Skip to main content
Calcimator

Distillation Reflux Ratio Calculator

Shortcut distillation design using Fenske-Underwood-Gilliland method. Calculate minimum stages, minimum reflux ratio, actual trays, and column material balance.

Inputs

%
%
%
%

Results

Minimum stages (Fenske)

6.43

Minimum reflux ratio R_min

1.1

Actual trays required

21

Actual reflux ratio R1.43
Theoretical stages (Gilliland)14.42
Distillate rate (kmol/hr)50
Bottoms rate (kmol/hr)50
Condenser duty estimate (kW)1,012.5
Reboiler Duty KW1,054.17
How to Use This Calculator
  1. Enter Feed composition, light key (mol%), Distillate purity, light key (mol%), and Bottoms composition, light key (mol%).
  2. Set Relative volatility α, Reflux multiplier (R/R_min), and Feed rate (kmol/hr).
  3. Adjust Overall tray efficiency (%) as needed.
  4. Review Minimum stages (Fenske), Minimum reflux ratio R_min, and Actual trays required.
  5. Use Actual reflux ratio R and Theoretical stages (Gilliland) to inform your decision.

How the result changes with Distillate purity, light key (mol%)

Distillate purity, light key (mol%)Minimum stages (Fenske)Minimum reflux ratio R_minActual trays required
100.820.012,593
352.540.015,053
653.890.016,983
905.610.8719

What each input means

Feed composition, light key (mol%)
Mole fraction of the light key component in the feed.
Distillate purity, light key (mol%)
Desired purity of the light key in the overhead product.
Bottoms composition, light key (mol%)
Allowed light key in the bottoms product.
Relative volatility α
Average relative volatility of the light key to heavy key.
Reflux multiplier (R/R_min)
Ratio of actual to minimum reflux. Typically 1.1–1.5; higher = more trays saved but more energy.
Feed rate (kmol/hr)
Molar feed rate to the column.
Overall tray efficiency (%)
Murphree or overall tray efficiency. Typically 50–80%.

What each result means

Minimum stages (Fenske)
Minimum theoretical stages at total reflux (Fenske equation).
Minimum reflux ratio R_min
Minimum reflux ratio from Underwood equation (infinite stages).
Actual reflux ratio R
Operating reflux ratio = R_min × multiplier.
Theoretical stages (Gilliland)
Number of theoretical stages from Gilliland correlation.
Actual trays required
Actual number of trays accounting for tray efficiency.
Distillate rate (kmol/hr)
Overhead product flow rate from material balance.
Bottoms rate (kmol/hr)
Bottom product flow rate.
Condenser duty estimate (kW)
Approximate condenser duty based on reflux and typical latent heat.

How this is calculated

Worked example, using the default values

  1. Identify Input Parameters
    4 parameters
    Feed composition, light key (mol%) = 50, Distillate purity, light key (mol%) = 95, Bottoms composition, light key (mol%) = 5, Relative volatility α = 2.5 = 7 input(s) provided
  2. Calculate Minimum stages
    Minimum stages = ln((xD / (1 - xD)) * ((1 - xB) / xB)) / ln(alpha)
    6.43 = 6.43
  3. Calculate Minimum reflux ratio R_min
    Minimum reflux ratio R_min = max(0.01, rMin)
    1.1 = 1.1
  4. Calculate Actual trays required
    Actual trays required = ceil(nActual)
    21 = 21
  5. Calculate Actual reflux ratio R
    Actual reflux ratio R = rMinClamped * refluxMultiplier
    1.43 = 1.43
  6. Calculate Theoretical stages
    Theoretical stages = (nMin + Y) / (1 - Y)
    14.42 = 14.42

Related Calculators

The questions that sit next to this one — chosen by subject, including calculators filed under a different category.

Chemical Engineering

Distillation Column Calculator

Estimate minimum and actual theoretical stages, minimum reflux ratio, and feed stage location using the McCabe-Thiele simplified approach.

Process Engineering

Energy Balance Calculator

Calculate steady-state energy balance for a process stream. Includes sensible heat (Q = mCpΔT), latent heat of phase change, and reaction heat contributions.

Process Engineering

Mass Balance Calculator

Solve steady-state mass and component balances around a separation unit. Calculate product/waste flow rates, component recovery, split ratio, and yield.

Process Engineering

Heat Exchanger Duty Calculator

Calculate heat exchanger duty using the Log Mean Temperature Difference (LMTD) method: Q = U × A × ΔTlm for counter-current or parallel flow.

More in Engineering.