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In the production process of screw compressors used in the petrochemical industry, there will be various failures and problems of different degrees. We need to improve our understanding of the principles and performance of screw compressors and improve our operating rules of screw compressors. In terms of application, operators can diagnose and analyze compressor failures in a timely manner, so as to continuously accumulate experience and improve the technical level.
The working process of the screw compressor is divided into four processes: suction, sealing and conveying, compression, and exhaust. The surrounding air is inhaled through the intake filter to enter the compressor host, and the male and female rotors change the volume of the host through meshing movement, and at the same time, the cavity continuously sprays oil and cools the screw, thus generating a heated oil-air mixture. The oil-air mixture after the temperature rise and pressure increase enters the oil-air separator through the exhaust check valve, and most of the oil in the main engine cavity is separated from the compressed air in the oil-air separator, and then returned to the main engine for recycling after cooling. When the air in the oil-gas separator reaches the required minimum pressure, the minimum pressure valve opens, and the high-temperature compressed air enters the cooler to cool down, and the compressed air we need is obtained.
Main advantages:
(1) High reliability. The compressor has few components and no wearing parts, so it operates reliably, has a long service life, and has a long interval between overhauls.
(2) Easy operation and maintenance. The screw compressor has a high degree of automation, and the operator does not need to undergo a long period of professional training and can realize unattended operation.
(3) Strong adaptability. It has the characteristics of forced gas delivery, and the volumetric flow rate is almost not affected by the exhaust pressure and is suitable for a variety of working fluids.
(4) Multi-phase mixed input. There is actually a gap between the rotor tooth surfaces of the screw compressor, so it can withstand the impact of liquid, and can transport liquid gas, dust gas, and easily polymerized gas.
Main disadvantages:
(1) High energy consumption. Due to its strong balance and high-speed operation, the power consumption is relatively high.
(2) The cost is high and the maintenance cost is high. After long-term operation, the screw gap will become larger, and the cost of regular repair or replacement will be relatively high.
(3) Cannot be used in high-pressure applications. Due to limitations in rotor stiffness and bearing life, screw compressors can only be used in medium and low-pressure ranges.
Failure cause analysis:
(1) The pressure on the pipeline exceeds the rated load pressure, and the pressure regulator is disconnected.
(2) The minimum pressure valve is out of order and does not act when loading, and the high-temperature compressed air cannot enter the cooler.
(3) If There is leakage on the control pipeline between the separator and the unloading valve, check the pipeline and connection, and repair if there is leakage.
Solution: If the air source pressure exceeds the rated pressure, no measures need to be taken at this time. The compressor will automatically load when the pressure on the pipeline is lower than the loading (position) pressure of the pressure regulator. If the minimum pressure valve fails, remove it for inspection and replace it if necessary. If there is leakage on the control pipeline between the separator and the unloading valve, check the pipeline and connection, and repair if there is leakage.
Analysis of the cause of the failure: The screw compressors use cooling oil in a closed cycle and operate at a relatively high temperature for a long time, so there may be varying degrees of deterioration of oil products such as carbon deposition, scaling, and acidification. Due to carbon deposits and other reasons, the electromagnetic valve and temperature control valve of the oil circuit components may be damaged, the oil circuit is blocked, and the heat exchange effect is not good.
Solution: Carry out maintenance of the oil circuit system, and replace the oil, air filter, oil filter, and oil separation components. If it is a water-cooled model, soak the water system with a scale cleaner. When cleaning the oil circuit, a carbon deposit cleaning agent should be used. First, ensure that enough compressor oil is drained so that the oil can be added to the storage tank. Then run the compressor continuously for 40 to 60 hours. To prevent the redeposition of suspended contaminants, the best results are achieved by completely draining the oil from the compressor while the oil is still hot.
Analysis of the cause of the failure: The environment in the computer room is poor, and the air contains a lot of dust. During operation, the air compressor frequently suffers from oil deterioration, filter clogging, and other faults, the oil change cycle is shortened, and the operation and maintenance cost is greatly increased.
Solutions:
(1) Correctly select the oil and establish a complete air compressor oil procurement, inspection, and acceptance management system.
(2) Determine the appropriate amount of oil supply. If the oil supply is too much, it is easy to form carbon deposits. However, it can’t be too little, too little oil supply, the cylinder block, and rotor are bad, and it is easy to burn the cylinder.
(3) Establish a minor repair cycle based on inspection and cleaning.
Failure causes analysis and solution: If the temperature in the machine room is within the allowable range and the oil level is in a normal state, first confirm whether the temperature measuring element of the machine is faulty, and you can use another temperature measuring instrument to calibrate it. If it is confirmed that the temperature measuring element has no problem, then check the temperature difference between the inlet and outlet of the oil cooler, which is normally between 5 and 8°C. If the temperature is higher than this range, it means that the oil flow is insufficient, the oil circuit is blocked, or the temperature control valve is not fully opened, and the oil filter needs to be checked. If the above methods fail to solve the problem, it is necessary to consider whether the oil circuit is blocked by foreign matter.
If the temperature difference is lower than the normal range, it may be due to poor heat dissipation. Check whether the water intake of the water cooler is insufficient, whether the inlet water temperature is too high, whether the water circuit part has scaled the cooler, whether the oil circuit part has grease in the cooler, and check whether the radiator is too dirty, whether there is grease in the radiator, whether the cooling fan is abnormal, etc. If the temperature difference is within the normal range and the machine is still at a high temperature, it means that the heat generation of the machine head is beyond the normal range. You should check whether it is overpressured, whether the oil is wrong, whether the oil is aging, whether there is a problem with the bearing of the machine head or even end face friction.
Failure cause analysis and solutions:
（1）Check whether the “before separation” and “after separation” two-position manual valve and pressure gauge are leaking. If there is air leakage, replace the manual valve or eliminate the leakage fault.
（2）Check and adjust the solenoid valve Whether there is air leakage, if it is air leakage, eliminate the fault, and replace the regulating solenoid valve if necessary;
（3）Check whether there is any leakage in the pipeline. If there is, the leakage point needs to be eliminated:
（4）Check whether the butterfly valve is fully opened. If it is, check the butterfly valve mechanism and solenoid valve, and check whether the solenoid valve is leaking. If so, find out the reason and whether it is necessary to replace the solenoid valve.
（5）Check whether the regulator is working normally. If there is any problem, replace the solenoid valve or readjust the pressure switch, check whether the upper and lower limits of the pressure switch are normal, if yes, readjust the pressure switch, and replace it if necessary.
Failure cause analysis and solution:
（1）Check whether the specified ambient temperature and exhaust pressure are exceeded, if so, adjust to the specified ambient temperature or exhaust pressure, check whether the oil is clean and the oil level is normal, if so, replace the oil or make up the amount of oil, check whether the oil grade is correct, if so, replace the oil with the correct grade.
（2）Whether the air volume of the fan is reduced, if so, check the speed of the fan motor and whether the exhaust port is blocked: Check whether the appearance of the aftercooler is clean, and clean the outer surface of the cooler.
（3）Check whether the environment affects the air intake and exhaust of the unit. If so, eliminate external factors to ensure normal ventilation of the unit.
（4）Check whether the temperature control valve element is damaged, if so, replace the element, Check whether the solenoid valve and electromagnetic coil are damaged: Check whether the diaphragm of the solenoid valve is damaged, if so, replace the coil and diaphragm.
（5）Replace the oil filter element.
The analysis of the cause of the failure and the solution are as follows: (1) Whether the condensed water discharged from the trap has a large oil content, if so, check the leakage point in the unit and eliminate it, check whether the oil level of the compressor is too high, if so, reduce the oil level; (2 ) Whether the opening pressure of the minimum pressure valve is normal, if so, troubleshoot, and it is necessary to replace the valve; check whether the oil return pipe is blocked, if so, clean or replace the oil return pipe: (3) Replace the oil separator core.
Failure cause analysis and solutions:
（1）The oil level is too high, and the injected engine oil is too much. Drain the oil to the normal position after the pressure is removed;
（2）The oil return pipe is blocked. It can be checked and replaced;
（3）The installation of the oil return pipe does not meet the requirements and can be readjusted;
（4）The exhaust pressure of the unit is too low when the unit is running, which will not cause this phenomenon because the pressure of the air storage tank is always high;
（5）Oil essence The internal damage of the separator barrel can only be found by disassembly and inspection;
（6）The oil has deteriorated or has been used for an extended period of time;
（7）The oil return check valve is out of control, which will cause the oil to flow back to the oil separator after the unit stops, and the oil will leak when it is restarted.
（8）Damage and rupture of the oil separator core.
