made great progress in performance and electrical control. Many screw chillers can simulate the main electric control system before starting, that is, the main engine of the unit is not powered on and the control system is powered on. Then, through the internal settings of the unit, the electrical control system of the unit can be tested to see if all components work normally. If there is any problem with the electronic control system, it can be solved in time. Finally, turn on the host power for debugging. During debugging, special attention should be paid to the following points:
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 operation data record table of screw chiller provided by the manufacturer, the data of screw chiller can be recorded, especially some main parameters must be recorded clearly.
7) During the operation of the screw chiller, 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 there is any abnormality in the screw chiller, it shall be stopped 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. (2) Start-up operation of screw chillers
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 of screw chiller during startup. After the unit is started and put into operation, the following contents should be checked to ensure the safe operation of the unit.
1) Whether the noise, vibration, pump outlet pressure, water temperature and other indicators during the operation of refrigerant pump, cooling water pump and cooling tower fan are within the normal working parameters.
2) 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. 3) Whether the suction pressure is within the range of 0.36 ~ 0.25. The compressor is 56MPa at full load. 4) Whether the compressor exhaust pressure is lower than 1.55MPa and the exhaust temperature is lower than 100℃.
5) Whether the running current of the motor is within the specified range when the screw chiller 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. 6) 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 screw chiller run with problems, so as not to cause major accidents. (III) Signs of normal operation of screw refrigeration compressor Signs of normal operation of screw refrigeration compressor are:
(1) The discharge pressure of the compressor is 1.8 ~ 1.47 MPa (gauge pressure);
(2) The exhaust temperature of the compressor is 45 ~ 90℃, and the maximum temperature does not exceed 65438 0.05℃; (3) The oil temperature of the compressor is about 40 ~ 55℃;
(4) The oil pressure of the compressor is 0.2 ~ 0.3 MPa (gauge pressure);
(5) When the compressor is running, the sound should be even and steady without abnormal sound;
(6) The condensing temperature of the unit should be 3 ~ 5℃ higher than the cooling water temperature; The cold pole and temperature should generally be controlled at about 40℃, and the inlet water temperature of condenser should be lower than 32℃; (7) The evaporation temperature of the unit should be 3 ~ 4℃ lower than the outlet temperature of cooling water, generally about 5 ~ 7℃.
(4) Stop the operation of the screw refrigeration compressor
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. In order to prevent the unit from stopping due to low suction pressure, the setting value of low-voltage relay can be adjusted to 0. 15MPa. When the suction pressure drops to about 0. 15MPa, the compressor stops. When the compressor stops, the low pressure value can be adjusted back. (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. (5) Maintenance of screw chiller
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 circulating loop, the tap water commonly used is recycled through the cooling tower. 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 methods for cleaning condenser water pipes:
(1) Use a special pig gun to clean the pipeline. (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. Replace the drying 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. Calibration of safety valve
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 it.
The harm that high pressure may cause 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.
(6) Operation management and shutdown precautions
1. Matters needing attention in operation and management of screw chillers
(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.