GPSA Ch. 16 / GPA 2140
| Parameter | Range |
|---|---|
| Pressure | 60–100 psig |
| Overhead Temp | 90–130°F |
| Bottoms Temp | 140–180°F |
| Reflux Ratio | 5–15 |
| Trays | 60–120 |
Fenske Equation (Minimum Stages):
Where xLK,D = light key (iC₄) mole fraction in distillate, xHK,B = heavy key (nC₄) mole fraction in bottoms, α = average relative volatility of iC₄ to nC₄ (typically 1.1–1.3).
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 deisobutanizer design, close-boiling iC₄/nC₄ separation challenges, and structured packing alternatives
The isobutane/normal butane separation is one of the most difficult in NGL processing because the relative volatility is very low (Ξ± β 1.1β1.3). This requires high tray counts and high reflux ratios, making the butane splitter an energy-intensive column.
The calculator uses the Fenske-Underwood-Gilliland shortcut method to determine minimum stages (Fenske equation), minimum reflux ratio (Underwood), and actual trays at operating reflux (Gilliland correlation) per GPSA Ch. 16.
The Fenske equation calculates the minimum number of theoretical stages required for a given separation at total reflux. It uses the light key and heavy key mole fractions in distillate and bottoms with the average relative volatility.
A typical butane splitter produces an isobutane overhead product with 95β99% purity and a normal butane bottoms product. The calculator allows user-defined purity targets and computes the required stages, reflux, and column dimensions per GPSA Ch. 16 and GPA 2140.