Nonlinear PI Control for High Purity Distillation Column

• Main Authors: Lin, Jyh-Ming, 林志銘
• Other Authors: Huang, Hsaio-Ping
• Format: Others
• Language: zh-TW
• Published: 1999
• Online Access: http://ndltd.ncl.edu.tw/handle/56515630932841410054

碩士 === 國立臺灣大學 === 化學工程學研究所 === 87 === High-purity distillation columns are very important unit operations in petrochemical industry. In addition to the process interaction problems and possible operating constraints, these columns exhibit very strong asymmetric nonlinear behavior, and tend to be very ill-conditioned too. Also, for most industrial columns, composition measurements are rarely available on-line; control is therefore often based on temperature measurements. When only one-point temperature control is implented, the control is relatively simple. In order to save energy consumption while tightly control product qualities of the top and the bottom streams, two-point temperature control strategy is necessary. Two-point temperature control of high-purity distillation column is an important challenging problem in petrochemical industry because of the particular difficult dynamic characteristics associated with the high-purity columns. Two-loop PID control because of its single-loop control nature and also because it is a linear controller, the closed-loop control performance is limited. In order to improve control, advance control of high-purity distillation column is advocated. This research utilizes a simple empirical nonlinear dynamic model form especially suited for high-purity column characteristics. A nonlinear PID control algorithm is proposed based on this nonlinear empirical model. In this nonlinear PID controllers, the controller gain and also the reset time will vary in response to the operating condition changes. Closed-loop results for a methanol-ethanol column and a debutanizer show superior control performance of this nonlinear PID controller. This nonlinear PID control method is very easy to implement, thus should have very good potential to be widely applicable in high-purity columns.