串级-比值控制系统在聚酯生产中的应用

Application of Cascade-Ratio Control System in Polyester Production

乙二醇(EG)与精对苯二甲酸(PTA)的摩尔比是聚酯生产中重要的控制参数,参与配比的EG和PTA,一般采用独立的PID调节回路来控制其添加量,由于缺少反馈,对摩尔比的控制仍属于开环控制范畴。在EG和PTA浆料密度与两种物料的摩尔比之间的经验公式基础上设计了以浆料密度为主回路,摩尔比比值为副回路的串级-比值控制系统,克服了因EG质量分数、温度变化或其他干扰导致的配比偏差,提高了摩尔比的控制稳定性及控制品质。该方案已获得实际应用,效果良好。

Molar ratio of EG （Ethylene Glycol） to PTA （Pure Terephthalic Acid） is a veryimportant process parameter in polyester production. Independent PID adjustment loop is usedto control its charging amount for involved EG and PTA. The molar-ratio control strategy isintrinsically an open loop due to shortage of feedback. A novel control of so-called cascade-ratiocontrol strategy is established based on an experiential formula demonstrating relation ofdensity of mixture slurry to ratio of EG to PTA. The slurry density serves as master variableand molar ratio as slave variable. The scheme has been applied in practical project with goodperformance.