Separators

Coalescence Crude Flash Drums Crude Oil Desalters/ Dehydrators Demisters Design and Engineering Distillate Reflux Drums Flare Drums Fuel Gas/Compressor Suction Knockout Drums Liquid Surge Drums Oil/Gas Production Separators Separators Settling Drums Spheroids Used for Degassing Crudes at Low Pressure Steam/ Blowdown Drums Two Phase Seperator Vapour Liquid seperation

Separators:

Separator is basically coming from category of Mechanical Static Equipment. However it is one of the pressure vessel type, based on its purpose. As its name implies the purpose as ‘Separation’. 

In oil and Gas separators are widely used equipment, which is summarized below with its basic details.

Principle

  • The three principles used to achieve physical separation of vapour and liquids are
    • Gravity
    • Momentum
    • Coalescence
  • Method used depends on difference in density between immiscible fluid phases.
  • Gravity separation – heavier fluid falls down to the bottom and lighter rises to the top.
  • Momentum – Centrifugal or cyclonic force used and separation is by reduction in velocity of mixed phases.

Coalescence

  • Very small droplets are coalesced to form larger droplets that will settle by gravity. Coalescing devices in separators force gas to follow a tortuous path.
  • The momentum causes them to collide with other droplets in the coalescing device and larger ones formed settle out of the gas phase by gravity.
  • Wire mesh demisters, vane elements and filter cartridges are examples of coalescing devices.
Separators

Fig.1

Demisters

  • Demisters are porous blankets of wire mesh used for removing entrained liquid droplets from a vapour stream.
  • Demisters are available in wide variety of densities and wire diameters.
  • Vapour moves freely through the demister but droplets cannot follow the gas stream and are collected on screen wires.
  • The liquid collected on the wires runs down the bottom surface and drops off the screen.

Categories

  • Based on phases
    • Two Phase
    • Three Phase
  • Based on construction
    • Horizontal
    • Vertical
    • Spherical
    • Single barrel
    • Double barrel

Vapour – Liquid Separation

  • Consist of 4 major sections and are shown in Fig.2.
  • Primary separation (section A) – Separates most of the liquids in the inlet stream which contains the inlet nozzle of the separator.
  • Secondary or gravity separation (section B) –  uses gravity to separate entrained droplets. Consists of the section through which gas moves at a low velocity and turbulence.
  • Coalescing (section C) – uses a coalesces or demister to remove the very small droplets of liquid from the gas by impingement on a surface where they coalesce.
  • Liquid collection (section D) – Receiver for all liquids
Separators

Fig.2

Types of Separators

  • Oil/Gas Production Separators
  • Crude Flash Drums
  • Crude Oil Desalters/ Dehydrators
  • Spheroids Used for Degassing Crudes at Low Pressure
  • Fuel Gas/Compressor Suction Knockout Drums
  • Liquid Surge Drums
  • Distillate Reflux Drums
  • Settling Drums
  • Steam/ Blowdown Drums
  • Flare Drums

Definitions

  1. Liquid-Liquid Separator: Separates two immiscible liquid phases taking advantage of the difference of density between the two.
  2. Three-Phase Separator: A vessel used to separate vapour & two immiscible liquids of different densities (e.g. vapour, water & oil).

Horizontal Separators

  • Most efficient for large volumes of total fluids with presence of dissolved gases.
  • More efficient than vertical separators.
  • More flexible in choice of nozzle arrangement.
  • Used for liquid-liquid systems and for slug flow
  • Larger vapour – liquid interface i.e. better ability to handle foaming crudes
  • Smaller in volume for high liquid loading service.
  • Length/diameter ratio between 1/1 & 5/1, 3/1 recommended

Vertical Separators

  • Commonly used when gas – liquid ratio is high i.e. low liquid loading service such as fuel gas knockout.
  • Liquid removed by inlet baffle falls to the bottom of the vessel.
  • The gas moves upwards passing through the demister to remove suspended mist and dry gas flows out.
  • Main advantage is a smaller plot area e.g. Offshore production platforms.
  • Length/diameter ratio 1/1 to 5/1, recommended is 3/1.

2 Phase Separator

Separators
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2 Phase Vertical Separator

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3 Phase Separator

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Vertical Centrifugal Separator

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Spherical Separator

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Separators