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.