Divided Wall Column for Industrial Multi Purpose Use

Divided wall columns (DWC) for the distillation of multicomponent mixtures have received much attention in the past 15 years and have experienced a booming development. Although the concept isn’t new and originates from the 1930s [1], it took a couple of decades until scientific investigations focused again on heat coupled columns [e.g. 2, 3]. Finally BASF in Ludwigshafen set up the first production scale column in 1985 [4]. The main advantages of DWC are the considerable savings in energy consumption and investment costs. This became increasingly important in times of rising energy costs and increased market competition. Therefore the number of installed units continuously increased since the 80’s and today this technique can be considered to be well established in chemical industry.

Since DWC demand higher efforts in equipment design and process control they are predominantly used in continuously operated dedicated production plants. Very little literature can be found where DWC are used in multi-purpose plants. The equipment in those plants, typically batch distillation, has to show a high degree of flexibility – an attribute that hardly seems to fit for divided wall columns.

Lonza set up a multi-purpose DWC on the production site in Visp that fully meets the demands of a steadily changing production. The column is constructed from hastelloy c22 which allows the distillation of corrosive mixtures used in this plant. A flexible inlet enables the feeding on different column segments as well as a flexible outlet allows a side draw from different stages.  Also simultaneously feeding on both sides of the dividing wall is possible which allows an operation mode comparable to that of a traditional distillation column This paper reports on the equipment design and the specific technical solutions that had to be implemented in order to meet the harsh specifications of multi purpose production. Particular attention is put on the modelling and simulation of the column and the control scheme that has been applied. The launch and operation of the column is explained in detail and finally the original simulations are compared to real operation data.

[1]        A. J. Brugma: Process and Device for Fractional Distillation of Liquid Mixtures, more Particularly Petroleum, US Patent 2.295.256 1942 (filed 1936)

[2]        F. B. Petlyuk V. M. Platonov, D. M. Slavinskii: Thermodynamically Optimal Method for Separating Multicomponent Mixtures, Int. Chem. Eng. 5, 1965, 555-561

[3]        W. J. Stupin, F. J. Lockhart: Thermally Coupled Distillation: a Case History, Chem. Eng. Progr. 88, 1972, 71-72

[4]        BASF company website