# Preliminary Sizing of Two-phase Vertical Separator

In previous post, I shared about how to size two-phase horizontal separator. In this pos, I want to share to you how to size two-phase vertical separator.

Schematic of Two-Phase Vertical Separator

Figure below is schematic drawing of two-phase vertical separator.

Step-by-Step Sizing of Two-Phase Vertical Separator

Figure below shows step-by-step sizing of two-phase vertical separator.

I will use an example to explain step-by-step sizing of two-phase vertical separator.

Example of Two-Phase Vertical Separator Sizing

Determine the diameter and height (seam-to-seam length) of a two-phase vertical separator for the following operating condition:

Gas rate:                              10 MMscfd

Gas specific gravity:            0.6

Oil rate:                               2000 BOPD (barrel oil per day)

Oil gravity:                          40o API

Operating pressure:           1000 psia

Operating temperature:     60oF

Let’s start sizing of two-phase vertical separator.

Step 1: Collect the Data

Gas rate, gas specific gravity, oil rate, oil gravity, operating pressure, and operating temperature are already defined above.

Step 2: Find Other Properties (Z factor, gas viscosity)

For 0.6 gas specific gravity, 1000 psia operating pressure, and 60oF operating temperature, we get Z factor 0.83. Use this figure to find Z factor for gas specific gravity 0.6.

For 0.6 gas specific gravity, 1000 psia operating pressure, and 60oF operating temperature, we get gas viscosity 0.013 cP. Use this figure to find gas viscosity.

Step 3: Calculate K (Constant used in gas capacity equation)

K is obtained from figure below.

K is a function of S P/T and oil API.

Where:

S = specific gravity of of gas capacity

P = pressure (psia)

T = temperature (oR)

From the case above,

S P/T = 0.6 x 1000 / (60 + 460)

S P/T = 1.154

For S P/T 1.154 and oil gravity of 40o API, we get K value of 0.28.

Step 4: Calculate Gas Capacity Constraint (d2)

Gas capacity constraint is calculated by using the following equation.

We get gas capacity constraint (d) is 24.68 in.

Step 5: Calculate liquid capacity constraint

Liquid capacity constraint is calculated by using the following equation.

Step 6: Calculate combinations of diameter (d) and seam-to-seam length (Lss) for various retention time (tr)

Seam-to-seam length (Lss) for liquid capacity constraint is calculated by using the following equation.

Table below shows combination of separator diameter and length for liquid capacity constraint.

Step 7: Calculate slenderness ratio (12 Lss/d). Choose between 3 or 4

See step 6.

Step 8: Graph results and choose reasonable size with a diameter and length combination above both gas capacity and liquid capacity constraint line

Graph below show vessel internal diameter and vessel length for various retention time.

Free Spreadsheet for Two-Phase Vertical Separator