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Separator Sizing Calculator

Work out separator sizing instantly with clear inputs, formula shown and shareable results.

About Separator Sizing Calculator

A two-phase separator must hold the liquid for long enough to release entrained gas — typically 1-3 minutes for oil, longer for foaming or viscous crude. Holdup volume is liquid rate converted to cubic feet per minute times retention time; the vessel is then sized with a length-to-diameter ratio of about 3 to 4.

Formulas

Liquid holdup

Holdup volume (ft3) = liquid rate (bbl/d) x 5.6146 / 1440 x retention time (min)

Vessel geometry

Size the shell for the holdup volume at a length-to-diameter ratio of 3 to 4

Worked example

With the default values below, Separator Sizing Calculator returns Required Liquid Holdup Volume of 58.485. Change any input above and every figure here is recalculated in your browser.

Inputs used

Liquid Rateminimum 0 bbl/day
5,000 bbl/day
Gas Rateminimum 0 MMscf/day
8 MMscf/day
Liquid Retention Timeminimum 0.01 minutes
3 minutes
Operating Pressureminimum 0.01 psig
250 psig

Results

Required Liquid Holdup Volume
58.485
Indicative Vessel Diameter
5.834
Indicative Vessel Length
17.502
Gas Volumetric Rate
5.1421

Step by step

  1. 1Values used
  2. 2Liquid holdup
  3. 3Vessel geometry
  4. 4Required Liquid Holdup Volume= 58.485
  5. 5Indicative Vessel Diameter= 5.834
  6. 6Indicative Vessel Length= 17.502
  7. 7Gas Volumetric Rate= 5.1421

Assumptions and limits

  • The result is derived only from the 4 inputs listed above. Anything not among them is not part of the calculation.
  • In particular, this calculator does not take inflation, tax, fees or charges or compounding frequency into account.
  • Figures are rounded for display to 4 decimal places, so totals built from several rounded parts can differ slightly from the unrounded arithmetic.
  • Pressure vessel design, sizing and relief protection must comply with the applicable pressure vessel code and be certified by a qualified engineer.

How these calculators are built and tested is described on the Methodology page. If a figure looks wrong, please report it.

Pressure vessel design, sizing and relief protection must comply with the applicable pressure vessel code and be certified by a qualified engineer.

Frequently Asked Questions

What sets the gas capacity of a separator?

The Souders-Brown droplet settling criterion, which limits gas velocity so that liquid droplets fall out rather than being carried over. It scales with the square root of the density difference.

Why do foaming crudes need larger separators?

Foam occupies vessel volume without separating, so retention time must be multiplied — often by two to four — or a foam-breaking internal fitted.

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