Decoupling control of a distillation column

✍ Scribed by Yi-Shing Changlai; Thomas J. Ward

• Publisher: American Institute of Chemical Engineers
• Year: 1972
• Tongue: English
• Weight: 272 KB
• Volume: 18
• Category: Article
• ISSN: 0001-1541
• DOI: 10.1002/aic.690180143

✦ Synopsis

Decoupling Control of a Distillation Column

Luyben (1 ) recently discussed the use of linear decoupling control for a binary distillation column. An ideal decoupling and a simplified decoupling approach were presented. A signal flow graph analysis is presented here to show how these two methods relate to previous decoupling procedures and to suggest other possible control approaches for this problem.

The specified control problem was the regulation of both the overhead composition XD and bottoms composition XB at their respective setpoints by the manipulation of the reflux rate R and the vapor boilup rate Vs in the face of such unmeasured disturbances as the feed composition XF and feed flow rate F,,. Luyben reduced the Laplace-transformed system differential equations (2) to the linear transfer matrix model commonly known as the P-structure. It is convenient here to also define the variables as perturbations from the desired steady state. This leads to the P-structure equations used by Luyben: which can be written as Equation (1) can be represented graphically by the signal Fig. 1. P-structure for distillation column example.