3 replies to this topic

[Mystified]

Hi all,

FYI i am learning hysys. I am trying to simulate flash drum with control over feed flow, vapor flow rate and liquid flow rate. I added all controllers. But to my surprise when i change set point, actually valve is closing completely. Please help in this regard.

And, also how to tune the controller according to the requirement?

[Zauberberg]

Raaj,

It's difficult to give any comment - there is no flowsheet available, control logic setup, independent and dependent variables etc. Almost nothing, in one word.

[Padmakar Katre]

Dear,
Zauberberg is right come up with the flowsheet of the flash drum with schematic of the configured control system. So that it would be easy to comment.

[Steve McGahey]

Hi all,

FYI i am learning hysys. I am trying to simulate flash drum with control over feed flow, vapor flow rate and liquid flow rate. I added all controllers. But to my surprise when i change set point, actually valve is closing completely. Please help in this regard.

And, also how to tune the controller according to the requirement?

Sounds to me like one of two things. Either

(1) You've got your controller acting in "direct" rather than "reverse".

You need to tell the controller that if the measured variable (flow) is too low, it needs to increase the controller output (which should be connected to the valve position). Or...

(2) Your valve is set to be fail open. This causes the valve to say "if I get no signal from the controller, I should drive myself 100% open". This then means that when the controller increases its signal (i.e. moving away from 0 signal), the valve closes in on itself.

See if either of those help.

- Steve.