Application of Dual Control Algorithm in Conditioning Section of Redryer

The regulation of high pressure water pump, mixed water flow and mixed steam in redryer's conditioning section was independent of each other, which resulted in low control accuracy of moisture content in output redried tobacco. Therefore, a dual control means was proposed on the basis of predictive PI control algorithm. The controller for frequency conversion of the water pump motor was used as a main controller because of its direct and quick effects on tobacco moisture content, and the controllers for mixed water flow and mixed steam were taken as subsidiary controllers to change the humidity in conditioning section due to their slow regulation speeds. The results of practical running showed that the control algorithm combining predictive PI algorithm with improved dual control algorithm effectively improved the control precision of moisture content in output redried tobacco, which was controlled within the range of ±0.2% of the setting value in 95% of processing time. The relationships between high pressure water pump, mixed water and mixed steam were timely coordinated, the regulation of pump motor's frequency conversion beyond its limits was avoided, operator's interference was also eliminated, and the automation level of redrying equipment was improved.