De-oiling Hydrocyclones

 
Skid mounted hydrocyclone package

VWS Westgarth has recently launched the STREAMLINER™ range of de-oiling hydrocyclones.

The purpose of a de-oiling hydrocyclone is to separate free oil from produced water prior to discharge or injection.

Usually situated after the primary separators, de-oiling hydrocyclones are normally regarded as the first stage in the treatment process. Long established as a process step, proven in service and having a compact footprint, they are one of the most commonly employed processes in a produced water treatment system. Energy to drive the process comes from the pressure in the separators.

The dimensions of the pressure vessel and the number of hydrocyclone liners employed are determined by the flowrate, characteristics of the produced water requiring treatment and separator pressure.

De-oiling hydrocyclones provide compact and rapid treatment with a retention time of the produced water in a hydrocyclone of just a few seconds.

Separation in this short time is achieved by the high centrifugal forces produced by the vortex within the hydrocyclone liner acting on the difference between the specific gravity of oil and that of water/solids.

How it works

VWS Westgarth STREAMLINER™ Hydrocyclone linerZoom

Produced water is injected under pressure into the larger diameter conical end of the hydrocyclone liner. The inlets are generally tangential to the wall of the liner so that the fluid entering the liner is made to rotate. Different inlet designs exist (depending on supplier) to induce this rotational vortex in the fluid. The conical shape of the hydrocyclone liner causes an increase in rotation speed as the diameter narrows, resulting in the development of high centrifugal forces and therefore the separation of the lighter oil from the heavier water and solids. Water and solids move along a vortex near the wall of the liner towards the outlet of the liner, whereas oil and gas will move in the opposite direction along a secondary vortex along the axis of the liner, towards the inlet end where it is extracted through the reject port which is located on the axis of the inlet end of the liner.

Hydrocyclone tubeZoom

Free oil removal is fully efficient for droplets larger than 15 to 30 microns (depending on the specific gravity of the oil and other characteristics of the application) with reducing efficiency at lower droplet sizes. With an inlet content of up to 1000mg/l, a typical outlet concentration of 40-60mg/l can be expected. Higher feed concentrations only cause a small increase in outlet oil concentration. Smaller droplets and emulsified/dissolved oil, as well as dissolved components such as benzene, heavy metals etc. remain in the treated water.

The oil concentration in the treated discharge of a hydrocyclone will most likely be above the limit set for open sea discharge and will also contain some gas. This makes a further stage necessary, most commonly a flotation process.

De-oiling hydrocyclones are very efficient at high throughput. With no moving parts and a compact footprint, their reliability means that this technology is popular in both on and offshore applications. Disadvantages of de-oiling hydrocyclones are a sensitivity to process fluctuations and the need for an elevated inlet pressure, although in most cases the operating pressure of the separator is adequate to feed them.

Produced water flow diagram


In most cases, de-oiling hydrocyclones are positioned downstream of de-sanding cyclones.

This is partly due to the high shear forces inherent in the process. Sand particulates have a very abrasive action on the liners of the de-oiling hydrocyclones, therefore to maximise the liner life, desanding hydrocyclones are positioned upstream.

Benefits of the VWS WESTGARTH STREAMLINER™ design

Building upon many years of oil & gas industry experience, VWS Westgarth has developed the new STREAMLINER™ range of de-oiling hydrocyclones. This design incorporates unique features for improved reliability, performance and efficiency together with simplified operation and maintenance. Available as retrofits for existing installations or integrated into a complete produced water system, the STREAMLINER™ offers an unbeatable combination of performance, economy and whole life support from the water treatment expert in upstream oil & gas.

Pressure vesselZoom

Benefits of the STREAMLINER™ design:

  • Annular axial inlets reduce turbulence
  • Multiple inlets improve wear resistance
  • Swirl inducer can be inspected without liner disassembly
  • Retractable swirl inducer allows for internal liner inspection and easier jet cleaning
  • Liners can be retrofitted into existing installations
  • Geometry optimised for capacity and efficiency

VWS Westgarth has a standard range of equipment sizes as well as an established service and spares organisation to fully support the installation.

Our process experts are available to help design the optimum treatment system for your application. We strongly advise that this is initiated as early as possible in the design process to maximise the benefits of our expertise.

In-house expertise

VWS Westgarth specialise in the design & build of water treatment process plant, in the worldwide oil & gas industry, therefore non-standard equipment and specifications can be easily incorporated into full treatment packages. This ensures our clients' requirements are met in the most efficient manner with either a standard plant or bespoke design.

View our STREAMLINER™ brochure.