Drying Technology, 20(7), 1319-1345 (2002) – mailto:courtois@ensia.inra.fr DYNAMIC OPTIMAL CONTROL OF BATCH RICE DRYING PROCESS A. Olmos 1 , I.C. Trelea 2 , F. Courtois 1 , C. Bonazzi 1 , G. Trystram 1 1 ENSIA, UMR Génie Industriel Alimentaire Cemagref, ENSIA, INRA, INAPG 1, Avenue des Olympiades, 91744 Massy, France 2 INA P-G, UMR Génie et Microbiologie des Procédés Alimentaires 78850 Thiverval-Grignon, France Key Words and Phrases: grain breakage, dynamic optimization, optimal control; paddy rice drying; sequential quadratic programming 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. INTRODUCTION The technological processing of paddy rice includes its drying from an initial moisture content contained between 220 and 750 g water / kg d.b. (dry basis) after harvesting down to a final moisture content of 140 g/kg d.b. or less. For some operating conditions the drying process may lead to endosperm breakage due to mechanical stress (1). From an economic point of view, the quality of rice is expressed as a head kernel yield. The term "head rice" denotes milled rice comprised of kernels three-fourths or more the original kernel. The rice