GPSA Ch. 16 GPA 2140

Calculation Mode:

Design Rate

Design: Size debutanizer from feed composition and product specifications.

Feed Conditions

Feed Rate (DeC3 Bottoms)

BPD

Feed Temperature

°F

Operating Pressure

psig

Feed Composition (mol%)

Propane (C₃) Trace from depropanizer

iso-Butane (iC₄)

n-Butane (nC₄) — Light Key

iso-Pentane (iC₅) — Heavy Key

n-Pentane (nC₅)

Hexane (C₆)

Heptane+ (C₇+)

Product Specifications

Max C₄ in Bottoms

mol%

Max C₅ in Overhead

mol%

Condenser Type

Column Design Parameters

Reflux Ratio Multiplier (R/R_min)

Overall Tray Efficiency

Tray Spacing

Design Flood Fraction

Typical Debutanizer Operating Conditions

Parameter	Range
Pressure	75–150 psig
Overhead Temp	120–160°F
Bottoms Temp	300–400°F
Reflux Ratio	1.0–2.5
Trays	25–40

Engineering Basis

Fenske Equation (Minimum Stages):

N_min = ln[(x_LK,D / x_HK,D)(x_HK,B / x_LK,B)] / ln(α)

Where x_LK,D = light key (nC₄) mole fraction in distillate, x_HK,B = heavy key (iC₅) mole fraction in bottoms, α = average relative volatility of nC₄ to iC₅.

Gilliland Correlation:

(N − N_min) / (N + 1) = f[(R − R_min) / (R + 1)]

Correlates actual stages N to actual reflux ratio R given minimum stages N_min and minimum reflux R_min from the Underwood equation.

Underwood Equation: Determines minimum reflux ratio R_min 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.

📚 Learn the Theory

Understand debutanizer design, nC₄/iC₅ separation principles, and natural gasoline production

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Results

Actual Trays

trays

N_min (Fenske) -

R_min (Underwood) -

R_actual -

N_theoretical -

Feed Tray -

Rectifying / Stripping -

Column Dimensions

Diameter -

Height -

Tray Spacing -

% Flood -

Shell Thickness -

Weight -

Duties & Utilities

Condenser Duty -

Reboiler Duty -

CW Flow -

T_condenser -

T_reboiler -

Butane (Overhead) -

C₅+ Gasoline (Bottoms) -

Design Guidelines

Operating Pressure: Debutanizers typically operate at 75–150 psig, lower than depropanizers, as the heavier C₄/C₅ separation allows condensation at lower pressures.

Natural Gasoline: Bottoms product (C₅+) is natural gasoline used for gasoline blending, petrochemical feedstock, or diluent.

Condenser Type: Total condensers produce liquid mixed-butane product. Air-cooled condensers are typical at these overhead temperatures.

Debutanizer (DeC4) Sizing Calculator