For a four-component feed, Kaibel (1987) proposed a single dividing wall column (DWC) with two side-streams. We will show that an analytic minimal energy expression for the Kaibel-arrangement is straightforward to deduce based on the methods presented by Halvorsen (2001). The expression is very similar to the expression for the 3-product Petlyuk column. Minimum energy for the generalized n-product Petlyuk arrangement is given in Halvorsen (2001), Halvorsen and Skogestad (2003). Halvorsen introduced the Vmin-diagram, and this tool is also suited to illustrate the performance of a Kaibel column.

Compared to the conventional 3 column direct split sequence, the Kaibel column can be built in a single shell, making it very interesting in terms of capital cost savings. In addition it performs quite well in terms of energy savings too. As an example, the potential energy savings are 33% compared to the direct sequence for an equimolar 4-component mixture with relative volatilities of 6:4:2:1. A full Petlyuk arrangement for four components will always save some more, but will not be very realistic to use in a real plant due to much higher complexity.

We will show how the methods can be used to compare a number feeds for a set of alternative arrangements. The feed may contain any number of components that are split into four products with both sharp and non-sharp splits between each product.

References:

Kaibel G., Distillation Columns with Vertical Partitions, Chem. Eng. Technol., 1987, Vol. 10, pp 92-98.

Halvorsen, I. J., Minimum Energy Requirements in Complex Distillation Arrangements. Dr. Ing. Thesis, NTNU, 2001. Available from the web page of Sigurd Skogestad, Department of Chemical Engineering, NTNU (http://www.nt.ntnu.no/users/skoge/publications/thesis/2001_halvorsen/)

Halvorsen I.J., Skogestad S,. Minimum Energy Consumption in Multicomponent Distillation. 3. More Than Three Products and Generalized Petlyuk Arrangements. Ind. Eng. Chem. Res. 2003, 42, 616-629