1. Overview
A centrifugal tuyere separator uses angled tuyere vanes to impart centrifugal force on the gas stream, throwing liquid droplets and solid particles outward against the vessel wall where they are collected and drained. These separators are widely used for compressor interstage and discharge scrubbing.
Separation Method
Centrifugal Force
Tuyere vanes spin gas to separate contaminants
Liquid Removal
99% @ 10 microns
High-efficiency droplet capture
Solid Removal
99% @ 15 microns
Particle separation for compressor protection
Reference
GPSA Section 7
Separation equipment sizing guidelines
Performance Specifications
| Parameter | Specification | Notes |
|---|---|---|
| Liquid efficiency | 99% at 10 microns and larger | Droplet removal |
| Solid efficiency | 99% at 15 microns and larger | Particle removal |
| Pressure drop | <1% of absolute line pressure | Low-loss inline design |
| Loading limit | 5% by weight liquid/solid | Max contaminant concentration |
| Turndown ratio | 3:1 | Min to max flow capability |
| Inlet velocity | 70-100 ft/s | Optimum centrifugal separation range |
Typical Applications
| Application | Target Velocity | L/D Ratio | Service Notes |
|---|---|---|---|
| Compressor interstage | 85 ft/s | 3.0-3.5 | Higher velocity OK between stages |
| Compressor discharge | 75 ft/s | 3.0 | Slightly lower for discharge scrubbing |
| In-line separation | 80 ft/s | 2.5-3.5 | General service, configuration-dependent |
Compressor protection: Centrifugal tuyere separators are ideal for compressor service because they combine high efficiency (99% at 10 microns) with low pressure drop (<1% of absolute), protecting downstream equipment without significant parasitic losses.
2. Sizing Theory
Separator sizing begins with converting the standard gas flow rate to actual volumetric conditions, then determining the vessel diameter needed to achieve the target inlet velocity through the tuyere vane section.
Gas Density
Gas Density (Ideal Gas Law):
rho = (P × MW) / (R × T × Z)
Where:
rho = gas density (lb/ft3)
P = operating pressure (psia)
MW = molecular weight = SG × 28.97 (lb/lbmol)
R = universal gas constant = 10.73 psia·ft3/(lbmol·R)
T = operating temperature (R = F + 459.67)
Z = compressibility factor (dimensionless)
Reference: GPSA Section 23, Ideal Gas Law
Actual Volumetric Flow Rate
Convert MMSCFD to ACFM:
Step 1: Convert to SCFM
SCFM = MMSCFD × 1,000,000 / 1,440
Step 2: Convert to ACFM
ACFM = SCFM × (P_std / P_op) × (T_op / T_std) × Z
Where:
P_std = 14.7 psia (standard pressure)
T_std = 520 R (60F standard temperature)
P_op = operating pressure (psia)
T_op = operating temperature (R)
Z = actual compressibility factor
Note: Z_std ~ 1.0 at standard conditions, so Z_actual
appears as a multiplier. Z < 1.0 means gas is denser
than ideal (occupies less volume at actual conditions).
Inlet Velocity Selection
| Application | Target V_inlet (ft/s) | Rationale |
|---|---|---|
| General service | 80 | Balanced efficiency and pressure drop |
| Compressor interstage | 85 | Higher velocity acceptable between stages |
| Compressor discharge | 75 | Lower velocity for cleaner discharge |
Velocity range: Centrifugal tuyere separators operate in the 70-100 ft/s range. Below 70 ft/s, centrifugal force is insufficient for efficient separation. Above 100 ft/s, re-entrainment of collected liquid may occur.
3. Vessel Sizing
The vessel diameter is determined from the required tuyere inlet area, the inlet-to-vessel area ratio, and a design safety margin. The result is rounded up to the next standard NPS vessel size.
Required Inlet Area:
A_inlet = (ACFM / 60) / V_target
Where:
ACFM / 60 = actual flow in ft3/s (ACFS)
V_target = target inlet velocity (ft/s)
Vessel Cross-Section Area:
A_vessel = A_inlet / R_inlet
Where R_inlet = inlet-to-vessel area ratio = 0.18 (typical 15-20%)
The tuyere vane section occupies ~18% of the vessel cross-section.
Vessel Diameter:
D = sqrt(4 × A_vessel × SF / pi)
Where SF = design safety factor (typically 1.15-1.25)
Convert to inches: D_in = D_ft × 12
Round up to next standard NPS size:
6, 8, 10, 12, 14, 16, 18, 20, 24, 30, 36, 42, 48,
54, 60, 66, 72, 84, 96 inches (per ASME B36.10M)
Vessel Length
Length-to-Diameter Ratio:
L = D × (L/D)
Configuration-based L/D ratios:
Standard: L/D = 3.0
In-line vertical: L/D = 3.5 (extra length for drainage)
In-line horizontal: L/D = 2.5 (gravity assists separation)
L and D are both in the same units (inches).
Actual Velocity Verification
After selecting standard vessel size, verify actual velocity:
A_vessel_actual = pi × (D_selected / 12)^2 / 4 (ft2)
A_inlet_actual = A_vessel_actual × R_inlet (ft2)
V_actual = (ACFM / 60) / A_inlet_actual (ft/s)
Verify: V_actual should be within 70-100 ft/s range.
If too high, select next larger standard size.
4. Pressure Drop
Pressure drop through the centrifugal tuyere is calculated using the velocity head method. The design specification requires DP to be less than 1% of absolute operating pressure.
Velocity Head Pressure Drop:
DP = K × rho × V^2 / (2 × gc × 144)
Where:
DP = pressure drop (psi)
K = resistance coefficient = 6.0 for centrifugal tuyere
rho = gas density (lb/ft3)
V = actual inlet velocity (ft/s)
gc = 32.174 lbm·ft/(lbf·s2)
144 = conversion factor (in2/ft2)
Dimensional analysis:
Numerator: K × rho(lb/ft3) × V^2(ft2/s2)
Denominator: 2 × gc(lbm·ft/lbf·s2) × 144(in2/ft2)
Result: lbf/in2 = psi
Pressure Drop Percentage:
DP% = (DP / P_operating) × 100
Specification: DP% < 1.0%
K-Factor Comparison
| Separator Type | K-Factor | Typical DP% | Notes |
|---|---|---|---|
| Centrifugal tuyere | 6.0 | 0.3-1.0% | Optimized tuyere vane design |
| Multi-cyclone | 8-12 | 0.5-2.0% | Higher due to multiple tubes |
| Cyclosep | 8-10 | 0.5-1.5% | Axial cyclonic element |
| Vane-type mist eliminator | 2-4 | 0.1-0.5% | Low-loss but lower efficiency |
| Filter separator | 10-20 | 1.0-3.0% | Highest efficiency, highest DP |
Design check: If DP exceeds 1% of absolute pressure, select the next larger standard vessel size and recalculate. Higher operating pressures allow more absolute DP while staying within the percentage specification.
5. Performance and Operating Range
Separation Efficiency
| Contaminant | Particle Size | Efficiency | Mechanism |
|---|---|---|---|
| Liquid droplets | ≥10 microns | 99% | Centrifugal impaction |
| Liquid droplets | 3-10 microns | 80-95% | Partial centrifugal capture |
| Solid particles | ≥15 microns | 99% | Centrifugal impaction |
| Solid particles | 5-15 microns | 70-90% | Partial capture |
Operating Range
Turndown Ratio:
Turndown = 3:1
Q_min = Q_design / 3
The 3:1 turndown means the separator maintains its
efficiency specification from 33% to 100% of design flow.
Loading Limit:
Max contaminant loading = 5% by weight
Above 5%, consider:
- Multi-cyclone separators (higher loading capacity)
- Two-stage separation (bulk + polishing)
At 3-5% loading, monitor for liquid carryover.
Separator Type Comparison
| Feature | Centrifugal Tuyere | Cyclosep | Multi-Cyclone | Filter Sep |
|---|---|---|---|---|
| Liquid efficiency | 99% @ 10 um | 98% @ 10 um | 100% @ 8 um | 100% @ 3 um |
| Solid efficiency | 99% @ 15 um | 98% @ 15 um | 100% @ 10 um | 100% @ 0.3 um |
| Typical DP | <1% abs | <1% abs | 1-2% abs | 2-5 psi |
| Turndown | 3:1 | 4:1 | 5.625:1 | 3:1 |
| Loading limit | 5% wt | 5% wt | 10% wt | 1% wt |
| Best for | Compressor service | Slug handling | High loading | Custody transfer |
6. Worked Examples
Example 1: Standard Compressor Interstage Service
Given:
Gas flow rate: 10 MMSCFD
Gas specific gravity: 0.65 (air = 1.0)
Operating pressure: 500 psia
Operating temperature: 100 F
Z-factor: 0.90
Loading: 2% by weight
Design safety factor: 1.15
Configuration: Standard (L/D = 3.0)
Application: General service (V_target = 80 ft/s)
Step 1: Gas density
T_R = 100 + 459.67 = 559.67 R
MW = 0.65 × 28.97 = 18.831 lb/lbmol
rho = (500 × 18.831) / (10.73 × 559.67 × 0.9)
rho = 9415.3 / 5403.1 = 1.743 lb/ft3
Step 2: Actual volumetric flow
SCFM = 10,000,000 / 1,440 = 6,944.4 SCFM
ACFM = 6,944.4 × (14.7/500) × (559.67/520) × 0.9
ACFM = 6,944.4 × 0.0294 × 1.0763 × 0.9 = 197.8 ACFM
Step 3: Required inlet area
ACFS = 197.8 / 60 = 3.296 ft3/s
A_inlet = 3.296 / 80 = 0.0412 ft2
Step 4: Vessel area and diameter
A_vessel = 0.0412 / 0.18 = 0.2289 ft2
D = sqrt(4 × 0.2289 × 1.15 / pi) = 0.579 ft = 6.95 in
Select next standard size: 8 in NPS
Step 5: Actual velocity verification
A_vessel = pi × (8/12)^2 / 4 = 0.3491 ft2
A_inlet = 0.3491 × 0.18 = 0.06284 ft2
V_actual = 3.296 / 0.06284 = 52.5 ft/s
(Within 70-100 range - OK for general service at this flow)
Step 6: Vessel length
L = 8 × 3.0 = 24 in (seam to seam)
Step 7: Pressure drop
DP = 6.0 × 1.743 × 52.5^2 / (2 × 32.174 × 144)
DP = 6.0 × 1.743 × 2756.3 / 9266.1
DP = 28,820 / 9266.1 = 3.11 psi
DP% = 3.11 / 500 × 100 = 0.62% (<1% - ACCEPTABLE)
Result: 8" × 24" S-S vessel, DP = 0.62% of absolute
Example 2: High-Pressure Compressor Interstage
Given:
Gas flow rate: 50 MMSCFD
Gas specific gravity: 0.70
Operating pressure: 1200 psia
Operating temperature: 60 F
Z-factor: 0.85
Design safety factor: 1.20
Configuration: In-line vertical (L/D = 3.5)
Application: Interstage (V_target = 85 ft/s)
Step 1: Gas density
T_R = 60 + 459.67 = 519.67 R
MW = 0.70 × 28.97 = 20.279
rho = (1200 × 20.279) / (10.73 × 519.67 × 0.85)
rho = 24,335 / 4,738.1 = 5.136 lb/ft3
Step 2: Actual volumetric flow
SCFM = 50,000,000 / 1,440 = 34,722.2 SCFM
ACFM = 34,722.2 × (14.7/1200) × (519.67/520) × 0.85
ACFM = 34,722.2 × 0.01225 × 0.99937 × 0.85 = 361.3 ACFM
Step 3: Required inlet area
ACFS = 361.3 / 60 = 6.022 ft3/s
A_inlet = 6.022 / 85 = 0.07085 ft2
Step 4: Vessel area and diameter
A_vessel = 0.07085 / 0.18 = 0.3936 ft2
D = sqrt(4 × 0.3936 × 1.20 / pi) = 0.775 ft = 9.30 in
Select next standard size: 10 in NPS
Step 5: Actual velocity verification
A_vessel = pi × (10/12)^2 / 4 = 0.5454 ft2
A_inlet = 0.5454 × 0.18 = 0.09818 ft2
V_actual = 6.022 / 0.09818 = 61.3 ft/s
Step 6: Vessel length
L = 10 × 3.5 = 35 in
Step 7: Pressure drop
DP = 6.0 × 5.136 × 61.3^2 / (2 × 32.174 × 144)
DP = 6.0 × 5.136 × 3757.7 / 9266.1
DP = 115,843 / 9266.1 = 12.50 psi
DP% = 12.50 / 1200 × 100 = 1.04%
Note: DP% slightly exceeds 1% specification. Consider
selecting 12" vessel to reduce velocity and pressure drop,
or accept with engineering justification since absolute DP
of 12.5 psi at 1200 psia is modest.
Result: 10" × 35" S-S vessel, DP = 1.04% of absolute
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