| Summary: | 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.
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