Design and application of state observers for exothermic fed-batch reactors with uncertain kinetics and heat transfer
Monitoring the limiting reactant concentration is a key question to maximize
the productivity and to guarantee the safety of exothermic fed-batch
processes. However in most applications, the concentration cannot be
measured in real-time since suitable devices do not exist or are too
expensive; the concentrations are then measured by off-line analyses. In
this context monitoring the concentrations via software sensors, or state
observer based estimators, is an attractive option.
The presence of model uncertainties is a major limitation when applying
state observers to real processes. More precisely, in fed-batch exothermic
reactors the bad knowledge of both the reaction kinetics and the heat
transfer may prevent the use of classical observers.
In this study, we propose two different approaches to estimate the
concentration of the limiting reactant in a class of single phase exothermic
fed-batch reactors with uncertain kinetics and heat transfer. The first
approach is based on a finite time converging observer that provides an
estimate for the reaction rate via the reactor energy balance equation. The
concentration is then computed from the reaction rate estimate via a
material balance equation. The main contribution of this approach is the use
of a finite time observer to limit the reconstruction error by guaranteeing
a small convergence time interval for the reaction rate estimate. The second
approach is based on an interval observer that provides two bounds for the
concentration by considering uncertainties related to both the heat transfer
and the reaction kinetics. The final estimate is then computed as the mean
of the bounds.
A systematic tuning procedure has been developed for each of both estimation
techniques. Both estimators have then been tested and validated with real
data coming from the production of different kinds of resins carried out in
10 tons reactors.
School:Université catholique de Louvain
Source Type:Master's Thesis
Keywords:state observers fed batch reactors calorimetry estimation
Date of Publication:12/12/2007