1 reply to this topic

[ChanderKaushik]

Hello All,

I am facing problem in keeping a steam screw compressor stable. It trips on high discharge temperature.

The screw compressor compresses steam from 0.3 bar to 4 bar and is controlled by VFD. The discharge temperature is controlled by Hot water injection on the compressor suction and discharge.

 

The controls valves function in auto and responds according to the temperature fluctuation.

 

I would really appreciate if you can help.

 

Attached file is the time vs temperature of the screw compressor.

 

Thanks

 

Chander

 

 

Attached Files

•  fluctuation in discharge temperature of screw compressor.png   36.19KB   0 downloads

[Saml]

It may be a number of different things. A sticky valve, change in the tuning, a faulty instrument, etc.

To check for a sticky valve, you can do a PV vs OP plot (Process Variable vs Controller Ouptut).

Check the article "Modelling Valv Stiction" form 2004. The full text is available in Reseach Gate. It has some interesting concepts.

 

However, there are many details missing that makes it impossible to answer with anything more than general concepts.

- You have two valves (suction and discharge). But only one measured variable (Temperature). That requires some aditional logic beyond a PID controller.

- It is a new system you are commisioning? or you have a history of good performance before these problems appeared?. In the first case I would concentrate on logic and tuning. In the second, on a element with degraded performance.

- What does the VFD controls? Discharge Pressure? Suction Pressure?. How that varies when you add more or less water?