Distillation Column Performance and Separation Metrics

Reflux Constant and Steam Flow Dynamics

Reduced heating reflux constant: The steam flow rate increases with respect to the liquid, which leads to: a change in the cutoff of the load (heavier products in the head and higher flow rates), a lighter and smaller product flow background, and increased column temperatures.

If steam flow increases: Increasing the steam flow with respect to the liquid causes a heavy component transfer to the head and rising temperatures throughout the column.

Lentil Charts and XY Balance

Lentil chart: This represents the possible boiling collection ranges for different mixtures.

XY: This represents the balance between liquid and vapor at a given pressure.

ASTM Curves and Quality Metrics

ASTM Curve: Used to determine the quality of the products in a distillation column. The GAP is known as the difference between the temperature at 5% of the unused ASTM curve and the temperature at 95% of the distillate ASTM curve. If the value is negative, it is called OVERLAP and indicates a bad division, while a positive GAP shows good performance.

Boiling Point and Azeotropic Distillation

Boiling Point: The boiling temperature is the point at which a liquid begins to boil; this occurs because the vapor pressure equals the pressure of the vessel in which it is located.

Azeotropic Distillation

Identification Techniques in Distillation

Depending on the characteristics of the column and the way the distillate and residue are operated, they will have greater or lesser purity. This is determined by the degree of separation achieved by a column. The quality of separation is denominated as the degree of fragmentation.

Chromatography allows us to identify the components of a product and determine which should not be present. These components are the reference from which to perform the separation and are called key components. In the event that you cannot identify the components, a standardized test must be used. An example is the column of gas concentration stabilization.

The last case we can encounter is when there is no analysis of the components that make up the distillate and residue. In this case, the process relies on the distillation curve, where the first reference point to obtain the desired performance is called the TBP cut point.

Cut Point and Power Factors

The power of splitting in a distillation column depends on three factors: the reflux ratio, the reflux-to-distillate ratio, and the vaporization ratio (the ratio of the steam generated in the reboiler to the flow of waste).

Entry point of load: The ideal position for the feed is one in which the feed plate has the same composition as the load. Between the two streams of distillate and residue is the cutoff, which is responsible for dividing the load into two products: distillates and residues. When the separation between light and heavy components is not 100%, it indicates that there are impurities in this flow.

Improving the Cutoff

To improve the cutoff, the following steps should be taken:

• 1. Increase the reflux ratio at the head (results in less heavy material in the light product).
• 2. Increase the heat in the kettle and lower the reflux ratio (results in less light material in the heavy product).