Research And Application Of Temperature Control Characteristics Of Large-scale Carbon Fiber Pre-oxidation Equipment

Large-scale pre-oxidation equipment is one of the key equipments for the production of PAN based carbon fiber. Its major technical parameters are essential to improve the production and performance of carbon fiber. How to shorten the pre-oxidation heating-up time, improve temperature uniformity and control accuracy, and reduce the energy consumption, is the key technology to be solved for domestic large-scale pre-oxidation equipment.With the help of computer simulation, a systematic study was conducted on the temperature control characteristics of large-scale pre-oxidation equipment. It includes:(1) Research and application of temperature control algorithmA temperature control system model of large-scale pre-oxidation equipment was established and a step response curve was acquired by experiments. Finally the model parameters were identified using the auxiliary variable least squares method.Fuzzy adaptive PID algorithm and BP-based adaptive PID algorithm were studied and simulated in MATLAB. The simulation results show that, compared with conventional PID, both algorithms have the advantages of high precision, small overshoot, and strong anti-interference ability. The BP-based adaptive PID algorithm is better than fuzzy adaptive PID in the aspect of overshoot and anti-jamming, but its response time is a little longer than fuzzy adaptive PID due to the complexity of BP algorithm.Aiming at the defects of fuzzy control quantization error, a linear interpolation method was used to refine the fuzzy rules, the corresponding formulas were derived and this method was implemented in PLC program, which can eliminate the quantization error and improve the system performance significantly.(2) Flow field and temperature field simulationThe mathematical model of gas flow and heat transfer of large pre-oxidation equipment was established based on the basic computational fluid dynamics and heat transfer equations. Using the finite volume method, the governing equations of flow and heat transfer were discretized and discrete equations of transient flow and heat transfer were derived. According to the SIMPLE algorithm, speed and pressure correction formulas were derived.Analyzing the structure characteristics of large-scale pre-oxidation equipment, a two-dimensional model with reasonable simplification was adopted to study the fluid field and temperature field. Models with different conditions were established and meshed in GAMBIT. FLUENT software was used for the simulation.Based on the simulation results, a series of optimization suggestions was proposed for structure improvement of large-scale pre-oxidation equipment, optimized rotation angles of wind scoopers and PAN fibers’distribution in chamber.The temperature filed simulation was conducted with improved structure and optimized rotation angles of wind scoopers, and the result shows that improved and optimized large-scale equipment without load has good temperature uniformity.(3)Control system design and software developmentBased on the research results of this paper, a set of temperature control system with high performance, high reliability, high cost performance and scalability was designed and it has been successfully applied to the development of a carbon fiber production line with annual output of800tons.The PLC software achieved high measurement precision of0.02℃using polynomial fitting and external compensation. Fuzzy adaptive PID algorithm and segmental temperature control strategy ware used to ensure the heating-up rate and control accuracy. USS communication based on RS485bus was utilized to control72inverters divided into3subnets and the real-time performance can meet the production requirements by reasonable parameter settings and software optimization. This paper also proposed an intelligent pre-oxidation scheduling algorithm which has been programmed. This intelligent scheduling algorithm can schedule all the available power by step heating and time-sharing control, it can reduce about35%of transformer capacity without temperature control precision loss.According to the research results, the air supply system of large-scale pre-oxidation equipment was optimized. The precision of two different large-scale pre-oxidation equipments with optimized parameters was tested and the temperature control precision is plus or minus1degrees C. Distributed multiple-thermocouple measurement and oxygen content tests of pre-oxidized fiber both proved that optimized large-scale pre-oxidation equipment has good temperature uniformity. The maximum temperature deviation in the chamber is2.6degrees C.