In 2004, Yuhua Yuhang Chemical Co., Ltd. built and expanded the “100,000-ton PVC plant and 100,000 tons of ion-exchange membrane caustic soda” project, using three sets of instrument fan units for the entire “Double Ten” project. And the manual pneumatic valve supply air source, there have been many failures in the operation of the instrument fan unit for more than two years, and the failure of the instrument fan unit will result in the loss of pressure of the entire instrument air system, which will affect the entire company's various types of pneumatics. The valve's switching status will endanger the safety, environmental protection and stable operation of the entire company. In the production process, we timely summarize the common fault phenomena and treatment methods of the instrument fan unit during operation, so that we can be in the shortest Time to judge and eliminate the fault.

1. Process air of the instrument air system The air is increased by a single screw air compressor (referred to as air compressor), and then the impurities, dust, part of the water and air are removed by a precision filter and a high-efficiency degreaser. The trace oil carried in the press is sent to the micro-heat regenerative adsorption dryer to remove the moisture in the air, and then the dust filter is used to remove the particles in the air and sent to the instrument wind storage tank, after buffering and storage. It is used in gas units.

2. Instrument Air System Important Equipment Introduction 2.1 Single-screw air compressor uses 5 single-screw air compressors to supply compressed air to the entire instrument air system throughout the instrument air system. The model number is OGFD20.2/7, rated The exhaust volume is 20.2m 3/min, and the nominal exhaust pressure is 0.7MPa.

The single-screw air compressor housing has a screw with six spiral grooves, and a pair of plane star wheels on both sides constitute a working chamber. The screw rotation drives the star wheel to rotate in the closed body to complete the inhalation, compression and exhaust of the cycle. Slewing movement. It mainly consists of pneumatic system, oil circuit system and electrical system. The main components are air filter, oil filter, oil separator, oil supply solenoid valve, unloading valve, minimum pressure valve, exhaust valve, adjustable Pressure switch, pressure control valve, loading solenoid valve, etc.

2.1.1 Gas flow process After the outside air is filtered by the air filter, it is compressed by the unloading valve into the compressor for compression, mixed with the lubricating oil in the compression chamber, and the compressed oil and gas mixture enters through the exhaust check valve. In the oil and gas barrel, after most of the oil is swirled out, the residual lubricating oil is filtered by the oil and gas submersible, and then the compressed air is sent out after passing through the minimum pressure valve, the air cooler, and the water separator. The unloading valve is mainly used to control the amount of gas entering the main engine of the compressor. The exhaust valve is to prevent the reverse rotation of the compressed air when the system is shut down. The function of the minimum pressure valve is to establish the lubricating oil when the main engine of the compressor is started. The circulating pressure is required to reduce the flow rate of the air flowing through the oil subdivision to ensure the oil separation effect; the loading solenoid valve is a normally open solenoid valve for controlling the increase and decrease of the air compressor; the pressure control valve is used In order to adjust the balance between the compressor supply air and the external air supply; the adjustable pressure switch function is to adjust the compressor to increase or decrease the load pressure.

2.1.2 Oil system oil is subdivided by oil and gas barrels and subdivided by oil and gas subdivision. After being filtered by oil cooler, oil supply solenoid valve and oil filter, it is sent to the compressor through the oil cut valve to the main engine and compressed air. It is cooled, lubricated, and then discharged into the oil and gas tank with compressed air through the compressor main unit to separate the oil and gas, and then proceed to the next cycle.

2.2 Micro-heat regeneration adsorption dryer (referred to as dryer) 2.2.1 Working principle The dryer uses activated alumina with pore diameter and water molecular diameter as the adsorbent, adopting the principle of variable temperature pressure swing adsorption, when adsorbed at normal temperature, The partial pressure of the water molecules in the compressed air is greater than the partial pressure of the water molecules in the adsorbent, the water molecules enter the interior of the adsorbent, condense into water droplets on the surface of the adsorbent, release the heat of condensation and store the heat in the upper part of the adsorption tower; About 5% of the dry air is heated by the heater to about 250 °C through the regeneration cylinder, so that the adsorption capacity of the adsorbent is greatly reduced, so that the adsorbent is desorbed, and the desorbed water is released to the atmosphere through the muffler, and the adsorbent passes through Regeneration, adsorption, and regeneration are used to obtain dry compressed air.

2.2.2 Working process The dryer is operated alternately through two adsorption towers to produce continuous dry air. In the first cycle, the compressed air enters the A tower through the pneumatic valve for adsorption drying treatment. At this time, the A tower performs gas production, 95% of the product gas is sent to the gas storage device through the one-way valve, and about 5% of the product gas After the restrictor orifice plate enters the heating cylinder and heats up to about 250 °C, it reaches the B tower through the one-way valve, and the adsorbent which has been adsorbed and failed in the tower B is regenerated and desorbed, and the desorbed water is carried by the gas of about 5%. Exhausted by a silencer; in the second cycle, the two towers A and B are exchanged, the B tower is adsorbed and gas is produced, and the A tower is regenerated and desorbed.

3. Common fault phenomenon and treatment 3.1 Single screw air compressor failure and treatment 3.1.1 Unloading valve fault Unloading valve In the working process of single screw air compressor, due to the unevenness of external air consumption, compression During frequent load shedding and load shedding, the machine is in an open, half-opened, closed state to maintain the stability of the instrument air system pressure. Due to frequent opening, the O-ring in the unloading valve is deformed and worn, the internal spring is insufficient, and the piston is insufficient. There is impurity in the surface area of ​​the shaft, which causes the unloading valve to be stuck, unable to open, and cannot be closed. When the unloading valve is faulty, the low pressure can not be loaded when the air compressor is low, the unloading at high pressure, and the abnormal displacement of the exhaust gas is obviously reduced. At this point, the air compressor should be stopped. After the pressure is released, the unloading valve is opened, the bonnet and the cylinder block are removed, the retaining ring and the piston are loosened, the piston shaft is pulled out, the impurities on the surface of the piston shaft are cleaned, and the surface is coated with lubricating oil. Check the O-ring wear condition, replace the O-ring, check or replace the spring.

3.1.2 Loading solenoid valve failure In the operation of single screw air compressor, the loading solenoid valve controls the increase and decrease of the air compressor. The failure or air leakage may also cause the air compressor to be unable to load the air supply. Abnormal phenomena such as failure to unload at high pressure and significant decrease in exhaust gas volume.

The general cause of failure of the loading solenoid valve is valve core fouling, solenoid valve diaphragm leakage, and electromagnetic coil failure. Use a multimeter to check if the coil is damaged. If the coil is burnt, replace the solenoid valve in time; open the solenoid valve spool to check for scale. If it is, clean it; check the diaphragm for air leakage. If it leaks, replace the diaphragm. .

3.1.3 Air filter blockage or filter net blockage Air filter or filter net is not cleaned for a long time, causing excessive accumulation of dust, blocking the filter, which will cause the air compressor to reduce the exhaust volume and exhaust temperature. Too high, so the air filter element and dust filter should be cleaned and purged regularly. We clean and purify the air filter element and filter net once a week during operation, and replace the air filter every 1500~2000 hours. The filter element of the device is made of a good quality filter element. The poor quality air filter element is easily blocked and flattened by the air compressor, resulting in frequent replacement, and its filtering effect is poor, so that a large amount of dust can easily enter the air compressor. In the oil, the oil change is frequent and the star wheel and the screw in the air compressor are worn out, which causes the operation cost to be too high.

3.1.4 Adjustable pressure switch failure or failure Adjustable pressure switch failure can cause the air compressor to frequently increase or decrease. When the air pressure of the air compressor is high, it cannot be unloaded, resulting in the safety valve taking off, the unit can not load the gas normally, and the compression. The machine has insufficient exhaust gas and other abnormalities. When the adjustable pressure switch is faulty, the outer cover should be removed, and the multimeter should be used to check whether the signal contact has a signal output when the unit pressure drops. If not, try to readjust the set value of the adjustable pressure switch (by rotating the upper pressure screw) And differential pressure screw), if it is still invalid, it must be replaced. If the compressor frequently increases or decreases the load, it is caused by the set value of the adjustable pressure switch being too small. At this time, the differential pressure set value should be adjusted appropriately, but pay attention to adjust the set value. The minimum pressure difference cannot be lower than 0.15MPa.

3.1.5 Oil filter plugging failure When the oil filter is used for too long, the pressure difference is too large, which will cause the compressor to supply insufficient oil, which will cause the exhaust gas temperature to be too high. The oil filter is equipped with a differential pressure transmitter, if an alarm occurs. , it is necessary to replace the filter element of the oil filter in time. If the differential pressure transmitter does not have an alarm, but the above abnormal phenomenon occurs, it is necessary to check whether the differential pressure transmitter is damaged. The filter element of the oil filter is generally replaced when the air compressor is operated for 2000 hours and the air compressor is replaced with new oil.

3.1.6 Minimum Pressure Valve Fault The function of the minimum pressure valve is to establish the circulating pressure required for the lubricating oil at the start of the compressor main engine and to reduce the flow rate of the air flowing through the fine separator of the oil to ensure the separation of oil and gas. When the spring or O-ring in the minimum pressure valve is worn, damaged or detached, when the dirt or impurities are accumulated on the valve core, the upper end of the minimum pressure valve may leak and the compressor may not start normally, and the air compressor cannot be unloaded normally. . When this happens, open all the pressure in the air compressor and open it. Check and replace the O-ring and spring to check and remove dirt and impurities on the main spool.

3.1.7 Air cooler and oil cooler failure Because the air compressor uses air for cooling, when the dust content of the outside air is too large, it will cause excessive oil accumulation in the oil cooling and air cooler, thus affecting heat exchange and causing air The press exhaust temperature is too high. At this point, the aluminum fins on the surface of the cooler should be inspected first. If there is too much dust, the industrial compressed air should be led to the cooler by the hose, and the cooler should be blown from different directions. If it is still dirty after blowing, use it. Washing products such as soot net, wash the cooler with water. We use compressed air every two weeks during the operation, and clean it with oil fume every 3 to 5 months to ensure the cooling effect of the cooler.

3.1.8 Leakage or blockage of the control pipelines Leakage or blockage of the control pipelines may cause the air compressors to fail to increase or decrease the carrier gas supply, and the exhaust gas volume is significantly reduced. Therefore, the air compressor should be inspected and controlled in time when the fault occurs. Pipeline conditions, especially at the gas line at the distribution station controlling the gas path and the control gas path at the unloading valve.

3.2 Micro-heat regeneration adsorption dryer failure and treatment 3.2.1 Check valve failure Because the dryer is in the normal operation process, the two towers work alternately, so long-term operation will cause the check valve spool to be stuck, because The check valve used in the dryer is internally constructed as a spring and a valve. When running for a long time, the spring will age and the valve core will be stuck. When the check valve fails, different check valve faults will be different. The phenomenon of failure.

When the B tower is in normal adsorption and the A tower is regenerated, if C1 is stuck and cannot act or can not function as a check valve, the pressure in the B tower will drop, and the normal working pressure will not be reached, and the silencer will be large. Exhaust, if the fault is not detected in time, the dryer will work normally in half a cycle in one cycle, and the gas will not be produced normally in half cycle, causing the instrument wind pressure to periodically decline; if it is C4 If it is stopped, it will cause the same phenomenon, and it will cause the B tower regeneration effect is not good, and the regeneration temperature is too low, which leads to excessive water content of the instrument wind when switching the A tower, which will seriously affect the failure of the pneumatic valve at each user; When the A tower is running and the B tower is regenerated, if the C2 and C3 fail, the fault phenomenon is the same as above. When a check valve malfunction occurs, carefully observe the operation of the dryer and quickly find the faulty check valve to replace it.

3.2.2 Pneumatic valve failure During the operation of the dryer, in order to ensure the normal and stable operation of the dryer, the four pneumatic valves are constantly switching and moving frequently, but the long-term operation will cause the pneumatic valve diaphragm to break and control the pneumatic valve. The electromagnetic head on the actuating pilot valve is burned out and malfunctions, so that the closed valve cannot be closed, and the opening cannot be opened, causing a malfunction. The fault phenomenon has different anomalies for different valves, mainly due to a large amount of exhaust at the muffler, the pressure in the regeneration tower gradually rises, the pressure in the operating tower is too low, and it cannot rise to the working pressure. At this time, the operation of the dryer is first performed. Change the time and time, shorten the switching cycle of the two adsorption towers, change the 60 minutes of normal operation to 5 minutes or 3 minutes, so as to carefully observe the action switching process of each pneumatic valve in time, find out the action but no action. The pneumatic valve firstly opens and closes the pneumatic pilot valve manually to see if the malfunctioning pneumatic valve has any action. If it is operated, the pilot valve body is not damaged. Then, the electrician is checked to see if the electromagnetic head of the pilot valve is burnt out. Finally, By disassembling the pneumatic valve part and its valve body part, it is judged whether the diaphragm is broken or the body is not tightly sealed, and corresponding measures are taken.

3.2.3 Silencer Fault The silencer fault is mainly caused by the large moisture content of the air after long-term operation, which causes the silencer to be rusted or blocked. At this time, it should be replaced in time.

3.3 Three-stage filtration failure The three-stage filter element is generally replaced when the system is running for 2000 to 3000 hours. However, during the operation, the three-stage filter was replaced on time, and the third-stage filter element did not reach the replacement time, but the intake pressure of the dryer was lower than the air compressor exhaust pressure (the air compressor discharge pressure was 0.65). MPa, while the pressure of the dryer is only 0.3 ~ 0.45MPa) and the safety valve of the air compressor takes off. At this time, the first two stages of filtration have become blocked and need to be replaced.

The main reason for this phenomenon is that in the humid season, the air humidity is relatively large, and the pipeline is made of carbon steel. Therefore, many rust stains are formed in the pipeline, which are blocked in the first two filters, causing filtration. The filter element needs to be replaced too early. When the blockage is serious, the air compressor has a large exhaust volume and the exhaust gas is not smooth, which instantaneously causes the pressure inside the air compressor to be too high, forming a safety valve to take off. In order to monitor this situation in time, we installed a pressure gauge on each stage of the filter to monitor the pressure difference at any time, so the filter replacement time should be shortened during the season when the air humidity is high.

4. Conclusion By summarizing the abnormal phenomena and treatment methods of the instrument fan unit, it provides a reliable method for timely and rapid processing of the instrument fan unit failure, thus ensuring the safety, environmental protection and stable operation of the production.

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