CYCLONE SEPARATOR SIMULATION USING DISCRETE PHASE MODELLING

OBJECTIVES:

Cyclone separators or simply cyclones are separation devices dry scrubbers that use the principle of inertia to removeparticulate 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. In addition, several cyclone separators can operate in parallel, and this system is known as a multicyclone.

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.

How It Works

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 Figure 2. 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.

Most cyclones are built to control and remove particulate matter that is larger than 10 micrometers in diameter. However, there do exist high efficiency. cyclones that are designed to be effective on particles as small as 2.5 micrometers. As well, these separators are not effective on extremely large particulate matter. For particulates around 200 micrometers in size, gravity settling chambers or momentum separators are a better option.

Out of all of the particulate-control devices, cyclone separators are among the least expensive. They are often used as a pre-treatment before the flue gas enters more effective pollution control devices. Therefore, cyclone separators can be seen as \"rough separators\" before the flue gas reaches the fine filtration stages.

Effectiveness

Cyclone separators are generally able to remove somewhere between 50-99% of all particulate matter in flue gas. How well the cyclone separators are actually able to remove this matter depends largely on particle size. If there is a large amount of lighter particulate matter, less of these par0ticles are able to be separated out. Because of this, cyclone separators work best on flue gases that contain large amounts of big particulate matter.

There are several advantages and disadvantages in using cyclone separators. First, cyclone separators are beneficial because they are not expensive to install or maintain, and they have no moving parts. This keeps maintenance and operating costs low. Second, the removed particulate matter is collected when dry, which makes it easier to dispose of. Finally, these units take up very little space. Although effective, there are also disadvantages in using cyclone separators. Mainly because the standard models are not able to collect particulate matter that is smaller than 10 micrometers effectively and the machines are unable to handle sticky or tacky materials well.

AIM FOR SIMULATION:

• A few words about the four empirical models used for cyclone separator efficiency.
• Performing an analysis on the given cyclone separator model and apply four different boundary condition types at the inlet i.e. reflect, trap, escape and wall-jet and submit images on your findings on the different conditions.
• Varying the number of particles through the inlet and run the simulation for 3 cases. Report the number of particles that pass through or remain in the cyclonic separator. Post images to show the same. For this question, use the “Reflect” option as the boundary condition for the Discrete Phase

FOUR EMPIRICAL MODELS ARE USED FOR FINDING THE CYCLONE SEPERATOR EFFICIENCY:

1.IOZIA AND LEITH MODEL
Iozia and Leith (1990) logistic model is a modified versionof Barth (1956) 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. Core length, zc, and core diameter,dc
, are given as
zc = H - S for dc < B for dc< B (1b)

The addition made by Iozia and Leith on the original Barth(1956) model are the core length zc and slope parameter β expression which is derived based on the statistical analysis of experimental data of cyclone with D = 0.25 m. The collection efficiency ηi of particle diameter dpi can be calculated from where dpc is the 50% cut size given by Barth (1956).

`etai=(1)/(1+((dpc)/(overline(dp i)))overset beta`

where,

`dp i` is the particle diameter and

`d pc` 50% out size by barth.

2.LI AND WANG MODEL:

The Li and Wang (1989) model includes particle bounce or re-entrainment and turbulent diffusion at the cyclone wall. A two-dimensional 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 cyclones.
• Boundary conditions with the consideration of turbulent diffusion coefficient and particle bounce re-entrainment on the cyclone wall are:
c = c0, at θ = 0

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

`eta i = 1- exp(-lambda theta1)`

3.KOCH AND LICHT MODEL
Koch and Licht (1977) collection theory recognized the inherently turbulent nature of cyclones and the distribution of gas residence times within the cyclone. Koch and Licht
describe 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.

`eta i= 1-exp[-2((GTiQ)/(D overset3``(n+1))^((0.5)/(n+1))]`

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 (1951) 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 (1951) to
calculate a 50% cut diameter, dpc,

Here the efficiency is given as:

`eta i= ((1)/((1+((dpc)/( overline dp i))^2)))`

Geometry setup of cyclone seperator:

• setting up the geometry with import step file data file.
• From the Geometry we need to extract the volume extract for fluid flow.
• And compress the physics for various component for further action.

SETTING UP MESH :

• Importing the Geometry updated file.
• Generating the mesh with mesh size 10 mm.
• with help of Name selection assign the inlet, outlet1,outlet2.

MESH QUALITY:

PRE-PROCESSING:

• Updating the mesh.
• selecting -Double precision.
• processor - 4.
• Analysis is steady state.
• Gravity was enable with y-axis =-9.81 m/s.
• Viscous model was selected as K-epsilon with RNG Formulation,Swrill dominated flow was enable.
• Selecting Discret phase modeling setting as
• Injection setting was incountered with antharsite particular are inserted with in the model setting with surface on inlet.
• Injection also set and the details such as particles diameter as 5e-6
• Velocity is 3 m/s.
• Boundary conditions on inlet condition are provided along with DPM .
• Boundary conditions ( only inlet condition are provided along with DPM) there are four conditions for DPM at inlet ie, reflect,trap,escape, wall jet for varry this condition.
• Soultion Method should with Turbulent kinetic Energy -Second order upwind.
• Soultion method should with Turbulent dissipation Rate -second order upwind.
• With standard initialization was done and calculation with 600 iteration.

CASE 2: CONSIDERING REFLECT DPM IN BOUNDRY CONDITION:

Residual scale:

DPM DATA:

vortex :

ANIMATION:

CASE 2 BY CONSIDERING TRAP DPM IN BOUNDARY CONDITION.

RESIDUAL SCALE:

DPM DATA:

VORTEX:

ANIMATION:

CASE 2 BY CONSIDERING ESCAPE DPM IN BOUNDARY CONDITION:

RESIDUAL SCALE:

DPM DATA:

VORTEX:

ANIMATION:

CASE 2 BY CONSIDERING WALL JET DPM IN BOUNDARY CONDITION:

RESIDUAL SCALE:

DPM DATA:

VORTEX:

ANIMATION:

CASE 3: VARYING THE NUMBER OF SIZE OF THE PARTICLES ITS DEPENDS ON MESH SIZE

1. MESH SIZE 10MM WITH REFLECT METHOD:

SETTING UP MESH :

• Importing the Geometry updated file.
• Generating the mesh with mesh size 10 mm.
• with help of Name selection assign the inlet, outlet1,outlet2.

MESH QUALITY:

PRE-PROCESSING:

• Updating the mesh.
• selecting -Double precision.
• processor - 4.
• Analysis is steady state.
• Gravity was enable with y-axis =-9.81 m/s.
• Viscous model was selected as K-epsilon with RNG Formulation,Swrill dominated flow was enable.
• Selecting Discret phase modeling setting as
• Injection setting was incountered with antharsite particular are inserted with in the model setting with surface on inlet.
• Injection also set and the details such as particles diameter as 5e-6
• Velocity is 3 m/s.
• Boundary conditions on inlet condition are provided along with DPM .
• Boundary conditions ( only inlet condition are provided along with DPM) there are four conditions for DPM at inlet ie, reflect condition.
• Soultion Method should with Turbulent kinetic Energy -Second order upwind.
• Soultion method should with Turbulent dissipation Rate -second order upwind.
• With standard initialization was done and calculation with 600 iteration.

CASE 3: CONSIDERING REFLECT DPM IN BOUNDRY CONDITION:

Residual scale:

DPM DATA:

vortex :

ANIMATION:

2. MESH SIZE 12MM WITH REFLECT METHOD:

SETTING UP MESH :

• Importing the Geometry updated file.
• Generating the mesh with mesh size 12 mm.
• with help of Name selection assign the inlet, outlet1,outlet2.

MESH QUALITY:

PRE-PROCESSING:

• Updating the mesh.
• selecting -Double precision.
• processor - 4.
• Analysis is steady state.
• Gravity was enable with y-axis =-9.81 m/s.
• Viscous model was selected as K-epsilon with RNG Formulation,Swrill dominated flow was enable.
• Selecting Discret phase modeling setting as
• Injection setting was incountered with antharsite particular are inserted with in the model setting with surface on inlet.
• Injection also set and the details such as particles diameter as 5e-6
• Velocity is 3 m/s.
• Boundary conditions on inlet condition are provided along with DPM .
• Boundary conditions ( only inlet condition are provided along with DPM) there are four conditions for DPM at inlet ie, reflect condition.
• Soultion Method should with Turbulent kinetic Energy -Second order upwind.
• Soultion method should with Turbulent dissipation Rate -second order upwind.
• With standard initialization was done and calculation with 600 iteration.

CASE 3: CONSIDERING REFLECT DPM IN BOUNDRY CONDITION:

Residual scale:

DPM DATA:

vortex :

ANIMATION:

3. MESH SIZE 15MM WITH REFLECT METHOD:

SETTING UP MESH :

• Importing the Geometry updated file.
• Generating the mesh with mesh size 15 mm.
• with help of Name selection assign the inlet, outlet1,outlet2.

MESH QUALITY:

PRE-PROCESSING:

• Updating the mesh.
• selecting -Double precision.
• processor - 4.
• Analysis is steady state.
• Gravity was enable with y-axis =-9.81 m/s.
• Viscous model was selected as K-epsilon with RNG Formulation,Swrill dominated flow was enable.
• Selecting Discret phase modeling setting as
• Injection setting was incountered with antharsite particular are inserted with in the model setting with surface on inlet.
• Injection also set and the details such as particles diameter as 5e-6
• Velocity is 3 m/s.
• Boundary conditions on inlet condition are provided along with DPM .
• Boundary conditions ( only inlet condition are provided along with DPM) there are four conditions for DPM at inlet ie, reflect condition.
• Soultion Method should with Turbulent kinetic Energy -Second order upwind.
• Soultion method should with Turbulent dissipation Rate -second order upwind.
• With standard initialization was done and calculation with 600 iteration.

CASE 3: CONSIDERING REFLECT DPM IN BOUNDRY CONDITION:

Residual scale:

DPM DATA:

vortex :

ANIMATION:

COMPARE THE VARIOUS DATE: