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Calcimator

Flash Drum Calculator

Calculate vapor-liquid equilibrium in a flash drum using the Rachford-Rice equation for a binary system.

Inputs

kmol/hr
mole fraction
°F
psi

Results

Vapor Fraction (ψ)

0.67

Vapor Flow Rate

66.67 kmol/hr

Vapor Composition (y₁)0.63 mole fraction
Liquid Composition (x₁)0.25 mole fraction
Liquid Flow Rate33.33 kmol/hr
How to Use This Calculator
  1. Enter the Feed Rate in kmol/hr and the Feed Composition (z₁) as the light-component mole fraction.
  2. Set the Flash Temperature in °C and Flash Pressure in kPa — these define the operating point of the drum.
  3. Enter the K-Value (equilibrium ratio K = y/x) for Component 1 (lighter) and Component 2 (heavier) at the operating temperature and pressure — obtain from process simulators or thermodynamic data.
  4. A K-Value above 1.0 means the component preferentially partitions to the vapor; below 1.0 it stays in the liquid.
  5. Read the Vapor Fraction (ψ) — 0 means all liquid, 1 means all vapor, values in between indicate two-phase equilibrium.
  6. Use Vapor and Liquid Compositions and Flow Rates to size the drum, downstream piping, and separators.

How the result changes with Feed Composition (z₁)

Feed Composition (z₁)Vapor Fraction (ψ)Vapor Flow Rate
0.1100 kmol/hr
0.350.2727.47 kmol/hr
0.651100 kmol/hr
0.891100 kmol/hr

What each input means

Feed Rate
Total molar flow rate of the feed stream.
Feed Composition (z₁)
Mole fraction of the light component in the feed.
Flash Temperature
Operating temperature of the flash drum.
Flash Pressure
Operating pressure of the flash drum.
K-Value Component 1
Equilibrium ratio (K = y/x) for the light component at operating conditions.
K-Value Component 2
Equilibrium ratio (K = y/x) for the heavy component at operating conditions.

How this is calculated

Worked example, using the default values

  1. Identify Input Parameters
    4 parameters
    Feed Rate = 100, Feed Composition (z₁) = 0.5, Flash Temperature = 100, Flash Pressure = 101.3 = 6 input(s) provided
  2. Calculate Vapor Fraction
    Vapor Fraction
    0.6667 = 0.6667
  3. Calculate Vapor Flow Rate
    Vapor Flow Rate
    66.67 = 66.67
  4. Calculate Vapor Composition
    Vapor Composition = Math
    0.625 = 0.625
  5. Calculate Liquid Composition
    Liquid Composition = Math
    0.25 = 0.25

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