Divided Wall Columns

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12 design variables: o Column pressure o Number of stages in 6 sections. (thus also fixing feed positions) o Liquid distribution to partition sides of wall o Vapor ...
Divided Wall Columns: Usefulness and Challenges Hilke-Marie Lorenz1, Daniel Staak1 ,Thomas Grützner2, Jens-Uwe Repke3 1Lonza

Specialty Ingredients, Lonza AG, Visp, Switzerland 2Ulm University, Institute of Chemical Engineering, Laboratory of Thermal Process Engineering, Ulm, Germany 3Technische Universität Berlin, Process Dynamics and Operations Group, Berlin, Germany

Evolution of Divided Wall Columns (DWC) “…Hence the present day challenge is to design distillation systems that at the same time are sustainable and economically feasible.” (Dejanovic et al. 2011)

More than the “conventional” DWC

Historical Steps •Full heat integration leads to Petlyuk-column (1965) •Further integration of prefractionator and main column in a single shell leads to DWC o Advantage: capital, space and energy savings (~ 30-50%) o Disadvantage: cannot vary pressures of the two columns anymore (can help in utilizing different heat sources)

„Kaibel“ Column

Extractive DWC

Multipurpose DWC

Reactive DWC

Cyclic DWC (Smith 2005, p 219)

(Petlyuk et al., 1965)

Aceotropic DWC

Concentric DWC

(Dejanovic et al. 2010) Source: Maleta CD

Design Aspects

Design Procedure

Consider a 3-component mixture, to be separated in a DWC with middle section wall (split shell column with divided overhead and divided bottoms section):

Source: LONZA AG

Simulation In commercial simulation package recently first models available, therefore homologous models are used:

 12 design variables: o Column pressure o Number of stages in 6 sections (thus also fixing feed positions) o Liquid distribution to partition sides of wall o Vapor distribution to partition sides of wall o One specification per product stream

(Asprion et al. 2010)

 Strategies available for approximate (short cut) and detailed design (model based, possibly including optimization)

(Grützner et al., 2016). 4-column model / 2-column model „Pre-Fractionator“ / 2-column model „Post-Fractionator“

Example: Extractive DWC in Operation  Separation Task

2-Column Sequence (Standard – Setup)

 Simple distillation not possible!

 Applying COSMO-RS for entrainer

screening revealed Ethylenglycol as a potential candidate

Extractive Dividing Wall Column

DWCs are still an ongoing research topic and the operation are sometimes challenging, but in cooperation with experts, DWCs have recently become standard unit operations with rules for designing, simulating, and controlling them, which are close to generalization.

References Asprion et al. (2010): Chemical Engineering and Processing: Process Intensification 49 (2), S. 139–146. DOI: 10.1016/j.cep.2010.01.013 Dejanović et al. (2010): Chemical Engineering and Processing: Process Intensification 49 (6), S. 559–580. DOI: 10.1016/j.cep.2010.04.001 Dejanović et al. (2011): Chemical Engineering Research and Design, 89, 1155–1167 Grützner et al. (2016): Chemical Engineering & Technology, 39 (19), 2016, 1835 – 1844 Petlyuk et al. (1965): Int. Chem. Eng. 5 (1965) 555–561 Smith, Robin (2005): Chemical process design and integration. Chichester, West Sussex, England, Hoboken, NJ: Wiley

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