5 Things that cyclones can and cannot do

The hydrocyclone design has been with us since 1891 when E. Bretney patented the first hydrocyclone. Over the years the design of the hydrocyclone has not changed much from the original. 

As people started to understand the cyclone, changes started to appear in terms of dimensions, available hydrocyclone configurations and the use of the unit in different applications. In 1945 the Dutch State Mines produced a patent for a dense medium cyclone.

The cyclone is a very versatile piece of equipment with the primary function of separating solids from liquid or separating material into a coarse and fine fraction. Or, in the case of dense medium separation, into different density products. The cyclone is also used to separate oil from water or any other two liquids with different characteristics. There are even air cyclones that separate fine particles from air, used mainly in dust extraction applications. 

The main challenge our cyclone engineers face is that our clients view the cyclone as a very basic and simple device. They are not wrong.

The design of a cyclone

The cyclone consists of the vortex finder that fits into the inlet head which then fits onto a cone, and the spigot attaches to the bottom end of the cone. That is as simple as it gets and although there are more complex designs, the majority of our cyclones consists of these parts.

It is understandable that clients do not think much of cyclones because they are so simple, and many neglect cyclone maintenance because their units always seem to work correctly. This is where our Multotec process and application engineers play a vital role. They educate our clients in understanding that the cyclone plays a critical role in ensuring the correct operation of their process.  

Although the cyclone is a simple piece of equipment, it forms part of the overall process and the engineers understand the process completely in order to provide the correct advice. Not only do they need to understand how the cyclone operates but also how the process operates. 

What CAN cyclones do?

1.    A cyclone can handle a wide range of volumetric flow rates
The smallest commercial classification cyclone we have has a volumetric flow rate of 1 m3/hr while the largest unit we’ve made to date, a 1 400 mm unit, can handle up to 3 500 m3/hr (that’s equivalent to taking 51 seconds to fill a standard 50 000 litre swimming pool). On dense medium cyclones, the smallest cyclone with a 200 mm diameter has a flow rate of 19 m3/hr and the largest unit, a 1450 mm cyclone, has a capacity of 3140m3/hr.

2.    It makes decisions in a matter of seconds
The average time a particle spends inside a cyclone is about 10 seconds. During this time the cyclone must decide where the particle should report. 

3.    It makes many decisions
In a classification cyclone treating 400 tph of silica sand of 2 mm diameter, 11 million particles enter the cyclone every second, and the cyclone must decide where the particles must report to.

4.    It makes expensive decisions
In a diamond mine in Lesotho, large diamonds are recovered through a dense medium cyclone. These diamonds are very rare and some have been sold for USD $16 to 19 million over the years. If the diamonds were in the dense medium cyclone for 10 seconds, then the value of the decision each second was between $1.6 and 1.9 million (that’s ZAR 24 million to ZAR 28.5 million at ZAR 15:1 USD).

5.    A cyclone can work under water
It is possible for the cyclone to work underwater, but it won’t separate as effectively as what it does above water.

What can cyclones NOT do?

1.    It cannot separate perfectly
If you have a few seconds to separate 11 million particles entering your office each second, then you will surely also make mistakes! The same happens in the cyclone. In diamond dense medium separation, it is the work of the Multotec Cyclone Division to ensure we supply the correct advice to ensure the cyclone separates efficiently and correctly.

2.    It cannot supply an underflow product that has no water
Classification cyclones are not only used to separate material but also to produce material that is as dry as possible. Clients sometimes require that the material coming from the cyclone underflow be completely dry, but this is not possible; without water the material cannot flow out of the
Cyclone (the water serves as a lubricant to help the material flow out).

3.    The cyclone cannot change the size of the particles when operating in a milling circuit
In a mill circuit, particles are broken down to smaller sizes before going to the next process. Clients sometimes want the cyclone to produce particles that are finer than what the mill can produce. To make particles finer, energy is needed, and if the cyclone could do that then we wouldn’t need mills. 

4.    The cyclone cannot work upside down
For a cyclone to work upside down, requires the use of a pump that delivers a very high pressure. The larger the cyclone diameter, the longer the cyclone becomes, and if you turned the cyclone upside down it would be very tall. It is very difficult for a pump to create pressure sufficient to push the liquid all the way to the top. 

5.    A cyclone cannot lie 
Often clients blame the poor performance in their process on the cyclone, while the cyclone is not the culprit. A cyclone reacts to the feed conditions provided and if those feed conditions are not good then it will not work correctly. The problem is likely found in the process, where an item is not working optimally on the plant. 

Looking for more info on cyclones? View our cyclone webinars, here.