Control Valve Tuning

[10815L]

Hi Als,
We are facing problem with one of our controller whic is not controlling smoth flow.
Control valve checked for plug demage and seat, both are ok and packing also changed but no use.
Variation in flow is 5-6m^3/hr
Service:Reformar Feed inlet.
Tuning parameter:K=0.3;T1=0.3;T2=0.08
Could you please advice me what could be best tuning parameters for this controller.
Thanks
10815L

 

[chemebabak]

10815L,

Please answer these questions to help troubleshoot your problem:

1. What changed in the system that began the "not controlling smoth flow" symptom? Is this a new valve?

2. Has the flow measurement instrument (or whatever instrument that controls this valve) been replaced or serviced?

3. Has this instrument been tested or calibrated? Was this done before or after the problems?

4. What is the "5-6m^3/hr" variation in percentage of total flow; 1%, 10%?

5. By variation, do you mean that in an hour you will observe the flow rise and fall in a range of 5-6 m^3? How many times per hour? How quickly will it take to rise and fall? That is, within how many minutes of a 5 m^3 rise will it fall?

6. What is the variation of the other parameters in the reformer or upstream of the reformer?

As you can see from this not exhaustive list, there are many parameters that must be considered. But on the other hand, maybe a quick adjustment of tuning parameters will solve the problem. The most important question to answer is the first one: What changed?

 

[FrancisL]

Excellent set of questions from chemebabak, one more is what is the flow and pressure difference through the control valve compared with it's design calculations?



Francis

http://www.controldraw.co.uk

http://www.s88control.blogspot.com

 

[10815L]

Hi Francis,
Design Flow is 70m^3/hr and up stream pressure is 12 barg and down stream pressure is 5barg (DP is 7barg)
This down stream is joing with Recycle gas line and going to CFE (combined feed Exchanger)
Thanks

 

[Fzob]

A simple test to narrow down your problems is to test the valve with a manual input. If you can't control in manual, then it may not be the tuning parameters. It may be the valve is sized wrong, or there on transient condition upstream (or downstream) not within the control envelope.