GPSA Ch. 16 / GPA 2140
| Parameter | Range |
|---|---|
| Pressure | 200–300 psig |
| Overhead Temp | 100–130°F |
| Bottoms Temp | 200–280°F |
| Reflux Ratio | 1.0–2.5 |
| Trays | 30–45 |
Fenske Equation (Minimum Stages):
Where xLK,D = light key (C₃) mole fraction in distillate, xHK,B = heavy key (iC₄) mole fraction in bottoms, α = average relative volatility of C₃ to iC₄.
Gilliland Correlation:
Correlates actual stages N to actual reflux ratio R given minimum stages Nmin and minimum reflux Rmin from the Underwood equation.
Underwood Equation: Determines minimum reflux ratio Rmin from feed composition, feed condition (q), and relative volatilities. Combined with Gilliland correlation to find actual stages at the design reflux multiplier.
Column Diameter: Sized from vapor/liquid traffic using Fair’s flooding correlation at the design flood fraction.
Understand depropanizer design, C₃/C₄ separation principles, and shortcut distillation methods
A depropanizer (DeC3) separates propane (C₃) from butanes and heavier components (C₄+). It produces HD-5 specification propane product as overhead and sends the bottoms to the debutanizer.
Typical depropanizer operating conditions include 200–300 psig pressure, 100–130°F overhead temperature, 200–280°F bottoms temperature, reflux ratio of 1.0–2.5, and 30–45 trays.
The depropanizer light key is propane (C₃) and the heavy key is iso-butane (iC₄). The calculator uses the Fenske-Underwood-Gilliland method with the relative volatility of C₃ to iC₄ per GPSA Ch. 16.
The Gilliland correlation relates actual stages to actual reflux ratio given minimum stages from the Fenske equation and minimum reflux from the Underwood equation. It is combined with a design reflux multiplier (typically 1.2× Rmin) to find the required number of trays.