separator-design

name	separator-design
description	Gas-liquid separator design — two-phase and three-phase separators, Souders-Brown coefficient (K-factor), vertical vs. horizontal separator sizing, retention time, mist eliminator (wire mesh, vane pack, cyclonic), inlet devices (half-pipe, diverter plate), nozzle sizing, ASME VIII vessel design, API 12J, degassing and sour service requirements, and offshore production separator train.
metadata	{"priority":7,"promptSignals":{"phrases":["separator design","gas liquid separator","Souders-Brown","mist eliminator","production separator","three-phase separator"],"minScore":3}}

Gas-Liquid Separator Design — Complete Skill

Separator Types and Selection

Two-Phase Separator (Gas-Liquid)

Applications: wellhead, compressor suction knockout, flash vessels, process separators Orientations:

• Vertical: good for high gas-to-liquid ratios; less slug capacity; smaller footprint; preferred for offshore
• Horizontal: handles slugging; large liquid surge volumes; easier to control; preferred onshore/high GOR inversion

Three-Phase Separator (Gas-Liquid-Liquid)

Added oil-water separation: Oil pad floats between water boot and gas; interface level controlled by weir or level transmitter Water retention time: 3–5 min (light oil); 5–20 min (heavy oil, emulsions) Oil retention time: 3–5 min for preliminary; 10–20 min for stable emulsion

Horizontal configuration preferred: provides more interface area for coalescing

Gas Capacity (Souders-Brown / K-Factor Method)

Vertical Separator

Superficial gas velocity at liquid surface: u_g = K × √[(ρ_L - ρ_G) / ρ_G] [m/s; K = Souders-Brown coefficient]

K-factor by separator type (Svrcek and Monnery): K = 0.107 m/s (without mist eliminator; conservative) K = 0.122 m/s (with wire mesh mist eliminator at 690 kPa; reduces to 0.085 at 7 MPa) K = 0.15–0.18 m/s (vane-type mist eliminator, high-efficiency) K_demisted = K_bare × pressure correction (K decreases at high pressure due to density ratio change)

Pressure correction for K (API 12J correlation): K_P = K_atm × (P_design / 689)^(-0.5) [P in kPa; K_atm ≈ 0.107 m/s]

Required gas flow area: A_G = Q_G / u_g [m²; Q_G = actual volumetric gas flow at separator T, P] Q_G = ṁ_G / ρ_G [m³/s; ṁ_G = mass flow gas [kg/s]]

Vessel internal diameter: D_i = √(4 × A_G / π) [m; round up to nearest standard size: 0.5, 0.6, 0.75, 0.9, 1.0, 1.2, 1.4, 1.6 m]

Example: ṁ_G = 20 kg/s; ρ_G = 25 kg/m³; ρ_L = 800 kg/m³; P = 3 MPa; wire mesh K = 0.107 × (3000/689)^(-0.5) = 0.107 × 0.479 = 0.051 m/s (high pressure; correct) Alternatively, use API 12J table for specific conditions u_g = 0.051 × √((800 - 25)/25) = 0.051 × 5.57 = 0.284 m/s (if no pressure correction), or apply correction With K = 0.085 (7 MPa correction): u_g = 0.085 × 5.57 = 0.473 m/s Q_G = 20/25 = 0.80 m³/s; A_G = 0.80/0.473 = 1.69 m²; D_i = √(4×1.69/π) = 1.47 m → select 1.5 m ID

Horizontal Separator Gas Capacity

Gas occupies upper portion; liquid lower: A_G = (1 - f_L) × π × D²/4 [f_L = fraction of cross-section occupied by liquid; typically 0.5 for 50% liquid fill] u_g = Q_G / A_G ≤ u_g,allow = K × √[(ρ_L - ρ_G)/ρ_G]

Effective length for gas: L_eff = L_TT - (L_inlet_device) - (mist eliminator space) [L_TT = tangent-to-tangent length] Typically L_TT = 3× to 4× D for two-phase; 4× to 5× D for three-phase

Liquid Capacity (Retention Time)

Liquid volume required: V_liquid = Q_L × t_retention [m³; Q_L = liquid volumetric flow [m³/s]; t_retention = residence time [s]]

Retention times (Svrcek & Monnery guidelines): Gas-liquid: t_L = 1–3 min (API 12J: minimum 1 min; typical 2–5 min) Oil-water separation: t_oil = 3–5 min (clean fluids); t_water = 3–5 min Crude oil (16–25°API, T = 40–60°C): t_oil = 10–20 min; t_water = 10–20 min (emulsion treatment)

Vertical separator liquid volume: V_L = π/4 × D² × H_L [H_L = liquid height; typically 50% of D ≤ H_L ≤ D] Surge volume: additional H_surge for slug handling (API 12J: 15% of total volume or slug volume, whichever greater)

Mist Eliminator Sizing

Wire Mesh Pad (Knitted Wire Mesh)

Standard 6" (150 mm) thick × full vessel diameter K_mesh = 0.107–0.122 m/s (at atmospheric; reduce for high P) ΔP across mesh pad = 25–75 Pa (clean); up to 250 Pa at design velocity Minimum spacing from liquid surface: 0.15 m (gas disengagement zone below mesh) Maximum loading: K ≤ 0.8 × K_flood (flooding velocity); re-entrainment above K_flood

Material: 304SS or 316SS knitted wire; for sour service: 316L SS or Monel; for FCC: proprietary alloys

Vane-Type (Chevron) Mist Eliminator

Higher liquid loading capacity; better for sticky/fouling service: K_vane = 0.15–0.18 m/s (inherently better than wire mesh at high pressure) ΔP across vanes: 100–500 Pa; drainage channels carry liquid away Applications: high-pressure gas, sour gas, glycol absorbers

Cyclonic / Centrifugal Mist Eliminator

Spin-element bundles (Peerless Centurion, OTP): G-force separation; efficient at high loadings; lower pressure drop than vanes K_cyclone = 0.20–0.30 m/s at separator pressure Applications: compressor suction KO drums, high-throughput

Inlet Devices

Purpose: distribute flow, prevent re-entrainment, reduce turbulence

Half-pipe inlet (schoepentoeter): Divert flow horizontally or downward; low momentum impact; good for high GOR ΔP = ρ_mix × u_inlet² / 2 → design u_inlet ≤ 15 m/s gas; ≤ 3 m/s liquid

Inlet diverter plate (impingement baffle): Simple; effective for slug handling; directs gas up, liquid down Plate area ≥ 1.2 × inlet nozzle area

Cyclonic inlet device (Peerless FLT, Shell SEPSEP): Centrifugal pre-separation at inlet; reduces mist eliminator duty significantly Useful for high liquid loading

Inlet nozzle velocity: ρ_G × u²_G + ρ_L × u²_L ≤ 1,500 kg/(m·s²) for inlet momentum criterion (prevents re-entrainment) Typical inlet nozzle velocity: 5–15 m/s gas; 2–5 m/s liquid

Vessel Sizing Summary

Overall Sizing Procedure

1. Calculate Q_G, Q_L from process mass balance and densities
2. Select K-factor (pressure; mist eliminator type)
3. Calculate u_g,allow and A_G → D_i from gas capacity
4. Check liquid retention time H_L for selected D → confirm V_L adequate
5. Set L_TT: horizontal = 4D to 5D; vertical: L = D + H_L + 0.6 m (gas disengagement) + mist eliminator space + nozzle zones
6. Check aspect ratio: H/D (vertical) = 3:1 to 4:1 typical; L/D (horizontal) = 3:1 to 5:1
7. Design nozzle sizes (inlet, gas outlet, liquid outlet, drain, manway, instruments)

Standard vessel dimensions: Heads: ASME 2:1 semi-ellipsoidal (depth = D/4); straight shell + 2 heads = L_TT + D/2 Manway: 18" (450 mm) minimum; 24" (600 mm) for vessels >600 mm ID Nozzle minimum: DN 50 (2") for small flows; velocity check per API 12J

ASME VIII Vessel Design

Shell thickness: t = P_d × R / (S_E - 0.6P_d) + C_A [P_d = design pressure; R = inside radius; S = allowable stress; E = joint efficiency; C_A = corrosion allowance] Minimum: 6 mm (1/4") for shell < 600 mm; 8 mm for larger MAWP: 110% of operating pressure (API 12J: operating + 20% or operating + 100 kPa, whichever greater)

Corrosion allowance: C_A = 1.5–3.0 mm for sweet service CS; 3–6 mm for moderate sour; 0 mm for SS/clad

Standards and References

Standard	Scope
API 12J	Specification for oil and gas separators
GPSA Engineering Data Book Section 7	Gas-liquid separation theory and design
Svrcek & Monnery (1993)	Size separators the right way — sizing methodology
ASME Sec. VIII Div. 1	Pressure vessel code
NACE MR0175/ISO 15156	Materials for sour service (H₂S)

Output

Provide: process conditions (gas and liquid mass flows [kg/s]; densities ρ_G, ρ_L [kg/m³]; P [kPa]; T [°C]; fluid composition; GOR), separator type (two-phase/three-phase; vertical/horizontal; basis for selection), gas capacity (K-factor at design pressure [m/s]; u_g,allow [m/s]; Q_G [m³/s]; A_G required [m²]; D_i selected [mm]), liquid capacity (Q_L [m³/s]; t_retention selected [min]; V_L required [m³]; H_L [mm] in vessel), vessel dimensions (D_i [mm]; L_TT [mm]; L/D ratio; head type), mist eliminator (type: wire mesh/vane/cyclonic; K_demisted; ΔP [Pa]; material), inlet device (type; inlet nozzle velocity [m/s]; momentum check [kg/m·s²]), nozzle summary (inlet/gas outlet/liquid outlet sizes [mm] with velocity check), vessel wall thickness t [mm] (ASME VIII; C_A; MAWP [kPag]), material selection (sweet/sour service; CS or SS; NACE MR0175 if H₂S), and applicable standard (API 12J; GPSA Sec. 7; ASME VIII).