Petroleum Plant Design: COLD SEPARATOR CALCULATION NOTE

1.0 INTRODUCTION

This document describes the calculations required to establish the vessel size for the cold separator

The separator is located inlet gas/gas exchangers and immediately upstream of the expander unit.

The cold fluid entering the separator is two phase.

2.1 Basic Consideration for cold separator

• Gas velocity constant K varies from 0.06 to 0.5 with the vessel type and whether or not mist eliminators are used – (GPSA data book)

• Applicable settling law used; intermediate law

2.2 Design Conditions

2.3 Assumptions

• Sizing is based on removing > 50 micron droplets

• Liquid retention time minimum 10 minutes for NGL feed to de-ethanizer

• L/D ratio 2 – 4 for vessels

• Mist extractor has been assumed

• Actual operating liquid level to be determined in detail engineering

4.0 EQUATIONS

Souders – Brown Relationship

Where:

= Allowable gas velocity at operating conditions, ft/sec

= Liquid density at operating conditions, lbm/ft3

= Gas density at operating conditions, lbm/ft3

= Separation Coefficient

The actual gas volume can be calculated from the standard conditions using the parameters given.

The vessel diameter can then be calculated from

Where:

= Vessel diameter, ft.

= Actual gas volume, ft3/sec

3.0 RESULTS

3.1 Gas Basis

Gas Volume Flow

Vessel diameter

3.2 Liquid Basis

Liquid flow-rate =

For 10 minutes liquid hold up, liquid elevation:

A L/D ratio of 3/1 will provide sufficient vapor space for nozzles, entrainment settlement and mist eliminator.

4.0 CONCLUSION

Based on the calculated diameter, the vessel has been sized as follows:

Cold Separator 7’ – 6” diameter x 21’ – 0” T/T vertical (2290 mm x 6400 mm)

Petroleum Plant Design