separator sizing -...
TRANSCRIPT
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SEPARATOR SIZING
Theory and Calculation
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SEPARATION THEORY
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Gas/Liquid Separation Theory
n Liquid droplet settling¨ Liquid drops separated from gas phase when its
velocity reach terminal (settling) velocity¨ Terminal velocity when Drag Force = Buoyant Force ¨ Drag Force depends on Drag Coefficient
n Re < 10
n Re > 1000
DC
Re24
=DC
34.0Re
3Re24
2/1 ++=DC
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Cont.
¨ Terminal velocity equations for different conditions
n Re < 10
n Re > 1000
¨ The value of is estimated and then used in the calculation of gas capacity constraint
( )µ
26 ..1078.1 mt
dGSV
∆×=
−
2/1
0199.0
−=
D
m
g
glt C
dV
ρρρ
DC
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Cont.
n But in production facility, flow almost always has Re > 1000. So how to find ?¨ Start with Re >>1000 so that ~ 0.34¨ Use = 0.34 to calculate ¨ Use to calculate Re¨ Use Re to calculate new ¨ Repeat process until values beginning to be the same¨ Use this latest value in the gas capacity equation…
DC
DCDC
DC
DC
tV
DC
tV
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Cont.
n Liquid retention time¨ Retention time is average time a liquid molecule is
retained in vessel¨ To ensure liquid and gas reach equilibrium so that
gas molecule can evolve from liquid phase¨ Retention time = Volume of liquid storage in vessel
Liquid flow rate¨ Usually 1 to 3 minutes
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Oil/Water Separation Theory
n Oil drop/water drop settling¨ Flow around oil drops in water or water drops in oil is
laminar – so water droplets fall at their terminal velocity
n Oil/water retention time¨ Need certain amount of oil storage so that oil reaches
equilibrium, entrained gas liberated, and ‘free’ water coalesced to fall into water storage
¨ Need certain amount of water storage for entrained large droplets of oil have time to coalesce and rise to oil-water interface
¨ Retention time 3 – 30 minutes
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SEPARATOR SIZING: TWO-PHASE SEPARATOR
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General sizing procedure
CALCULATE1. Gas capacity constraint
¨ Minimum vessel diameter OR Relationship between diameter and effective length that satisfy gas capacity constraint
2. Liquid capacity¨ Relationship between diameter and effective length OR height
that satisfy liquid capacity constraint3. Seam-to-seam length, Lss
¨ For Gas capacity and Liquid capacity4. Slenderness ratio
¨ For each Lss calculated
SELECT reasonable vessel size (diameter and length)!
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VERTICAL SEPARATOR
Liquid capacity
Seam-to-seam Length Lss
Diameter d
Height h
Liquid Outlet
InletGas capacity
Mist extractor
Gas outlet
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Vertical separator sizing procedure
1. Determine CD using iterative procedure
2. Calculate d for gas capacity constraint using
3. Calculate d2h for liquid capacity constraint
2/1
2 5040
−
=
m
D
gl
gg
dC
PTZQ
dρρ
ρ
12.0
2 lrQthd =
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Cont. vertical4. Set retention time tr to be 1, 2 and 3 minutes
(usual case)
5. For each tr , calculate and tabulate values ofa) d b) hc) Lss
§ OD < 36”à
§ OD > 36”à
d) Slenderness Ratio (SR), (12)Lss/d
1276+
=h
Lss
1240min ++= dhLss
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Cont. vertical
n From table, select possible choices of separator size (d x Lss) based on the values of (12)Lss/d Ø Select (12)Lss/d values range 3 – 4Ø d values must be greater than the calculated minimum
vessel diameter for gas capacity constraint (Step 2)
q Your final selection should be based on your judgment on the costs of each possible separator
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Example of separator selection
Possible size
36” x 10’
30” x 10’
30” x 10’ or30” x 8’
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HORIZONTAL SEPARATOR
Liquid capacity (50%)
Gas capacity (50%)
Seam-to-seam Length Lss
Effective Length Leff
Inlet Liquid Outlet
Gas molecule flowing at average gas velocity, Vg
Liquid droplet dropping at settling velocity Vt relative to gas phase
Gas-oil interface
Diameter d
Gas outlet
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Horizontal separator sizing procedure
1. Determine CD using iterative procedure
2. Calculate dLeff for gas capacity constraint
3. Calculate d2Leff for liquid capacity constraint
7.0
2 lreff
QtLd =
2/1
P420
=
− mdCTZQ
dL Dggeff
gl ρρ
ρ
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Cont. horizontal
4. Set retention time tr to be 1, 2 and/or 3 minutes (usual case)
5. For each tr , calculate and tabulate values of a) d b) Leff for
Ø Gas capacity à from equation Step 2Ø Liquid capacity à from equation Step 3
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Cont. horizontal
c) Lss for Ø Gas Capacityà
Ø Liquid capacity à
d) Slenderness ratio (SR), (12)Lss/d
12dLL effss +=
effss LL34=
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Cont. horizontal
n From table, compare the values of Leff for each gas and liquid capacity that governs the design of the separator¨ The one with larger required length governs
n Then, select possible choices of separator size (d x Lss) based on the values of SR Ø Select SR values range 3 – 5Ø Lss values selected are the one that governs the design
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Example of separator selection
1.66.23.70.848
2.17.44.90.942
39.16.61.136
5.112.79.51.3303
9.919.914.91.724
17.128.521.4220
33.544.733.52.516
SRLiquid
LssGas Lss
Liquid LeffGas Leffdtr
Horizontal Separator ExampleDiameter vs. Length
Liquid capacity constraint governs since it has the largest required length
Use the liquid Lss valuesto select separator size
Possible size
36” X 10’
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That’s basically it.