GPSA Ch. 16 GPA 2140

Calculation Mode:

Design Rate

Design: Size depropanizer from feed composition and product specifications.

Feed Conditions

Feed Rate (DeC2 Bottoms)

BPD

Feed Temperature

°F

Operating Pressure

psig

Feed Composition (mol%)

Ethane (C₂) Trace from deethanizer

Propane (C₃) — Light Key

iso-Butane (iC₄) — Heavy Key

n-Butane (nC₄)

iso-Pentane (iC₅)

n-Pentane (nC₅)

Hexane+ (C₆+)

Product Specifications

Max C₃ in Bottoms

mol%

Max C₄ in Overhead

mol%

Condenser Type

Column Design Parameters

Reflux Ratio Multiplier (R/R_min)

Overall Tray Efficiency

Tray Spacing

Design Flood Fraction

Typical Depropanizer Operating Conditions

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

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 (C₃) mole fraction in distillate, x_HK,B = heavy key (iC₄) mole fraction in bottoms, α = average relative volatility of C₃ to iC₄.

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.

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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 -

Propane (Overhead) -

C₄+ (Bottoms) -

Design Guidelines

Operating Pressure: Depropanizers typically operate at 200–300 psig, allowing overhead condensation with air-cooled or water-cooled exchangers.

HD-5 Propane: Overhead product must meet HD-5 specification (≤2 mol% C₄+) for commercial propane sales.

Condenser Type: Total condensers are typical for depropanizers, producing liquid propane product. Partial condensers may be used when vapor propane delivery is required.

Depropanizer (DeC3) Sizing Calculator