Re: Steady State Gain of distillation column using Hysys

Hello,

At 11:49 PM 12/4/2001 -0800, you wrote:
>Dear Prof. Skogestad,
>
>I have a question,
>in order to obtain SS gain, we give pertubation to one
>input whereas others remain constant. Let said a
>distillation column, Output is XD(Distillate Comp.),
>XB(Btm. Comp), P(Pressure), LB(Bottom Base),
>LT(Condenser Level)and the input is
>R(Reflux),D,B,Qr,and Qc.
>
>Let said i do a pertubation analysis on Qr and all
>remaining input remain constant. This is imposible in
>Simulation like hysys where we only can specify 2
>degree of freedom, that is perhaps is Qr and one
>remaining varible.

A distillation column has only two steady-state degrees of freedom at
steady-state (with given feed and pressure)
because the levells (Md and Mb) have no steady-state effect - so use of
Hysys will work fine!

>This is what appeared in your book.
>If we give a pertubation to one inout, other variable
>will change. So what is your opinion on this aspect.
>Or there is other method to calculate the steady state
>gain.

I would recommend linearzing the model and obtaining the steady-state gain
as G(0) = -C A^-1 B, but this does not work with Hysys i think.

-Sigurd Skogestad

>Thanks.
>
>Regards,
>Derrik Ling
>University of Technology Malaysia
>
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Received on Wed Dec 5 17:42:56 2001