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Vertical Vessel
Without Mesh Mist Eliminator
D-2002
Design and Principles
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Content

1 Description

2 Design Procedure
2.1 Select proper Orientation
2.2 Select and Size proper Inlet Device, Inlet and Outlet ID
2.3 Calculate Vessel Diameter
2.4 Calculate Vessel Height
2.5 Select and Size Manholes, Vent, Drain, Vortex Breaker
2.6 Select a well-designed mist eliminator pad
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Description

The objective of this vessel is to separate liquid particle from the gas. The vessel is

located after Heat exchanger to separate condensate produced from gas stream.

Operating Parameters
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Design Procedure

1. Select proper Orientation

2. Select and Size proper Inlet Device, Inlet and Outlet ID

3.Calculate Vessel Diameter

4. Calculate Vessel Height

5.Select and Size Manholes, Vent, Drain, Vortex Breaker

1st Step: Select proper orientation

Since the application is gas dominant a vertical vessel is selected.

Since no downstream requirement is emphasized no de-mister pad is needed.

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nd
2 Step: Select and Size proper Inlet Device

Half Pipe has proven itself to be not only effective in large capacities but cost-effective as well

and in many applications is preferred to Diffuser whose performance is superior but too costly.

It is also necessary to maintain the inlet velocity head, J, within proper limits for the selected

inlet device to insure good gas distribution and minimum liquid shattering.

Where,

J = (ρV²)
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The maximum mixed phase velocity head range used in the industry guidelines varies for the
different inlet devices. Some typical maximums are:
•6000-9000 max. typ, up to 15 000 max kg/m s2 for diffuser distributor
•975-2250 max kg/m. s2 for no inlet distributor
•1500-3750 max kg/m. s2 for inlet half pipe or elbow distributor
•1500-3750 max kg/m. s2 for v-baffle or other simple inlet diverter designs
In addition, some users limit the inlet vapor phase velocity to 9 m/s or 18 m/s. The velocity
should always be below the erosion velocity for the service.
In order to calculate head velocity, at first, we need to perform the followings:
1. Estimation of inlet nozzle ID; Consider inlet pipe ID near the vessel as first and best
estimation.
2. Calculate ρmixture and subsequently Vmixture
3. Calculate J by multiplying ρmixture × (Vmixture)^2 and compare it with the last-page criterion.

Parameter Value Value Unit

Estimated ID 34 36 inch

Nozzle Area 0.58 0.65 m2

ρmixture 10.31 10.31 kg/m3

Vmixture 21.38 19.07 m/s

J 4714 3751 kg/m.s2

Criterion 3750 3750 kg/m.s2

The licensor has selected 34 inch probably due to inlet piping diameter match the velocity

requirement of the inlet to the separator 10 pipe diameters upstream of the separator to

provide a flow regime which is fully developed before entering the separator.
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Vapor Outlet Section

The sizing of the vapor outlet nozzle should be such that given the above placement of the

mesh pad, the velocity is not high enough to cause channeling of the gas through the mesh

pad. The nozzle outlet size is typically based on the lesser of that required for piping pressure

drop, or a maximum velocity head criterion. Typical ranges for the maximum velocity head

allowed for the vapor outlet are 4500–5400 kg/m • s2. In addition, some users limit the

absolute velocity to 18 m/s. The pipe size can be decreased to the appropriate size based on

pressure drop considerations, 5-10 pipe diameters downstream of the separator, as required.

Parameter Value Value Unit

Estimated ID 30 34 36 inch

Area 0.45 0.58 0.65 m2

Vg 27.4 21.36 19.05 m/s

ρVg2 7367 4465 3552 Kg/m. s2

Criterion 4500 4500 4500 Kg/m. s2

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Liquid Outlet Nozzle

Many users limit the liquid outlet nozzle velocity based on pump suction line criteria

Parameter Value Value Value Unit

Estimated ID 3 4 6 inch

Area 0.004 0.008 0.018 m2

Vl 1.64 0.92 0.41 m/s

Criterion Max 1.2 Max 1.2 Max 1.2 m/s

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3rd Step: Calculate Vessel Diameter

Each and every licensor and company has developed a design basis procedure for sizing

vessels. In this article, a GPSA-based method, Foster-Wheeler-based method and the

Licensor method will be explored.

GPSA

1. Use the following equation and next-page K-values to calculate terminal velocity

According to GPSA, thanks to the fact that a vertical vessel without demister pad has
been chosen, a K value of 0.046 is selected.
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Parameter Value Unit

ρl 903 kg/m3

ρv 9.78 kg/m3

Kselected 0.046

Ug 0.43 m/s

Qg 12.51 m3/s

ID 6022 mm

Required-ID 6022 mm

Selected-ID 6000 mm

Notes

For ID calculation, the following equation has been utilized.

The selected ID is not in harmony with the Licensor selected ID, which is 3750 mm.
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Foster-Wheeler

The basis of sizing is the critical velocity Vc (m/s)

The maximum gas velocity is K×Vc

K is a coefficient depending on the service, and the use or the absence of wire mesh.
Recommended K values are given hereafter for different services.

If a vane pack internal is used, the recommended K value is 3.3.

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Parameter Value Unit

ρl 903 kg/m3

ρv 9.78 kg/m3

Kselected 1.7

Vc 0.45 m/s

Vmax 0.78

Qg 12.51 m3/s

ID 4521 mm

Required-ID 4521 mm

Selected-ID 4500 mm
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Svercheck-Method
1. Use the following equation and next-page K-values to calculate terminal velocity

Notes
For ID calculation, the following equation has been utilized.

Uv = 0.75 UT
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Svercheck Method-K value

K = 0.35 – 0.01 (364.5-100/100) = 0.3235
For vertical vessel without mist eliminator
Kselected = 0.32/2 = 0.16
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Parameter Value Unit

ρl 903 kg/m3

ρv 9.78 kg/m3

Kselected 0.16

Ug 1.52 m/s

Uv 1.14

Qg 12.51 m3/s

ID 3728 mm

Required-ID 3728 mm

Selected-ID 3750 mm
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Explanation, Comparison and Discussion

Different criteria have been used to size the vary separator and the difference in

diameter results stem from the selected K that each licensor or criterion has set based

on their experience. The following table provides the K value and diameter calculated.

Method GPSA FW Svercheck Licensor

K-Value 0.046 0.0816 0.12 0.12

Diameter 6000 4000 3750 3750

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4th Step: Height Calculation

Each and every licensor and company has developed a design basis procedure for sizing
vessels. In this article, a GPSA-based method, Foster-Wheeler-based method and the Licensor
method will be explored.
GPSA
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Retention/Surge Time
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Height GPSA LICENSOR Unit

Elements

H1 450 500 mm

H2 100 400 mm

H3 1500 695 mm

H4 865 865 mm

H5 3000 2400 mm

H6 - - mm

H7 - - mm

HT 5915 4850 mm
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Calculation, Explanation, and Discussion

H1 mostly depends on instrument mount position and the number of instrument devices used.
The Licensor for most of his vertical vessel has selected 500 mm in accord with his FCS and
ESD Control System, whereas in GPSA 450 mm is selected as the basis.
H2 is a function of retention time. It seems from the back-calculation that the licensor has
selected 10minutes for retention time. Likewise, in GPSA a retention time of 2-5 minutes has
been selected for Flash drums. The licensor general retention time table is given in next-page
H3 in GPSA for Half Open pipes is 0.25D and has been the basis for calculation.
H4 is the size of inlet Half Open pipe which is the same size of upstream pipe for both licensor
and GPSA.
H5 in GPSA for Half Open pipes is 0. 5D and has been the basis for calculation.
H6 is the demister pad thickness which is 150 mm for both licensor and GPSA.
H7 in GPSA is minimum 150 mm but in other sketch in GPSA there is a formula for X4 which
connects the upper part of demister pad to outlet nozzle which can not be used for comparison
here.
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Retention Time provided by the licensor

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Foster-Wheeler
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Height FW LICENSOR Unit

Elements

H1 300 500 mm

H2 150 400 mm

H3 - 695 mm

H4 865 865 mm

H5 - 2400 mm

H6 - - mm

H7 - - mm

HT - 4850 mm
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Svercek Method
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Height Svercek LICENSOR Unit

Elements

HLLL 150 500 mm

HH 125 400 mm

Hs 200 695 mm

HLIN 1200 865 mm

HD 1875 2400 mm

H6 - - mm

H7 - - mm

HT 3550 4850 mm
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Method GPSA FW Svercek Licensor

Height 5915 - 3550 4850

Diameter 6000 4500 3750 3750

Volume
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Manholes, Drain and Vents

Foster-Wheeler

Size of manholes
For vessel diameter < 1000 mm
Flanged vessel shall be considered if equipment contains internals
Otherwise, size of manholes = 18”
For vessel diameter ≥ 1000 mm
Toxic service size of manholes = 24”
Non-toxic service size of manholes = 20”
(Or up to 24” if internals need to be removable through
manhole.)

The drain of the vessel shall always be at the lowest point of a vessel. For vertical vessels they
shall be connected to the bottom outlet line at the low point. For horizontal vessels the drain
point shall be directly on the bottom of the drum at the lowest point ensured through vessel
slope (1:100).
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Licensor Criteria
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Comparison
1. The size of manhole for both licensor and FW is 24’.
2. There is no need to have Vent on this drum since there is a control valve to flare system
and if purging is required then by use of these means the task could be performed.
3. The drain valve sized by licensor is 2’ and but by Foster-Wheeler is 3’

Parameter FW Licensor

Manhole 20-24 24

Vent 2 2

Drain 3 2

Vortex Breaker Yes Yes