Sunday, August 5, 2012

Flow Separators Types, Working and Functions

A cylindrical or spherical vessel used to separate oil, gas and water from the total fluid stream produced by a well. Separators can be either horizontal or vertical.

Separators can be classified into two-phase and three-phase separators (commonly called free-water knockout). The two-phase type deals only with oil and gas, while the three-phase type handles oil, water and gas. Additionally, separators can be categorized according to their operating pressure. Low-pressure units handle pressures of 10 to 180 psi [69 to 1241 kPa]. Medium-pressure separators operate from 230 to 700 psi [1586 to 4826 kPa]. High-pressure units handle pressures of 975 to 1500 psi [6722 to 10,342 kPa].

Gravity segregation is the main force that accomplishes the separation, which means the heaviest fluid settles to the bottom and the lightest fluid rises to the top. Additionally, inside the vessel, the degree of separation between gas and liquid will depend on the separator operating pressure, the residence time of the fluid mixture and the type of flow of the fluid. Turbulent flow allows more bubbles to escape than laminar flow.

Horizontal Longitudinal Flow Separator (HLF)

Standard HLF Separator

Typical Production Separator
Cup (Dished Head) & Shelf Inlet Diverter
Involute Separator
Porta-Test™ Revolution
NATCO Performax® & Serpentine Vane
Three Phase Separator (Fixed Weir)
Three Phase Separator (Spillover Weir)
Three Phase Bucket & Weir
Bucket and Riser 

The HLF is the most popular and versatile separator in the industry. Designed with a wide range of internals specific to each application, it is suitable for a full range of gas/oil ratios, pressures, and flow rates. The horizontal design offers the advantage of large gas/liquid and oil/water interfacial areas to speed the separation process.

How It Works

Like all separators, the HLF must perform four distinct functions – inlet momentum control, vapor demisting, liquid retention, and liquid outlet control.

Normally, the inlet is on one end of the horizontal separator, and the gas and liquid outlets are on the opposite end. As fluid enters, bulk separation occurs at the inlet device. The phases separate within the liquid retention section and flow to their respective outlets. Demisting and coalescing devices assist in the phase separation, and vortex breakers prevent the re-entrainment of phases.

Inlet Momentum Control

In the horizontal separator, several alternatives are available for controlling inlet momentum. Splash plates, dished heads, the Porta-Test Involute and the Port-Test Revolution™ are available from NATCO Group. The inlet device controls the inlet momentum by redirecting the inlet stream and dissipating the energy of the inlet fluid. The Porta-Test Revolution additionally utilizes the energy of the incoming fluid to eliminate foam.

Vapor Demisting

There are several options available for vapour demisting. Wire mesh, serpentine vanes and Performax® are all viable alternatives for removing the liquid droplets from the flowing gas stream. Performax® and serpentine vanes are normally installed vertically (perpendicular to flow) in the gas phase across the vessel diameter. The tortuous flow path of the devices creates an inertial separation mechanism. Wire mesh utilized in a separator may be installed in a horizontal position at the gas outlet for final cleanup. Wire mesh relies on droplet impingement and coalescence as the separation mechanism.

Liquid Retention

In 3-phase designs, oil and water separate in the liquid retention section. NATCO Performax® elements are normally utilized to speed the liquid/liquid coalescing process. Sizing of the liquid section is normally based on retention time. The retention time required is heavily influenced by the crude oil gravity, the operating temperature and the required outlet BS&W. Sand jet systems may also be added in this section to allow sand removal from the vessel during operation.

Liquid Outlet Control

The purpose of the outlet control section is to prevent re-entrainment of the separated phases. Several alternative configurations are available for 3-phase outlets – bucket and weir, bucket and riser, fixed weir, spillover weir and standpipe. NATCO can recommend the proper configuration for your application. Liquid and gas outlet vortex breakers are also typically included in this section. NATCO vortex breaker designs and placement focus on preventing vortexes from occurring.


Because of their versatility, horizontal separators are used successfully as production separators, test separators, gas scrubbers, wellhead separators, slug catchers, free water knockouts, degassing drums, flare scrubbers, inlet separators and floating production separators.


Horizontal separator performance is determined by the characteristics of the fluid being separated, the size of the vessel and the type of internals installed. In general, liquid carryover in the effluent gas stream will not exceed 0.1 gallons of particles larger than 10 microns per million standard cubic feet of gas if serpentine vanes are utilized for gas demisting. Performance is even better if wire mesh is utilized. To enhance oil/water separation in 3-phase separators, Revolution internals, perforated baffles and Performax® coalescing sections may all be added. BS&W content in the outlet oil stream can be significantly reduced with the inclusion of one or a combination of these items.

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