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Why High Temps when loading centrifugal after purge.

Why High Temps when loading centrifugal after purge.

(OP)
Why is the compressor experiencing high temperatures in the range of 180F (RTD at discharge 10' comp. flange) when we simply gas-load the centrifugal compressor after a purge.

The impellers are not turning, we are just filling in the compressor with a loading valve before opening discharge for compression, at this point we experience gas temp alarms. However once the unit compressor starts turning and discharge valve opens and we are moving the gas, the temperature drops.

What is causing this spike in temperature, and is there a way to mitigate this high temps by controlling compressor gas velocities or any other component or variable.

Any help and direction will help.


Application: Gas Transmission compression station
Medium: transmission gas quality gas
Compressor Type: Rolls Royce RFA-24

RE: Why High Temps when loading centrifugal after purge.

It impossible for the introduction of gas into a compressor that is not running to cause an increase in temperature. This would violate laws of physics. I only see two options that explain your situation.

The piping which is used to transfer the gas into the compressor could be heat-traced. The piping is hot because of the steam or electric tracing. When the gas passes through the hot piping, it picks up heat and reaches the machine hotter than it was when it left the source.

The other option would be that your temperature measurement is inaccurate.

Johnny Pellin

RE: Why High Temps when loading centrifugal after purge.

How is it being pressurised?

What is end pressure?
Inlet temperature of incoming gas?

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

RE: Why High Temps when loading centrifugal after purge.

Pressure X Volume / Temperature = Constant (Boil's law)
If Pressure increases the temperature has to increase too to keep the low. This is why when a gas is compressed the temperature always increases.

RE: Why High Temps when loading centrifugal after purge.

That's my point. If the incoming gas is being pressurised by a compressor from a low preassure then it can heat up. However if its being pressurised by dropping pressure from a higher one then temperature should fall or be no higher than the inlet gas temperature.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

RE: Why High Temps when loading centrifugal after purge.

The OP states that they are filling the compressor with a loading valve. I interpret that to mean that they are opening a valve and allowing a higher pressure gas to flow into the compressor. This is what we would commonly do with our compressors. If all you do is open a valve, no work has been added to the gas and the temperature cannot go up.

Johnny Pellin

RE: Why High Temps when loading centrifugal after purge.

Both experience and theory show that when you charge a vessel from a high pressure gas source the temperature of the gas inside the vessel will rise. This is why when you are filling a vessel to a required pressure at room temperature, you have to charge it either very slowly or wait until it cools down to room temperature and then recheck the pressure inside the vessel and add gas accordingly. Because the temperature rises during the filling process the pressure inside the vessel rises too. You think you reached the correct temperature but when the gas cools down to room temperature the pressure decreases too. Another way to correctly fill the vessel is to weigh the gas added to the vessel, this will assure the gas pressure when it cools down.

RE: Why High Temps when loading centrifugal after purge.

Correction: In line It should read "You think you reached the correct pressure" instead of "You think you reached the correct temperature"

RE: Why High Temps when loading centrifugal after purge.

Have you spoken to the instrumentation engineer to see if the RTD and TT assembly is installed correctly ? When was it last calibrated ?

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