Challenge

Week 8 - Simulating Cyclone separator with Discrete Phase Modelling

SSuvrajit Champatiray4 Jan 2022

AIM:

To perform analysis on cyclone separator and calculate the separation efficiency and pressure drop for each of the cases.

OBJECTIVE:

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

INTRODUCTION:

CYCLONE SEPARATOR:

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. 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).
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 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.

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.
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.
Cyclone efficiency will generally increase with increases in particle size and/or density; inlet duct velocity; cyclone body length; number of gas revolutions in the cyclone; ratio of cyclone body diameter to gas exit diameter; inlet dust loading; smoothness of the cyclone inner wall.
Similarly, cyclone efficiency will 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.

EMPERICAL MODELS USED TO CALCULATE 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 165 the influence of two forces: a centrifugal force, Z and a flow resistance, W. The collection efficiency 'η' of particle diameter dpi can be calculated from
`η_i = 1 / (1 + (d_(pc)/d_(p))^ β)`
`beta` is an expression for slope parameter derived based on the statistical analysis of experimental data of a cyclone with D = 0.25 m given as
`beta = 0.62 − 0.87 ln( (d_pc )/100) + 5.21 ln ((ab) / D^2) + 1.05 (ln [(ab) / D^2 )]^2`
And dpc is the 50% cut size given by Barth
`d_(pc) = [(9muQ)/(pirhoZ_cv_(rmax)^2)]^0.5`
Where core length, Zc and core diameter dc are given as,
`Z_c = (H-S)-[(H-S)/((D/B)-1)][(d_c/B)-1]` for dc > B
`Z_c = H-S` for dc < B
`d_c = 0.47D((ab)/D^2)^-0.25(D_e/D)^1.4`

2. LI AND WANG MODEL:

The Li and Wang 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:
1. The radial particle velocity and the radial concentration profile are not constant for uncollected particles within the cyclone.
2. Boundary conditions with the consideration of turbulent diffusion coefficient and particle bounce re-entrainment on the cyclone wall are
`c=C_0` at `theta = 0`
`Dr (∂c)/(∂r) = (1 − α)wc, at r = D/2`
The tangential velocity is related to the radius of cyclone by: uR^n = constant.
The concentration distribution in a cyclone is given as:
`c(r,theta) = (c_0(rw − rn) exp { −λ [ 1/ (K(1+n)) r^ (1+n)]}) / ( int_(r_n)^(r_w) exp { 1 / (K(1+n)) r^(1+n) }dr`
Where `K = ((1-n)(rho_p-rho_g)d^2Q)/(18mub(r_(w)^(1-n) - r_n^(1-n)))`
and `lambda = ((1-alpha)Kw_w) / (D_rr_w^n`
The resultant expression of the collection efficiency for particle of any size is given as
`eta_i = 1-exp[-lambdatheta_1]`
where `theta_1 = (2pi(S+L))/a`

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:
1. 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.
2. The tangential velocity is related to the radius of cyclone by: u R^n = constant.
A force balance and an equation on the particles collection yields the grade efficiency η
`eta_i = 1 − exp{ −2 [ (Gτ_i Q) /D^3 (n + 1)]^(0.5/(n+1))}`
Where,
`G = (8K_c)/(K_a^2*K_b^2)`
`n = 1- { 1-((12D)^0.14)/2.5}*{(T+460)/530}^0.3`
`tau_i = (ρ_pd_p^ 2) / (18µ)`
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 to calculate a 50% cut diameter, dpc, is
`d_(pc) = [(9mub)/(2piN_ev_i(rho_p-rho_g))]^(1/2)`
Where, Ne is the number of revolutions
`N_e = (1/a)[h+(H-h)/2]`
The efficiency of collection of any size of particle is given by
`eta_i = 1/(1+(d_(pc) + d_p)^2)`

SIMULATION METHODOLOGY:

Case - 1:

Particle Size = 1 micrometer = 1e-06 m
Particle Velocity = 3m/s
Flow Velocity = 3m/s
Mesh element size = 5.0mm
Total mesh elements = 294520

GEOMETRY:

MESHING:

Used Hex Dominant method for meshing of the fluid volume extracted from the cyclone separator geometry.

SETUP:

RESULTS:

RESIDUALS:

PARTICLE TRACKING (ANTHRCITE PARTICLE TIME):

PRESSURE CONTOUR:

VELOCITY CONTOUR:

ANIMATION LINK:

CALCULATION:

Cyclone Separation Efficiency:

`eta =` Total number of Trapped Particles / Total number of Injected Particles

= (139/200) * 100%

= 69.5 %

Case - 2:

Particle Size = 3 micrometer = 3e-06 m
Particle Velocity = 3m/s
Flow Velocity = 3m/s
Mesh element size = 5.0mm
Total mesh elements = 294520

GEOMETRY:

MESHING:

Used Hex Dominant method for meshing of the fluid volume extracted from the cyclone separator geometry.

SETUP:

RESULTS:

RESIDUALS:

PARTICLE TRACKING (ANTHRCITE PARTICLE TIME):

PRESSURE CONTOUR:

VELOCITY CONTOUR:

ANIMATION LINK:

CALCULATION:

Cyclone Separation Efficiency:

`eta =` Total number of Trapped Particles / Total number of Injected Particles

= (159/200) * 100%

= 79.5 %

Case - 3:

Particle Size = 5 micrometer = 5e-06 m
Particle Velocity = 3m/s
Flow Velocity = 3m/s
Mesh element size = 5.0mm
Total mesh elements = 294520

GEOMETRY:

MESHING:

Used Hex Dominant method for meshing of the fluid volume extracted from the cyclone separator geometry.

SETUP:

RESULTS:

RESIDUALS:

PARTICLE TRACKING (ANTHRCITE PARTICLE TIME):

PRESSURE CONTOUR:

VELOCITY CONTOUR:

ANIMATION LINK:

CALCULATION:

Cyclone Separation Efficiency:

`eta =` Total number of Trapped Particles / Total number of Injected Particles

= (190/200) * 100%

= 95.0 %

Case - 4:

Particle Size = 5 micrometer = 5e-06 m
Particle Velocity = 1m/s
Flow Velocity = 1m/s
Mesh element size = 5.0mm
Total mesh elements = 294520

GEOMETRY:

MESHING:

Used Hex Dominant method for meshing of the fluid volume extracted from the cyclone separator geometry.

SETUP:

RESULTS:

RESIDUALS:

PARTICLE TRACKING (ANTHRCITE PARTICLE TIME):

PRESSURE CONTOUR:

VELOCITY CONTOUR:

ANIMATION LINK:

CALCULATION:

Cyclone Separation Efficiency:

`eta =` Total number of Trapped Particles / Total number of Injected Particles

= (138/200) * 100%

= 69.0 %

Case - 5:

Particle Size = 5 micrometer = 5e-06 m
Particle Velocity = 3m/s
Flow Velocity = 3m/s
Mesh element size = 5.0mm
Total mesh elements = 294520

GEOMETRY:

MESHING:

Used Hex Dominant method for meshing of the fluid volume extracted from the cyclone separator geometry.

SETUP:

RESULTS:

RESIDUALS:

PARTICLE TRACKING (ANTHRCITE PARTICLE TIME):

PRESSURE CONTOUR:

VELOCITY CONTOUR:

ANIMATION LINK:

CALCULATION:

Cyclone Separation Efficiency:

`eta =` Total number of Trapped Particles / Total number of Injected Particles

= (190/200) * 100%

= 95.0 %

Case - 6:

Particle Size = 5 micrometer = 5e-06 m
Particle Velocity = 5m/s
Flow Velocity = 5m/s
Mesh element size = 5.0mm
Total mesh elements = 294520

GEOMETRY:

MESHING:

Used Hex Dominant method for meshing of the fluid volume extracted from the cyclone separator geometry.

SETUP:

RESULTS:

RESIDUALS:

PARTICLE TRACKING (ANTHRCITE PARTICLE TIME):

PRESSURE CONTOUR:

VELOCITY CONTOUR:

ANIMATION LINK:

https://youtu.be/AeoJ4XnYRjI
https://drive.google.com/file/d/1hsncRmrbtboRGCtU_jvQ6nTVI1-_Ja4R/view?usp=sharing

CALCULATION:

Cyclone Separation Efficiency:

`eta =` Total number of Trapped Particles / Total number of Injected Particles

= (200/200) * 100%

= 100.0 %

TABULATION:

SL NO.	PARTICLE SIZE (m) (1`mu`m = 1e-06 m)	PARTICLE VELOCITY (m/s)	FLOW VELOCITY (m/s)	SEPARATION EFFICIENCY (%) (`eta`)
01.	1e-06	3	3	69.5
02.	3e-06	3	3	79.5
03.	5e-06	3	3	95.0
04.	5e-06	1	1	69.0
05.	5e-06	3	3	95.0
06.	5e-06	5	5	100.0

CONCLUSION:

From the above assignment we learnt about the Cyclone Separator and we performed the analysis on the Cyclone Separator with different particle size and different particle velocity to study the nature and behavior of flow inside the Cyclone Separator.
From the above table we can observe that for the first case where the Particle velocity and Inlet Flow velocity are constant and as we increase the size of the particle the Separation Efficiency increases.
Also, we can observe from the table for the second case where the particle size is constant as we increase the particle velocity and inlet flow velocity the Separation Efficiency increases.
Cyclone efficiency will generally increase with increases in particle size and/or density; inlet duct velocity; cyclone body length; number of gas revolutions in the cyclone; ratio of cyclone body diameter to gas exit diameter; inlet dust loading; smoothness of the cyclone inner wall.
Similarly, cyclone efficiency will 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.

Week 8 - Simulating Cyclone separator with Discrete Phase Modelling

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in your own course.

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Ship work like thisin your own course.

Talk to a career counsellor

Ship work like this
in your own course.