An Experimental Investigation of a Dividing Wall Distillation Column
- Sponsors: Eastman Chemical Company, Emerson Process Management, and Sulzer Chemtech
- Principal Investigator: Dr. Bruce Eldridge
- Graduate Research Assistant: Bailee Roach
- Status: Complete
Distillation is a thermally inefficient traditional unit operation, which separates a chemical mixture by exploiting differences in boiling points. Energy usage is immense and multiple distillation columns are required to achieve high purity constraints. Traditionally, two components can be separated in one distillation tower (Fig. 1A), while separating three components requires three towers (Fig. 1B). In both schemes, the concentration of the middle component would reach a maximum somewhere in the middle of the tower, but would be lower in the bottom and top outlet, resulting in a thermodynamic loss.
A dividing wall distillation column (DWC) is a distillation column with a vertical partition, essentially dividing the column into two sides; the feed side acts as the prefractionator and the product side as the main column (Fig. 1C). The integrated wall insures that abrupt changes in liquid composition are avoided and a concentrated amount of the middle component is removed via a side-draw. These abrupt changes, often found in distillation trains, lead to entropic energy losses. This configuration reduces the need for additional columns for a ternary separation. Typically, a DWC can achieve between 25-50% energy savings over traditional separation techniques.
The DWC internal design is based on preliminary mass transfer and hydraulic coefficients modeled using AspenPlus. The steady state Aspen simulation models demonstrated successful separation with a divided column. The modeling was constructed using four columns, Figure 2, to simulate the DWC.
The pilot scale experimentation was conducted using The University of Texas’s Process Science Technology Center’s (PSTC) six inch diameter distillation column, shown in Figure 3.
In order to develop a fundamental understanding of a DWC, a packing study determined the impact of the wall on packing. From this study, the holdup, pressure drop, and effective mass transfer area for the dividing wall geometry was analyzed. The SRP has an existing absorption tower (Fig. 4) which was retrofitted as a dividing wall column. The experimental column consisted of a PVC cylinder cut lengthwise, with a wall placed in the middle to create the semi-circular shape of a DWC.