Two-Point Composition−Temperature Control of Binary Distillation Columns

Abstract

Although the two-input-two-output (2I-2O) dual composition (DC) and two-point temperature (TPT) distillation control problems have been studied extensively, the development of two-input-four-output (2I-4O) composition-temperature (CT) control schemes, driven by two composition and two temperature measurements, lags far behind. The difficulty of the 2I-4O CT control problem is due to the lack of systematic means to screen the large number of combined structural-algorithmic design degrees of freedom. With contradictory results, the problem has been recently addressed with linear and nonlinear approaches. Based on a constructive control framework, in this work, a rather simple solution to the combined 2I-4O CT control problem is obtained. The resulting scheme consists of linear PI components and static interaction compensators, has a systematic construction procedure with reduced model dependency, and has easy-to-apply tuning guidelines. The proposed approach is applied to three representative examples through simulations, yielding behaviors that improve those of previous linear and nonlinear cascade control schemes.

Decentralized control of a kinetically controlled ideal reactive distillation column

“…Detuning of the temperature loops is implemented to avoid rapid and large changes in the column inputs. The need for detuning control system component gains as a trade-off between regulation and control effort is noted by Castellanos-Sahagun et al (2006) for two-point composition-temperature control of binary distillation systems. Table 3(a) and (b) reports the ultimate gain, ultimate period and controller tunings for the temperature and composition loops, respectively, for the proposed control structures.…”

“…More recently, Castellanos-Sahagun et al (2005) propose a methodology for two-point temperature control structure and algorithm design for binary distillation columns. A systematic procedure for the combined structure-algorithm design for the more complex two-point composition-temperature control of binary distillation columns has been developed by Castellanos-Sahagun et al (2006). It is shown that the composition based temperature set-point adjustment must always be decentralized.…”

“…Of the large number of structural-algorithmic possibilities, only the simplest ones using decentralized linear PI temperature and composition loops are thus studied here. It is worth highlighting that the combined structure-algorithm design problem solution for the two-point temperature composition control of a binary distillation column obtained by Castellanos-Sahagun et al (2006) always consists of decentralized composition loops.…”

“…Among the more significant recent work on distillation control, Castellanos-Sahagun et al (2005) propose a two-point temperature control structure and algorithm design methodology for binary distillation columns combining feedforward, feedback and internal model control concepts. Castellanos-Sahagun et al (2006) address the problem of jointly designing the control structure and algorithm for the two-input-four-output composition temperature control schemes for binary distillation columns driven by two temperature and two composition measurements. The work provides a systematic methodology for screening the large number of combined structural-algorithmic design degrees of freedom for a binary distillation column and also provides a common tuning procedure to compare the structures.…”

Two-point Lyapunov Control of Binary Distillation Columns with four temperature measurements

“…Consequently, the related MIMO feedback control design has been and still is an important industrial problem that has been extensively studied with a diversity of linear and nonlinear approaches. Basically, the related two-input (reflux and vapor flow rate via manipulation of the reboiler heat duty) problem design has been studied with several linear and nonlinear control schemes: (i) two composition measurements (DC) [4,6,28], (ii) two point temperature (TPT) schemes [3,5,13], and (iii) cascade composition-to-temperature (DCT) controllers on the basis of one (or two) effluent composition primary measurements in conjunction with one (or two) temperature secondary measurements located in the most sensitive tray per section [2,5,8,25,30]. The DC schemes have the capability of offsetless composition regulation, but yield poor (oscillatory and sluggish) transient response for high-purity columns with measurement dead-times, instrumentation errors as well as feed rate, composition and enthalpy load disturbances.…”