Regarding the discussion on whether the unit bearing temperature should be included in the interlock system – whether it is necessary to include it, and if so, the voting criteria...
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This post was last edited by 328104062 on 2016-3-21 at 19:40. The compressors used in these systems generally come equipped with Kimberley bearings or Michelin bearings; they are available in 5-lobe, 6-lobe, 8-lobe, etc., configurations. These bearings are made of babbitt alloy, and two platinum resistors are inserted symmetrically within each bearing (usually at the top and bottom).1. Centrifugal compressor units: Hangzhou Steam Turbine + Shenyang Gas Compressor + Jiaxing AX quick-shut components. The conditions that trigger interlocks in such units include compressor vibration, displacement, tripping speed, differential pressure of the dry gas seal (details not specified here), low lubricating oil pressure, and exhaust pressure of the back-pressure steam turbine (the interlock value was 0.85 MPa, but this requirement has been removed). Among these interlock conditions, there is no requirement related to high bearing temperature. Why isn’t such a condition included? What is the maximum allowable bearing temperature? (In our case, it’s normally between 65–72°C.)
2. Piston compressor units: Imported ones, those from Wuxi, etc. The conditions that trigger interlocks in these units include low lubricating oil pressure, shutdown of the oil injector (after 15 minutes), exhaust temperature, and temperature of the outlet cylinder. Again, there is no requirement related to high bearing temperature. Why isn’t such a condition included? What is the maximum allowable bearing temperature? (In our case, it’s normally between 65–72°C.)
Questions:
1. Why aren’t interlocks set for high bearing temperature in these units? 2. What is the failure temperature of babbitt alloy? (It is said that the melting temperature is 105°C; our experience shows that when the temperature reaches 95°C, the compressor starts to vibrate more intensely and shuts down.) 3. Has anyone set up an interlock mechanism for high bearing temperatures? If so, what are the interlock values and the decision-making criteria? Manager Discussion Group
Both turbines and compressors have high-temperature interlocks, and in such cases shutdown occurs when one of them reaches the set value; usually it’s a ratio of one to two, meaning two measurement values for each bearing.
Our company’s key equipment, namely screw compressors, are equipped with high-temperature alarm systems and interlock shutdown functions
We have a bearing temperature interlock shutdown here.
Our reciprocating piston compressors have these interlocks, while smaller vertical compressors do not have such interlocks
Our main fans and air compressors use Kingsbury bearings; the alarm threshold is 90°C, the interlock shutdown threshold is 120°C, and the operating temperature should remain below 85°C. The interlock shutdown temperature for the reciprocating machine bearing bushes is 65°C, with an operating temperature below 50°C. If no alarms or interlocks are provided for bearings, accidents such as bearing burnout and shaft seizure can occur easily.
In our factory’s compressor units, there are no temperature sensors for the bearings nor any interlocks; however, each motor has a free-end and a coupling-end, with the interlock threshold set at 95 degrees Celsius for both. The other two imported expanders have a total of 8 bearing temperature measurement points (radial and axial), with an interlock value of 90 degrees Celsius~~
It is better to install it if the conditions permit, as very high bearing temperatures can lead to serious consequences; when doing this, be careful of errors in the signals that might cause unintended shutdowns. It is recommended to set an alarm at 80 degrees and trigger an interlock shutdown at 90 degrees. Because the operating temperature of bearings should generally be below 80 degrees.
1. Why is no high bearing temperature interlock installed in the unit? Our units here are generally equipped with a high bearing temperature interlock; although some relatively smaller units (using 380V voltage) do not have such an interlock for high bearing temperatures, they do have a high motor stator temperature interlock! 2. What is the failure temperature of babbitt alloy? (It is said that the melting temperature is 105°C; our experience shows that when the temperature reaches 95°C, the compressor starts to vibrate more intensely and shuts down.) This aspect has not been studied in great depth yet, so it is recommended to seek advice from experts in the mechanical field! 3. Is there anyone who has set up a high bearing temperature interlock? If so, what are the interlock values and voting conditions? Yes. The voting condition is majority rule. That is, when the bearing temperatures of the unit are both greater than 90°C, an interlock action is triggered, causing the unit to shut down!
Our unit’s centrifugal compressors (for reformed cycle hydrogen: manufactured by Ebara in Japan) and reciprocating compressors (for pressurized hydrogen: also manufactured by Ebara in Japan) are equipped only with temperature indicators and alarms. For the centrifugal compressors, both the radial bearings and thrust bearings have two measurement points per bearing; the normal operating temperature for thrust bearings is 55–70°C, while that for radial bearings is 80–85°C. The alarm threshold is set at 95°C. There is no integration with the SIS system, so shutdowns are not triggered as a result of excessive temperatures. However, the compressors cannot be started if the temperature exceeds 132°C. In my opinion, due to space constraints, it is not possible to install multiple temperature measurement points on the bearings – one must choose between two options. Having just one temperature measurement point can easily lead to incorrect readings from the instruments, resulting in the shutdown of the entire unit. If the temperature does rise to a critical level, it will cause vibrations that trigger an automatic shutdown. Therefore, the design provides only monitoring capabilities, without any interlock functions； The temperature of the motor shaft bearings in the reciprocating machine is 45–50°C, while the temperature of the shaft bearings in the isolation chamber stuffing box is 45–55°C. An alarm is set at 60°C for both types of shaft bearings. If these temperatures rise, it does not trigger an interlock shutdown since no signal is sent to the SIS system. In my opinion, an increase in the temperature of these shaft bearings is usually caused by a disruption in the cooling water supply; once an alarm is triggered, on-site inspection can be carried out to confirm the issue, after which the compressor can be switched back on. In the worst case, severe wear of the shaft bearings can lead to rod settlement or excessive vibration, thereby triggering an interlock shutdown.