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Vertical Knockout Drum Sizing

By understanding the right criteria and tools, sizing a vertical knockout drum for a process plant inlet is not that much complex!
4.9/5 - (8 votes)

Last updated

11/2023

English

Vertical Knockout Drum Sizing

By understanding the right criteria and tools, sizing a vertical knockout drum for a process plant inlet is not that much complex!
4.9/5 - (8 votes)

Last updated

11/2023

English

1. Basic Math and Excel Skill
2. Have a Computer
3. Have a Desire

1.What is a seperator?
A pressure vessel designed to divide a combined liquid–gas system into individual components that are relatively free of each other for subsequent disposition or processing.

2.What are the different types of separators?
Separators are usually characterized as vertical, horizontal, or spherical.

3.How do you size a separator?
Design Procedure for seperators is the following:
1.Select proper Orientation
2.Select and Size proper Inlet Device, Inlet and Outlet ID
3.Calculate Vessel Diameter based on Saunders-Brown K-value
4.Calculate Vessel Height
5.Select and Size Manholes, Vent, Drain, Vortex Breaker
6.Select a well-designed mist eliminator pad

4.What is the difference between vertical and horizontal separators?
The criterion to select the orientation of the vessel is application-based. While for the application which is gas dominant vertical orentiation is selected, for the application which is liquid dominant horizontal orientation is selected. Horizontal orientation offers a higher interface between liquid and dissolved gas.

Why vertical orientation is selected for the knock-out drum based on GPSA Table.

Overview

Factors that Determine Vessel Orientation

Feature Vertical Horizontal
Compact Separators Yes Yes
Small Footprint Yes _
Small Liquid Surge Drums Yes _
Solids Removal with Liquid Yes _
Small Capacity Flare K.O. Drums Yes _
Gas Dominated Service Yes _
Liquid Dominated Services _ Yes
Three-Phase (G/L/L) Separation _ Yes
Liquid-Liquid Separation _ Yes
High Liquid Degassing Residence Time _ Yes
Pigging & Slug Flow Separation _ Yes
Foaming Feeds _ Yes
High Liquid Surge Capacity _ Yes
Large Capacity lare K.O. Drums _ Yes
Solid Removal Thriugh Jetting _ Yes
High Vapor and Liquid Flow Rates Yes Yes

Why half-open pipe is selected and what the downstream criteria are, by means of which liquid and vapor outlet nozzles are sized.

Overview

How Inlet section can impact seperation?

The first stage, primary separation, uses an inlet diverter so that the momentum of liquid

entrained in the vapor causes the largest droplets to impinge on the diverter and then drop by

gravity.

Inlet Devices — Proper selection of the inlet device is critical in separator design. Inlet

devices should reduce the momentum of the inlet stream, initiate gas-liquid separation

with minimum creation of fine droplets, and distribute gas flow evenly throughout the

inlet and gravity separation section of the vessel

There are several types of inlet devices used in the industry. The more common devices are

shown below.

  1. How to use GPSA,Svercek, Foster Wheeler, and Haldor Topsoe Methodologies to calculate vessel diameter and Height for the knock-out drum

Overview

The next stage, secondary separation, is gravity separation of smaller droplets as the

vapor flows through the disengagement area.For secondary separation, the allowable velocity

must be calculated so that the disengagement area can be subsequently determined.

Performing a force balance on the liquid droplet settling out provides the necessary relationship. When the net gravity force the drag force . The heavier liquid droplets will settle at a constant terminal velocity. Equating these two forces results in  Here as long as Uv < UT the liquid droplets will settle out. Typically, the allowable vertical velocity Uvis set between 0.75 UTand UT. This could be rearranged to a Saunders-Brawn equation.

In vessels with no internals, gravity settling is the only mechanism of separation. Thus, terminal velocity of the minimum particle size desired for separation is critical. For vertical vessels, a liquid droplet will settle out of the gas phase when the vertical gas velocity is less than the droplet’s terminal velocity. The terminal droplet velocity can be obtained by using the appropriate settling law expression, or an industry experience K value. The target droplet diameter, or K value, is selected to prevent excessive entrainment based on experience. In either case a target droplet size of about 250 to 500 microns is typically used for many gas liquid gravity separator designs.

In this part you learn how to use standardized Table to specify the minimum sizing of manholes, drains, and vents.

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