Analysis and Treatment of Faults in Air Separation Unit with Several Self - regulating Valves
November 29 15:08:52, 2023
Yankuang Lunan Fertilizer Plant 28000m3 / h air separation plant supplied by Hangzhou Oxygen Co., Ltd. complete sets of supply, supporting Shaanxi Shan and Drum jointly produced RIK112S air compressor and RBZ45 turbocharger, the use of Hangzhou Steam Turbine Co., Ltd. The company's all-condensing turbine drag. The device uses full low-pressure molecular sieve adsorption purification turbocharger Turbocharged refrigeration, full distillation hydrogen-free argon, air pressurization cycle of oxygen and nitrogen double pump internal compression process. The device in the end of May 2008 began a single test run, June 29, 2008 to produce qualified oxygen. More than 3a system to run well, but in operation some of the valves exposed a series of problems, many times led to the system was forced to stop and overhaul. This article is mainly on the operation of the device appears liquid nitrogen throttle spool off, high-pressure liquid throttle valve stem fracture, liquid oxygen pump inlet valve leakage, liquid oxygen pump valve stem vibration eccentric wear and other issues and take Rectification measures for discussion, for your discussion and reference. 1 liquid nitrogen throttle V3003 spool off 1.1 Phenomenon September 6, 2008 at about 6:00, inspection staff found that air separation cold box on the eastern side of the phenomenon of liquid leakage. The investigation found to go on the tower liquid nitrogen throttle V3003 valve gland at the spray. Immediately contact the instrumentation staff to deal with the problem after the spray solution, but the valve is constantly there vibration and noise emitted. September 6 valve factory technicians to the factory, the analysis of suspected valve spool off or stem fracture, need to stop processing. September 16, short airspace, fractional distillation system to maintain the tower after the micro-positive pressure demolition seized V3003 and found the valve stem and valve stem at the junction of desalination, spool slight signs of wear and tear. System replacement after the replacement of the new valve drive, the initial valve is working properly, but less than a month V3003 valve stem fracture again, the system was forced to stop overhaul. 1.2 Analysis and treatment of reasons for the V3003 multiple fracture problems, the first suspected is the valve selection is too small, because the design of the valve design of the early caliber of DN125, the final design to DN80. However, DN80 diameter accounting results fully meet the design requirements. V3003 valve stem and stem connection occurred 2 times off the weld fracture, and the fracture surface is the spool and the valve stem welding Department, it is suspected that the valve core and the valve connection strength is not enough, the valve plug and stem embedded connection can not meet Operating requirements. So in consultation with the Hang Oxygen Tooling technical staff, the spool guide sleeve bold, lengthened, and then increase the threaded connection after welding, while the valve stem and the use of the rivet pin. After the system is restored to drive, the V3003 is running no abnormality so far (the valve has been stable for nearly 3 years so far and there is no problem again). 2 high-pressure liquid air throttle valve V3015 valve handle fracture 2.1 phenomenon July 2008 air separation plant normal operation, the air supercharger end of the high-pressure air relief valve multiple over-pressure take-off. Through investigation, it was found that V3015 high-pressure liquid-air throttle valve vibration larger, and the field valve position and control room display there is deviation. Valves will still vibrate after replacing a new valve positioner with a maintenance opportunity in October. February 2009 parking inspection valve found: stem guide sleeve worn seriously, there is a about 30mm wide, 5mm deep annular groove, and the stem there is a slight bending deformation, the spool of the three throttle surfaces are different degrees Of the wear, the deepest up to 3mm, the valve seat has three gaps, the deepest up to 4mm. Because there was no corresponding spare parts replacement, was forced to high-pressure liquid-air throttle valve guard operation, 20d after the stem suddenly rupture, the valve violent vibration (even cold plate and platform can also feel the vibration), the system was forced to stop overhaul. 2.2 Reason Analysis and Treatment V3015 rated flow of 74400m3 / h, the maximum flow of 78120m3 / h, the valve diameter DN80, but the actual operation of high pressure air flow sometimes far more than 80000m3 / h, deviate from the valve rated conditions. Valve diameter is too small, will result in faster fluid flow, and produce cavitation and flash, resulting in serious spool valve parts wear. For this purpose and Oxygen designer dedicated to communicate, according to the actual operating conditions, the valve is replaced with DN100 caliber valve, valve parameters have also been properly adjusted, while the valve structure by a reduction of blood pressure to three Step-down and step-down, reducing valve flow at the media flow rate and reduce the amount of media flash and cavitation. In addition, the import and export of valves in the operation of large pressure drop, the media easily flashed gasification, spool erosion serious situation, the new valve for the valve material to improve the level (nickel content of 13.4%, about 3% , Effectively improve the strength of the body, toughness and wear resistance). After the system is strengthened, the operation of the valve is monitored: Reduce the temperature before V3015 valve, control below -160 ℃, try to keep the original design value of -171 ℃ as much as possible to reduce the post-throttling vaporization rate; Valve abnormalities in a timely manner to control the adjustment. After the change of nearly 3a during the operation, the valve repeatedly dismantling, no abnormalities were found, the internal parts did not appear worn. 3 liquid oxygen pump inlet valve leakage 3.1 Phenomenon Since the system has been driving, the liquid oxygen pump inlet valve V3501A / B there is always the problem of internal leakage, both on the liquid oxygen pump high load operation have an impact, but also result in liquid oxygen pump, import filter , Check valves, etc. can not exit from the system, overhaul. To this end, all previous air separation maintenance valve will be included in the dismantling plan, and had 2 replacement of the new valve, but still not completely solve the valve leakage problem. 3.2 Analysis and treatment (1) for the valve leakage problem, first of all suspect that the device is foreign objects such as aluminum chips stuck in the spool, resulting in lax valve closure. This device parking opportunity to verify: from the closure of the valve to the system after the liquid drain to stop disassembly inspection, has been to keep the valve is closed, but in the final inspection of the valve did not find any foreign body, thus excluding The suspicion. (2) By referring to the relevant information of the valve, it was found that the inlet valve of the liquid oxygen pump is a product of HangXiang KOSO and is the first used for the internal compression process. The designed leakage level is Grade IV, and a certain amount of leakage is allowed but no To meet the internal compression process liquid oxygen pump online out of system maintenance requirements. In view of the valve to bring the system security risks, Hang oxygen for the valve re-design and selection of the original DN200 three eccentric butterfly valve replaced TYCO three eccentric butterfly valve (DN150, the valve requires zero leakage level). Replacement of the new valve, the valve does not appear in the operation of internal leakage situation. 4 liquid oxygen pump return valve stem vibration, partial wear 4.1 Phenomenon In 2009, the system operation process with the device load increases, liquid oxygen pump return valve V3511A / B are varying degrees of "surge", can hear the valve cavity There is an abnormal noise, especially when the system to increase the load (the valve opening more than 40%), the valve stem can be seen around 10mm up and down, resulting in out of bounds oxygen pressure fluctuations of 0.1 ~ 0.2MPa, the scene can hear the sound of a tractor , Bringing a great threat to the stable operation of the gasifier. In fact, the two return valve in the previous parking dismantlement has been found A pump backflow valve V3511A spool has serious wear and tear, can not be with the main pump long-term operation; B pump backflow valve V3511B spool there are different degrees of wear and tear. 4.2 Analysis and treatment of the reasons for the valve stem up and down the issue of movement, the first suspected is the low positioner output pressure. By referring to the valve design parameters provided by the manufacturer, the output pressure of the valve positioner of the return valve is 0.15-0.3MPa. After field inspection, the output pressures of the two valve positioners are 0.15-0.25MPa and 0.15-0.23MPa respectively, Value is slightly lower. So the instrument staff on the scene after the air filter to adjust the air pressure to 0.35MPa, to improve the output pressure of the valve positioner to the design value, but the effect is not obvious. Re-check the actual operating parameters of the scene and found that for such high-pressure throttling decompression (inlet / outlet pressure of the valve 6.34 / 0.377MPa), through the flow medium when the media flashes on the spool flush valve are generally selected flow-type valve , While the air separation plant on-site valve for the open type. Due to the general medium flashes damage occurred more downstream of the valve orifice, and flow-type valve is characterized by downstream throttle can be away from the valve and other key parts, reduce the media flash on the spool and other key parts of the erosion Wear and improve valve life, so the replacement of V3511A / B valve when the valve from the open type to flow-type, while the valve temperature from the original design -178.27 ℃ to -175.15 ℃, making the new spool More adaptable to the actual conditions. Liquid oxygen pump return valve after the transformation, the actual operation by strengthening the maintenance of the valve, monitoring, as far as possible to control the return valve opening of 40% or less, to avoid a large number of liquid oxygen back to the spool erosion; strengthen inspection and found that the valve vibration timely Adjust. Systematic addition and subtraction no longer occur when the valve stem vibration, followed by many dismantling did not find the valve core wear and tear.