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: 40^{o} API

Operating pressure: 1000 psia

Operating temperature: 60^{o}F

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 60^{o}F 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 60^{o}F 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 (^{o}R)

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 40^{o} API, we get ** K value of 0.28**.

**Step 4: Calculate Gas Capacity Constraint (d ^{2})**

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 (L _{ss}) for various retention time (t_{r})**

Seam-to-seam length (L_{ss}) 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 L _{ss}/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**

You can download and learn about the sizing step by downloading this spreadsheet: Sizing two-phase vertical separator.

I hope you find this post useful.

**References:**

- Surface Production Operation Vol. 1: Design of Oil-Handling Systems and Facilities