1Overview 4 sets of existing oxygen production equipment of Tiantie Group Air Separation Plant, the total production capacity can reach 310 million m 3 / a oxygen per year. The No. 3 air separation unit uses Kaifeng air separation plant equipment with a production capacity of 15,000 m 3 / h of oxygen. The process uses an internal compression process design. The DA-70 air compressor is one of the key equipment for the No. 3 air separation. Its normal operation is the basic guarantee for the normal production of the whole set of equipment, and its role is very important. Since it was put into production in 1997, it has been running continuously for nearly 9 years.
2 The discovery of abnormal vibration of air compressor DA-70 air compressor is a centrifugal compressor produced by Kaifeng Air Separation Factory. It is driven by steam turbine with two-stage intercooler. The equipment adopts the tilting pad bearing with better anti-vibration performance, and there are 4 vibration monitoring points (two vertical and horizontal) at the two ends.
In September 2005, the operating personnel found that the vibration of the primary bearing of the DA-70 air compressor has a rising trend. In consideration of the production, the operation continues, and the vibration still keeps rising. After one week, it has reached 75 μm, which seriously exceeds the equipment. The normal operating technical parameters, so the factory decided to stop for maintenance.
3 Preliminary analysis reasons The main reasons for the bearing vibration exceeding the standard are as follows: 3.1 The dynamic balance deviation of the steam turbine, the coupling and the equipment rotor itself causes the equipment to generate large centrifugal force at high speed, thus producing the bearing. Larger impact, increased vibration value.
3.2 Intercooler leakage, causing scale to enter the compressor with the airflow, attached to the rotor impeller or the interstage pipe wall during the compression process, resulting in poor airflow and bearing vibration deviation from normal values.
3.3 The air filter has poor filtering effect, and the impurities in the air enter the compressor, which has a great impact on the high-speed rotating rotor and the impeller, so that the bearing is unevenly stressed and generates vibration deviation.
3.4 The bearing has a serious wear phenomenon, causing the bearing vibration value to deviate from the normal range.
3.5 The gap between the bearing pad and the rotor is deviated, causing the bearing vibration to deviate from the normal range.
3.6 The phenomenon of misalignment of the turbine, coupling and air compressor rotor causes the vibration of the equipment to deviate from the normal value during high-speed operation.
4 Preliminary inspection results For the reasons of the above analysis, the equipment was inspected item by item, and the inspection results are as follows.
4.1 In order to determine the dynamic balance performance of the rotor, the air compressor rotor and the coupling were sent to the Kaifeng air separation plant for dynamic balance correction experiments. From the test data, it can be concluded that the main reason for the increase in the vibration of the primary bearing is not caused by the problem of the dynamic balance of the rotor and the coupling of the equipment.
4.2 From the surface, the inside of the equipment is relatively clean, and there is no dirt on the impeller and rotor, which eliminates the possibility of water entering the equipment.
4.3 The gas seals at all levels and the impellers did not find serious wear and tear. Only the balance disc seals were slightly worn, which could eliminate the poor filtering effect of the air filter.
4.4 The primary bearing support tile has no obvious wear. The top clearance of the lead-bearing lead is 1.58μm, the clearance is small, and the interference is 0.35μm. This interference is small.
4.5 After the alignment check, the test data is shown. It can be concluded that excessive bearing vibration is not caused by this reason.
4.6 Considering that the turbine may have problems, causing the vibration of the air compressor to be abnormal. Before the normal test, the turbine was tested in a single machine. When the rated speed was reached, the vibration value was less than 20μm, which did not exceed the design requirements. The cause of the turbine can be ruled out.
5 The initial rectification measures rectified the problematic parts according to the results of the inspection, replaced the balance disc seal, adjusted the bearing clearance, and met the design requirements. The air compressor rotor, coupling and turbine rotor alignment were recalibrated to meet the equipment installation requirements.
6 The first test situation After all the corrective measures were completed, the test was carried out, and the primary bearing was tested using a portable vibrometer. During the test run, it was found that the first-order vibration reached 35μm at the beginning of the rushing speed, and continued to rise during the rushing process. After the critical speed reached 8000r/min, the primary bearing vibration increased rapidly, close to 90μm, and the speed was connected. An abnormal sound occurred when entering 1 0000r/min and was forced to stop.
7 Analysis of the failure of the test run Considering the cause of the vibration caused by the initial analysis, the results of the test failure are combined with the results of the data measured by the vibrometer.
The field measurement data of the portable vibrometer (the upper direction is the radial direction and the lower picture is the axial direction). The field measurement data is analyzed by the vibrometer. Due to the occurrence of 2, 3, 4 times the rotational frequency, and the radial vibration amplitude is large. (Double speed frequency), the axial vibration amplitude is small (two times the speed frequency). Therefore, consider the looseness of the bearing and housing or equipment foundation.
8 Re-measures for the above analysis According to the above analysis, the equipment bearing including the bearing housing was thoroughly inspected, and it was found that there was looseness between the root of the primary bearing seat and the base of the equipment. After further analysis and inspection on the spot, it was found that the horn was loose under the equipment. Therefore, all aspects of analysis focus on the reasons for the looseness of the bearing housing and equipment foundation, which is consistent with the situation reflected by the vibrometer. The following measures were taken based on the analysis.
8.1 The reaming of the positioning connection between the bearing housing and the base is re-established to ensure that there is no looseness in the bearing housing. At the same time, the bearing was replaced and the gap was re-adjusted to meet the technical requirements of the equipment installation.
8.2 Taking into account the needs of production, it was decided to take a small range of rectification of the equipment foundation, re-adjust the horn, fix the weld, and add a support point below the base of the equipment. Then grind again.
9 Trial vibration monitoring record again After all the corrective measures have been implemented, it is determined that all the test conditions are available and then the test is carried out. One-watt vibration and speed record of DA-70 air compressor.
When the rotation speed is very low, the vibration of one watt is not small compared with the previous rotation speed. However, as the rotation speed increases, the vibration value does not increase significantly. When the critical speed is passed, the vibration does not fluctuate greatly and rises to 10000 r/min. The vibration value is basically stable at about 30 μm, and there is no significant increase when the rated speed is reached. After the equipment was loaded, the vibration value decreased slightly, and the test was successful.
10 Conclusions The DA70 air compressor is a high-speed rotating machine, which causes many factors of bearing vibration. After our accurate diagnosis and scientific analysis, a series of measures have been taken to successfully complete the repair task of the equipment, and the vibration control of the bearing is now running. Within the allowable range, there have been no major fluctuations. This accident is a good warning for us. The use of scientific means, advanced tools and correct methods in the process of equipment inspection and maintenance will achieve twice the result with half the effort.
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