Introduction to the handling of abnormal axial tile temperature in power plant operation

Introduction to the handling of abnormal axial tile temperature in power plant operation
I. Background
The combustion turbine power plant adopts STAG-109FA-SS single-shaft combined cycle unit, which consists of PG9351FA gas turbine, D10 two-cylinder double-flow turbine with triple-pressure reheat system, 390H hydrogen-cooled generator, and natural circulation waste heat boiler with triple-pressure reheat but with condenser deaeration [1]. Except for the waste heat boiler, which is matched by Hangzhou Boiler, the rest is supplied by Harbin Power Equipment Company Limited and General Electric Company of the United States. The gas turbine, steam turbine and generator are rigidly connected in series on a long shaft with the shaft configuration in the form of GT (combustion turbine)-ST (steam turbine)-GEN (generator). The whole shaft system is supported by a total of 8 bearings, 2# and 1# bearings support the combustion engine, 3# and 4# bearings support the high medium pressure cylinders, 5# and 6# bearings support the low pressure cylinders, and 7# and 8# bearings support the generator, among which the 1#, 2#, 3#, 4#, 5# bearings are tilting tile bearings and the rest are elliptical tile bearings. This paper mainly discusses the problem of high temperature of axial tile of 4# bearing in operation.
Second, the current situation of bearing operation
The gas turbine unit was shut down for a long time after inspection type A repair. After cold start-up, it was found that the metal of the 4# bearing shaft tile of the unit appeared to have a high temperature. When the unit was running at full load, the temperature of the 4# axial tile, 5# axial tile and the lubricant feed oil was monitored in real time. Through the monitoring data, it can be found that when the unit is running at full load, the data of both tile temperature measurement points of 4# bearing are in the vicinity of the high alarm value of shaft tile temperature, while the temperature of 5# shaft tile is basically below 100℃, and there is an abnormal phenomenon of high temperature of the 4# bearing shaft tile in operation, which threatens the safe and stable operation of the unit [2].
Third, abnormal analysis of the temperature of the axial tile
The power plant 4 # bearing belongs to tilting tile bearings, the surface of the shaft tile is covered with a layer of pasteurised alloy, the temperature is high or when the stress on the shaft tile is abnormal, the pasteurised alloy will be deformed. When the bearing is in normal operation, a layer of oil film will be established between the axial tile 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 affecting the establishment of the oil film, including lubricant oil quality and oil temperature, the size of the lubricant inlet, the gap between the axial tile and the rotor, the lubricant in the bearing pressure holding capacity and so on. In addition to this, the 4# bearing is adjacent to the shaft seal of the high medium pressure cylinder, which does not exclude the influence on the temperature of the bearing shaft tile when the shaft seal leakage is large.
(A) analyse the lubricant oil quality and oil temperature on the impact of the temperature of the axial tile
The oil quality of lubricant affects the establishment of oil film, which often occurs in operation, such as unqualified lubricant particle size. After investigation, it is found that the plant will regularly sample and analyse the lubricating oil, and at the same time, the unit has been using external oil filter to filter the lubricating oil for a long time, and no problem is found in the lubricating oil quality.
(ii) Analysing the influence of lubricant oil temperature on the temperature of the axial tile
In the operation of the unit, the operator always monitors the lubricating oil temperature to ensure that the lubricating oil temperature is within the normal permissible range. At the same time, by looking at the two-day operation data, it can be seen that the lubricant oil temperature has been at about 41 ℃, which belongs to the normal operating range.
(C) Analyse the impact of the leakage of the shaft seal at the medium and high pressure cylinders on the bearing temperature
When the high temperature of 4# shaft tile appeared, the maintenance personnel of the plant inspected the environment around 4# bearings several times and measured the temperature at the shaft seal on the side of the medium-pressure cylinder by using a point temperature gun, and no abnormal phenomenon was found.
(iv) Analysing the influence of lubricant oil intake on bearing temperature
The quantity of lubricant oil intake affects the quality of oil film establishment. When the unit is built, the quantity of lubricant oil intake is stipulated by the Electric Power Design Institute and is generally not changed. By checking the maintenance history of the unit found that the unit had 5 # bearing high temperature phenomenon, after communicating with the manufacturer, respectively, 4 #, 5 # bearing oil inlet hole diameter adjustment, increase 5 # bearing oil inlet, reduce the 4 # bearing oil inlet, trying to reduce the 5 # bearing tile temperature, but the adjustment did not not have the expected effect. Subsequent investigation revealed that the temperature measurement point of 4# and 5# bearings in the plant was reversed.
(v) Analysing the influence of the clearance between the bearing tile and the rotor on the high temperature of the bearing tile
The unit's 5# bearing had a centre adjustment, lifting the 5# bearing as a whole by 0.17mm, but the unit operation found that the temperature change of the bearing shaft tile was not as obvious as expected, and it was suspected that the uneven distribution of the rotor load led to the deformation of the bearing shaft tile, resulting in the poor quality of the oil film in the bearing, which was unable to effectively cool the 4# bearing shaft tile, thus resulting in the phenomenon of high temperature of the 4# bearing shaft tile.
Four, bearing overhaul

After analysis, this bearing overhaul includes two elements, the first is to restore the 4# and 5# bearing throttle orifice plate to the initial design value, and the second is to dismantle and inspect the 4# and 5# bearings and re-pour the axial tiles if necessary. After dismantling the bearings, the appearance of the bearing tiles was first checked, and it was found that obvious indentation appeared in the centre area of the lowest tile of the bearings, which was in contact with the hard steel area on the inner surface of the bearings, and was the main stress area of the tiles, and this phenomenon could be inferred that the tiles were subjected to a large load, and that the tiles were likely to be deformed. In order to further verify the appeal inference, the lower half of the bearing was subjected to the step of pressing the false shaft to check the contact between the axial tile and the rotor. After pressing the false shaft, the traces of reddish Dan on the axial tile appeared to be unevenly distributed, and it could be judged that the axial tile was deformed and needed to be returned to the factory for re-pouring. After the axial tile was poured, the bearings were reassembled into the unit, and the bearings were centred on the rotor to find the centre, and the relative positions of the bearings and the rotor were restored to the pre-repair state. After the unit was switched on, by checking the operation curve, the temperature of the 4# bearing axial tile was significantly improved after the overhaul, and the temperature of the axial tile dropped by about 10℃ on average when the unit was at full load, as shown in Table 1:

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