1. Background introduction
The gas turbine power plant adopts the STAG-109FA-SS single-shaft combined cycle unit, which consists of a PG9351FA gas turbine, a two-cylinder two-flow steam turbine with a D10 three-pressure reheat system, a 390H hydrogen-cooled generator, and a triple-pressure reheat but with a condenser The natural circulation waste heat boiler for deoxygenation is composed of [1]. Except that the waste heat boiler is supplied by Hangzhou Boiler, the rest are provided by Harbin Power Equipment Co., Ltd. and General Electric Company of the United States. The gas turbine, steam turbine and generator are rigidly connected in series on a long shaft, and the shaft configuration is in the form of GT (gas turbine)-ST (steam turbine)-GEN (generator). The entire shafting system is supported by 8 bearings, 2#, 1# bearings support the gas turbine, 3#, 4# bearings support high and medium pressure cylinders, 5#, 6# bearings support low pressure cylinders, 7#, 8# bearings support generators , Of which 1#, 2#, 3#, 4#, 5# bearings are tilting pad bearings, and the rest are elliptical pad bearings. This article mainly discusses the problem of high bearing bush temperature during operation of 4# bearing.
2. Status of bearing operation
The gas turbine unit has been shut down for a long time after inspection type A repairs. After the cold start-up, it was found that the temperature of the bearing bush metal of the unit 4# was high. When the unit is running at full load, real-time monitoring of 4# bearing bush, 5# bearing bush and lubricating oil inlet temperature is carried out. Through the monitoring data, it can be found that when the unit is running at full load, the temperature measurement points of the two bushes of 4# bearing are near the high alarm value of the bearing bush temperature, while the temperature of the 5# bearing bush is basically below 100℃, and the 4# bearing bush is in operation. There is an abnormal phenomenon of high temperature, which threatens the safe and stable operation of the unit [2].
3. Analysis of bearing temperature abnormality
The 4# bearing of the power plant is a tilting pad bearing. The surface of the bearing pad is covered with a layer of babbitt alloy. When the temperature is high or the bearing pad is subjected to abnormal stress, the babbitt alloy will be deformed. When the bearing is working normally, an oil film will be established between the bearing bush and the high-speed rotor, and the oil film plays the role of lubrication and cooling. In operation, the successful establishment of the oil film is an important guarantee for the normal operation of the bearing. There are many factors that affect the establishment of the oil film, including the oil quality and temperature of the lubricating oil, the amount of lubricating oil, the gap between the bearing bush and the rotor, and the pressure holding capacity of the lubricating oil in the bearing. In addition, the 4# bearing is adjacent to the shaft seal of the high and medium pressure cylinder, which does not rule out the influence of the shaft seal on the temperature of the bearing bush when the shaft seal leaks a lot.
(1) Analyze the influence of lubricating oil quality and oil temperature on bearing temperature
The oil quality of the lubricating oil affects the establishment of the oil film, and situations such as unqualified lubricating oil particles often occur during operation. After investigation, it was found that the factory would regularly sample and analyze the lubricating oil. At the same time, the unit used an external oil filter to filter the lubricating oil for a long time, and no problems with the lubricating oil quality were found.
(2) Analyze the influence of lubricating oil temperature on bearing temperature
During the operation of the unit, the operating personnel monitor the lubricating oil temperature at all times to ensure that the lubricating oil temperature is within the normal allowable range. At the same time, by looking at the two-day operating data, it can be seen that the lubricating oil inlet temperature has been around 41°C, which is within the normal operating range.
(3) Analyze the impact of shaft seal leakage at the high and medium pressure cylinders on the bearing temperature
When the temperature of the 4# bearing bush was high, the maintenance personnel of the plant repeatedly inspected the surrounding environment of the 4# bearing and used a spot temperature gun to measure the temperature of the shaft seal on the medium pressure cylinder side. No abnormal phenomenon was found.
(4) Analyze the influence of lubricating oil intake on bearing temperature
The lubricating oil intake affects the quality of the oil film establishment. During the construction of the unit, the lubricating oil intake is specified by the Electric Power Design Institute and generally does not change. By checking the maintenance history of the unit, it was found that the unit had experienced high temperature of the bearing bush of 5# bearing. After communicating with the manufacturer, the inner diameters of the oil inlet holes of the 4# and 5# bearings were adjusted to increase the 5# bearing inlet. Oil quantity, reduce the oil intake of 4# bearing, try to reduce the temperature of 5# bearing bush, but the adjustment did not reach the expected effect. The follow-up investigation found that the bearing bush temperature measuring points of 4# and 5# of the factory were connected reversely.
(5) Analyze the impact of the bearing bush and rotor clearance on the high temperature of the bearing bush
The 5# bearing of this unit has been adjusted centrally, and the 5# bearing is raised by 0.17mm. However, the temperature of the bearing bush is not as obvious as expected. It is suspected that the uneven distribution of the rotor load causes the deformation of the bearing bush, resulting in poor quality of the oil film in the bearing. , The 4# bearing bush cannot be cooled effectively, resulting in high temperature of the 4# bearing bush.
Four, bearing maintenance
After analysis, this bearing inspection includes two contents. The first item is to restore the 4#, 5# bearing orifice plate to the original design value, and the second item is to remove the 4#, 5# bearing and inspect it. , Re-pouring the bearing bush if necessary. After removing the bearing, first check the appearance of the bearing bush. It is found that there are obvious indentations in the center area of the lowermost bush of the bearing. This area is in contact with the hard steel area on the inner surface of the bearing and is the main stress area of the bush. This phenomenon can be It is inferred that the pad has received a relatively large load, and the bearing pad is likely to be deformed. In order to further verify the appeal inference, the lower half of the bearing was pressed against the false shaft, and the contact between the bearing bush and the rotor was checked. After pressing the false shaft, the red lead on the bearing bush was unevenly distributed. It can be judged that the bearing bush has been deformed and needs to be returned to the factory for re-pouring. After the bearing bush is poured, the bearing is reinstalled into the unit, and the bearing and rotor Find the center and restore the relative position of the bearing and the rotor to the state before repair. After the unit is turned on, by checking the operating curve, the temperature of the 4# bearing bush has been significantly improved after overhaul. When the unit is fully loaded, the temperature of the bearing bush will drop by about 10°C on average, as shown in Table 1:
Table 1 Bearing temperature at full load
Concluding remarks
In the operation of the power plant, the temperature of the bearing bush is one of the important data to ensure the safe operation of the unit. The operating regulations of the power plant stipulate that the high alarm setting value of bearing bush temperature is 115.5℃, and the setting value of high bearing bush temperature-high alarm is 126.7℃. After analyzing the high temperature of the bearing bush during full-load operation of the power plant gas turbine unit, corresponding maintenance and treatment measures have been formulated to improve the safety of the equipment in the operation of the power plant and ensure the economic benefits of the power plant.
Post time: Sep-24-2021