(119c) Simulating Maldistribution in Packed Columns

Maldistribution has long been known to be inevitable in packed columns and that it can significantly worsen the separation performance of a packed column. A recent presentation by L. Spiegel (The Maldistribution Story - An Industrial Perspective, Distillation and Absorption 2018, Florence) provides a convenient summary of the research on maldistribution up to relatively recent times.

Parallel column models sometimes are used to investigate the sensitivity of the HETP (the Height of an Equivalent Theoretical Plate) in a packed column due to maldistribution. In such models the vapor and liquid flows are split into two parts, which then enter one of two parallel columns. Billingham and Lockett (2002) proposed a two-column model for investigating maldistribution. Schultes (2000) studied maldistribution by modeling it with three parallel columns in a process simulator, and Stichlmair and Stemmer (1987) modeled maldistibution with no less than one hundred parallel columns! Although it is possible to develop a parallel column model using a process simulator, it takes considerable effort to arrange and specify the columns.

Recently, we have described what we call a Parallel Column Model PCM (Zhou et al., AIChE National Meeting, Orlando, 2018). While the model was developed with the aim of making it easier to model Dividing Wall Columns, we realized that it also is possible to use the ChemSep PCM to model maldistribution in packed columns. Both equilibrium stage and rate-based column models can easily be used within this framework. Our PCM can be used as a tool to study maldistribution inside any CAPE-OPEN compliant process simulation package.

In this paper we review the ChemSep PCM for DWCs and show how easily it may be used to describe maldistribution in packed columns. Cases considered examined by Fractionation Research Inc. (FRI), and summarized by Billingham and Lockett, as well as a case examined by Schultes, are used to study the liquid maldistribution with the help of our PCM.

References

Spiegel L., 2018, The maldistribution story - an industrial perspective, Chemical Engineering Transactions, 69, 715-720.

Billingham, J. F., and M. J. Lockett. "A simple method to assess the sensitivity of packed distillation columns to maldistribution." Chemical Engineering Research and Design 80.4 (2002): 373-382.

Schultes, M. "Influence of liquid redistributors on the mass-transfer efficiency of packed columns." Industrial & engineering chemistry research 39.5 (2000): 1381-1389.

Stichlmair, J., and A. Stemmer. "Influence of maldistribution on mass transfer in packed columns." Inst. Chem. Eng. Symp. Ser. Vol. 104. 1987.