Cyclone separators or simply cyclones are separation devices (dry scrubbers) that use the principle of inertia to remove particulate matter from flue gases. Cyclone separators is one of many air pollution control devices known as precleaners since they generally remove larger pieces of particulate matter. This prevents finer filtration methods from having to deal with large, more abrasive particles later on.

It is important to note that cyclones can vary drastically in their size. The size of the cyclone depends largely on how much flue gas must be filtered, thus larger operations tend to need larger cyclones. For example, several different models of one cyclone type can exist, and the sizes can range from a relatively small 1.2-1.5 meters tall (about 4-5 feet) to around 9 meters (30 feet)—which is about as tall as a three story building.

WORKING :

Cyclone separators work much like a centrifuge, but with a continuous feed of dirty air. In a cyclone separator, dirty flue gas is fed into a chamber. The inside of the chamber creates a spiral vortex, similar to a tornado. The lighter components of this gas have less inertia, so it is easier for them to be influenced by the vortex and travel up it. Contrarily, larger components of particulate matter have more inertia and are not as easily influenced by the vortex.

Since these larger particles have difficulty following the high-speed spiral motion of the gas and the vortex, the particles hit the inside walls of the container and drop down into a collection hopper. These chambers are shaped like an upside-down cone to promote the collection of these particles at the bottom of the container. The cleaned flue gas escapes out the top of the chamber.

Four empirical models used to calculate the cyclone separator efficiency :

1.Iozia and Leith Model :

Iozia and Leith logistic model is a modified version of Barth Model, which is developed based on force balance. The model assumes that a particle carried by the vortex endures the influence of two forces: a centrifugal force, Z and a flow resistance, W. The collection efficiency η_i of particle diameter d_pi can be calculated from

β is an expression for slope parameter derived based on the statistical analysis of experimental data of a cyclone with D = 170 0.25 m given as

and dpc is the 50% cut size given by Barth

2.Li and Wang Model :

The Li and Wang model includes particle bounce or reentrainment and turbulent diffusion at the cyclone wall. A twodimensional analytical expression of particle distribution in the cyclone is obtained. Li and Wang model was developed based on the following assumptions:

• The radial particle velocity and the radial concentration profile are not constant for uncollected particles within the cyclone.
• Boundary conditions with the consideration of turbulent diffusion coefficient and particle bounce reentrainment on the cyclone wall are:

• The tangential velocity is related to the radius of cyclone by: uRⁿ = constant.

The concentration distribution in a cyclone is given as:

The resultant expression of the collection efficiency for particle of any size is given as

3.Koch and Licht Model

Koch and Licht collection theory recognized the inherently turbulent nature of cyclones and the distribution of gas residence times within the cyclone. Koch and Licht described particle motion in the entry and collection regions with the additional following assumptions:

• The tangential velocity of a particle is equal to the tangential velocity of the gas flow, i.e. there is no slip in the tangential direction between the particle and the gas.
• The tangential velocity is related to the radius of cyclone by: uRⁿ = constant.

A force balance and an equation on the particles collection yields the grade efficiency η_i

G is a factor related to the configuration of the cyclone, n is related to the vortex and τ is the relaxation term.

4.Lapple Model

Lapple model was developed based on force balance without considering the flow resistance. Lapple assumed that a particle entering the cyclone is evenly distributed across the inlet opening. The particle that travels from inlet half width to the wall in the cyclone is collected with 50% efficiency. The semi empirical relationship developed by Lapple [1] to calculate a 50% cut diameter, d_pc, is

where N_e is the number of revolutions

The efficiency of collection of any size of particle is given by

PROCEDURE :

STEP 1 : GEOMETRY USED

1.Importing the 3D model:

The first step is to import the 3D model to the space claim.

2.Volume extraction:

Fluid volume extraction is defined as extracting the volume of the fluid .

STEP 2 : MESHING

Coarse mesh fine mesh mesh details

In this case , we are considering only the fine mesh for the study case.

STEP 3 : SET UP & SOLUTION

[ Velocity varing from 1 m/s to 5m/s and constant particle size @ 5 μm]

Readings :

Graphical_Discussion :

Animation :

velocity at 1 m/s and particle size @ 5 micrometers 5m/s @ 5micrometers

Conclusion :

- Particles entering the cyclone at different inlet positions give different separation efficiency. Generally, particles entering from the top part of the inlet have higher separation efficiency than those from the bottom part of the inlet.

- From graphs , we conclude that there is an increase in the pressure drop in the system with the increase in inlet velocity and constant in the case 2 where we used same velocity by varying particle size.

- Also , As the velocity increased, seperation efficiency also increased . Similarly , separation efficiency increases with increase in the particle size.

- Particles with a size exceeding a critical diameter, which may depend on cyclone geometry and flow condition, will not be collected at the cyclone bottom and may stagnate on the conical wall of the cyclone as a result of the balanced forces such as the supporting force from the wall, the gas drag force and the gravity force.

References :

Cyclone separator - Energy Education

https://www.sciencedirect.com/science/article/pii/S0307904X06000291

https://www.researchgate.net/publication/232747389_A_CFD_Study_on_the_Prediction_of_Cyclone_Collection_Efficiency