Re: Scaling of Distillation model

Dear rusli huandra

>My understanding is:
>If I want to use the nominal feed flowrate for the two inputs, I have to
>put magnitude one in both inputs blocks in the simulator (simulink).

If you are referring to the LINEAR model, then note that all variables are
deviation variables, so nominal values of inputs and outputs are zero.

But you are probably talking about making a change in the
inputs (L or V) by 1. Since the scaling is "1" this means that
the change in physical variables is 1 kmol/min.

>I want to include 20% change for each disturbance, I have to put
>magnitude one into the disturbance blocks.

Yes, the disturbances (F, zF) have been scaled such that "1"
corresponds to a 20% change.

>So, if I put magnitude one into the inputs blocks and disturbances blocks,
>should I expect the outputs to be magnitude one also?

Actually, without any control, the effect of a unit change in the
inputs make the outputs change by about 100, e.g. see (12.17), and
a unit disturbance makes the outputs change by about 10, see (6.50).
This shows you that control is needed, because we want the outputs
to be less than 1 in magnitude.

>Can I put magnitude two in the inputs blocks? If I do that, does it mean
>I put two times the nominal inputs to the plants?

Yes.

All the above answers assume that you were referring to the
linear model given in the book.

However, there is also a nonlinear simulink model available over the
internet, but that model has NOT been scaled, i.e. it is in physical units.

Best regards,
Sigurd Skogestad
Received on Mon Apr 28 09:15:34 1997