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Due to nonlinearity, loop interaction and ill conditioning of
high-purity distillation columns, it is difficult to describe
dynamic behavior of such columns using simple linear
mathmatical models. Also for most industrial column,
composition are rarely available on-line. Control is therefore
often based on temperature measurements. Chien(1994) have
proposed a model form for temperature-based control system.
The model form is:τ(y)*dy/dt=-y+k(y)*u The nonlinear functions
of τ and k are very simple forms which depend on operating
conditions and top and bottom temperatures. The parameters in
this model form are identified by optimizations method using
various input/output data. The model''s prediction ability is
also compared to other nonlinear dynamic models such as
logarithmic temperature transformations and nonlinear ARX
model, and is validated using several input sequences. The
results show the model derived from optimization method is the
best in capturing process dynamic behavior. This model can be
used in a model-based control framework to improve the control
performace.
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