Abstract
This paper addresses the question of the automatic control of the moisture content of products during spray drying using a model based scheme. A dynamic model of the process was developed from first principles and was then validated experimentally to assist in control simulation studies. A simple control scheme was implemented to overcome the limitations of conventional systems, based on the steady-state relationship between the air outlet temperature and the product moisture content. The scheme uses the feed flow-rate as the manipulated variable to control the outlet air temperature; in turn, the controller set point is provided by the steady-state model. Thus, changes in the quantitative relationship between the air outlet temperature and the moisture content of the solid can be taken into account. Simulations using this feedforward cascade control scheme show that the moisture content of the product can be maintained within required levels even under drastic changes in air inlet saturation conditions. This study illustrates the importance of models in gaining a deeper understanding of process behaviour, and it highlights their use in the analysis and synthesis of advanced control schemes.
Published Version
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