Research On Advanced Control Strategy For CTD Airflow Dryer

Tobacco drying is one of the most important steps during tobacco producing process. Tobacco drying process not only affects the quality of the final product, but also affects the benefits of the cigarette enterprises. Comas Tower Dryer(CTD) is the new tower airflow dryer using constant dehydration which is produced by Comas, Italy. CTD is convenient to maintain with the integration of expansion and drying.Based on characteristics of CTD airflow dryer, a novel control scheme which is based on dual control is designed to improve the control precision of the outlet moisture of CTD. The key technologies include: Kalman filtering technique, predictive PI techniques, dual control technologies. Simulation results show that the new dual control algorithm based on predictive PI is of satisfactory robust stability and strong anti-disturbance. From data processing, model building, design of control scheme, real-time simulation and analysis to engineering implementing, innovation of this paper mainly focuses on the following three parts:1. Due to the big noise in moisture, we apply Kalman filtering method for outlet moisture filtering to avoid the frequent fluctuations in the output of the controller and minimize the delay with traditional filtering method. Meanwhile, according to the mechanism of the process and testing results, mathematical models of moisture with respect to both the temperature of hot wind and moisture exhaust valve is established.2. Since the outlet moisture with respect to moisture exhaust valve is a class of large time delay process, we propose a new dual control based on predictive PI control. Predictive PI controller is simple in structure, convenient to adjust, especially suitable for controlling with large delay. Dual control based on predictive PI not only significantly improves control accuracy, but also especially maintains the economic rationality of the dying process.3. Finally we carry out engineering realization of the proposed control strategy by using OPTO 22 PAC Project platform. This strategy is realized in C language and a good user interface is developed. In order to verify the effectiveness and reliability of the control system, we build a real-time simulation system based on OPTO 22 and OPC server.