Francis Courtois

Optimal constrained non-linear control of batch processes: Application to corn drying

A predictive optimal control algorithm for on-line control of a batch drying process is presented. An optimal command profile is computed off-line and is corrected on-line taking into account feedback measurements. A simple non-linear process model is used for predictions in both off-line and on-line optimization. The problem is entirely stated in time domain and includes technological constraints.

Dynamic Models for Drying and Wet-Milling Quality Degradation of Corn Using Neural Networks

ABSTRACT Non-linear dynamic models of corn drying and wet-milling quality degradation are obtaineddirectly from experimental data. No assumptions about the underlying mechanisms are made. Relative advantages of recurrent versus explicit-time models and technical issues are discussed. This type of model is well suited for very fast on-line simulations, for example in a predictive optimal control algorithm.

DYNAMIC OPTIMAL CONTROL OF BATCH RICE DRYING PROCESS

ABSTRACT The drying of paddy rice may result in quality degradation, expressed as a head kernel yield, leading to significant commercial depreciation of the product. A mathematical model of the drying and of the quality degradation process was combined with a dynamic optimization algorithm to determine the drying conditions (air temperature and relative humidity as functions of time) that ensured the highest possible final product quality for a specified drying time and a specified final moisture content. The robustness of the optimal drying strategy with respect to the initial state of the product, to the model parameters and to the initialization of the optimization algorithm was verified. The compromise between the highest achievable final quality and the allowed total drying time was studied. The combination of simulation and optimization yielded a new insight in the rice drying process and in the quality preservation strategies.

CONTROL STRATEGIES FOR CORN MIXED-FLOW DRYERS

ABSTRACT This paper relates work which has been conducted in order to obtain a control strategy for French mixed-flow dryers. Special emphasis is given to the system analysis ( static and dynamic). Potential difficulties for the dryer control are: non-linearities, long delay, high order, high disturbances. Special emphasis is also made on the importance of signal pre-processing. Then, different control slrategies are compared on a simulation basis : classical Pl. pole-placement and non-linear Pl controllers. The conclusion is experimentally based.

DESIGN AND CONTROL OF DRUM DRYERS FOR THE FOOD INDUSTRY. Part 1. Set-up of a moisture sensor and an inductive heater.

Abstract The aim of this work is to analyse different ways for controlling the final moisture content of a product dried on a drum dryer, and to reduce its unevenness in order to obtain a high-quality product and to increase dryer productivity. A new way to determine product moisture content by means of product temperature measurement is presented, which is convenient for a moving and low thickness film. The product temperature is directly related to moisture content, because drying on a drum dryer takes place by boiling: this relation comes from the experimental desorption isobar, or boiling curve of the product. This measurement allows the detection of wet zones, and the correction of the moisture profile across the width by means of an additional inductive heater.

Moisture Sorption Isotherms, Thermodynamic Properties, and Glass Transition of Pears and Apples

Moisture sorption isotherms of apples and pears were determined at 30, 45, and 60°C and water activity (a w ) range of 0.04–0.83 using a standard static gravimetric method. The sorption isotherms of both fruits decreased with increasing temperature and exhibited type III behavior according to Brunauer–Emmett–Teller (BET) classification. The moisture desorption data fitted well with the Peleg model (0.997 ≤ r ≤ 0.999, 0.009 ≤ SE ≤ 0.071, and 4.840 ≤ p ≤ 13.779). The glass transition temperature (T g ) of both fruits decreased linearly with the increase in water activity (a w ). The variation in glass transition temperature versus water activity (T g ∼ a w ) and glass transition temperature versus solid fraction of pears and apples (T g ∼ W s ) were adequately predicted by Khalloufi et al.s model (0.998 ≤ r ≤ 0.999 and 0.007 ≤ SE ≤ 4.088) and the Gordon and Taylor model (0.879 ≤ r ≤ 0.979 and 9.798 ≤ SE ≤ 18.507). The thermal transition and desorption isotherms data were used to establish state diagrams of pear and apple and evaluate suitable fruits storage conditions.

Computer-Aided Design of Corn Dryers With Quality Prediction

ABSTRACT A new dynamic model of corn drying based on compartmental structure and quality prediction was built up from a thin layer model to industrial scale. From the system analysis to the programming, we focus mainly on numerical resolution of the equations and on the ergonomy of the software.

Design and control of drum dryers for the food industry. Part 2. Automatic control

Abstract Changes in operating conditions and process disturbances produce unevenness in the final moisture content of a product dried on a drum dryer. Moisture unevenness exists as a function of both time and drum width. The aim of this work is to control the final moisture content of the product and to reduce its unevenness, in order to obtain a high quality product and to increase dryer productivity. Among all input process variables, two control variables were chosen: the drum speed ( Vrc ), and the heating steam pressure ( pv ). These variables were used to keep constant the average final moisture content Xf ∗ . In this paper we present a case where classic control is not enough to correct some process perturbations. Therefore, the facility has been modified by adding an actuator, in this case an inductive electric heater. Local complementary heating power ( Pind ) is used to correct local heterogeneity of Xf to obtain Xf = Xf ∗ at every point across the drum.

Modelling the interactions between free phenols, L-ascorbic acid, apple polyphenoloxidase and oxygen during a thermal treatment

The kinetics of degradation of chlorogenic acid (CG), (-) epicatechin (EPI), L-ascorbic acid (AA) and polyphenoloxidase (PPO) activity from Marie-Ménard apple in pH 3.8 solutions at 20 and 50°C were investigated to provide information on the impact of the presence of CG, EPI and/or AA on PPO thermostability. The effect of the heat treatment on their degradation by enzymatic and/or nonenzymatic ways was also studied. Stoechiokinetic reactions on the basis of experimental data and literature and determination of the kinetic constants (k) at 20 and 50°C were elaborated before modelling the interaction among reactants, by fitting the reaction curves to predictive model. Apple PPO was thermolabile, denaturing after 10min at 70°C. Losses of PPO activity were favoured by the presence of EPI in model solutions, compared with CG, due to the formation of o-quinones of EPI (QEPI) lowering PPO stability. Temperature quickened both enzymatic phenol oxidations before PPO deteriorated and the whole set of the chemical reactions, including the production of secondary oxidation products and CG or EPI regeneration. Results also confirmed that AA in excess induced a fast regeneration of CG and EPI from the corresponding o-quinones formed enzymatically via redox chemical reactions.

Reverse Methodology to Identify Moisture Diffusivity During Air-Drying of Foodstuffs

The effective moisture diffusion is a key parameter for the simulation of the drying process of food products. A conventional procedure includes an identification step performed on thin-layer drying kinetics followed by a validation step on deep-bed drying kinetics. Unfortunately, this approach requires several experiments at different air temperatures while only using moisture data is accounted for identification purposes. For this reason, a reverse approach was developed. Results showed that identification on a single deep-bed kinetic allows for valid simulations of thin-layer kinetics on a wide range of temperatures. In addition, two correlations for moisture diffusivity are tested.