Inputs
Example data table
| Case | Type | Gas flow | Liquid flow | Pressure | Temp | K | Residence | Output (calc D) |
|---|---|---|---|---|---|---|---|---|
| A | Horizontal | 5000 m³/h (actual) | 20 m³/h | 10 bar(g) | 35°C | 0.10 m/s | 5 min | ~0.8–1.1 m |
| B | Vertical | 3 MMSCFD (standard) | 200 bbl/d | 150 psig | 90°F | 0.12 m/s | 3 min | ~0.6–0.9 m |
| C | Horizontal | 12000 m³/h (actual) | 60 m³/h | 6 bar(a) | 25°C | 0.10 m/s | 7 min | ~1.1–1.6 m |
Example outputs are indicative. Your results will vary with fluid properties and assumptions.
Formula used
- ρg = (P · MW) / (Z · R · T)
- Vmax = K · √((ρL − ρg) / ρg)
- Ag = Qg / Vmax
- D = √(4 · Ag / π)
- Vliq = QL · tres
- Vertical: h = Vliq / A
- Horizontal: V = f · (πD²/4) · (L/D · D)
- Horizontal D ∝ (V / (f · L/D))^(1/3)
This calculator focuses on early sizing. Final design typically also checks nozzle sizing, inlet devices, droplet distribution, foaming, slugging, carryover limits, and code requirements.
How to use this calculator
- Pick separator orientation based on layout and expected liquid holdup.
- Select gas basis: actual flow at operating, or standard flow conversion.
- Enter operating pressure and temperature for density estimation.
- Set MW and Z to match your gas composition and conditions.
- Choose a K-factor aligned with your mist eliminator approach.
- Define residence time for the liquid handling requirement.
- For horizontal separators, set L/D and working level fraction.
- Click Calculate, then export the result as CSV or PDF.
Capacity basis and gas density inputs
This calculator sizes an API separator from flow, pressure, temperature, and fluid properties. Gas density is estimated from ρg = (P·MW)/(Z·R·T). For example, at 10 bar(g), 35°C, MW 20 kg/kmol, and Z 0.95, ρg is about 9.1 kg/m³, which directly affects allowable gas velocity. Liquid density is taken as ρL = SG·1000 kg/m³, so SG 0.85 corresponds to 850 kg/m³.
Souders–Brown velocity selection
Gas capacity is checked using Vmax = K·√((ρL−ρg)/ρg). A higher K increases allowable velocity, but only when internals and droplet removal targets support it. Typical early K ranges are 0.07–0.15 m/s. Because the √((ρL−ρg)/ρg) term shrinks as gas density rises, higher pressure often reduces Vmax even when the volumetric flow falls.
Horizontal holdup and residence time
Liquid holdup volume is computed as Vliq = QL·tres. For horizontal vessels, working level fraction f and the chosen L/D ratio determine capacity: V ≈ f·(πD²/4)·(L/D·D). When holdup dominates, diameter scales with the cube root of volume; doubling residence time increases the holdup‑driven diameter by about 26%.
Interpreting results and safety margin
The tool reports required diameter, a suggested standard diameter, and a gas velocity margin based on Vsup/Vmax. If the margin is low or negative, increase diameter, reduce K, or revisit gas basis and property inputs. Standard diameters are rounded up to common nominal sizes (24–120 in). Selecting the next size provides fabrication tolerance and debottlenecking capacity. For horizontal separators, confirm that Vliq capacity at the selected working level meets or exceeds the target holdup.
Practical checks beyond this calculator
Preliminary sizing should be followed by checks for inlet device performance, nozzle sizing, slug handling, foaming tendency, and mist eliminator selection. Confirm materials, corrosion allowance, code requirements, and layout constraints. Use the CSV and PDF exports to compare cases and document assumptions across design reviews.
FAQs
What does the K-factor represent?
K is a capacity constant in the Souders–Brown method. It reflects mist eliminator type, droplet size target, and service severity. Use conservative values early, then confirm with vendor data and your separation performance requirements.
Should I enter standard or operating gas flow?
Use operating (actual) flow if you have it. If you only know standard flow, select the standard option so the tool converts to operating using pressure, temperature, and Z assumptions. Verify the standard base used matches your project basis.
Why does the calculator convert gauge pressure to absolute?
Gas density depends on absolute pressure. When you enter gauge pressure, the tool adds atmospheric pressure to estimate absolute pressure before calculating ρg. Using absolute pressure prevents underestimating gas density and overestimating allowable gas velocity.
What if the horizontal holdup capacity is below the target?
Increase L/D ratio, raise the working liquid level fraction within safe limits, or increase diameter. Recheck residence time needs for separation and control. If slugging is expected, add dedicated surge volume rather than relying on normal holdup.
How should I interpret a negative gas margin?
A negative margin means the superficial gas velocity exceeds the allowable velocity. Increase diameter, lower K, reduce gas rate, or reassess properties and basis conversions. Also review inlet device performance, because poor distribution can cause carryover even at lower velocities.
Is this calculator sufficient for final separator procurement?
No. It supports preliminary sizing and comparison. Final specifications should include mechanical design, code compliance, nozzle sizing, internals selection, carryover limits, and vendor confirmation. Use the exported report to document assumptions and guide detailed engineering.