Process Facilities often have intermediate storage facilities that store liquids prior to transporting to downstream equipment. The period of storage is short, i.e., of the order of minutes to hours & is defined as Holdup time. The Holdup time can also be explained as the reserve volume required to ensure safe & controlled operation of downstream equipment. The intermediate vessel also acts as a buffer vessel to accommodate any surge/spikes in flow rates, and is termed as surge time. Vessel Volume is an input data required in Process Dynamic Simulation and the following exercise covers estimation of volume required for single phase liquid flow into an intermediate vertical/horizontal/flat bottomed process vessel

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Single Phase Liquid Vessel Sizing for HYSYS Dynamics
Process Facilities often have intermediate storage
facilities that store liquids prior to transporting to
downstream equipment. The period of storage is
short, i.e., of the order of minutes to hours & is
defined as Holdup time. The Holdup time can also
be explained as the reserve volume required to
ensure safe & controlled operation of
downstream equipment.
The intermediate vessel also acts as a buffer
vessel to accommodate any surge/spikes in flow
rates, and is termed as surge time.
Vessel Volume is an input data required in
Process Dynamic Simulation and the following
exercise covers estimation of volume required for
single phase liquid flow into an intermediate
vertical/horizontal/flat bottomed process vessel.
Problem Statement
Water at 1,341 m3
/h, flows into a vessel & held
for a holdup time of 1 min before discharging into
downstream equipment. The vessel’s liquid
percent level is desired to be held at 50% (half
full) for a certain drain rate. Estimate the size of
the vessel required for an L/D ratio of 1.
Design Methodology & Results
Based on the above data, the vessel volume [V]
for a flow rate of 1,341 m3
/h is,
𝑽 = 𝑸[𝒎 𝟑
𝒉⁄ ] ×
𝑻 𝒉𝒐𝒍𝒅𝒖𝒑[𝒎𝒊𝒏]
𝟔𝟎
×
𝟏𝟎𝟎
% 𝑳𝒊𝒒𝒖𝒊𝒅 𝑳𝒆𝒗𝒆𝒍
(1)
Based on the vessel volume estimated for the
holdup time, the dimensions of the vessel are,
𝑫 = √
𝟒𝑽
𝝅𝑳
; 𝑾𝒉𝒆𝒓𝒆 𝑳 = 𝒏 × 𝑫 (2)
Substituting the values for vessel dimensions,
𝑽 = 𝟏𝟑𝟒𝟏 ×
𝟏
𝟔𝟎
×
𝟏𝟎𝟎
𝟓𝟎
= 𝟒𝟒. 𝟕𝒎 𝟑
(3)
Taking L = D, i.e., L/D ratio of 1.0
𝑫 = √
𝟒×𝟒𝟒.𝟕
𝝅
𝟑
≈ 𝟑. 𝟗 𝒎 (4)
Since L = D; Therefore L = 3.9 m.
Surge Study
From the estimates, the vessel chosen is flat
bottomed on concrete foundation & is subjected
to a peak flowrate rise of 1,474 m3
/h in a 2 min
interval. The liquid level rises to ~57% from 50%.
Figure 1. Surge Flow rate increase on % Liquid Level
Thumb Rules
The different arrangement types are as follows,
Figure 2. Intermediate Storage Vessel Types & L/D Ratio
1. Holding time for most intermediate tanks is 10
min (half full tanks)
2. Holding time for feed tanks to furnace is 30
min (half full).
3. The optimum ratio is 3 for commonly used L/D
ratios of 2 to 5.
4. Vessels < 4 m3
, are vertically mounted with L/D
ratio of 2 to 5 on leg supports/ brackets.
5. Vessels 4 m3
< V < 40 m3
is horizontal & saddle
supported with L/D ratio of 2 to 5.
6. Vessels V > 40 m3
is flat bottom tank on
concrete foundation with L/D ratio of 0.5 - 1.5.
References
Perry’s Chemical Engineers Handbook, 7th
Edition