Empirical Modeling for Spray Drying Process of Sticky and Nonsticky Products

摘要

Spray drying is a common drying technique in food industries to convert liquid to powder form. A good understanding on the dynamic behavior of the process is important to ensure proper control. The aim of this study is to develop empirical models for spray drying of whole milk powder (non sticky) and orange juice powder (sticky) using a nozzle atomizer spray dryer. Maltodextrin DE 10-15 was used as the drying agent material in spray drying of orange juice powder as it is considered as sticky powder. A preliminary study on the effect of several inputs such as inlet air temperature, feed flow rate and maltodextrin concentration on the product quality was studied. The selection of suitable inputs is important to ensure the desired quality of final products (moisture content). It was found that inlet air temperature gave more significant effect on outlet air temperature and powder moisture compared to feed flow rate and feed concentration. Inlet air temperature and outlet temperature were selected as the manipulated variable and controlled variables respectively. Empirical models were developed by applying step change in the inlet air temperature. Outlet air temperature for spray drying of orange juice powder was faster to achieve steady state because maltodextrin inhibited sticky behaviour. Both empirical models that showed the effect of inlet air temperature on the outlet air temperature can be represented as first order plus time delay (FOPTD) models. The obtained model was valid for process control because R~2≥0.6. The model for orange juice spray drying showed a faster response with higher gain and smaller process time constant.