Non-interacting control system design methods in distillation

Abstract A new method to select the appropriate temperature measurement locations in a distillation column for feedback control is developed. The proposed method is based on the trade-off of measurement sensitivity vs inferential accuracy. Singular value analysis (SVA) is used to design structural compensators for the material balance control scheme in distillation. The material balance control scheme does not require an input compensator because the right singular vectors (input rotation matrix) are naturally aligned with the standard basis vectors. The output compensator (measurement matrix) is designed to create a non-interacting output frame. The resulting control scheme pairs distillate flowrate with the sum of two tray temperature, and reboiler heat duty with the difference between the same tray temperatures. These results indicate that for many chemical processes output decoupling, rather than input decoupling, may be an effective multivariable control strategy. Singular value analysis is a quick, reliable tool to aid in the control strategy screening process.

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