[ Follow Ups ] [ Post Followup ] [ Control Consulting ] [ FAQ ]
Posted by Mike McCarty on February 27, 2000 at 21:18:13:
In Reply to: Controlling Flooding Correlations posted by Sri Sampath on February 15, 2000 at 21:04:50:
In general, I think it's quite difficult to develop a flooding
correlation that would be useful as a CV to keep a column that
is prone to flooding from doing so. The best you could do is
calculate internal liquid traffic at the critical location
(assuming downcomer flooding), or vapor traffic for jet flooding,
and use these to limit how high the controller is allowed to push
the load on the column (possibly based on design loadings).
Note that this would necessarily be below the true incipient
flood point, and so this would limit the operation of the column
below its true load limit. However, if you can develop a
flooding correlation that "captures the change in flooding /
loading conditions fairly well", then yes, use it as a CV. But
note that you really want to control the point where the flooding
condition starts, not just control the change in loading.
Without proper DP measurements across the different operating
sections of a complex distillation column, I don't have a good
method to find the onset of flooding. I'd say DP measurements are
necessary to find the incipient flood point. Also note that when
using DP as a CV, once you start to flood the DP measurement
becomes non-linear. See a previous paper by Hoffman on this
board for a powerful DP linearization technique.
Mike