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In 1984, Zhenhai Refining and Chemical Co., Ltd. started with the status monitoring of the five major fertilizer units, and cooperated with Xi'an Jiaotong University to fully realize online status monitoring of the five major units. The system has been put into use for more than ten years and has solved many practical problems in production. In May 1989, after the low-pressure cylinder of the nitrogen compressor was overhauled, the vibration during operation was relatively large. Based on the analysis and diagnosis based on the spectrum chart and the actual situation of equipment maintenance, it was recommended that the unit should not be reworked for maintenance to avoid a loss of 8.25 million yuan. In 1999, based on the actual problems of system operation, production needs and technological progress requirements, we continued to follow the road of localization and adopted the ND3000 online monitoring system to realize online monitoring of six large fertilizer units. The ND3000 system is a real-time holographic status monitoring system based on DSP digital signal processor technology. It realizes complete machine channel synchronization, real-time spectrum monitoring, multi-machine parallel real-time processing, and network information sharing. It is a distributed networked real-time online monitoring system. 1 Friction failure of steam turbine before carbon dioxide compressor overhaul http://www.nmtech.com.cn/jishuwang/upload/0602051608048751.jpg On January 12, 2002, the ND3000 online monitoring system was still in the debugging stage. As shown in Figure 1, the vibrations of the four measuring points on the front and rear bearings of the carbon dioxide compressor turbine increased simultaneously. Among them, the measuring point X105H with the largest vibration value increased from 30 μm to 44 μm, with a time interval of about 20 hours. During this period, the vibration of the two measuring points X106 on the turbine side of the low-pressure cylinder also increased at the same time. After that, the vibration values of each measuring point remained unchanged. At 7:38 on January 15, the vibration values of each measuring point began to decrease slightly. The vibration value of X105H was 41 μm at 14:21. Then the vibration of each measuring point of the steam turbine of the subsequent unit was basically stable. 1.1 Test data and spectrum analysis 1) The vibrations of a total of six measuring points including X104, X105 and low-pressure cylinder X106 of the steam turbine increased simultaneously. The analysis believed that the possibility of sensor failure was small. It was confirmed that the on-site sensor was working normally, so it was confirmed that it was a problem with the unit itself. In the vibration of the low-pressure cylinder and gearbox, except for the simultaneous increase in the vibration of X106, the other measurement points have no obvious changes. Therefore, it is believed that the increase in the vibration amplitude of the low-pressure cylinder X106 is transmitted from the steam turbine, and the vibration source is the steam turbine. 2) Looking at the measuring point spectrum diagram of the ND3000 system, the vibration at the four measuring points of the unit's turbine is dominated by power frequency, accompanied by frequency components such as double frequency. Will January 14, 2002 13: 30 data with 10 on December 26, 2001: Comparing the data of 10, it can be seen that the increase in the pass frequency value of the four measuring points of the steam turbine is caused by the increase in the power frequency amplitude, while there is no obvious change in components such as the second frequency. The axis tracks on both sides become larger overall to varying degrees. 3) Analyze the time domain waveforms of the four measuring points of the steam turbine. It is found that there is local clipping in the lower part of the waveform of X105H, the measuring point with the maximum vibration value. 4) The phase difference values between December 26, 2001 and January 14, 2002 changed significantly, indicating that when vibration occurs, the unbalance vector changes in size, angle, and position. Various phase difference values stabilized after January 14th. The power frequency phase changes on the front and rear sides of the steam turbine are shown in Table 1. http://www.nmtech.com.cn/jishuwang/upload/0602051608446192.jpg1.2 Steam turbine operating condition analysis 1) On November 1, 2001, the unit started up after repairing the high-pressure cylinder. The vibration of X105 increased by 19% compared with the vibration value before shutdown, mainly with the increase of power frequency amplitude. ； The main steam flow rate of the steam turbine increases by about 15t/h compared with before shutdown, and the load is higher. Analysis shows that the steam turbine is under high load for a long time, which has a greater impact on the components of the rotor. 2) In November 2001, the turbine main steam flow, pressure and temperature all experienced sudden changes to varying degrees. Among them, the most obvious change in the X105 vibration is that the main steam flow suddenly increased to nearly 120t/h on November 15, corresponding to the X105 vibration rising by one step (4 μm), and then the steam flow stabilized at about 113t/h, but the turbine vibration did not decrease. 3) The pressure and flow rate of the main steam and extraction steam of the steam turbine were relatively stable a few days before the sudden change in the turbine vibration value, and the unit load was also relatively stable. After the vibration changes, the vibration value does not change significantly during the unit load adjustment. Based on the above analysis, a preliminary diagnosis opinion can be drawn: ①There is friction in the steam turbine ； ②The unbalance of the steam turbine rotor increases and components are damaged. ； ③When the main steam flow rate, temperature, etc. do not change significantly, the turbine vibration can basically maintain the status quo, and there is no need to shut down for emergency repairs. Make recommendations based on faults: ①Keep the main steam flow, temperature and pressure stable. When the working conditions need to change, the transition should be smooth. This can keep the vibration trend of the turbine stable in the future. ； ② During the 2002 fertilizer overhaul, the steam turbine of this unit should be overhauled. During the biennial maintenance of the unit in March 2002, an overhaul of the unit's steam turbine was arranged, and the inspection results were consistent with the diagnostic conclusions. The steam turbine maintenance status is as follows:: ①Check that there is friction in the lower steam seals of stages 5 to 11 of the steam turbine, and the friction points are in a straight line. Grinding was carried out during maintenance. ②The inspection found that the dynamic balance block at the final wheel disc of the steam turbine rotor was eroded and fell off a section of nearly 1mm long, which corresponds to the sudden increase in vibration of X105 on the exhaust side of the steam turbine from 30 μm to 44 μm. The dynamic balance state of the rotor was instantly destroyed, but the weight loss was not too large. 2 After the overhaul, the carbon dioxide compressor high-pressure cylinder rotated and stalled. After the unit was overhauled in April 2002, the problem occurred on the 11th and 13th of April 2002.: 30 The urea device introduces steam and establishes a heat network. A single test was conducted on the compressor and no abnormalities were found. http://www.nmtech.com.cn/jishuwang/upload/0602051609481165.jpg http://www.nmtech.com.cn/jishuwang/upload/0602051610398753.jpg April 13 to 15: 45 unit compressor heating pipe, 19: 00 carbon dioxide compressor unit rush, 20: 02 passed the critical point, and the compressor pressure reached 14MPa. The ND3000 online monitoring system was used to analyze the frequency spectrum of the four measuring points of the high-pressure cylinder (see Figure 2). It was found that sub-asynchronous frequency components appeared in all of them, which were similar to the characteristics of previous rotating stall faults. The operating conditions of the unit were analyzed and it was found that the pressure in the three stages of the unit was high and the flow rate in the fourth stage was low. It is believed that the high-pressure cylinder of the unit has suffered a rotational stall failure. 13th 22: The vibration of unit 45 was still difficult to eliminate after adjusting the load, so the unit was withdrawn. The vibration spectrum of the four measuring points of the high-pressure cylinder was analyzed, and it was found that the power frequency was dominant. 23: 12. Restart the operation. Because the vibration of the unit is still large, 1 on the 14th.: 06Decided to shut down for maintenance. The high-pressure cylinder was disassembled and inspected for emergency repairs. The "O" ring was normal. It was found that there was a lot of rust in the impeller flow channel and partition plate. They were cleaned and the high-pressure cylinder rotor was dynamically balanced. The machine was started on April 14, and no abnormalities were found in the vibration spectrum analysis of each measuring point. The above two cases are examples of the application of the ND3000 online monitoring system. The system provides reliable analysis data and multiple analysis methods to condition monitoring personnel in a timely manner, playing a great role in successfully diagnosing unit faults and avoiding unnecessary shutdowns and necessary timely inspections and repairs. The commissioning of the condition monitoring system for large units can bring huge economic benefits to large units for carrying out predictive maintenance and saving inspection and maintenance costs.