Optimization design of control system for moisture content in cut stems out of pneumatic dryer

To reduce the fluctuation of moisture content in cut stems out of the pneumatic dryer, the control system in the pneumatic dryer was optimized as following: 1) Relocating the testing point of moisture meter from the outlet to the electronic weigher next to pneumatic cut stem conveying. 2) Adding a metering tube to the feeding airlock at the outlet of pneumatic conveying. 3) Optimizing PID control program, resetting the delay time of control points and the data feedback from each processing step and increasing the step of tobacco flow from 2 to 5 kg/s to ensure accurate tobacco flow control. The results showed that after improvement, the moisture content in dried cut stems was 12.61%, which conformed to the technical standard; the qualified rate raised from 78.52% to 99.40% ; and the sigma level of process control increased from 2.86 to 4.07. The equipment ran stably, the process control of pneumatic drying and the quality of dried cut stems were promoted.