Control System Design for Energy Efficient On-Target Product Purity Operation of a High-Purity Petlyuk Column

Abstract

Energy efficient, on-target product purity operation of a high-purity three product benzene–toluene–xylene ternary Petlyuk column is studied. The basic regulatory control system consists of four temperature inferential control loops with a fixed prefractionator vapor-to-fresh feed ratio. An economic control system on top of the regulatory layer adjusts these five set points. It consists of three product purity controllers that adjust three temperature set points along with a reboiler duty reduction controller that adjusts the remaining two free set points in the regulatory layer. The latter makes these adjustments to prevent the downward curvature in the prefractionator and main column middle section temperature profiles from being too large. Closed loop results for large feed composition changes show significant energy savings (up to 15%) are realized via temperature profile curvature control compared to constant set point column operation. The case study highlights the need for innovative control strate...