The Phenomenon And Reason Of High Temperature Of Tilting Tile Bearing And Its Treatment Measures

Tilting tile bearing structure and working principle

The tiltable tile bearing is composed of five arc tiles, the upper half bearing is three tiltable tiles, the lower half bearing is two tiltable tiles, the tile can tilt freely on the fulcrum, the tile can swing freely when working, forming a multi-oil wedge around the shaft neck. The lubricating oil of the bearing enters the annular channel of the bearing shell through the oil inlet at the bottom of the bearing. The lubricating oil enters the bearing tile through 5 oil holes from the annular channel. The lubricating oil is distributed along the journal and discharged from both ends of the journal to complete the cooling and lubrication effect.

The phenomenon of temperature rise of tilting tile bearing

In the process of unit starting up speed, the temperature of tilting tile bearing rises slowly, and the temperature of tilting tile bearing reaches 78℃ after constant speed. After the unit runs at full load, the temperature of tilting tile bearing reaches about 85℃, and the oil return temperature is 56℃. With the increase of unit running time, the temperature of tilting tile bearing gradually increases, increasing by about 1℃ on average every day. The oil return temperature of tilting tile bearing reaches 65℃, which is higher than the average oil return temperature of other bearings of 54℃. Check the operation parameters of the unit, the bearing oil inlet pressure and temperature are normal, and the temperature of other bearings are all within the standard range. Only the temperature of the tilt-tile bearing tile and the oil return temperature are high. It is found in the field inspection that the shaft seal pipe after medium pressure is tightly attached to the foundation of the tilt-tile bearing box, the thickness of the insulation layer is thin, and the temperature of the foundation surface is detected, up to 170℃.

Analysis of the causes of high temperature of tilting tile bearing

1. Factors that can be excluded

(1) During the installation of the bearing, the relevant inspection such as penetration and ultrasound has been carried out, and the results meet the installation requirements. The influencing factors of the defects such as urgeon ejection and damage existing in the bearing bush are excluded.

(2) Shaft center finding and bearing installation through multiple measurement and acceptance, are in line with the installation requirements, can exclude the influence of this factor.

(3) The temperature of other bearings is normal, only the temperature of tilting tile bearings rises, so the influence of oil temperature, oil pressure and oil quality is excluded.

(4) Field test to eliminate the influence of temperature measuring element error.

2.Can cause the high temperature of tilting tile bearing

(1) Influence of steam leakage from medium pressure rear shaft seal: this type of turbine adopts high pressure pressure cylinder structure, the length of the rotor is shortened, the bearing is very close to the medium pressure rear shaft seal, and the steam leakage and heat radiation of the medium pressure rear shaft seal are greatly affected in operation.

(2) Uneven bearing load distribution. Although the medium pressure wheel center is 0.30mm lower than the low pressure wheel center when the wheel is centered, that is, the upper limit of the design value is reserved, the temperature of the tiltable tile bearing is still high after the unit is put into operation, which indicates that the actual load of the tiltable tile bearing is too heavy, and the oil film is easy to break, resulting in local dry friction between the bearing bush and the shaft journal, which increases the bearing temperature.

(3) Influence of cylinder heat radiation: the tile bearing box is very close to the medium pressure cylinder, and the insulation construction at the back of the medium pressure cylinder is limited by space and position, and the insulation quality is not good, which causes the tilting tile bearing box and bearing to be radiated by the heat of the cylinder, so that the temperature of the tilting tile bearing rises.

(4) The design and installation of the steam sealing supply pipeline after medium pressure is unreasonable, and the distance between the vertical pipe section and the foundation of the tilting tile bearing box is very small. The insulation layer of the pipeline is close to the foundation, the thickness of the insulation layer is insufficient, and the insulation effect is poor. The insulation material partially inserted affects the air circulation and heat dissipation. The tilting tile bearing box is lifted slowly, which increases the load of the tilting tile bearing and causes the temperature of the tilting tile bearing to rise continuously.

(5) Influence of lubricating oil amount: bearing lubricating oil has the function of lubrication and cooling. If the bearing oil inlet channel is narrow, insufficient oil inlet or poor oil discharge will occur, resulting in the rise of bearing temperature.

Treatment measures and effects

Through operation data analysis and field investigation, combined with the characteristics of the unit, the measures to solve the temperature rise of tilting tile bearing are as follows:

1. Improve the heat insulation measures of tilting tile bearing box and foundation

Check the original thermal insulation layers such as the rear of the medium pressure cylinder, the rear shaft seal and the steam supply pipeline of the medium pressure shaft seal, and re-conduct the thermal insulation layer with defects, large gaps and thin. Insert 15mm thick composite heat insulation plate between the steam supply pipeline of the medium pressure rear shaft seal and the base of the medium bearing box and fix it firmly. There is a gap of about 30mm between the insulation layer of cylinder and shaft seal and the tilting tile bearing box, which is convenient for air circulation to take away the heat in time and establish effective thermal insulation measures.

2. Improve the heat exchange effect of tilting tile bearing

The diameter of the oil inlet throtloff hole of the tilting tile bearing is expanded by 2mm, and the beveled edges of the oil inlet and outlet of the black metal of the tilting tile bearing are fixed and scraped to reduce the flow resistance of the lubricating oil, thus increasing the cooling flow rate of the lubricating oil of the tilting tile bearing and improving the heat exchange effect of the tilting tile bearing.

3. Adjust the elevation of tilting tile bearing appropriately and distribute the load of bearing again

In view of the high temperature of the tilting tile bearing, considering the factors such as rotor lift, steam seal clearance, oil barrier clearance and maintenance work quantity, it is decided to re-allocate the bearing load and reduce the 2# bearing tile pillow iron by 0.05mm ~ 0.08mm, thus reducing the load of the tilting tile bearing.

4. Grind tilting tile bearing pad iron to ensure that the contact of pad iron meets the requirements of bearing maintenance process

When adjusting the pad iron, it is necessary to ensure that the contact point between the pad iron and the bearing seat sag reaches more than 75% of the total area of the pad iron, and the contact point is evenly distributed. For the pad iron with oil holes, the contact point around the oil hole must be tight to avoid the leakage of lubricating oil. Check the clearance of each part of the shaft and bearing bush and the bearing tightness to meet the requirements of relevant specifications.

After the above treatment, after the unit is put into operation at full load, the temperature of tilting tile bearing is stable at about 76℃, and the temperature of #3 bearing is slightly increased compared with that before repair, but it still meets the operation standard, and other bearing parameters are normal. Through the comparison of bearing parameters before and after repair, it is shown that adjusting bearing load is an important means to deal with bearing temperature.

Conclusion

Bearing is an important part of steam turbine, and its working state directly affects the safe and stable operation of the unit. Through the case analysis of the temperature rise of the tilting tile bearing, this paper finds out the cause of the temperature rise of the tilting tile bearing, and carries out measures such as strengthening the heat insulation of the middle bearing box and the foundation, readjust the load distribution of the shaft system, and strengthening the heat exchange of the bearing. The problem of temperature rise of tilting tile bearing of steam turbine is successfully solved, which has certain reference value for the same type of units to solve the problem of high bearing temperature.