Week 8 - Simulating Cyclone separator with Discrete Phase Modelling

AIM:-

To perform analysis cyclone separator and calculate the separation efficiency and pressure drop.

OBJECTIVE:-

1. To write a few words about any four empirical models used to calculate the cyclone separator efficiency.
2. To perform an analysis on a given cyclone separator model by varying the particle diameter from 1 μm to 5 μm and calculate the separation efficiency in each case. Discuss the results. [Use both the velocity's as 3m/sec.]
3. To perform an analysis on a given cyclone separator model by varying the particle velocity from 1 m/sec to 5 m/sec and calculate the separation efficiency and pressure drop in each case. Discuss the results. [Use particle diameter size as 5 μm for all cases & keep flow velocity same as particle velocity]

THEORY:-

Cyclone separators are separation devices that use the principle of inertia to remove particulate matter from flue gases. Cyclone separator is one of many air pollution control devices known as pre-cleaners 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. In addition, several cyclone separators can operate in parallel, and this system is known as a multi-cyclone.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. This spiral formation and the separation is shown in the Figure below. 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.

There are models used to calculate the cyclone separotor:-

1) Iozia and Leith Model

Iozia and Leith logistic model 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 ηi of particle diameter dpi can be calculated from

2)Koch and Licht Mode:

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 describedparticle motion in the entry and collection regions with the ad- 200
ditional following assumptions:

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 u Rn = constant.
Aforce balance and an equation on the particles collection yields
the grade efficiency

3) Li and Wang Model:
1.The Li and Wang model includes particle bounce or reentrainment and turbulent diffusion at the cyclone wall.

2.A twodimensional analytical expression of particle distribution in thecyclone is obtained.

3.Li and Wang model was developed based on the following assumptions:

Assumptions:

• The radial particle velocity and the radial concentrationprofile are not constant for uncollected particles within
the cyclone.
• Boundary conditions with the consideration of turbu185 lent diffusion coefficient and partic bounce reentrainment on the cyclone wall are:
c = c0, at θ = 0

Dr ∂c/∂r= (1 − α)wc, at r = D/2

The tangential velocity is related to the radius of cyclone by: u Rn = constant.
The concentration distribution in a cyclone is given as:

4)Lapple Model
1.Lapple model was developed based on force balance without considering the flow resistance.

2.Lapple assumed that a particle entering the cyclone is evenly distributed across the inletopening.

3.The particle that travels from inlet half width to thewall in the cyclone is collected with 50% efficiency.

4.The semiempirical relationship developed by Lapple to calculate a
50% cut diameter, dpc, is

SOLUTION:-

PROCEDURE:-

Geometry:-

• Import cyclone separotor file to ansys fluent from the files.
• Then go to prepare and select fluid or volume extract and select edge extract and then select inlet and two outlet edges.
• Then mark on green arrow and supress physics

Mesh:-

• Select the face model and select inlet and two outlet and select name
• Then change the mesh model size to 10mm to refine the mesh

Setup:-

• After mesh refine go to setup with double precision solver and select 4
• Then select pressure based solver and tick on gravity option and enter the -9.81 value to the y-axis

• Select a viscous model K-eplision>RNG>swirl dominated flow.

• Select Discrete phase model

• Then select Injection option and select surface

• Create a boundary condition for inlet is v=3m/s
• Check dpm and use reflect
• Outlet(top)=Escape
• Outlet(bottom/dustbin)=Trap

Solution:-

case1(a):- Inlet velocity=3m/s, Dia of particle=1e-6

Residual plot:-

Contour plot:-

Cyclone separator efficiency:-

Separator efficiency= no of particles trapped / no of particles reacked

Efficiency = (120/214)*100

=56%

Case 1(b):- Inlet velocity = 3m/s, Dia of particle = 2e-6

Residual plot:-

Contour plot:-

Cyclone separator efficiency:-

Separator efficiency= no of particles trapped / no of particles reacked

Efficiency = (137/218)*100

=62%

Case 1(c)=Inlet velocity= 3m/s, Dia of particle = 3e-6

Residual plot:-

Contour plot:-

Cyclone separator efficiency:-

Separator efficiency= no of particles trapped / no of particles reacked

Efficiency = (120/242)*100

=49%

Case 1(d):- Inlet velocity=3m/s, Dia of particle= 4e-6

Residual plot:-

Contour plot:-

Cyclone separator efficiency:-

Separator efficiency= no of particles trapped / no of particles reacked

Efficiency = (240/412)*100

=58%

Case 1(e)= Inlet velocity:-3m/s, Dia of particle = 5e-6

Residual plot:-

Contour plot:-

Cyclone separator efficiency:-

Separator efficiency= no of particles trapped / no of particles reacked

Efficiency = (240/347)*100

=69%

Case 2 (a):-

Inlet velocity=1m/s, Dia of particle = 5e-6

Residual plot:-

Contour plot:-

Pressure drop=inlet-outlet

=101326.71 - 2.3187991

=101324.39

Cyclone separator efficiency:-

Separator efficiency= no of particles trapped / no of particles reacked

Efficiency = (7/91)*100

=7.69%

Case 2 (b):-

Inlet velocity=2m/s, Dia of particle = 5e-6

Residual plot:-

Contour plot:-

Pressure drop=inlet-outlet

=101332.42 - 9.8674503

=101322.55

Cyclone separator efficiency:-

Separator efficiency= no of particles trapped / no of particles reacked

Efficiency = (7/182)*100

=3.85%

Case 2 (c):-

Inlet velocity=3m/s, Dia of particle = 5e-6

Residual plot:-

Contour plot:-

Pressure drop=inlet-outlet

=101341.97 - 22.471504

=101318.72

Cyclone separator efficiency:-

Separator efficiency= no of particles trapped / no of particles reacked

Efficiency = (8/94)*100

=8.51%

Case 2 (d):-

Inlet velocity=4m/s, Dia of particle = 5e-6

Residual plot:-

Contour plot:-

Pressure drop=inlet-outlet

=101355.79 - 40.573272

=101315.21

Cyclone separator efficiency:-

Separator efficiency= no of particles trapped / no of particles reacked

Efficiency = (9/213)*100

=4.22%

Case 2 (e):-

Inlet velocity=5m/s, Dia of particle = 5e-6

Residual plot:-

Contour plot:-

Pressure drop=inlet-outlet

=101373 - 63.286742

=101309.7133

Cyclone separator efficiency:-

Separator efficiency= no of particles trapped / no of particles reacked

Efficiency = (14/249)*100

=5.62%

Conclusion:-

• Cyclone separator efficiency depends on velocity abd size of particle.
• The efficiency is increasing with increase particle size.
• With increase in velocity pressure difference also increase.
• Velocity has more effect on pressure difference.
• With the help of more refined mesh the result may very and those results are more accurate than above obtained results.