Single-cyclone separators

Cyclone dust collectors can be designed with either large or narrow diameters depending on the application. Small diameter cyclones have high dust collection efficiencies at low dust loads (0.1 to 6 grains per cubic foot) and high pressure drop of 6 to 10 inches w.c. (water column). Owing to the small diameter they have the tendency to plug at high dust loads. Large diameter cyclones can handle high dust loads (50-100 grains per cu.ft) with low pressure drops (1.5 to 3 inch w.c.) efficiently. They are not very efficient at low dust loads.

To improve efficiencies, design considerations are,

1. high narrow inlets reduce distances traveled by dust to the wall and thereby improve collection efficiencies
2. small diameters have higher forces than larger diameter cyclones
3. smooth transition ensures maximum efficiency.

Use of expansion hoppers in dust discharge:
In high pressure drop cyclones, dust collecting at the discharge point could be swept upward to the outlet tube. This phenomenon occurs due to the powerful inner vortex that is formed inside the main swirling stream at the discharge point. Use of expansion hoppers allows dust to be discharged through an airtight feeder. Expansion hoppers effectively squeeze out moisture in some heavy moisture applications.

Multiple-cyclone separators

Also known as multiclones, consist of a number of small-diameter cyclones, operating in parallel and having a common gas inlet and outlet, as shown in the figure. Multi-clones operate on the same principle as cyclones--creating a main downward vortex and an ascending inner vortex.

Multiclones are more efficient than single cyclones because they are longer and smaller in diameter. The longer length provides longer residence time while the smaller diameter creates greater centrifugal force. These two factors result in better separation of dust particulates. The pressure drop of multiclone collectors is higher than that of single-cyclone separators. This is the same way a Dyson vacuum works