Two-Point Temperature Control Structure and Algorithm Design for Binary Distillation Columns

Abstract

In this paper the problem of designing a two-point linear temperature controller for the regulation of the product compositions in binary distillation columns is addressed. The combination of feedforward, feedback, and internal model control concepts yields a control design methodology with (i) criteria to choose the (decentralized and one-or two-way) decoupling structure and the temperature measurements location, (ii) a linear control system that consists of a static interaction compensator and a pair of decoupled proportional-integral controllers with feedtemperature-based setpoint adjustment, (iii) an implementation that requires the static dependencies of the measured tray temperatures on the feed temperature, the slopes of the operating lines, and the temperature-gradient-to-holdup quotients in the measurement trays, and (iv) a conventional-like tuning scheme that resembles the ones employed in linear firstorder controllers and filters. The linear controller recovers the behavior of a material-balancebased feedforward-feedback nonlinear controller. The proposed design is applied to two representative examples through simulations, in the presence of holdup dynamics, nonideal thermodynamics, and actuator errors, as well as measurement delays and lags.

A Note on a Double Temperature-Cascade Control Strategy for Distillation Columns

“…Based on transfer functions (3) and (4) two secondary controllers (both are proportional type) are designed for each cascade scheme, C RT13 and C QT3 , for tracking the temperature references signals (T 13,ref and T 3,ref ) given by the primary controllers; in this case reflux flow (R ) and reboiler heat input (Q ), respectively are their control outputs. The previous structures are consistent with reported results (Castellanos-Sahagun et al, 2004 and2005) for the design of robust control structures for distillation columns. Figure 1 shows a scheme of the distillation column with two cascade control schemes previously described.…”

Geometric Estimation of Binary Distillation Columns

“…In Figure 1 are presented the singularity (s ι ) and ill conditioning (c ι ) measures (12) of the estimation matrix O (9a) as function of the sensor location pair (l 1 , l 2 ), for a completely observable structure σ (5) with estimation order pair κ = (κ 1 , κ 2 ) = (6, 6) and κ ι = κ 1 + κ 2 = 12 = n = N (i.e., complete model with observable structure), showing that: (i) the largest singularity and illconditioning values are obtained with the sensor stage location pair (l 1 , l 2 ) ≈ (1 to 2, 12), (ii) the smallest singularity and illconditioning values are obtained with the sensor location (l 1 , l 2 ) ≈ (1, 2) [ or (11, 12)] with two adjacent sensors in the bottom (or top) of the column, followed by the sensor location (l 1 , l 2 ) ≈ (5, 6) with two adjacent sensors above or below the feed tray (5). These consideration lead to the following conclusions: (i) the two sensors should not be in the same section, and (ii) the best location pair for complete profile estimation is given by These location results are in agreement with location criteria employed in: (i) two-point temperature PI control of distillation columns (Tolliver, 1980;Castellanos-Sahagun et al, 2005), and (ii) previous distillation column studies with EKF (Baratti et al, 1995;Oisiovici and Cruz, 2000).…”

Decentralized control of a kinetically controlled ideal reactive distillation column

“…Yu and Luyben, 1984;Fuentes and Luyben, 1983). 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).…”

“…The presence of interaction between the temperature loops suggests that the incorporation of an interaction compensator can significantly improve the closed loop control performance. Castellanos-Sahagun et al (2005) have shown recently that for the two-point linear temperature feedforward-feedback decoupling control of binary ordinary distillation columns, the one-way decoupling structure yields the best overall behavior compared with decentralized or twoway decoupling. A comparison between decentralized and decoupling control structures for RD systems needs to be further researched.…”

“…Skogestad and Morari, 1987a;Skogestad et al, 1990;Lee et al, 1995). 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.…”