Selecting the best distillation control configuration

Abstract

The selection of an appropriate control configuration (structure) is the most important decision when designing distillation control systems. The steady state RGA is commonly used in industry for selecting the best structure. One counterexample to the usefulness of this measure is the DB configuration, which has infinite steady state relative gain array (RGA) values, but still good control performance is possible. This is indicated by high-frequency RGA values close to 1. In this paper it is stressed that decisions regarding controller design should be based on the initial response (high-frequency behavior) rather than the steady state.Based on a frequency-dependent RGA analysis and optimal PI controller designs of four different configurations, the (L/D) (V/B) configuration is found to be the best choice for two-point composition control. The conventional LV configuration performs poorer than the above system, but is preferable if one-point control is used. AIChE JournalMay 1990 Sigurd Skogestad Petter Lundstriim Elling W. JacobsenChemical Engineering Norwegian Institute of Technology (NTH) N-7034 Trondheim, Norway Figure 1. Two-product distillation column with single feed and total condenser.

Dynamic effects of diabatization in distillation columns

“…The control structure synthesis problem for dual composition control for a CDiC is usually solved by considering a decentralized 2 × 2 control problem (Skogestad et al, 1990). This procedure has been employed in this study as well, implying perfect control for the remaining loops not concerning compositions.…”

“…A value of 10 and above is typically considered as the highend condition number of the process matrix. The frequency range of importance for feedback control in a distillation column, is the range of 0.01-1 min −1 corresponding to 0.6-60 h −1 (Skogestad et al, 1990).…”

Pattern-based predictive control for ETBE reactive distillation

“…The control configuration problem addressing which of the five degrees of freedom should be used in those three loops has been extensively discussed, e.g. [8]. Two more loops can be designed for purity and conversion control.…”

A New Representation of the Generalized Relative Dynamic Gains

“…Hence, the GRDG ) ( 11 s (z-axis) can be plotted as a function of the frequency (x-axis), for several specifications of the second loop (y-axis), leading to a 3D graphic. The yaxis is graduated with the -3dB bandwidth to analyze on the x-axis is the one corresponding to the -3dB bandwidth of the first closed-loop 22,23 . Therefore, the x-axis is labeled as However, the worst points are not necessarily the farthest points from unity since the GRDG scale, as the RDGA and the RGA ones, is not linear.…”