Analysis and Treatment of the Problem of High Bearing Temperature in Compressors

In Analysis and Treatment of the Problem of High Bearing Temperature in Compressors

Centrifugal compressors make the gas entering the impeller rotate at a high speed under the action of the impeller blades. Driven by the centrifugal force generated during rotation, the gas flows towards the outlet of the impeller. Meanwhile, due to the diffuser effect of the impeller, its pressure energy and kinetic energy are increased. After the gas enters the diffuser, the kinetic energy is further converted into pressure energy. Then the gas flows through the bends and return channels into the next-stage impeller for further compression until the gas pressure meets the requirements of the process.

One of the important factors for the long-term and stable operation of centrifugal compressors is the high bearing temperature. Through research and analysis, the reasons for the high bearing temperature are mainly caused by the following two aspects:

I. Analysis of the Reasons for High Bearing Temperature

High Bearing Temperature Caused by the Lubricating Oil System

1.When the amount of lubricating oil is insufficient or the lubricating oil supply is interrupted, the bearing temperature will rise, causing the bearings to seize up. In severe cases, the babbitt metal may melt.

2.If the lubricating oil contains foreign substances such as sand particles and impurities and is not clean enough, it will cause scratches on the bearing bush after being brought into the bearing. In severe cases, the bearing temperature will rise and cause the babbitt metal to melt. The lubricating oil in the oil tank should be circulated and filtered to remove the impurities in the oil. Check and clean the oil filters on the oil supply pipelines. If necessary, replace the new filter elements to improve the oil filtering effect.

3.If the oil cooler in the lubricating oil system does not work properly, the inlet oil temperature is too high, and the viscosity of the oil is insufficient, it will not be able to take away the heat from the bearings in a timely manner, resulting in the failure to form a good lubricating oil film in the bearing bush. The cooling water flow rate of the oil cooler can be increased. If scaling or blockage occurs, descaling and dredging are required to improve the cooling effect.

4.If the water content in the lubricating oil increases, the performance of the lubricating oil will be reduced, affecting the formation of the pressure oil film. A separator should be used to separate the oil and water in the oil tank to separate the water in the oil. 

Reasons for the Centrifugal Compressor Unit and Bearings

1.Excessive bearing vibration caused by the imbalance of the compressor rotor will lead to wear of the bearing bush during the operation process. According to the operating state of the rotor, it should be sent back to the manufacturer for regular dynamic balance calibration to reduce the unbalance amount.

2.The installation of the bearings does not meet the requirements. On the one hand, if the bearing housing of the thrust bearing is skewed, it will lead to uneven load on the thrust bearing pads. The temperature of the loaded pads will rise, greatly reducing the bearing capacity of the bearing and may cause damage to the thrust bearing. If the radial or thrust bearing clearance is too small, it will affect the normal formation of the lubricating oil film. At the same time, the lubricating oil cannot be fully drained, and the heat generated by friction cannot be taken away in a timely manner, which will also cause the temperature of the bearing bush to rise. Therefore, when installing bearings, it is necessary to be careful to ensure that all requirements meet the technical standards.

3.The casting quality of the babbitt metal of the bearing bush does not meet the standards, containing impurities such as iron filings and sand particles, or the babbitt metal has defects such as peeling, cracks, and blowholes. High-speed and light-load babbitt metal should be selected. After chemical analysis, the alloy composition must meet the requirements to improve the casting and processing quality.

4.Due to the unreasonable bearing structure, the bearing bush operates under overload, and liquid friction cannot be formed between the bearing bush and the bearing. The design structure of the bearing should be improved to improve the load-bearing condition of the bearing bush and effectively reduce the operating load of the bearing to ensure the normal operation of the bearing under the liquid friction state.

5.If the compressor diaphragm leaks or the balance disc seal and inter-stage sealing teeth are damaged, the axial force on the rotor shaft will increase, and the load on the thrust bearing will increase. At this time, the compressor should be disassembled and overhauled, the parting surface of the diaphragm should be repaired to avoid air leakage, or the balance disc and inter-stage seals should be replaced. If necessary, a thorough renovation can be carried out.

6.If the balance pipe is blocked, the pressure in the secondary pressure chamber of the balance disc cannot be released, and the function of the balance disc cannot be exerted normally, which will increase the axial force on the rotor shaft and the load on the thrust bearing. The balance pipe should be carefully inspected, and the blockages should be completely removed so that the pressure in the secondary pressure chamber of the balance disc can be released in a timely manner and the function of the balance disc can be exerted normally.

II. Solutions for Handling High Thrust Bearing Temperature

Thrust Bearing

1.Recheck the thrust bearing clearance of the thrust bearing to ensure that the thrust clearance meets the design requirements.

2.Thrust Pads

3.Base Ring and Leveling Blocks

4.Thrust Disc

Solutions for Handling High Radial Bearing Temperature

1.Check the fit clearance of the bearing bush, scrape and grind the inner diameter of the bearing bush to make the fit clearance between the bearing bush and the journal meet the standard requirements.

2.Check the oil inlet throttle orifice plate of the bearing, increase the throttle orifice diameter to make the amount of lubricating oil meet the usage requirements.

3.Open the water valve of the oil cooler wider to increase the flow rate of the cooling water and reduce the flow rate of the lubricating oil to meet the usage requirements.

4.Improve the design structure of the bearing to improve the load-bearing condition of the bearing bush, reduce the operating load of the bearing bush, and ensure the normal operation of the bearing under the liquid friction state.

In conclusion, the bearing structure itself, the quality of manufacturing, installation and maintenance, the changes in the operating conditions of the compressor, and the working condition of the oil supply system will all affect the normal operation of the bearings. Therefore, maintenance must be carried out in strict accordance with the provisions of the maintenance process standards to ensure the quality of the bearings. During operation, attention should be paid to monitoring the temperature of the bearing bush, the temperature of the lubricating oil, the axial displacement, whether the oil supply system is working normally, whether the vibration of the bearings is excessive, and whether there are abnormal noises. If there are any abnormalities, immediate analysis and judgment should be made, and effective measures should be taken to deal with them to avoid accidents.