Air Pollution and Control: Cyclone Separator

Cyclone separator:

Cyclone separators provide a method of removing particulate matter from air or other gas streams at low cost and low maintenance. This separator is mainly used for the separation of solids from liquids. It mainly consists of a tangential inlet to feed the materials inside the chamber. It has solid and fluid outlets which separate fluid through one side and solids through the other side.

Principle of Cyclone Separator:

In the cyclone separator, the centrifugal force is used to separate solids from the fluids (liquid or gas/air). The separation depends on the particle size as well as on the density of the particles. Hence depending on the fluid velocity, the cyclone separator can be used to separate all types of particles. Especially it is used to remove only coarse particles and allows fine particles to be carried through with the fluid. It simply transforms the inertia force of a gas particle to a centrifugal force using a vortex generated in the cyclone body.

 

Construction of Cyclone Separator:

It consists of a cylindrical vessel referred to as the barrel with the conical base, Fig.1. 4 The upper part of the vessel is fitted with a tangential inlet and a fluid outlet and at the base, it is fitted with the solid outlet. Cyclones have no moving parts and are available in many shapes and sizes.

For example, cyclone separators of 1 to 2 cm diameter are used for particle size analysis, and up to 5 m diameter is used after wet scrubbers, but the basic separation principle remains the same.

Working of Cyclone Separator:

In the suspensions of a solid gas usually, the air is introduced tangentially at a very high velocity so that rotary movement takes place within the vessel. The fluid (gas) is removed from the central outlet at the top. The rotatory flow within the cyclone separator causes the particles to be acted on by a centrifugal force. The solids are thrown out to the walls forming an outer vortex, thereafter it falls to the conical base and discharged out through the solids outlet. The increasing air velocity in the outer vortex results in a centrifugal force on the particles separating them from the air stream. When the air reaches the bottom of the cone, it begins to flow radially inwards and out at the top as clean air/gas while the particulates fall into the dust collection chamber at the bottom of the cyclone.

The collection efficiency of cyclones varies as a function of density, particle size, and cyclone design. Cyclone efficiency generally increases with an increase in particle size and/or density, inlet duct velocity, cyclone body length, number of gas revolutions in the cyclone, the ratio of cyclone body diameter to gas exit diameter, inlet dust loading, smoothness of the cyclone inner wall, etc. Similarly, cyclone efficiency may decrease with increases in the parameters such as gas viscosity, cyclone body diameter, gas exit diameter, gas inlet duct area, gas density, leakage of air into the dust outlet, etc.

Advantages of Cyclone Separator:

1.      Cyclone separator requires low capital investment.

2.      It has high efficiency for 5 - 200 µm particles.

3.      It produces a high volume flow rate.

4.      A lack of moving parts reduces wear and tear.

5.      It can be operated on a continuous or batch process.

6.      It requires virtually no downtime for maintenance or recovery.

7.      It has versatile applications.

8.      It is small in size relative to other separation equipment.

9.      It can be operated at a wide range of temperatures and pressures.

 

Disadvantages of Cyclone Separator:

1.      It shows reduced efficiency when overloaded than its capacity.

2.      It finds difficulty in obtaining good separation of substances with similar densities.

3.      It cannot handle the viscous flow.

4.      Clogging of the dust outlet is common in reverse flow cyclones.

 

Applications of Cyclone Separator:

A cyclone separator is most often used to separate "heavies" from a liquid mixture originating at a centrifugal pump or some other continuous source of pressurized liquid. A cyclone separator is most likely to be the right choice for processes where "lights" are the greater part of the mixture and where the "heavies" settle fairly easily. These may be used to separate solids from water.

1.      A cyclone separator is used to separate the suspensions of a solid in a gas or air. It can be used with the liquids suspensions of solids.

2.      It is used in the production of active pharmaceutical ingredients (API) through drying systems such as spray or fluid bed drying.

3.      It can also be used for the separation of particles based upon the size, specific gravity, porosity, and concentration from solids, liquids, and gases.

4.      In the pharmaceutical industry, it is mostly used for the separation of fines from coarse granules.

5.      In tablet compression cyclone is used to extract waste powder before it reaches the central extraction system.

6.      It can be used in air-handling systems to produce particle-free clean air.

7.      It is used in the oil industry to separate oil from water or vice versa.