Journal of Process Control 57 (2017) 50–65 Contents lists available at ScienceDirect Journal of Process Control j our na l ho me pa g e: www.elsevier.com/locate/jprocont An experimentally validated simulation model for a four-stage spray dryer Lars Norbert Petersen a,b , Niels Kjølstad Poulsen a , Hans Henrik Niemann c , Christer Utzen b , John Bagterp Jørgensen a,* a Department of Applied Mathematics and Computer Science, Technical University of Denmark, DK-2800 Kgs. Lyngby, Denmark b GEA Process Engineering A/S, DK-2860 Søborg, Denmark c Department of Electrical Engineering, Technical University of Denmark, DK-2800 Kgs. Lyngby, Denmark a r t i c l e i n f o Article history: Received 10 May 2016 Received in revised form 27 March 2017 Accepted 6 May 2017 Available online 3 April 2017 Keywords: Spray drying Multi-stage dryer Process simulation Process modeling Experimental data a b s t r a c t In this paper, we develop a dynamic model of an industrial type medium size four-stage spray dryer. The purpose of the model is to enable simulations of the spray dryer at different operating points, such that the model facilitates development and comparison of control strategies. The dryer is divided into four consecutive stages: a primary spray drying stage, two heated fluid bed stages, and a cooling fluid bed stage. Each of these stages in the model is assumed ideally mixed and the dynamics are described by mass- and energy balances. These balance equations are coupled with constitutive equations such as a thermodynamic model, the water evaporation rate, the heat transfer rates, and an equation for the stickiness of the powder (glass transition temperature). Laboratory data is used to model the equilibrium moisture content and the glass transition temperature of the powder. The resulting mathematical model is an index-1 differential algebraic equation (DAE) model with 12 states, 9 inputs, 8 disturbances, and 30 parameters. The parameters in the model are identified from well-excited experimental data obtained from the industrial type spray dryer. The simulated outputs of the model are validated using independent well-excited experimental data from the same spray dryer. The simulated temperatures, humidities, and residual moistures in the spray dryer compare well to the validation data. The model also provides the profit of operation, the production rate, the energy consumption, and the energy efficiency. In addition, it computes stickiness of the powder in different stages of the spray dryer. These facilities make the model well suited as a simulation model for comparison of the process economics associated to different control strategies. © 2017 Elsevier Ltd. All rights reserved. 1. Introduction Spray drying is a processing technique for drying of liquids or slurries. A spray dryer produces a free flowing powder. Spray drying is widely used in the food, chemical and pharmaceutical industries [1]. The main purpose of drying foodstuffs is to increase the shelf life as well as to reduce cost of transportation over long distances. Examples of spray dried foods are instant coffee, coffee whitener, eggs, milk, soups, baby foods, sweeteners, and cheese in powdered form [2]. Also, many powders occur in cooking. Chemicals are often dried to form non-dusty agglomerates that are easier to handle. * Corresponding author. E-mail addresses: lnpe@dtu.dk (L.N. Petersen), nkpo@dtu.dk (N.K. Poulsen), hhn@elektro.dtu.dk (H.H. Niemann), christer.utzen@gea.com (C. Utzen), jbjo@dtu.dk (J.B. Jørgensen). These may be agrochemicals used in cultivation as well as optical brighteners used in households and many more. Pharmaceuticals are dried for the production of tablets. Aspirin, paracetamol and vitamins are typical examples. In this paper, we consider a spray dryer with both an integrated and an external fluid bed. This is the preferred type of dryer for production of food powders. It provides product flexibility and the best energy efficiency compared to other spray dryers. It is a challenge and non-trivial to operate a spray dryer in an optimal way. One must maximize energy efficiency and production while minimizing down time [3]. These two goals are often conflicting, as increased production and efficiency may lead to an increase in the hours lost on process-related problems such as plugging, powder build-up, cleaning in place (CIP), etc. Constantly changing external disturbances, such as the ambient air humidity and feed composi- tion, are the main reasons that the powder turns sticky and deposits start to build up on the dryer walls. The operator must perform http://dx.doi.org/10.1016/j.jprocont.2017.05.001 0959-1524/© 2017 Elsevier Ltd. All rights reserved.