1 LMF marine air compressor unit works In general, an air compressor with a displacement of 11 m 3 / min uses a prime mover to drive a piston air compressor mode. When the displacement is greater than 11 m 3 / min, the first stage uses a screw machine, and the second, third and fourth stages use a piston machine. This unit is usually called a composite compressor unit. The following is an example of a composite unit. After the unit is powered, the control unit automatically detects whether the relays and status parameters are within the specified range. If the unit is ready to be installed within the specified range, it can be turned on. When the unit is started, the unit operates the fresh water cooling pump, seawater cooling pump, and lubricating oil pump in sequence according to the predetermined opening sequence. After that, the unit will automatically start under no-load condition, and gradually increase the speed to the specified speed and close the automatic drain valve to enter the normal working state. The air first enters the intake control valve on the inlet of the screw machine through the filter, and then is compressed into the screw machine. The air in the oil separation tank is separated from the oil and gas mixture. The compressed air is then cooled in the second stage cylinder of the piston machine after being cooled in the intercooler. And so on, until the cylinder is discharged from the last compression stage, and the working pressure required for the air gun excitation is reached after the fisherman valve pressure control. The unit is equipped with a SIEM ENS PLC control cabinet for real-time detection and status monitoring of the unit's operating parameters. The yellow indicator light is used to alarm the parameter exceeding the preset alarm value. When the preset shutdown protection parameter is exceeded, the unit will automatically stop to protect the unit. 2 LMF unit structure features The unit includes: body components, power drive, lubrication, cooling, electrical appliances, automatic control and other systems. It usually includes a drive machine, a screw machine, a piston compressor, an electrical control cabinet and various electric pumps. The original drive machine can be either a diesel engine or an electric motor. The original drive is installed in the middle of the screw machine and the piston machine. The two machines are connected by a flexible coupling. These components are all mounted on the common base. The working pressure of the unit output is generally 138 207 bar. 3 LMF unit common faults Common faults of LM F units can be divided into power supply, temperature, working pressure, lubrication system, filter, transmission system failure and so on. The following is a brief analysis of the above common faults for peer reference. 3. 1 power supply failure 3. 1. 1 power supply phase sequence reverse When the unit is installed for the first time, if the phase sequence of the three-phase power supply wiring is incorrect, it will not be able to enter the startup state, and the power failure and phase sequence reversal will be displayed on the PLC control cabinet. It is necessary to stop the power supply and replace the wiring position of the two power cords connected in reverse. This is a human error. It should be checked repeatedly and then powered on. 3. 1. 2 insufficient power supply The LM F unit controlled by the PLC system has strict power requirements for power supply. If the power supply is not only supplying power to the LMF unit, but also supplying power to other large power equipment, once the power supply of the main power supply is relatively small, the already operating LMF unit may be subjected to a large starting current of another equipment. An automatic shutdown failure occurs due to the impact. In this case, you need to reconfigure the power supply and properly control the start and stop operation of the power equipment. When configuring the equipment, you should consider or calculate the power supply load problem at the same time. 3. 1. 3 PLC control cabinet internal electrical components failure In operation, if a control component inside the PLC control cabinet fails, such as a safety trip or other similar power failure, the air compressor will automatically stop. When troubleshooting, the maintenance personnel are required to be very familiar with the internal circuit principle. Check whether there is internal circuit burning, PLC module failure or abnormal air switch position according to the fault prompt information displayed on the instrument panel of the PLC control cabinet. Containerized units are fixed on the deck of the ship. During construction in winter or rainy season, various PLC electrical faults are prone to occur due to the influence of moisture on the sea. Operators need to carefully analyze and find out the cause according to the fault information. 3. 1. 4 Line connection is loose When there is an intermittent fault shutdown during the operation of the unit, when the control cabinet is displayed as a power system failure, the maintenance personnel need to check whether the line connected to the internal electrical components is loose or false. If the shutdown phenomenon often occurs when the airgun activates the hull to be subjected to large vibrations, it can be further judged that the line is loose. 3. 1. 5 Battery failure in the PLC control unit After powering the PLC control cabinet, $545 db 101 01 20 not avail is displayed on the dashboard. No matter which button is pressed on the dashboard, the fault information on the screen cannot be cleared and cannot be turned into the normal power-on state. After opening the PLC control cabinet, it is found that the battery fault indicator light is on in the leftmost power module of the PLC control cabinet, indicating that the battery is not working properly and needs to be replaced. In the absence of a spare battery, you can dial the power switch in the leftmost power module of the PLC control cabinet, and then dial up and reset. Then observe each power running indicator and it should all turn green. And successively heard the relay action of each relay inside the PLC control cabinet reaches the normal working state, and then performs the normal starting operation. 3. 2 temperature failure 3. 2. 1 Fresh water cooling temperature is abnormal When the geophysical ship equipped with the air compressor unit is subjected to air gun excitation in the sea near the coastline, in order to improve the coverage of the ship operation, it is necessary to approach the shore as much as possible, which will cause the sediment to be inhaled by the sea water pump along with the seawater. In the plate cooler, the sediment and marine shells are gradually attached to the titanium alloy plate wall of the plate cooler to form a hard thermal insulation layer, which will greatly reduce the heat exchange efficiency of the plate cooler, which in turn leads to automatic unit heating due to high temperature. Stop. Remedy: Disassemble the plate heat exchanger, inspect and clean the internal sand and the shells. Then reassemble according to the process and then perform a pressure test to see if there is a leak in the seal. At the sea inlet of the plate cooler, a flow sensor is installed to detect in real time whether the flow of the inhaled seawater meets the specified minimum requirements. If the inhaled seawater is affected by the sediment and the suction port is accidentally blocked, causing the flow to be too low, a yellow fault alarm will appear on the PLC dashboard to remind the operator to troubleshoot. 3. 2. 2 Temperature sensor failure The PT No. 100 temperature sensor is used extensively in the LM F unit. The sensor uses a platinum wire as the thermal temperature sensing element. When the temperature is 0 degrees, the thermistor is 100; at 100 degrees, the thermistor is 138.5. As the temperature increases, the resistance increases proportionally. If the automatic stop suddenly occurs during the operation of the unit and a certain temperature value is 33333 degrees on the PLC control panel, it can be judged that the PT No. 100 temperature sensor in the part is damaged, possibly due to the internal thermistor wire. Caused by the break. When the PLC controller does not detect the normal range of temperature values, the system will not be able to return to the state that can be turned on. If there is no PT No. 100 sensor that can be replaced at the site, you can temporarily connect the PT No. 100 sensor directly to the original cable with a resistor of about 110, and provide the PLC with a false temperature reference value to make the unit reach the startable state. . Some LM F units are equipped with a diesel unit coolant automatic temperature control system. When the temperature is lower than 15 degrees, the control system will automatically heat the diesel coolant when the unit is powered by the control cabinet. When it reaches 15 degrees or more, it indicates that the unit is ready to start normally. If the diesel engine heating system fails and cannot be heated, in an emergency, the PT No. 100 temperature sensor on the diesel engine body can be removed and placed in warm water, so that the PLC control cabinet detects a false temperature value and reaches it. A state that can be started normally. 3. 2. 3 Compressed cylinder temperature is abnormal It is usually first detected to determine if the PT No. 100 sensor is operating normally. Then consider whether the internal intake and exhaust valves are faulty or damaged. Because when the valve is not tightly closed, the temperature will rise. If the fault cannot be eliminated after the above inspection, it is necessary to check whether the cooling water system and the piston ring are normal according to the working hours of the unit. 3. 3 abnormal working pressure During the operation of the unit, a pressure gauge monitors the working pressure of each cylinder, and a pressure sensor transmits the real-time pressure value to the PLC control cabinet. When the pressure value exceeds the specified value, the fault alarm will be displayed by the PLC; when the pressure value is greater than the specified stop reference value, the automatic protection stop will be realized. The pressure of a certain stage of compression cylinder is abnormal, which is generally caused by poor working condition of the valve or blockage of the filter. It can be analyzed and judged by observing the magnitude of the pressure value, disassembling the gas valve, and monitoring the valve for abnormal noise. 3. 3. 1 Inlet and exhaust valve failure Each stage of air intake and boost discharge of the piston machine is automatically realized through the intake valve and the exhaust valve. Usually the abnormality of the air pressure value of each stage is caused by the abnormality of the intake or exhaust valve. One type of air compressor has two fourth-stage cylinders. To monitor the cylinder's working condition, a temperature sensor is installed on the pipeline behind each cylinder exhaust valve. An automatic alarm suddenly appears during the operation of the air compressor, and the yellow signal light flashes. After a few seconds, the red indicator light flashes and stops. The fault information found is message code no. 0138 diff. temperature 3rd stage cy l. 3/ 4 > max SD . The analysis shows that the difference between the instantaneous operating temperature of the No. 3 cylinder and the No. 4 cylinder of the third stage compression is greater than 30 degrees, which exceeds the setting value of the shutdown protection. The reason for the analysis may be that the exhaust gas temperature is abnormal due to the damage of the exhaust valve of the No. 3 or No. 4 cylinder, and a large temperature difference is formed. According to this maintenance idea, after opening the valve, it was found that the valve piece in the No. 3 cylinder exhaust valve was broken by the airflow, causing abnormal operation. After the valve is replaced, it works well. The increase in pressure at any stage (eg, the second compression stage) is due to the failure of the valve at a later stage, ie, a higher level of pressure (eg, the third compression stage). Because the leak occurs when the latter stage suction valve is faulty, the gas may flow back into the previous compression stage during the compression process, which is equivalent to reducing the gas flow rate of the latter stage. In this case, the latter stage can only inhale less gas than normal, while the previous level of air pressure rises. When the exhaust valve is faulty and leaks, as in the above case, the amount of gas sucked from the previous stage is also reduced, and the outlet pressure of the previous stage is increased. For some air compressor units, because the PLC control mode is not used, the temperature difference of the same stage compression cylinder cannot be compared. In this case, the judgment can be made by observing the value of the working pressure of the compression cylinder. 3. 3. 2 The first stage working pressure of the composite air compressor is abnormal. The first stage pressure is the pressure after being compressed by the screw machine and separated by the filter in the oil separation tank. The pressure value is generally 11 bar. If the pressure of the stage is abnormal during operation, the pressure value is as low as 3 5 bar. , then the plugging of the filter is the main reason for the first level of working pressure is too low. The oil and gas separation filter should be checked and replaced at this time. 3. 3. 3 Unable to establish final exhaust pressure If the final exhaust pressure of the unit cannot be established and is always running at a lower pressure, you can find the cause by looking at the following aspects. (1) Abnormal operation of the air compressor unit intake system For the composite unit, it is first necessary to check whether there is any blockage inside the intake air filter of the screw machine. Generally, the filter operates for a long time in a poor working environment, and this problem occurs if it is not replaced in time. When the working pressure of the first stage screw machine is very low, or the pressure cannot be established at all, the working state of the valve piece and the relevant displacement control valve of the screw machine intake control should also be checked. First remove the spring of the intake control valve and let the unit run. If the pressure at each level is normal, it indicates that the intake control valve control system has failed, causing the air from the air filter to fail to enter the screw machine and being compressed, so that the pressure cannot be established. After the fault has been determined, reinstall the spring back into the intake control valve and check the auxiliary pneumatic control system until the fault is completely eliminated. Under normal circumstances, because the airway control system is controlled by the oil and water pollution inside the air, the I/P converter fails to work, and the air intake system of the air unit will work abnormally. (2) Check whether the manual and automatic dehumidification valves of all levels are working properly when the above filter failure is eliminated and the unit is still unable to establish normal pressure at all levels. For air compressors that automatically control dehumidification at all levels, the manual dehumidification valve should be closed. If air is discharged from the drain pipe for a long time, the dehumidification control system is faulty. After checking that the external objects are working properly, enter the dehumidification control menu on the PLC control panel dashboard to check the value of each stage of automatic dehumidification time setting. The interval between each stage of dehumidification is generally 600 900 s and the duration is 5 s. If the interval between dehumidifications is set to 60 s by mistake, continuous dehumidification will occur, resulting in failure to establish working pressure. (3) Check and verify the fisherman valve setting value that controls the final pressure. Setting the final exhaust pressure to a normal value is an important prerequisite for ensuring that the final pressure is normal. (4) Check whether the working pressure at all levels is normal and whether there is air leakage in each pipeline system. 3. 4 Lubrication system failure Lubrication and replacement are usually required in accordance with the lubricant requirements specified by LM F. The piston machine part has a special lubricating oil pressure regulating valve. By adjusting the valve, the lubricating oil pressure of the piston machine can be adjusted. When the piston machine is running, the working pressure of the lubricating oil needs to be kept within an appropriate range. When the pressure drops below the specified value, a fault alarm and automatic shutdown will occur. The management of lubricants needs to consider the following issues. 3. 4. 1 Counterfeit inferior lubricating oil causes abnormal lubrication pressure In some countries, sometimes the lubricants of poor quality are provided by the supplier incorrectly, and the lubricant pressure is abnormal after replacement. Usually after a period of operation, as the lubricant temperature becomes higher, the lubricant pressure drops below the specified alarm value. In this case, even if the pressure regulating valve of the unit is artificially adjusted, the pressure cannot be controlled within the normal range. At this time, it can be determined that the quality of the changed lubricating oil is poor, and the qualified lubricating oil should be replaced as soon as possible. 3. 4. 2 screw machine working temperature setting and lubricating oil replacement cycle It is usually necessary to replace it with reference to the oil change cycle specified by LM F. When conditions are met, oil sample testing should be performed and judged whether it needs to be replaced according to the results of each test. According to LM F, when the working temperature of the screw machine lubricating oil is higher than the normal value (85 degrees), due to the ambient temperature and humidity, when the screw machine needs to work at a higher temperature, the replacement cycle of the lubricating oil needs to be shortened accordingly. . For every 5 degrees increase in operating temperature, the oil change interval needs to be shortened by 20% 25%. When the working environment temperature and humidity are relatively high, and the operator does not clearly understand the correct setting of the screw machine lubricating oil working temperature, the following problems will occur: After daily operation, the operator opens the oil drain valve next to the double filter. At that time, it was found that nearly 500 mL of water first flowed out, and then the lubricating oil flowed out. The root cause of this problem is: The operator does not correctly set the working temperature of the screw machine oil according to the operating environment of the unit, so that the moisture sucked from the air cannot be separated from the oil and gas after being compressed by the screw machine, and before entering the piston machine. Exhausted from the unit. This will cause damage to the internal bearings and gears of the screw machine. When the screw machine working pressure is 15 bar, the set operating temperature should be greater than the pressure dew point temperature. The upper horizontal axis is the operating temperature of the air compressor unit, and the vertical data on the left side is the relative humidity of the air. The value of the two values ​​cross-converge is the operating temperature of the screw machine oil that needs to be set. According to this temperature setting, it is ensured that the moisture in the intake air is compressed and heated by the screw machine, separated from the compressed air and discharged through the first-stage oil-water separator, thereby prolonging the use time of the lubricating oil. The maximum operating temperature of the screw machine is 115 degrees. However, the actual set operating temperature value shall not exceed the temperature value specified by the reasonable oil change interval of the lubricating oil used. The operating temperature of the screw machine can be achieved by adjusting the oiling temperature. Synthetic based lubricants should be used when the operating temperature is above 100 degrees. 3. 5 filter failure The number and variety of filters used in the composite LMF air compressor are quite numerous, generally: air intake air filter of air compressor, oil and gas separation filter of screw air compressor, double oil filter , side flow filter, air filter for CAT diesel engine, oil filter for CAT diesel engine, oil filter for piston air compressor. A differential pressure alarm indicator is typically installed next to each filter. When the filter inlet pressure and outlet pressure difference reach a predetermined value, the indicator piston inside the alarm indicator will move to the red mark position, reminding the operator to replace the filter immediately, so as to avoid other malfunctions. Example of filter failure: After replacing all air filters and oil filters of the whole unit for 200 h, the CAT diesel engine gradually decreases from the rated 1205 r/min to 1100 r/ at each start of operation. Min, the diesel engine appears to be unstable when the speed is unstable. The item-by-item elimination method was adopted during troubleshooting, and professional CAT repair personnel were asked to check the high-pressure oil pump, valve clearance, etc., and found no problems. Finally, it is suspected that the load of the air compressor may increase. The oil separator of the screw machine is found to be inwardly recessed inside the oil-gas separation filter, causing the first-stage air compressed by the screw machine to be separated. , the smooth passage of the filter does not occur, and the resistance increases. It is precisely because of this increase in resistance that the diesel engine speed drops or even stops. The reason for the premature clogging of the filter is: The ship is constructed in a waters close to the coastline in the Middle East. When it is exposed to sandstorms, fine particles of dust will enter the screw machine through the air filter. , causing clogging at the oil and gas separation filter. Therefore, the time interval for replacing the filter cannot be determined solely by the working time, and the special working environment should be fully considered. 3. 6 drive system failure For the composite air compressor unit, the crankshaft driving the diesel engine is directly connected to the screw machine and the piston air compressor through the elastic couplings on the left and right sides. The flexible coupling is an important part of the transmission system, which can reduce the transmission vibration and play an important role in the smooth start and stop of the unit. Flexible couplings are rubber materials that operate at higher temperatures for extended periods of time, making life easier. The inspection should be intensified after 5000 7000h of operation. When the first stage working pressure of the screw machine is abnormal, the oil pressure cannot be established normally, and only the diesel engine is running and the screw machine is not working properly, the coupling between the diesel engine and the screw machine should be checked for damage. 4 Conclusion (1) Operations and management personnel need to carefully study and understand the working principle of each unit of the unit, especially the principle of the control circuit. Only when you understand the working principle can you quickly and accurately analyze and judge the fault point and cause in the event of a fault. (2) Replacing the filter and lubricating oil according to the working condition of each filter in time is the basic condition for ensuring the normal operation of the unit. A filter that is not clean or clogged can cause a series of malfunctions. (3) In accordance with the requirements of the manual, carefully manage the equipment and find that the hidden troubles should be solved in time.
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Research on Operation Mechanism and Fault Treatment of Marine Air Compressor
Austria LM F is a professional manufacturer of high-pressure air compressors for marine seismic exploration. At present, most marine exploration vessels and geophysical towline vessels have selected the company's large-displacement high-pressure air compressor units to provide 138 207 bar of stable and reliable high-pressure air for the airgun source. The stable operation of the air compressor unit is one of the prerequisites for ensuring the high efficiency construction of the geophysical ship. Therefore, it is a basic requirement for on-site operators to ensure reliable operation of the unit and rapid elimination of faults.