Comprehensive analysis of the exhaust inertia of screw compressor

Comprehensive analysis of the exhaust inertia of screw compressor

With the deepening of the degree of social and economic subdivision, twin screw compressors, as an important source of power equipment, are increasingly used in various production fields, so their operating status will directly affect the production and operation of gas-consuming enterprises . Once it is improperly operated and poorly maintained, various failures will occur during operation, which will affect the service life of the equipment and the production efficiency of the enterprise. In severe cases, it may also cause personal safety and property equipment losses. Today we will discuss the inertia of screw compressors in terms of exhaust

　1. Working principle of screw compressor

Inhalation process: When the rotor rotates, the volume between the teeth formed by the main and auxiliary rotors gradually expands, and this volume is only connected to the suction port, and outside air is sucked into the volume between the teeth. When the volume between the teeth increases, the volume between the teeth is disconnected from the suction port, and the suction ends. This is the intake process.

Sealing and conveying process: At the end of air inhalation, the peaks of the main and auxiliary rotors are sealed with the casing, and the air in the volume between the teeth is enclosed in the enclosed cavity composed of the main and auxiliary rotors and the casing, which is closed process. The two rotors continue to rotate, the teeth of the main and auxiliary rotors mesh with each other, the meshing surface gradually moves to the exhaust end, and the air in the volume between the teeth is also transported to the exhaust end, that is, the conveying process

Compression and fuel injection process: During the conveying process, as the rotor rotates, the volume between teeth decreases continuously due to the meshing of the rotor teeth, and the volume of gas in the volume between teeth also decreases. The gas is compressed and the pressure increases. , This is the compression process. While compressing, the lubricating oil is sprayed into the tooth groove and mixed with air due to the pressure difference

Exhaust process: When the rotor turns to the volume between the teeth to communicate with the exhaust port of the casing, the compressed gas begins to discharge. This process continues until the profile line at the end of the tooth is completely meshed. At this time, the volume between the teeth is zero and the gas is Exhaust completely, complete; exhaust process

2. Analysis and treatment of common failures

2.1 Exhaust gas temperature is too

　 Once the exhaust gas temperature exceeds the preset protection temperature value, the over-temperature alarm self-stop switch on the compressor will act and cause shutdown fault spray. Generally, the exhaust temperature is in the range of 70～95℃, some brands will be higher.

(1) Inspection of regular parts. Routine inspections are generally carried out in the order of easy first and then difficult. ①Due to the lack of oil in the compressor system, the machine head cannot be cooled well, so that the exhaust temperature of the machine head is too high. At this time, the lubricant should be added in time. ②Oil filter. The oil filter of the screw compressor has high precision. The filter element is easy to block, resulting in insufficient oil supply of the main engine and excessive exhaust temperature. Use special tools to remove the oil filter, carefully check whether the filter element contains dirt, if the filter element is dirty, it should be replaced in time. ③Cooling fan. The cooling fan is a key component of the air-cooled unit, which can perform forced heat dissipation on the oil cooler and air aftercooler. As the power source, the fan can circulate the cooling air between the casing and the external space, and improve the heat dissipation effect of the machine. Once the fan stops rotating, the exhaust temperature of the compressor will reach the alarm self-stop level within a certain period of time. In view of the large area of the cooling fan, slender blades, poor rigidity, and easy deformation, it needs to be checked frequently and adjusted if necessary. ④ Cooler. Oil cooler and air after cooler are the main radiator components and must be cleaned regularly. The dirt on the outer surface of the cooler is mainly the sludge formed by cooling oil and dust, and the cooler is mostly made of finned tubes. The sludge sandwiched between the fins is difficult to remove. The low-pressure steam spray cleaning effect is better; inside the cooler tube The fouling is mainly the carbon deposits produced in the oil circulation process, and it is generally washed with a special cleaning agent until the carbon deposits are completely removed.

(2) Check the pressure switch. The discharge pressure of the main engine of the twin-screw compressor is set by the pressure switch. Once the pressure switch is damaged or the locking device is not tightly locked, the set value will easily drift due to the influence of machine vibration, causing the discharge pressure to exceed the limit value, which will cause Unit exhaust over temperature

(3) Check the temperature control valve. The temperature control valve is a three-way valve. When the compressor starts to cool, the oil can bypass the cooler and be directly injected into the main engine to achieve a rapid rise in oil temperature to prevent water vapor in the compressed air from condensing in the oil separator. When the oil temperature rises to 65℃, the temperature control valve will gradually open the main circuit as the oil temperature rises. The oil temperature is controlled by adjusting the proportion of the oil flowing through the oil cooler and the bypass to ensure the compressor The fuel injection temperature is maintained at the optimal point; if the temperature control valve fails, the lubricating oil may be directly injected into the main engine without passing through the oil cooler, and the oil temperature cannot be lowered, resulting in high exhaust temperature and shutdown. After shutting down, check the temperature of the oil cooler entering the oil discharge pipe first. If the temperature difference is not large, check the temperature control valve. Possible failures of the temperature control valve: ①The thermal spring on the spool can not operate normally with the change of oil temperature; ②The valve body is worn out and does not move properly and cannot work normally. It should be repaired or updated in time according to the actual situation.

(4) Check the oil cut solenoid valve. If the unit is operated in automatic start-stop mode for a long time, the oil cut-off solenoid valve is easily damaged due to frequent start and stop, causing the main engine to cause excessive exhaust temperature due to insufficient fuel supply or interruption of fuel supply.

(5) If the compressor does not use special lubricating oil, but replaces it with inferior lubricating oil, under high temperature conditions, the lubricating oil is not enough to protect the various parts of the compressor, which will cause the exhaust temperature to rise instantly. Excessive temperature of the air compressor is a common fault, which often fails to attract enough attention of the operators. The continuous high temperature will reduce the production efficiency, double the equipment consumption and shorten the equipment life.

(6) 2.2 Exhaust pressure is low

The low exhaust pressure of the main engine is mainly caused by insufficient air intake, exhaust leakage and other reasons. It needs to be checked from the following aspects: 　①The air release valve is faulty (cannot be closed during loading); ②The pressure switch is set too low (relay control unit); ③Pressure gauge failure (relay control unit), replace the pressure gauge; ④Pressure switch failure (relay control unit), repair, and replace the pressure switch if necessary; ⑤Control pipeline leakage: air compressor control pipeline leakage will cause the inlet The air valve cannot be fully opened so that the load of the unit cannot be full; ⑥The air demand is greater than the supply volume: check whether the valve on the air supply pipe is open or whether there is air leakage in the system, reduce the air consumption; ⑦The air filter is blocked: air The function of the filter is to filter the inhaled air to ensure that the air entering the air compressor is clean. If the air filter element is severely clogged, it will affect the air intake of the unit. Therefore, the filter element must be replaced in time; ⑧ Pressure regulator malfunction or damage: The function of the pressure regulator system is to automatically adjust the compressor according to the gas consumption of the customer to achieve a balance between supply and demand. Therefore, the damaged pressure regulator should be replaced in time, and the failed pressure regulator should be adjusted in time; ⑨Oil-air separator blockage: due to more or less impurities in the oil system, the filter element will be blocked after working for a period of time The resistance of the compressed air through the filter element increases, which affects the normal operation of the unit. Therefore, the operator should replace the filter element in time according to the signal displayed on the monitor panel.

2.3 Exhaust oil content is too high High compressor exhaust oil content will not only reduce the cleanliness of the gas, pollute the equipment, but also increase fuel consumption and increase production costs. When the exhaust gas oil content exceeds the standard, the following aspects can be checked.

(1) The oil separation core is damaged

During the operation of the screw compressor, if the oil separation core is damaged, such as breakage or perforation, it loses its function of oil and gas separation. That is to say, the mixed gas and the exhaust pipe of the compressor are directly connected, and a large amount of cooling oil is not separated, and the gas is discharged out of the body together with the gas, causing an oil-carrying fault during the exhaust process.

(2) Failure of oil return pipeline

In the working process of the screw compressor, the oil return pipeline shoulders important responsibilities. A pressure difference is formed between the inside of the oil separation core and the compressor inlet. Under the action of this pressure difference, the oil return pipeline is responsible for removing the oil. The oil collected at the bottom of the separation core is transported back to the compressor for continued use during the next cycle. If the oil return path is blocked, broken, or installed incorrectly, the oil collected at the bottom of the oil separation core cannot be transported back to the compressor, resulting in excessive oil accumulation at the bottom, so this part of the oil is not transported back to the compressor As the gas is exhausted, oil will appear during the exhaust process.

(3) System pressure control is too low

During the operation of the screw compressor, the system pressure control is too low, which will cause the centrifugal force in the separator to be less than the required centrifugal force of the work, then the function of the separator will not be fully reflected, and it will cause the separator to enter the next stage. The oil content of the gas in the core is too high, which exceeds its separation range, which leads to incomplete separation of oil and gas, and an oil-carrying fault occurs during the exhaust process of the compressor.

(4) The minimum pressure valve fails

　During the operation of the screw compressor, the function of the minimum pressure valve is to ensure that the system pressure is controlled above the minimum pressure during the operation. If the minimum pressure valve fails, the minimum pressure of the system cannot be guaranteed. Because the air consumption of the air transport equipment is very large, the system pressure will be too low and the oil return line cannot return oil. The oil accumulated at the bottom of the oil separator core will not be able to return to the compressor, and will be discharged from the compressor with the compressed gas, causing oil-carrying failure during the flat exhaust process.

(5) Too much cooling oil is added in the compressor. Before the screw compressor is operated, too much cooling oil is added, which exceeds the range of the compressor. During the operation of the compressor, the oil level is too high, although the oil level is too high. The system separates the oil and gas, but in the discharge of the gas, the gas will also involve the cooling oil in the gas for discharge, causing the oil content in the exhaust gas to be too high, and an oil fault occurs.

(6) Unqualified cooling oil quality Before the compressor is running, unqualified cooling oil is added, or the cooling oil exceeds the applicable time, and the cooling effect cannot be achieved. Then during the operation of the screw compressor, the cooling oil loses its function and cannot separate the oil and gas. Then there will be oil faults during the exhaust process.　

2.4 Inlet return oil

After the compressor is stopped, the cooling oil is sprayed from the air inlet of the main engine. This phenomenon is the return of oil at the air inlet. The main reasons for this phenomenon are as follows.

　(1) Check valve failure. The exhaust pipe of the main engine is the only channel for compressed air to flow back to the main engine. The check valve spool cannot be completely closed or the valve spool is worn and sealed in long-term operation can cause the compressed air to flow back, drive the main engine rotor to reverse, and make the lubrication into the main engine Oil sprayed from the air intake. Disassemble the check valve, check the valve core and seal, and replace if damaged. This kind of failure is relatively rare. 　(2) The oil cut-off solenoid valve is faulty. The oil cut-off solenoid valve is a normally closed valve, whose function is to cut off the oil circuit after the machine stops and prevent the lubricating oil from entering the main engine from the oil separator. The oil cut-off solenoid valve is not closed tightly. When the pressure is not completely unloaded, the oil will enter the main engine from the oil tank, causing the air inlet to reverse injection. Check the oil cut solenoid valve, if it is damaged, replace it with a new one.

　(3) The discharge valve is not vented. During the shutdown process, the drain valve should be opened to release the pressure in the oil separator and oil filter. If the valve is damaged and cannot normally discharge and reduce pressure, and the oil cut-off solenoid valve is not closed in time, it will cause the lubricating oil to enter the main engine from the air intake. Spouting from the mouth. Check the discharge valve and replace if damaged

　Conclusion

　Although screw compressor is a kind of mechanical equipment with stable performance and few wearing parts, various factors can cause its failure during operation. Only when we have more understanding and mastery of the compressor malfunctions in operation, can we ensure its safe and reliable operation and better serve production.