Vessel Design

The following shall be considered in vessel design:

1.Prepare Input Data

-Operating Conditions – service, T, P, flowrate, etc.
-Performance Requirement: holding time, min. droplet size, allow. DP, etc.
-Mechanical Design data: codes, design conditions, material

2.Type of Vessel and Orientation

a.Purpose

-To accommodate vapor or liquid
-To separate entrained liquid/solid from vapor or heavier liquid (function as separator)

b.Orientation

b1.Vertical Drum

-V/L ratio is high
-Stable V/L separation is required, even if liquid Level fluctuates frequently
-Re-mixing of fluids should be avoided
-Limited plot plan area

b2.Horizontal Drum

-V/L ratio is Low
-Large no. of liquid has to be accommodated
-Foaming liquid or Liq-Liq separation
-Large liquid surface area is required
-Head space is restricted

3.Process Requirement

HOLDING TIME: volume of the vessel divided by the draw-off rate. In general, holding time consists of the following:

-Equipment protection Volume (TL-LLL)
-Control Band Volume (HLL-LLL)

4.Mechanical Requirement

a.Vessel diameter

a1.Commercial pipe to be used for small drum up to 24” OD
a2.When drum is fabricated, the following increment is used:

ID (m)                         Increment (mm)
450 – 1000                50
1000 – 3000              100
3000 – 5000              200
5000 – up                  200 or 300

a3.L/D RATIO: The higher the design Pressure of the drum or the grade of material, the larger the L/D ratio is preferred.

-2:1 semi-ellipsoidal head: 3:1 to 6:1
-Hemispherical head: 2:1 to 4:1

Design Pressure (kg/cm2G)        L/D
18 and smaller                             3
18-35.5                                       4
35.5 and larger                            5

b.Wall thickness

T = Pd x D / 1442 + 3.0    Carbon steel, Pd < 30
T = Pd x D / 2300        SUS, Pd < 30
Where: Pd – design Press. (kg/cm2G), D: vessel diameter

c.Vessel length

Standard length from economical view point:

-L= 1500, 2000, 2500, 3000, 4500, 6000
-L= 5 ft, 10 ft, 15 ft, 20 ft.

d.Internals

Internals are provided when high efficiency is required. Other internal accessories:

-Distributors or baffles for inlet nozzles are provided for primary separation or to avoid disturbance of vapor-liquid or liquid-liquid interface:
-Vortex Breakers should be provided at draw-off nozzle, normally with flow, especially at pump suction nozzle to avoid pump cavitation

e.Nozzles

-Nozzles for inlet and outlet shall be same as piping size determined by hudraulic calculation.
-MH, LC-LG nozzle, vent and drain

f.Skirt height

Skirt height shall be determined by the hydraulic design of the liquid transport system.