Hydrocyclones

CYCLONES

Cyclones have been used to separate solids from air or water for over 100 years.  Liquid/Liquid cyclones were developed in the 1980's/90's to solve the problems of increased water cuts in upstream oil production.

Types of Cylcones

Merpro supplies cyclones to suit three differeing separation applications:

• Liquid/liquid cyclones are used to de-oil produced water.  They are manufactured in duplex stainless steel/stellite 6 (other specialised materials available) and are shown in Figure 1.
• Liquid/soild cyclones are used for desanding and sand cleaning.  They are manufactured in ceramic materials and are shown in Figure 2.
• Liquid/gas cyclones are specially designed to separate solids contained in gas flows.  The materials of construction are specially selected to ensure the solids being separated do not erode the cyclone during separation.

How Cyclones Work

Liquid/liquid cyclones – On entering the cyclone tangentially, the fluid begins to spin.  This creates a radial force that directs the heavier phase towards the edges of the cyclone and then out of the cyclone underflow owing to differential pressure.  The less dense phase is concentrated in the centre of the cyclone before passing out of the cyclone overflow, again due to differential pressure.

Figure 1 – Liquid / Liquid De-oiling Cyclone

Compared with traditional alternatives, such as settling or skim tanks, the cyclone separator system yields much faster separation within a smaller space.  Why? Because one ‘g’ of gravitational force is replaced by many ‘g’s of radial force.  This also means that hydrocyclones are insensitive to motion and orientation, making them ideal for off-shore applications.

Just how efficient the separation is in the liquid/liquid hydrocyclones depends on the available pressure drop, operating temperature, fluid viscosity, density difference and the oil droplet size.

The separation efficiency is maintained by controlling the differential pressure ration (PDR) across the cyclone.  PDR is defined as:

PDR = (Inlet Water Pressure – Overflow Pressure [Reject Oil Stream]) / (Inlet Water Pressure – Underflow Pressure [Water Outlet Stream])

Separation efficiency is at an optimum when the differential pressure ratio across the hydrocyclone is between 1.5 and 1.7, giving a reject rate of 2.1% to 3.7% respectively.

Solid/liquid cyclones – Cyclones can also be used to remove high volumes of solids from slurry streams, both efficiently and quickly.

Figure 2 – 2" Solid / Liquid Cyclone

Here's how they work:

Figure 3 - Solid/Liquid Cyclone

There are many factors that affect the efficiency of the cyclone, the main parameters being as follows:

• cyclone geometry and size
• density differential between the solids and liquid phases
• operating temperature (and therefore the viscosity of the liquid phase)
• the pressure drop available to drive separation
• the concentration and size distribution of solid particles within the incoming process stream.

For further information, contact your local Merpro office.