The oxygen plant of Nanjing Iron and Steel United Co., Ltd. put into operation a set of 20000m3/h air separation plant in 2005. The supporting RIK804 air compressor is the original imported equipment of MANTURBO. The air compressor's regulating system is mainly composed of the vane adjusting device of the air compressor inlet pipe, the venting valve anti-surge control of the outlet pipe and the DCS system. The exhaust pressure of the air compressor is 0.62 MPa (A), and the exhaust flow rate is 111,000 m3/h. After the production, the high-frequency vibration of the inlet pipe of the RIK804 air compressor is more and more serious, and the fault of the inlet guide vane adjustment device is coming. The more the air compressor caused the anti-surge valve venting failure, causing the air separation equipment to stop frequently. The technical modification of the valve positioner in the air inlet guide vane adjusting device completely eliminates the influence of the high frequency vibration of the air compressor inlet pipe on the inlet guide vane adjusting device, and ensures the stable operation of the air compressor and the air separation device.
1 Air compressor inlet guide vane original adjustment device structure principle 1.1 inlet guide vane original adjustment device structure inlet guide vane original adjustment device structure as shown. The inlet vane adjustment device includes an actuator and a valve positioner, and the valve positioner has a built-in position transmitter. The actuator is directly connected to the guide vane; the valve positioner is mounted on the actuator, the two gas source tubes are connected to the sides of the cylinder of the actuator, the feedback link is connected to the actuator; and the valve position transmitter is installed in the valve positioner.
Instrument Supervisor Engineer of Oxygen Plant of Iron United Co., Ltd.
Original air compressor inlet guide vane adjustment device 1 actuator 2 - valve positioner 3 - valve position transmitter 4 - actuator and valve positioner connector 1.2 guide vane adjustment device working principle valve positioner accepts from DCS system The 420 mA current signal, according to the signal size, outputs different air source signals from C1 and C2, and controls the position of the piston in the actuator cylinder to adjust the opening of the vane. When the DCS system outputs a 4 mA current signal, the C2 output pressure is much larger than the C1 output pressure, and the vanes are fully closed; when the DCS system outputs a 20 mA current signal, the C1 output pressure is much greater than the C2 output pressure, and the vanes are fully open; when the DCS system outputs When the current signal is between 420 mA, the vanes are at the corresponding current signal opening. The opening of the vane corresponds to the position of the piston in the actuator cylinder, and the piston rod inputs the vane stroke information to the valve positioner through the feedback link. The valve positioner receives the mechanical feedback signal and outputs a 420 mA current signal to the DCS system via the built-in position transmitter to monitor the vane opening.
2 The failure phenomenon of the air compressor before the transformation 51, the solenoid valve of the air compressor venting valve suddenly loses power, and the air compressor is emptied. At 02:15 on October 13, 2010, the instrument personnel finished processing, the air compressor began to increase, and the working conditions gradually recovered.
54. The air compressor outlet pressure drops again. Since the small flow interlock is not input, the venting valve interlock is not opened, but the working condition to be established is paralyzed. After adjusting the working conditions, the oxygen supply is restored.
00, the vent valve solenoid valve lost power again, the air compressor emptied, after investigation, and 11:51 on the 12th. The instrument personnel limit the minimum opening of the guide vane to 75% through the mechanical limit, and barely maintain production.
3 Analysis of the cause of the failure (1) Analysis of the differential pressure (flow) curve of the inlet of the hollow compressor of the DCS system and the opening curve of the venting valve. When the venting valve is not opened, the pressure difference (flow) of the inlet of the air compressor is reduced. When the inlet guide vane of the press is closed, when the closing is small to a certain opening degree, the inlet pressure difference is less than 5 kPa, causing the venting valve solenoid valve to be de-energized, and the venting valve is fully open.
The output signal and the feedback signal input to the DCS system by the inlet guide vane adjusting device are compared, and the feedback signal is reduced, the output signal is not changed, and the fault is determined from the inlet guide vane adjusting device itself.
(3) The high-frequency vibration of the inlet pipe of the air compressor, the inlet guide vanes of the air compressor installed on the pipeline are vibrated at high frequency, and the vane adjusting device is also vibrated with the vane, causing the electrons in the valve positioner in the adjusting device. The components are damaged and faulty. The valve positioner output air source signal is abnormal, so that the piston rod of the actuator is walking to the right, the air guide inlet guide vane is out of control, and the opening degree is small.
(4) The high-frequency vibration of the inlet pipe of the air compressor is a problem that has always existed since the start-up, and it also occurs frequently in the brother units. It is a common defect of the RIK80 air compressor. In order to eliminate the fault, several improvements have been implemented: 1 The valve positioner is installed on the column that is not connected to the air compressor, which reduces the vibration of the valve positioner, but the actuator piston rod is still connected with the valve positioner feedback link. Not obvious; 2 regularly replace the valve positioner to shorten the service life of the valve positioner; 3 change the stainless steel air circuit signal tube into a hose. Although the reliability of the operation of the air compressor is improved and the frequency of the fault is reduced, the anti-surge valve venting failure is still not completely solved.
4 valve positioner technical transformation method and implementation effect equipment professionals use a variety of methods to make the high-frequency vibration of the air compressor inlet pipe slightly improved, but the impact of vibration on the inlet guide vane and vane adjustment device installed on the pipeline It cannot be completely eliminated, and the phenomenon of emptying of air compressors still occurs from time to time. The safe and stable production of air separation equipment is continuously affected.
Since the characteristics of the air compressor determine that the high-frequency vibration of the inlet pipe cannot be eliminated, it is only necessary to find a solution from the instrument professional. Looking for a valve positioner, the valve positioner in the inlet guide vane adjusting device is separately installed from the vane actuator, and the valve position feedback signal is softly connected with the valve positioner through a cable, etc., eliminating the high frequency vibration of the inlet tube to the valve positioner. influences.
4.1 Selection of the valve positioner in the inlet guide vane adjustment device After technical exchange, it is decided that the air compressor inlet guide vane valve positioner uses the 3730 series digital electric valve positioner with the split type position sensor.
(1) Valve position transmitter: The valve position feedback signal output from the 3730 series digital electric valve positioner to the DCS system is provided by the position transmitter in the valve positioner. The position transmitter is a two-wire transmitter. The signal of the position sensor is processed by the microprocessor. The position transmitter transmits a 420 mA current signal corresponding to the valve position. Since the valve position change output signal of the valve positioner is independent of the valve positioner input control signal (the valve positioner minimum input working current is 3.8 mA), it is a real-time signal of the controlled valve position (angular stroke).
Special cable: 10m, durable, flexible, oil resistant and other corrosive media.
(3) Split valve position sensor: The stroke is the same as the valve positioner, the temperature is allowed to be -60150*C, and the vibration resistance is up to 10g in the range of 102000Hz. The implementation of the scheme is to install the valve positioner separately from the vane actuator. The split valve position sensor is mounted on the vane actuator, and the valve positioner is installed in a place where the vibration is neglected. The valve position signal is output by the split type position sensor, and is connected to the valve positioner through a dedicated cable, and the valve positioner output The air supply signal is transmitted from the external air hose to the vane pneumatic actuator. The structure of the inlet guide vane adjustment device after the modification is as shown.
Air compressor inlet guide vane adjustment device 1 after the transformation 1 actuator mechanism - valve positioner 3 - valve position transmitter 4 - split valve position sensor 4.3 modified inlet guide vane adjustment device operating characteristics due to only high vibration resistance split type The valve position sensor is rigidly connected with the actuator. The valve positioner works in a vibration-free and high-temperature environment, and is connected to the split valve position sensor by a flexible special cable. The high frequency vibration cannot affect the valve positioner, ensuring the valve positioner. The valve positioner works normally, which improves the reliability. At the same time, it avoids the loss caused by the frequent replacement of the valve positioner (the valve positioner must stop the air compressor), which ensures the safe and stable operation of the air compressor.
5 Conclusion 804-type air compressor inlet tube high-frequency vibration can not be eliminated, from the instrument control point to find a solution to the problem, take effective measures to carry out the technical transformation of the valve positioner installation method in the inlet guide vane adjustment device. The transformation was very successful, completely eliminating the influence of the high-frequency vibration of the air compressor inlet pipe on the inlet guide vane adjustment device, and solving the technical problems that have been plagued for many years. The 80-4 air compressor has been running stably for two years, and there has not been any failure of the air compressor due to the failure of the inlet guide vane adjustment device, which satisfies the production requirements of the air separation plant. The transformation measures are simple and easy to implement, with strong practicability and remarkable effects. They can be used as reference for RIK 80 series air compressor users to solve similar problems. ,
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