An ethylene glycol column is studied in this paper, where the main objective is to describe the
bifurcation diagram with respect to the reboiler boilup ratio. The bifurcation analysis reveals
the existence of a unique equilibrium point at low reboiler heat inputs and three equilibrium
points (two stable and one unstable) at high reboiler heat inputs. Moreover, the existence of
input multiplicities at moderate and high product purity is also revealed.
The simple reactor/separator process with recycle has recently been used as a benchmark case
to gain insights into the problem of plantwide control structure selection. This paper explores
the use of a balanced control scheme aimed at improving the disturbance rejection capabilities
of the controlled process. The idea is to change the operating conditions in both the reactor and
the separator so that the composition control effort in the presence of production rate changes
is distributed. To this end, a parallel control structure is proposed where the product composition
is regulated by means of simultaneous feedback manipulations of the vapor boilup rate and the
reactor temperature. In this way, the use of the reactor temperature as a secondary control
input reduces the snowball effects reflected in large vapor boilup rate changes in response to
relatively small production rate changes. Nonlinear simulations show that effective composition
control can be obtained with moderate vapor boilup control efforts.
In this work, an output-feedback control for the regulation of distillate purity via manipulations of the reflux ratio in reactive batch distillation is designed. The approach is based on an approximate model of the composition dynamics and makes use of a reduced-order observer to estimate the modeling error. An input/output linearizing feedback is proposed where the estimated modeling error is included to achieve robust tracking of a composition reference. It is shown that the resulting controller has the structure of a proportional-integral derivative (PID) controller with antireset windup. The controller performance is tested using a simulation example including strong uncertainties in the reaction model. An interesting finding is that the required reflux ratio policy to reach asymptotically a constant reference resembles the reflux ratio policy obtained from posing an optimization technique (
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