Development of Distillation Column Model for MLNG Depropanizer Column - Incorporating Redlich-Kwong Equation of State

The growing importance of propane as an alternative fuel and refrigerant has intensified
the need to optimize the production of propane from the MLNG depropanizer column.
In order to achieve on-line optimization for the depropanizer column using Advanced
Process Control Teclmiques (APC), an accurate distillation column model is essential.
This report presents the preliminary work in developing an accurate distillation column
model for the depropanizer column. The depropanizer column modeled is a 47-stage
column processing feed which contains Propane, i- and n- Butane, i- and n- Pentane and
n- Hexane. The model was developed based on MESH equations, using MA TLAB
programming tool, as required by MLNG. The depropanizer column model was
developed to account for the non-ideality of the mixture by incorporating RedlichKwong
equation of state in the enthalpy balances. The outputs obtained from the model
include vapor and liquid flow profiles, composition profiles and temperature profile of
the depropanizer column. The model developed in the study was able to predict the flow
profiles, plate composition and temperature to good accuracy. In the depropanizer
column, vapor and liquid flow rates, and column temperature decrease from the bottom
tray up to top tray. The composition of the desired product (propane.) -increases
ascending the column. The inverse trends occur for other heavier components. "WhatIf'
analysis, which can be used for optimization study, was also carried out on feed flow
rate and reflux ratio. Conclusively, a functional model of the MLNG depropanizer
column was successfully built.