Currently, in the papermaking industry, both domestic and international paper manufacturers of all sizes still widely use traditional oil-heated and steam-heated paper drying cylinders. Over many years of production, traditional paper drying cylinder equipment has revealed numerous shortcomings, including low energy efficiency, high equipment investment, environmental pollution, and frequent production accidents. With the increasing international energy shortages and growing environmental awareness in recent years, various industrial sectors are continuously upgrading outdated equipment and developing new, energy-efficient, and high-performance equipment.
As a major energy consumer in paper production lines, the transformation of paper heating and drying cylinders requires a fundamental change from the heating method that uses hot oil and superheated steam as heating media, seeking a simple, convenient, and pollution-free alternative. Induction heating is a suitable heating method, characterized by high thermal efficiency, uniform heating, and safety, and has already been successfully applied in industries such as steel smelting and automobile manufacturing.
The innovation of this paper lies primarily in applying induction heating to the development of paper drying cylinder equipment. Based on this approach, a small-scale experimental paper machine medium-frequency induction drying cylinder with a diameter of 1200mm and a width of 400mm was designed and implemented. A low-cost, precise, and easy-to-operate control system was developed using a SIEMENS SS7-200 series PLC. After trial operation, the electromagnetic induction drying cylinder fully meets the requirements of the original production process, operates stably, and demonstrates significant energy savings. It can serve as a replacement for traditional drying cylinders and has broad market prospects.
This article describes the entire system from several aspects, including the principle of induction heating power supply, the design of the drying cylinder and papermaking process, and the selection and control algorithm of the PLC control system.
Its content mainly includes the following aspects:
(1) The advantages and disadvantages of traditional drying cylinders were analyzed, and the theoretical basis of induction heating and the development and application results of induction power supply were introduced.
(2) The commonly used parallel and series induction power supplies and their characteristics were analyzed and compared. The principles of several commonly used power adjustment methods were introduced. The series PWM & PFM method was selected for use in the drying cylinder. The relationship between power and phase angle ψ and angular frequency ω was found. The control circuit used was briefly explained.
(3) The two combinations of induction coil and drying cylinder were compared, and the paper drying process composed of drying oven and drying cylinder, the exhaust circulation system of humid air, etc. were introduced. Based on the actual situation, the detection methods and instruments of each key variable were selected, and the PLC system module was selected.
(4) A PLC control system program was developed using the PID algorithm. The principles of filtering algorithms, digital PID algorithms, and various improved algorithms were introduced. The "sliding mean filtering algorithm with dead zone", "derivative-first PID algorithm", "PID algorithm with dead zone", and "incomplete derivative PID algorithm" were applied to the program implementation, which improved the control effect.
