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Oil & Gas · Professional Microtool
Separator Sizing Calculator
Diameter · Height · Vapour velocity
Size a vertical two-phase separator: Souders-Brown for the diameter the gas needs to disengage, retention time for the height the liquid needs to settle, and the next fabricated size up.
Start from an example: 25 MMSCFD with 300 m³/day of condensate at 60 bar a →
Full output
- —Minimum diameter
- —Vessel height
- —Height to diameter
- —Maximum vapour velocity
- —Suggested K at this pressure
- —Actual vapour velocity
- —Margin below the limit
- —Liquid height
- —Retention volume
- —Gas density
- —Actual gas volume
Minimum vessel diameter against operating pressure
Diameter falls with roughly the fourth root of pressure, because denser gas means both less actual volume and a higher allowable velocity. Separating early, at pressure, buys a far smaller vessel than separating after a let-down.
Keep it
Both carry the figures you entered, in the part of the address that is never sent to a server. Share only where that is appropriate. To keep a copy for a project file, print the page — it lays itself out as a document.
Need sizing against a real feed characterisation?
We can work from your actual fluid data, slug and surge behaviour and internals selection, and build it into your facility engineering workflow.
Calculation basis 6 steps · view the method →
Gas density = P·MW ÷ (Z·R·T)—Actual gas volume = mass flow ÷ gas density—Maximum velocity = K × √((ρ liquid − ρ gas) ÷ ρ gas)—Minimum diameter from the area that velocity requires—Liquid height = liquid flow × retention time ÷ vessel area—Height = liquid height + inlet zone, disengagement space and mist extractor—
Assumptions & limitations Screening estimate for preliminary vessel sizing · 7 assumptions →
This is a preliminary sizing aid, not a vessel design. It covers a vertical two-phase separator in steady service and excludes slug and surge behaviour, foaming and emulsions, three-phase water separation, inlet device selection, nozzle sizing and momentum limits, level instrument spans, and all mechanical design — thickness, code, materials and relief. Mechanical design must follow the applicable pressure vessel code with a qualified engineer, and the process duty should be confirmed against a real feed characterisation.
- Vertical two-phase vessel with a mesh mist extractor, in steady service.
- Souders-Brown with the K factor entered. K is not a constant: the suggested value follows the usual screening correlation, which walks K down from 0.35 ft/s as pressure rises above 100 psig. It takes no account of foaming, surface tension or the specific internals.
- Slug and surge volume is not included — a slug catcher or surge allowance is a separate calculation.
- The height allowance above the liquid is a screening stack: 0.6 m inlet zone, disengagement of at least 0.9 m or half the diameter, and 0.3 m for the mist extractor.
- Diameters are rounded up to 6-inch increments; fabricators may offer a different set.
- Three-phase separation, water dropout and emulsion behaviour are out of scope.
- Nothing mechanical is calculated: thickness, nozzles, supports, relief and code compliance are all separate work.
Worked examples
- 25 MMSCFD with 300 m³/day of condensate at 60 bar a
Open with these figures → - The same duty separated at 15 bar a instead
Open with these figures →
About this tool
A separator has two independent jobs and they set two different dimensions. The gas has to slow down enough for droplets to fall out, which fixes the diameter; the liquid has to sit still long enough to degas, which fixes the height. This tool keeps them apart so each assumption — the K factor, the retention time — can be argued on its own. Written for process and facilities engineers doing preliminary work.
Go deeper
Oil & Gas Operations challenge
Separation, custody transfer, allocation and volume correction.
Digital Twins & Asset Management challenge
Keeping the model of a facility honest about the plant it describes.