Elsevier

Journal of Food Engineering

Volume 30, Issues 1–2, October–November 1996, Pages 171-183
Journal of Food Engineering

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

https://doi.org/10.1016/0260-8774(95)00054-2Get rights and content

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.

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    Citation Excerpt :

    The existing literature on this topic can be given a first classification according to the type of dryers, and to the desiccated materials. Many types of dryers are used: drum dryers (Courtois & Trystram, 1994; Rodriguez et al., 1996a, Rodriguez, Vasseur, & Courtois, 1996b), cross-flow dryers (Douglas, Jones, & Mallick, 1994a–c), solar dryers (Farkas, Mészàros, & Seres, 1998a), fluidised-bed (van Boxtel, & Knol, 1996; Temple & van Boxtel, 2000) and fixed-bed (Farkas, Remenyi, & Biro, 1998b) dryers, mixed-flow (Courtois, Nouafo, & Trystram, 1995) and cross-flow (Platt, Rumsay, & Palazoglu, 1992) dryers, and rotary dryers (Douglas et al., 1993) are just the main example of existing dryers. The variety of desiccated material is huge: maize (Courtois, Lebert, Duquenoy, Lasseran, & Bimbinet, 1991), rice (Bonazzi et al., 1994; Toyoda, 1989, 1992), corn (Courtois, 1995; Courtois et al., 1995; Trelea, Trystram, & Courtois, 1997), agricultural products (Toyoda et al., 1997), tea leaves (Temple & van Boxtel, 1999) are just a few examples.

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