Two typical failures in the application of the hot

2022-08-21
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Analyze two typical faults in the application of filters

the air supply system of the mechanical seal of the centrifugal compressor, the oil supply system of the bearing, the oil supply system of the bearing bush and bearing of the reciprocating piston pump, and the intercepting device of the fluid inlet of the rotating equipment all need to be equipped with filters. There are many kinds of filters, including fiber and metal. According to the different requirements of equipment for lubricating media, filters are divided into fine filter and coarse filter. The fine filter is generally used in the gas or liquid lubricant required by the friction pair of the equipment, which requires high filtration accuracy, and the equipment is often high-speed, high-pressure and heavy-duty. Once it is careless, the consequences will be serious; The coarse filter is generally used in the fluid inlet pipeline of rotating equipment such as pumps to block dirt and impurities, and protect the equipment body from large debris interference. It should be said that the filter is an auxiliary device. In practical application, the purpose is selected according to the accuracy of the equipment to the fluid medium, and whether to replace the filter element is determined according to the situation of the on-site differential pressure gauge. The safety in operation is guaranteed

however, the fine filter element is generally wrapped by asbestos fiber on the reinforcement rolled by steel plate, which has strong directionality. If the fluid is introduced from the reverse direction, asbestos and other fibers will be blown into the friction pair, causing the damage of the friction pair; In order to block impurities and precipitate impurities, the coarse filter is also designed with directionality. Once the direction is installed in the opposite direction, the fluid will be irregularly cut off, and the lubrication of the equipment itself and subsequent main equipment may be affected. It is precisely because of this directionality of the filter that there is a real installation error. The application of filters in Chongqing Jianfeng Chemical Fertilizer Co., Ltd. is quite common. Since the start-up, there have been some problems with the filters more or less, but from the perspective of installation, there are two problems, one is the filter failure of the sealing gas of the high-pressure cylinder of the carbon dioxide compressor, and the other is the filter failure of the crankcase circulating oil of the small ammonia pump feeding the urea synthesis tower. This paper analyzes the causes of the problems from the phenomena of these two faults, and improves the ability of equipment maintenance such as filters in large-scale devices through the analysis of two typical faults

two typical failures in the operation of urea plant:

failure of sealing system of high-pressure cylinder of carbon dioxide compressor

carbon dioxide compressor is a centrifugal compressor made in Nuovo Pignone, Italy. It is driven by steam turbine, with four sections and two cylinders. The first and second sections form a low-pressure cylinder, which is directly driven by steam turbine, and the design speed is 8400r/nfin; 3、 The four sections form the high-pressure cylinder, and the power is transmitted from the low-pressure cylinder rotor to the high-pressure cylinder rotor through the gear speed increase box, with the design speed of 12300r/min; The inlet gas pressure is 0.2MPa, and the outlet gas pressure is 17:6mpa. C02 from the decarbonization system in the synthesis battery limit is sent to the urea synthesis tower through the compressor to synthesize urea

the LP cylinder is a transverse half section structure, model 2mcl527, and the shaft end seal is a three-stage comb labyrinth seal. The high-pressure cylinder is of longitudinal head end cover structure, model 2bcl306/A, and the shaft end seal adopts the combination of comb seal and johncrane28at mechanical seal. The three-stage shaft seal uses two-stage labyrinth seal plus one set of mechanical seal, and the four-stage shaft seal uses three-stage labyrinth seal plus one set of mechanical seal. The connection between labyrinth seal and mechanical seal. The grating sensor has the advantages of easy digitization, high precision (the highest resolution can reach the nanometer level at present), strong anti-interference ability, no artificial reading error, convenient installation, reliable use and so on. The seal gas is the C02 gas after decompression at the outlet of the fourth section of the high-pressure cylinder through the orifice plate, which is filtered by the filter, Provide the pressure and flow necessary for the normal operation of 28AT mechanical seal. See Figure 1 for the process flow

the key of this process is to ensure that 28AT mechanical seal forms gas dynamic pressure lubrication. In addition to the special structure of friction pair and a certain speed, fluid flow, pressure, water content, impurities and other important factors affecting the normal operation of mechanical seal. 28AT mechanical seal is characterized by 12 wedge-shaped shallow grooves on the surface of the moving ring. At a certain speed, the sealing gas enters the shallow groove to form a self pumping effect, pushing the dynamic and static rings of the mechanical seal away, forming a 3M air film to protect the dynamic and static rings from contact wear. Once the gas film cannot be formed or destroyed, the contact friction of the dynamic and static rings will instantly generate a lot of heat under high-speed rotation, causing the thermal cracking and destruction of the dynamic and static rings. Since the unit was completed and put into operation, the high-pressure cylinder of the carbon dioxide compressor has generally operated well. However, after 1995, a strange phenomenon occurred one after another. The mechanical seal was easy to be damaged when driving again, especially after the system tripped. Specifically, when the unit speed rises to 6800r/min, shortly after the seal gas is changed to CO2, or shortly after the speed reaches the normal load speed, the rotor vibration increases sharply, and the seal gas vent pipe smokes and emissions increase. The disassembly inspection found that the static ring of the mechanical seal had been crushed and broken, and the asbestos fiber of the filter element was found in the sealing cavity. After the mechanical seal was replaced and the sealing gas was purged again, the start-up was normal

fault analysis:

in view of the mechanical seal damage of high-pressure cylinder one after another and the asbestos fiber in the seal cavity during start-up, the filter is mainly studied. Actively serve Tongling Copper based new material industry base. When studying the drawing of the filter, it was found that the installation direction of the filter inlet and outlet was opposite to the design installation direction, as shown in Figure 3 and Figure 4

for the filter installed, the fluid flows from the inside of the filter element to the outside. The filter design requires the fluid to flow from the outside of the filter element to the inside. This design requirement is consistent with the structure of the filter element, which is made by wrapping asbestos rope layer by layer on the inner perforated steel cylinder, and the outer surface is not covered with filter cloth. If the fluid flows from the inside of the filter element to the outside, it is easy to blow the asbestos rope, causing the asbestos to fall off and accumulate at the bottom of the filter. During emergency start-up after the system stops, if the shower guide is not opened or the discharge is not complete, when C02 seal gas is put into use, the accumulated asbestos fiber will enter the high-pressure cylinder mechanical seal with the seal gas through the filter outlet, destroying the gas film established by the self pumping action between the dynamic and static rings of the mechanical seal, causing damage to the mechanical seal. The analysis confirmed the existence of asbestos fibers left in the seal cavity after disassembly. At the same time, the sealing filter was transposed, and the mechanical seal did not fail during startup

of course, there are many factors that cause the damage of the mechanical seal, such as the large water content of the seal gas, the quality problems of the mechanical seal itself, the large amount of axial installation of the rotor, etc., but from the continuous occurrence of the same accident phenomenon for a period of time, the problem of filter installation should be the most important

plunger horizontal or pendulum shaft is too dirty or rusty reciprocating pump crankcase oil cooling system fault

three plunger horizontal reciprocating pump is a technical transformation equipment implemented in 2002. It is proposed to solve the problem of increased vibration of high-pressure ammonia pump caused by increased device load, and is produced by Shanghai Dalong machinery factory. The oil cooling system of the upper crankcase is designed, including 1 Y-type filter, 1 gear oil pump, 1 cooler and 2 fiber filters (switched during operation). The process is shown in Figure 2

due to the friction between the crankcase crankshaft and the bearing bush during operation, the circulating oil will contain a small amount of iron filings. At the same time, the circulating oil circuit may also bring rust residue to the oil and produce bolts, gaskets and other sundries accidentally caused by loose connections, causing damage to the gear pump. Therefore, two kinds of filters are designed in the oil cooling system, metal Y-type coarse filter and non-metal fiber fine filter. The Y-type filter is designed at the front end of the gear pump to remove large particle impurities in the oil and protect the gear pump; The fine filter is designed at the oil return port of crankcase to further remove impurities in the oil and meet the running in requirements of crankcase crankshaft and bearing bush

after the completion acceptance of the pump, it operated intermittently for a period of time, and there was no major problem in the oil cooling system. However, during the continuous operation in June and July 2003, the oil cooling system appeared abnormal phenomenon, intermittent large-scale vibration of the pipeline, accompanied by abnormal sound of the oil circuit, and the oil pressure gauge showed large fluctuations. This condition usually lasts for more than ten minutes and repeats in less than one hour. Venting through the pressure gauge and other places can not solve the problem, which has buried a dangerous hidden danger for the stable operation of the pump

fault analysis:

for the problems in the crankcase oil cooling system of horizontal reciprocating high-pressure ammonia pump, many aspects have been studied and analyzed, including possible pipe joint cross-talk, heat exchanger fluid resonance, pump body cavitation, etc., but the problems have not been solved. Due to the installation problem of the sealing filter of the carbon dioxide compressor in front, the installation direction of the other oil circuit fine filter was checked, and no error was found. Therefore, it was decided to check the Y-type filter, and it was found that the installation direction of the Y-type filter was opposite to that of the commonly used Y-type filter. According to the design drawing, the installation direction of Y-type filter is opposite to that of common Y-type filter, which indicates that the design problem of Y-type filter flow direction occurred in the design of oil cooling system, and it was not corrected in time during installation. Results during operation, the unstable or blocked steel wire filter element in the Y-type filter cut off the oil circuit, causing pipe vibration and abnormal sound. At the same time, the Y-type filter on site is installed in a relatively hidden position, which is not convenient for maintenance personnel to inspect and diagnose, making the high-pressure ammonia pump operate with faults for a period of time. When the Y-type filter is reinstalled, the abnormal problem of the oil circuit system can be solved immediately, and a major hidden danger of the reciprocating piston pump is eliminated

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