GRAIN DRYING IN FIXED BED WITH SUPERVISORY SYSTEM OF PROCESS FOCUSING IN ENERGY SAVING AND QUALITY OF PRODUCTS

A fixed bed dryer was dimensioned, built and implemented in this work aiming at drying 50 kg of grains from 25% initial moisture content down to a final 13%, with emphasis on energy saving and product quality. A set of finned electric resistors (1,800 W) was installed for air heating in a range of 50 to 70°C. Air temperature and humidity were measured using Pt 100 resistance temperature detectors and resistive sensors positioned at diverse places of the drying bed. A supervisory application for the drying process was developed using the LabView software with the goal of enabling control of the potency of the electric resistors and ventilator motor, in order to regulate the drying air temperature and airflow ratio. This supervisory application was named CONT/DRY-1. The LabView uses graphical programming language based on virtual instruments. The set point value can be altered on the front panel by specifying the upper and lower temperature limits. Hence, the proportional-integral-derivative controller (PID) operates with varied increments accordingly to the predetermined temperature and drying kinetic ranges. The CONT/DRY-1 allows real-time monitoring of air temperature and humidity at various sites of the drying bed. In addition, it allows estimates of massive airflow ratios, engine rotation and energy consumption. The data are visualized as graphics, and accessed by means of an interactive man-machine graphical interface, which enables the operator to supervise, analyze and interact with the data. The results of the present work demonstrated the suitability and efficiency of the proposed CONT/DRY-1 supervisory system for a real time computational control of the fixed bed grain drying process.