Steam compressor shaft vibrations 1

[ProcessJim]

Hi all,

I'm afraid this question is more of a question about what questions to ask as we have an issue on site which I am not really involved with, yet I feel we maybe missing something.

My understanding of the system is that we have a process stream of steam fed from a crystaliser and topped up by a steam generator which passes through a demister to a compressor turbine supplying high pressure steam to heat exchanger. I believe such an arrangement is know as 'mechanical vapour recompression'?

There is a by pass line from the compressor outlet to the inlet to the compressor via a steam valve. It appears from the P&ID that water can be added to this by pass to control its temperature.

The problem that we have is that the compressor keeps tripping out due to shaft vibrations shortly after startup.

My question is basically, what obvious things should we be looking for? Is the problem likely to be a process issue or a mechanical issue? The turbine has been inspected and deemed to be ok. What further details of the system would you need for me to better frame this question?

Sorry that my description is vague, I am not really involved in this part of the plant at all...

 

[JJPellin]

The terms you use are strange to me. But, I would have a few comments. If water is being injected into a stream of steam to control the temperature, we would normally refer to that as a de-superheater. We use this to reduce the temperature of superheated steam to saturation. If this is what your system is doing, then the nozzle that injects the water is important. This would normally be a special atomizer nozzle that produces a very fine mist of water. This nozzle would be designed for a particular supply pressure for the water. If the nozzle was washed out or if the water pressure was not correct, you could get larger droplets of water instead of the fine mist. The injection rate of the water is also very important. If the rate of injection was designed for a particular steam temperature, you could have problems if the temperature was different than the original design. Ideally, there would be a control system sensing the temperature downstream of the water injection point and controlling the water flow rate to maintain the desired temperature. A malfunction of a temperature control system could result in too much water injected. Any liquid passing through a turbine or a compressor can be very destructive. High vibration could easily be caused by improper operation of the water injection system. The problem could be flow rate, supply pressure, nozzle condition or something else.

Johnny Pellin

 

[mjpetrag]

You need a vibration analysis of the machine to narrow down where and what the vibration is.

In the meantime, look at the alarms you get when it shuts down. Then start digging through the manual for the machine and look at the troubleshooting guide in the back. From here, you'll have some idea of what is happening.

-Mike