Cyclone Separator Challenge

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

Introduction:

Cyclone Seperator:

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)—which is about as tall as a three story building

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.

Objective - 1:

Empirical models used to calculate the cyclone separator efficiency.

(i) Iozia and Leith Model:

Iozia and Leith logistic Model is a modified version of 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 flow resistance, W.

The collection of efficiency can be calculated by

(ii)Li and Wang Model:

The Li and Wang model include 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

The efficiency is calculated by

(iii)Leith and Licht:

According to Leith and Licht (1972), collection efficiency for a cyclone can be expressed by

where Q is the gas volumetric flow rate and t_i is called relaxation time, given by

where d_pi and r_p are the particle diameter and density, respectively, and m the gas viscosity.

The exponent, n, normally called the vortex index, can be estimated as a function of cyclone diameter (in ft) and of gas temperature (in ⁰F) by the following expression:

The effects of cyclone configuration on separation efficiency are considered using factor G, given by

where

The annular volume above the exit duct up to the middle of the gas entrance duct, V_s, is given by

The natural length of the vortex, l, can be estimated by

For l <(H-S), volume V_nl,, which is the volume of the region that includes the natural length of the vortex excluding the central core, can be estimated by

where the diameter of the central core, d_n, is defined by

For l>(H-S), volume V_H, which is the volume of gas below the gas exit duct excluding the core, can be calculated by

These design criteria, proposed Leith and Licht (1972), will be used for comparison throughout this work. A more detailed description of each one of these terms can be found in the above reference.

(iv)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,is

The efficiency of collection and size of particle is given by

Case setup:

Geometry:

The cyclone seperator model which we work is shown below.

We need to extract the fluid region.

After extraction:

The extracted fluid region is

Mesh:

The details of Mesh

The generated MEsh

Setup & Solution:

Solver - pressure based

Velocity formulation - Absolute

Gravity - enabled in Y direction

Viscous Model - K epsilon, RNG, Swirl Dominated Fluid, Standard wall functions.

Descrete Phase Model:

Particle diameter, Particle velocity and Velocity of fluid need to be changed as per our data need to be generated.

Injection type - surface, enabled at inlet

Results & Discussion:

Objective-2:

(i)

particle diameter = 5e-06

fluid velocity = 3m/s

particel velocity = 3m/s

Efficiency = 74%

Residuals:

Particle Time:

Maximum number of tracks - 100

Massflow at top both outlets:

Pressure:

https://drive.google.com/file/d/1e9OVN3cO0dtqdiIbBHnUMcjVJWHO_0uA/view?usp=sharing

(ii)

particle diameter = 3e-06

fluid velocity = 3m/s

particel velocity = 3m/s

Efficiency = 64%

Residuals:

Particle time:

Maximum number of tracks - 100

Pressure:

https://drive.google.com/file/d/1mzP_AbXs0VvrrDzQw53B0BUrQ1FNTVI8/view?usp=sharing

(iii)

particle diameter = 1e-06

fluid velocity = 3m/s

particel velocity = 3m/s

Efficiency = No. of particles Trapped/No. of particles tracked

therefore Efficiency = 55%

Residuals:

Particle Time:

Maximum number of tracks - 100

Pressure:

Objective-3:

(i)

particle diameter = 5e-06

fluid velocity = 1m/s

particel velocity = 1m/s

Efficiency = 40%

Residuals:

Particle Time:

Maximum number of tracks - 100

Velocity Vortex Core Region:

Pressure:

https://drive.google.com/file/d/1FGjSQH3_em4Dr671Vff71hxkGioTZ-EW/view?usp=sharing

(ii)

particle diameter = 5e-06

fluid velocity = 3m/s

particel velocity = 3m/s

Efficiency = 74.16%

Residuals:

Particle time:

Maximum number of tracks - 100

Pressure:

Pressure Vortex:

Velocity Vortex:

https://drive.google.com/file/d/1m9rco-6RcSi1VWXeSLC6kPKNI2SSCSAH/view?usp=sharing

(iii)

particle diameter = 5e-06

fluid velocity = 5m/s

particel velocity = 5m/s

Efficiency = 85%

Rediduals:

Particle time:

Maximum number of tracks - 100

Pressure:

Velocity Vortex:

Pressure vortex:

https://drive.google.com/file/d/1m0HPPLr2VK8JTR6B853NIxDRiLJq3SF0/view?usp=sharing

Conclusion:

For Objective-2:

Both velocities are 3m/s

for 1e-6 particle diameter = 55% efficiency

3e-6 particle diameter = 64% efficiency

5e-6 particle diameter = 74% efficiency

For Objective-3:

Fluid Velocity and particle velocity used are 1m/s, 3m/s, 5m/s by using particle diameter as 5e-6.

(i)particle diameter = 5e-06

for 1m/s = 40% efficiency

3m/s = 74% efficiency

5m/s = 85% efficiency

From both cases,

we can say that

by increasing both particle diamater,

increasing the fluid velocity,

increasing the particle velocity we can achieve more efficiency.