CLOSED DRAIN DRUMS CALCULATION NOTE

1.0    INTRODUCTION
The purpose of this calculation note is to provide the preliminary sizing of Closed Drain Drums at the NGL Plant. Preliminary volumes are used for the calculations based on estimated liquid contingencies. The systems shall be reviewed again during detail engineering when vessel sizes are finalized.
2.0    BASIS OF DESIGN
2.1    Capacity
The Closed Drain Drums shall be sized to accommodate the liquid from the largest single liquid contingency; for example discharge scrubber, if it is necessary to evacuate the contents of that vessel.
2.2    Assumptions
•    The Closed Drain Drum is sized to accommodate liquid from a vessel operating at its NLL.
•    Storage vessels are not considered for this calculation note.
•    The liquid from the piping system to Closed Drain Drum is included and assumed to be 20% of the liquid volume.
•    The liquid from the vessel will occupy the volume between LL to HL in the Closed Drain Drum, which is 75% of the drum volume.
•    The Closed Drain Pump shall be sized to discharge the liquid contained in the Drum within 30 minutes from HL to LL.

3.0    CLOSED DRAIN DRUM CALCULATIONS
3.1    Basis
Liquid volume accommodated from LL to HL
LL to HL to be 75% of vessel volume
Applying 20% design margin for piping
The Closed Drain Drum is segregated to separate heavy and light liquids
Oil and water overflows to individual compartment, where a 2 ft length per each of oil and water compartment is available

3.2    Calculation

Largest liquid contingency.
Liquid Volume = 350 ft3
Required volume of drain drum (350 x 1.2) / 0.75 = 560 ft3
 
4.0    CONCLUSION
Based on the calculated diameters, the vessels have been sized as follows:
NGL Plant:
Closed Drain Drum dimension is
6’ – 3” diameter x 18’ – 9” T/T horizontal (1900 mm x 5700 mm)