Temperature difference control and pressure-compensated temperature difference control for four-product extended Petlyuk dividing-wall columns

Abstract

The four-product extended Petlyuk dividing-wall column (FPEP-DWC) saves 50% more energy than traditional distillation sequences. However, the complex structure of FPEP-DWC results in strong interactions between different control loops and highly nonlinear behaviors. For the control of the FPEP-DWC, the temperature control (TC) scheme fails to handle the disturbances inserted into the process and none of the existing control schemes can, to the best of our knowledge, avoid the use of a composition controller (which is not recommended in industrial processes). The proposed TC scheme in the current work is also unable to handle the disturbances. Therefore, a kind of temperature difference control (TDC) scheme is investigated for the FPEP-DWC to improve its controllability and operability. A pressure-compensated temperature difference control (PCTDC) is also studied for the FPEP-DWC to compensate the pressure variations. To provide an illustrative example of the FPEP-DWC fractionating, a mixture containing methanol, ethanol, 1-propanol, and n-butanol was used to verify the feasibility of the TDC and PCTDC schemes while a wide range of feed disturbances are confronted. The outcomes show that the dynamic performances of the FPEP-DWC are substantially enhanced in most cases by using the proposed TDC and PCTDC schemes, which are conducive to the industrialization of the FPEP-DWC.