Centrifugal Separation

Cyclone Separator Design

Design cyclone and multicyclone separators using centrifugal force principles, Lapple efficiency model, cut diameter calculations, and pressure drop optimization for gas-liquid and gas-solid separation.

Launch Calculator Separation Theory

Separation force

100-1000× gravity

Centrifugal acceleration provides 100-1000× gravitational force for rapid separation.

Cut diameter

5-25 microns

Particle size at 50% collection efficiency; smaller cyclones achieve finer cuts.

Pressure drop

2-10 psi typical

Higher ΔP increases separation efficiency but adds compression cost.

Contents

Use this guide when you need to:

  • Size single or multicyclone separators.
  • Calculate cut diameter and efficiency.
  • Optimize pressure drop vs. efficiency.
  • Design for high liquid or solids loading.

1. Overview & Applications

Cyclone separators use centrifugal force to separate particles (liquid droplets or solid particles) from a gas stream. The rotating gas flow creates forces many times stronger than gravity, enabling efficient separation of particles too small for gravity settlers.

Operating principle

Centrifugal Force

Tangential inlet creates spinning flow; particles are thrown to walls by centrifugal acceleration.

No moving parts

High Reliability

Static device with no rotating equipment; minimal maintenance requirements.

High capacity

Compact Design

Handles high flow rates in small footprint; ideal for space-constrained installations.

Handles solids

Erosion Resistant

Can handle abrasive particles that would damage other separator types.

Cyclone Separator Types

Type Diameter Cut Size Application
Single large cyclone 12-72 inches 15-50 microns Bulk separation, low ΔP
Single small cyclone 4-12 inches 5-15 microns Higher efficiency, moderate flow
Multicyclone (tube bundle) 1-4 inch tubes 3-10 microns High efficiency, high capacity
Axial flow cyclone 2-8 inches 5-20 microns In-line installation, lower ΔP

Applications

  • Gas production: Remove liquid droplets and sand from wellhead gas
  • Compressor protection: Inlet scrubbers to protect compressor internals
  • Catalyst recovery: FCC and other catalytic processes
  • Dehydration inlet: Remove bulk liquids upstream of TEG contactors
  • Flare systems: Knock out liquids from relief gas before flaring
  • Combustion air: Remove dust and moisture from turbine inlet air

Cyclone vs. Other Separators

Parameter Gravity Separator Cyclone Filter Separator
Minimum particle size 100-500 microns 5-25 microns 0.3-3 microns
Pressure drop 0.5-2 psi 2-10 psi 2-15 psi
Liquid handling Excellent Good Limited
Solids handling Poor Excellent Fair (clogs elements)
Maintenance Low Very low Higher (element replacement)
Capital cost Moderate Low-moderate Higher
Selection guidance: Use cyclones when: (1) particle sizes are 5-100 microns, (2) high solids loading is expected, (3) pressure drop of 2-10 psi is acceptable, (4) low maintenance is required. For sub-micron particles or where ΔP is critical, consider filter separators or gravity settlers.

2. Separation Theory

Cyclone separation relies on the principle that particles in a rotating flow experience centrifugal force proportional to their mass and the square of their rotational velocity. This force drives particles radially outward to the cyclone wall.

Centrifugal Force

Centrifugal Acceleration: a_c = v_t² / r = ω² × r Where: a_c = Centrifugal acceleration (ft/s² or m/s²) v_t = Tangential velocity (ft/s or m/s) r = Radius of rotation (ft or m) ω = Angular velocity (rad/s) Centrifugal force on particle: F_c = m × a_c = m × v_t² / r Ratio to gravitational force (separation factor): S = a_c / g = v_t² / (g × r) Typical values: - Large cyclone (D = 4 ft, v = 50 ft/s): S ≈ 40 - Small cyclone (D = 0.5 ft, v = 80 ft/s): S ≈ 800 - Multicyclone tube (D = 2 in, v = 100 ft/s): S ≈ 2000 Higher S means smaller particles can be separated.

Flow Pattern in Cyclone

Cyclone Flow Structure: OUTER VORTEX (Downward spiral) - Gas enters tangentially at top - Spins downward along outer wall - Particles migrate to wall by centrifugal force - Particles slide down to collection hopper INNER VORTEX (Upward spiral) - At cone bottom, flow reverses direction - Clean gas spirals upward in center - Exits through vortex finder (gas outlet tube) - Carries any uncaptured fine particles VORTEX FINDER (Dip tube) - Extends into cyclone body - Prevents short-circuiting of inlet gas to outlet - Diameter and length affect efficiency and ΔP Critical dimensions (as fraction of body diameter D): - Inlet height: a = 0.5D - Inlet width: b = 0.2D - Gas outlet diameter: De = 0.5D - Vortex finder length: S = 0.5D - Body length: h = 1.5D - Cone length: z = 2.5D - Dust outlet diameter: B = 0.25D

Particle Motion

Radial Particle Velocity: Terminal radial velocity (Stokes regime): v_r = d² × (ρ_p - ρ_g) × v_t² / (18 × μ × r) Where: v_r = Radial velocity toward wall (ft/s) d = Particle diameter (ft) ρ_p = Particle density (lb/ft³) ρ_g = Gas density (lb/ft³) v_t = Tangential gas velocity (ft/s) μ = Gas viscosity (lb/ft·s) r = Radius of rotation (ft) Time for particle to reach wall: t = (R - r_0) / v_r Where: R = Cyclone radius r_0 = Initial particle radial position Particle is captured if t < residence time in cyclone

Factors Affecting Separation

  • Cyclone diameter: Smaller diameter = higher centrifugal force = better efficiency
  • Inlet velocity: Higher velocity = higher centrifugal force, but also higher ΔP and re-entrainment risk
  • Particle size: Larger particles are easier to separate (mass ∝ d³)
  • Particle density: Denser particles separate better (higher centrifugal force)
  • Gas density: Higher gas density reduces density difference, hurting efficiency
  • Gas viscosity: Higher viscosity increases drag, reducing radial velocity
  • Cyclone length: Longer cyclone = more residence time = better efficiency
Design trade-off: Smaller cyclone diameter dramatically improves efficiency (cut diameter ∝ √D) but reduces capacity per cyclone. Multicyclone designs use many small tubes in parallel to achieve both high efficiency and high capacity.

3. Lapple Model & Cut Diameter

The Lapple model is the most widely used method for predicting cyclone performance. It calculates the "cut diameter" - the particle size at which 50% of particles are collected - based on cyclone geometry and operating conditions.

Lapple Cut Diameter Equation

Lapple Model (1951): d_50 = √[9 × μ × b / (2 × π × N × v_i × (ρ_p - ρ_g))] Where: d_50 = Cut diameter, 50% collection efficiency (ft or m) μ = Gas dynamic viscosity (lb/ft·s or Pa·s) b = Inlet width (ft or m) N = Number of effective turns (typically 5-10) v_i = Inlet velocity (ft/s or m/s) ρ_p = Particle density (lb/ft³ or kg/m³) ρ_g = Gas density (lb/ft³ or kg/m³) In practical units: d_50 (microns) = 3.54 × √[μ (cP) × b (in) / (N × v_i (ft/s) × (ρ_p - ρ_g) (lb/ft³))] Number of turns correlation: N = v_i × [h + z/2] / (π × D × v_i) = [h + z/2] / (π × D) Where h = cylinder height, z = cone height, D = body diameter

Standard Cyclone Proportions

Dimension Symbol High Efficiency Conventional High Throughput
Body diameter D 1.0 1.0 1.0
Inlet height a/D 0.44 0.50 0.75
Inlet width b/D 0.21 0.25 0.375
Gas outlet diameter De/D 0.40 0.50 0.75
Vortex finder length S/D 0.50 0.60 0.875
Cylinder height h/D 1.40 2.00 1.50
Cone height z/D 2.50 2.00 2.50
Dust outlet diameter B/D 0.40 0.25 0.40

Pressure Drop Correlation

Cyclone Pressure Drop: Shepherd & Lapple correlation: ΔP = K × (ρ_g × v_i²) / 2 Where: ΔP = Pressure drop (lb/ft² or Pa) K = Pressure drop coefficient ρ_g = Gas density (lb/ft³ or kg/m³) v_i = Inlet velocity (ft/s or m/s) Pressure drop coefficient: K = 16 × (a × b) / De² Where a, b, De are inlet height, inlet width, and outlet diameter. In practical units: ΔP (inches H₂O) = K × ρ_g (lb/ft³) × v_i² (ft/s) / 1152 ΔP (psi) = K × ρ_g × v_i² / 27,680 Typical K values: - High efficiency design: K = 8-12 - Conventional design: K = 6-8 - High throughput design: K = 4-6 Typical inlet velocities: - Liquids: 20-70 ft/s - Solids: 50-80 ft/s - Optimal range: 50-70 ft/s

Cut Diameter Calculation Example

Example: Conventional Cyclone Sizing Given: Gas flow: 10,000 ACFM Gas density: 3.0 lb/ft³ Gas viscosity: 0.015 cP Particle density: 62.4 lb/ft³ (water droplets) Cyclone body diameter: D = 36 inches = 3.0 ft Cyclone proportions (conventional): b = 0.25 × D = 0.75 ft = 9 inches a = 0.50 × D = 1.5 ft h = 2.0 × D = 6.0 ft z = 2.0 × D = 6.0 ft De = 0.50 × D = 1.5 ft Step 1: Inlet area and velocity A_inlet = a × b = 1.5 × 0.75 = 1.125 ft² v_i = Q / A_inlet = (10,000/60) / 1.125 = 148 ft/s (Too high! Typical range is 50-80 ft/s) Step 2: Resize for v_i = 60 ft/s A_required = (10,000/60) / 60 = 2.78 ft² For a/b = 2: a = 2.36 ft, b = 1.18 ft D = b / 0.25 = 4.72 ft ≈ 57 inches Step 3: Calculate number of turns N = (h + z/2) / (π × D) = (2×4.72 + 4.72) / (π × 4.72) = 0.95 Use N = 5 (typical assumption for conventional cyclone) Step 4: Calculate cut diameter μ = 0.015 cP = 1.0 × 10⁻⁵ lb/ft·s d_50 = √[9 × 1.0×10⁻⁵ × 1.18 / (2π × 5 × 60 × (62.4 - 3.0))] d_50 = √[1.06×10⁻⁴ / 111,566] = 9.7 × 10⁻⁴ ft = 30 microns Step 5: Calculate pressure drop K = 16 × (2.36 × 1.18) / (0.5 × 4.72)² = 16 × 2.78 / 5.57 = 8.0 ΔP = 8.0 × 3.0 × 60² / 27,680 = 3.1 psi
Lapple model limitations: The Lapple model assumes ideal conditions and standard cyclone proportions. Actual performance may vary ±20% due to inlet configuration, particle properties, and operating conditions. Use manufacturer data when available for final design.

4. Efficiency Curves

Cyclone collection efficiency varies with particle size, following an S-shaped curve. The cut diameter (d_50) represents 50% efficiency; particles larger than d_50 are collected with higher efficiency, smaller particles with lower efficiency.

Grade Efficiency Curve

Lapple Grade Efficiency: η = 1 / [1 + (d_50/d)²] Where: η = Collection efficiency for particle diameter d d_50 = Cut diameter (50% efficiency point) d = Particle diameter This gives the characteristic S-curve: d/d_50 η (%) ------ ----- 0.25 5.9 0.50 20.0 0.75 36.0 1.00 50.0 1.25 61.0 1.50 69.2 2.00 80.0 3.00 90.0 5.00 96.2 10.00 99.0 Rule of thumb: - 2× cut diameter: ~80% efficiency - 3× cut diameter: ~90% efficiency - 5× cut diameter: ~96% efficiency

Overall Collection Efficiency

Overall Efficiency Calculation: For known particle size distribution: η_overall = Σ (η_i × w_i) Where: η_overall = Overall mass collection efficiency η_i = Grade efficiency for size fraction i w_i = Mass fraction of particles in size fraction i Example: Size Range Mass % η_i Contribution 0-10 μm 10% 15% 1.5% 10-20 μm 20% 35% 7.0% 20-40 μm 30% 65% 19.5% 40-80 μm 25% 88% 22.0% >80 μm 15% 98% 14.7% ---------------------------------------- Overall efficiency: 64.7% Note: Most of the collected mass comes from larger particles. Efficiency is strongly dependent on particle size distribution.

Factors Affecting Efficiency

Factor Effect on d_50 Effect on η Notes
Increase inlet velocity Decreases Increases But increases ΔP and re-entrainment risk
Decrease cyclone diameter Decreases Increases Main reason for multicyclone design
Increase gas density Increases Decreases High pressure reduces efficiency
Increase gas viscosity Increases Decreases High temperature reduces efficiency
Increase particle density Decreases Increases Solids separate better than liquids
Increase solids loading Decreases Increases Particle-particle interactions help

Re-entrainment

At excessive inlet velocities, separated particles can be re-entrained back into the gas stream:

  • Wall bounce: High-velocity particles bounce off wall instead of adhering
  • Vortex pickup: Inner vortex picks up particles from cone bottom
  • Saltation: Particles sliding down wall get re-entrained by high shear
Re-entrainment Velocity: Critical velocity for liquid re-entrainment: v_crit ≈ 0.1 × √(σ / ρ_g) Where: v_crit = Critical inlet velocity (ft/s) σ = Surface tension (lb/ft) ρ_g = Gas density (lb/ft³) For water at atmospheric conditions: v_crit ≈ 70-80 ft/s For hydrocarbon liquids: v_crit ≈ 50-60 ft/s (lower surface tension) Design guideline: Keep inlet velocity below 70 ft/s for liquids.
Efficiency optimization: Maximum efficiency occurs at an optimal inlet velocity - typically 50-70 ft/s. Below this, centrifugal force is insufficient. Above this, re-entrainment reduces net collection. Plot efficiency vs. velocity to find the optimum for your application.

5. Multicyclone Design

Multicyclone separators use multiple small cyclone tubes operating in parallel to achieve both high efficiency (from small diameter) and high capacity (from multiple tubes). This is the most common configuration for high-performance gas-liquid separation.

Multicyclone Principle

Why Multicyclones Work: Cut diameter scales with √D: d_50 ∝ √D Reducing cyclone diameter from 36" to 2": d_50 reduction = √(36/2) = √18 = 4.2× A 36" cyclone with d_50 = 30 microns becomes 2" tubes with d_50 = 7 microns Capacity scales with D²: Q_single ∝ D² For same total capacity: N_tubes = (D_single / d_tube)² N_tubes = (36/2)² = 324 tubes Multicyclone achieves: - Same total capacity as single large cyclone - 4× better cut diameter (7 vs 30 microns) - ~90% efficiency at 15 microns vs ~50%

Multicyclone Configurations

Axial flow tubes

Swirl Vanes

Fixed vanes induce rotation; compact, lower ΔP, moderate efficiency.

Tangential tubes

Mini-Cyclones

True cyclone geometry at small scale; highest efficiency, higher ΔP.

Tube bundle

Vertical Array

Multiple tubes mounted on tube sheet; common in scrubbers.

Skid mounted

Packaged Unit

Complete separator vessel with multicyclone internals; ready to install.

Multicyclone Design Parameters

Parameter Axial Flow Tangential Notes
Tube diameter 2-6 inches 1-4 inches Smaller = higher efficiency
Cut diameter 8-15 microns 3-8 microns At design conditions
Pressure drop 2-5 psi 4-10 psi Per tube bank
Inlet velocity 40-80 ft/s 50-100 ft/s Per tube
Liquid capacity Moderate Good With proper drainage

Multicyclone Sizing

Number of Tubes Required: N = Q_total / Q_tube Where: N = Number of cyclone tubes Q_total = Total actual gas flow (ACFM) Q_tube = Flow per tube at design velocity (ACFM) Flow per tube: Q_tube = v_i × A_inlet For 2" diameter axial flow tube: A_inlet = π × (2/12)² / 4 = 0.0218 ft² At v_i = 60 ft/s: Q_tube = 60 × 0.0218 = 1.31 CFM per tube Example: Size multicyclone for 5000 ACFM N = 5000 / 1.31 = 3817 tubes (at 60 ft/s) N = 5000 / (80 × 0.0218) = 2863 tubes (at 80 ft/s) Vessel diameter estimation: For triangular pitch with tube spacing = 1.25 × d_tube: A_vessel ≈ N × (1.25 × d_tube)² × 1.1 / cos(30°) D_vessel = √(4 × A_vessel / π)

Liquid Handling

  • Tube drainage: Separated liquid flows down tube walls to collection area below tube sheet
  • Liquid seal: Maintain liquid level below tube sheet to prevent gas short-circuiting
  • Re-entrainment baffle: Prevents high-velocity gas from picking up collected liquid
  • Surge capacity: Size sump for expected liquid slugs plus 2-5 minutes holdup
  • Drainage: Level control dumps liquid to prevent flooding tubes
Multicyclone advantage: A multicyclone with 2" tubes can achieve 99% efficiency at 10 microns, compared to ~50% for a single large cyclone. This makes multicyclones the preferred choice for compressor inlet scrubbers and other applications requiring high-efficiency mist removal.

6. Specialized Centrifugal Separators

Several specialized centrifugal separator designs are available for gas processing applications. These designs offer specific performance characteristics for different service requirements.

Single vs. Multi-Cyclone Comparison

Aspect Single Cyclone Multi-Cyclone
Advantages Less expensive
Efficient in small sizes		 Greater turndown ratio (5.625:1)
Very efficient in all sizes
Disadvantages Lower turndown ratio
Not efficient in large sizes		 More expensive
More complex

Cyclosep Separator

The Cyclosep is a centrifugal separator designed for gas-liquid or gas-solid separation with slug handling capability.

Parameter Specification
Application Gas/Liquid or Gas/Solid
Efficiency 98% removal of liquid droplets or solid particles ≥10 microns
Pressure Drop Less than 1% of absolute line pressure
Liquid/Solid Loading Handles liquid slugs
Turndown Ratio 3:1
Coalescer None
Solids Service Outlet tube extended downward; bottom head replaced with cone

Ready to use the calculator?

→ Launch Calculator

Centrifugal Tuyere Separator

The Centrifugal Tuyere separator is designed for compressor interstage and discharge service where high efficiency and low pressure drop are critical.

Parameter Specification
Application Gas/Liquid or Gas/Solid
Liquid Efficiency 99% removal of liquid droplets ≥10 microns
Solid Efficiency 99% removal of solid particles ≥15 microns
Pressure Drop Less than 1% of absolute line pressure
Liquid/Solid Loading 5% by weight maximum
Turndown Ratio 3:1
Coalescer None
Configurations Available in numerous standard configurations

Size a Centrifugal Tuyere separator:

Open Centrifugal Tuyere Calculator

Exhaust Head Separator

A specialized tuyere separator designed for gas venting to atmosphere, typically at low pressures below 50 psig.

Parameter Specification
Application Gas/Liquid (atmospheric venting)
Efficiency 99% removal of liquid droplets ≥10 microns
Pressure Drop Less than 1% of absolute line pressure
Liquid Loading 10% by weight
Turndown Ratio 3:1
Operating Pressure Typically below 50 psig

Multi-Cyclone Separator

High-efficiency multi-cyclone scrubbers for natural gas and chemical processing applications.

Parameter Specification
Application Gas/Liquid or Gas/Solid
Efficiency at 8+ microns 100% removal
Efficiency at 5-8 microns 99% removal
Pressure Drop Varies in direct proportion to ratio of absolute pressure
Liquid Loading 0.5-2.0 GPM per tube
Solid Loading 0.25 lbs/min per tube
Turndown Ratio 5.625:1
Options Slug handling design available; Tube plugs for extended turndown

Internal Purifiers / Receivers

Centrifugal separation devices installed inside receiver vessels or process equipment.

Model Configuration Liquid Efficiency Solid Efficiency
Model FR Downflow, Single Stage 98% at 10 microns 95% at 10 microns
Model FRXD Downflow, Two Stage 99% at 10 microns 99% at 10 microns
Model AFE Upflow, Two Stage 99% at 10 microns 99% at 10 microns
Model AFEXD Upflow, Two Stage 99% at 10 microns 99% at 10 microns

Vertical Gas Separator (VGS)

The Vertical Gas Separator is designed for gas-liquid separation with slug handling capability. It's commonly used at compressor suction for bulk liquid removal.

Parameter Specification
Application Gas/Liquid
Efficiency 100% removal of droplets ≥8 microns, <0.1 gal/MMSCF
Pressure Drop Generally less than 1 PSI
Liquid Loading Slugging OK; internal design limits vane loading to 15% by weight
Turndown Ratio None
Coalescer Available (improves to 100% at 3 microns)
Other Features Integral liquid/liquid separation available

Size a production separator:

Open Separator Sizing Calculator

Three-Phase Separator

Three-phase separators handle simultaneous gas-oil-water separation with controlled interface levels.

Parameter Specification
Application Gas/Liquid/Liquid (Gas-Oil-Water)
Efficiency 100% removal of liquid droplets ≥8 microns in gas phase
Pressure Drop Generally less than 1 PSI
Liquid Loading Slugging OK; internal design limits vane loading to 15% by weight
Turndown Ratio None
Coalescer Available
Other Features Foam breakers and wave breakers available; two sets of controls (oil and water levels)

Size a three-phase separator:

Open Three-Phase Separator Calculator
Centrifugal force principle: All centrifugal separators operate on the same fundamental equation: Fc = mV²/R. The centrifugal force is inversely proportional to the radius of curvature, which is why smaller diameter devices achieve higher separation efficiency. Pressure drop is a fixed number of velocity heads: ΔP = C × ρ × V².

7. Design Procedure

Cyclone separator design involves selecting the appropriate configuration, sizing for required efficiency and capacity, and verifying pressure drop is acceptable.

Design Steps

Cyclone Design Procedure: STEP 1: Define Requirements - Gas flow rate (ACFM at operating conditions) - Gas properties (density, viscosity) - Particle properties (density, size distribution) - Required efficiency or outlet quality - Allowable pressure drop STEP 2: Select Configuration - Single cyclone: Low efficiency OK, low ΔP required - Multicyclone: High efficiency needed - Two-stage: Very high efficiency or wide size range STEP 3: Determine Cut Diameter Required From efficiency curve, find d_50 for target efficiency: - 80% efficiency: d_50 ≈ d_target / 2 - 90% efficiency: d_50 ≈ d_target / 3 - 95% efficiency: d_50 ≈ d_target / 4.5 STEP 4: Size Cyclone/Tubes Use Lapple equation to find required dimensions: - Select cyclone proportions (high-eff or conventional) - Calculate diameter for target d_50 and velocity - Verify inlet velocity in acceptable range (50-70 ft/s) STEP 5: Calculate Number of Tubes (multicyclone) N = Q_total / (v_i × A_tube) STEP 6: Calculate Pressure Drop ΔP = K × ρ_g × v_i² / 2 Verify ΔP is acceptable; resize if needed STEP 7: Size Vessel - Diameter: Accommodate tube bundle + shell clearance - Height: Inlet plenum + tubes + collection sump - Internals: Tube sheet, baffles, level control

Design Example: Compressor Inlet Scrubber

Example: Multicyclone Scrubber Requirements: Gas flow: 25 MMSCFD at 500 psia, 100°F Gas MW: 18, Z = 0.92 Liquid loading: 2 bbl/MMSCF (water + condensate) Target: 99% removal of droplets > 10 microns Max ΔP: 5 psi STEP 1: Calculate actual flow Q_std = 25 × 10⁶ / 1440 = 17,361 SCFM ρ_std = 18 × 14.7 / (10.73 × 520) = 0.0474 lb/ft³ ρ_op = ρ_std × (500/14.7) × (520/560) / 0.92 = 1.63 lb/ft³ Q_act = 17,361 × 0.0474 / 1.63 = 505 ACFM STEP 2: Select configuration - Need 99% at 10 microns → multicyclone required - From efficiency curve: d_50 ≈ 10/4.5 = 2.2 microns STEP 3: Select tube size For d_50 = 2.2 microns, need small tubes Try 1.5" diameter tangential cyclone tubes Typical d_50 for 1.5" tube ≈ 3-5 microns May need two stages for 2.2 micron cut STEP 4: Size first stage (d_50 = 5 microns) Select 2" axial flow tubes At v_i = 70 ft/s: A_tube = π × (2/12)² / 4 = 0.0218 ft² Q_tube = 70 × 0.0218 × 60 = 91.6 ACFM/tube N = 505 / (91.6/60) = 331 tubes STEP 5: Calculate pressure drop K = 6 for axial flow ΔP = 6 × 1.63 × 70² / 27,680 = 1.7 psi ✓ STEP 6: Calculate efficiency First stage d_50 = 5 microns At 10 microns: η = 1 / [1 + (5/10)²] = 80% Not sufficient - add second stage Second stage with 1.5" tangential tubes: d_50 ≈ 3 microns At 10 microns: η = 1 / [1 + (3/10)²] = 92% Combined efficiency: η_total = 1 - (1 - 0.80)(1 - 0.92) = 98.4% Close to 99% target ✓ Total ΔP: 1.7 + 3.5 = 5.2 psi (slightly over, acceptable) STEP 7: Vessel sizing Tube bundle OD ≈ 24" Vessel ID = 30" (allows clearance) Height = 4' inlet plenum + 3' tubes + 3' sump = 10'

Common Design Issues

  • Undersized tubes: Too few tubes = excessive velocity = re-entrainment
  • Poor liquid drainage: Flooded tubes lose efficiency completely
  • Inlet maldistribution: Uneven flow to tubes reduces efficiency
  • Plugging: Solids accumulation in small tubes; need cleanout provisions
  • Erosion: High-velocity abrasive particles wear tube walls
  • Pressure drop creep: Fouling increases ΔP over time
Design verification: Always verify cyclone performance with manufacturer's published data when available. The Lapple model provides good estimates, but actual performance depends on specific tube geometry, inlet conditions, and particle characteristics. Request performance curves for your operating conditions.

8. Compressor Station Separator Selection

Selecting the right separator type for each position in a compressor station is critical for protecting equipment and ensuring efficient operation. Each position has different requirements based on flow conditions, contaminants, and downstream equipment sensitivity.

Compressor Station Separator Positions

OUT IN VGS SUCTION Bulk Liquid Removal 1st STAGE COMPRESSOR TUYERE SEP INTERSTAGE Condensate & Cooling 2nd STAGE COMPRESSOR FILTER SEP or Ultrasep DISCHARGE Final Polish & Protection → → → → → Low P Med P Hot High P High P

Compressor Station Separator Selection Guide

Separator Selection by Position

Position Recommended Separator Types Primary Function Key Considerations
Suction • Vertical Gas Separator (VGS)
• Multi-Cyclone Scrubber
• Filter/Separator 		Bulk liquid and solids removal before compression • Highest liquid loading
• Must handle slugs
• Protects 1st stage cylinders
Interstage
(Between 1st & 2nd Stage)		 • In-Line Vane Separator
• Centrifugal Tuyere Separator 		Remove condensate from compression cooling • Hot gas from compression
• Liquid condensing as gas cools
• Low pressure drop critical
Discharge • In-Line Vane Separator
• Centrifugal Tuyere Separator
• Filter/Separator
• Ultrasep 		Final polishing for pipeline or downstream equipment • Highest pressure
• Finest mist removal
• Meets pipeline or custody specs

Why Different Separators at Each Position?

Suction Position

High Liquid, Slug Handling

Suction gas often contains free liquids and may experience slugging from gathering systems. VGS and multi-cyclone designs handle high liquid loading and protect first-stage compressor cylinders from liquid damage.

Interstage Position

Low ΔP, Condensate Removal

After first-stage compression, gas is hot. As it cools in the interstage cooler, liquids condense. Centrifugal tuyere and in-line vane separators provide efficient removal with minimal pressure drop to preserve compression efficiency.

Discharge Position

Fine Mist, High Quality

Discharge gas must meet pipeline or custody transfer specifications. Filter/separators and Ultrasep provide the finest mist removal (100% at 3 microns) for maximum outlet gas quality.

Compressor Protection Requirements

Why Separator Selection Matters: Compressor damage from liquid carryover includes: • Cylinder scoring and wear (reciprocating) • Valve damage and failure • Piston ring erosion • Hydrostatic lock (catastrophic) Compressor damage from solids includes: • Valve seat erosion • Cylinder bore scoring • Packing wear • Rod and piston damage TYPICAL INLET SPECIFICATIONS: • Liquid: < 0.1 gal/MMSCF (custody transfer) • Liquid: < 1.0 gal/MMSCF (compressor protection) • Solids: < 15 microns @ 99% removal SEPARATOR EFFICIENCY REQUIREMENTS BY POSITION: • Suction: 99% @ 10-15 microns (bulk removal) • Interstage: 99% @ 10 microns (condensate) • Discharge: 100% @ 3-8 microns (final polish)

Quick Selection Guide

If You Need... Use This Separator Calculator Link
Slug handling + high efficiency Vertical Gas Separator (VGS) Separator Sizing
Maximum efficiency (100% @ 8μm) Multi-Cyclone Scrubber Cyclone Separator
Low ΔP + in-line installation Centrifugal Tuyere Centrifugal Tuyere
Finest mist (100% @ 3μm) Filter/Separator Filter Separator
Fuel gas conditioning Fuel Gas Filter/Separator Fuel Gas Filter
Help choosing separator type Type Selector Wizard Separator Selector
Design tip: When in doubt, use the Separator Type Selector wizard to get a recommendation based on your specific application, operating conditions, and constraints. The wizard considers all factors and recommends the optimal separator type with match percentages.

Ready to use the calculator?

→ Launch Calculator