Cyclone Separator Challenge
Aim:- To perform analysis on cyclone separator and calculate the separation efficiency and pressure drop.
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 calculate the separation efficiency in each case. Discuss the results. [Use 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 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]
Boundary Conditions:-
Inlet and wall:- Reflect
Outlet(Top):- Escape
Outlet(Bottom/dustbin) - Trap
Software used: Ansys Fluent
Theory:
Cyclone separators or simply cyclones are separation devices 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 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.
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 below Figure 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 micrometres in diameter. However, there do exist high efficiency cyclones that are designed to be effective on particles as small as 2.5 micrometres. As well, these separators are not effective on extremely large particulate matter. For particulates around 200 micrometres 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 Efficiency Empirical Models:
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 of particle diameter dpi can be calculated from
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
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:
- The radial particle velocity and the radial concentration profile are not constant for uncollected particles with in the cyclone.
• Boundary conditions with the consideration of turbulent diffusion coefficient and particle bounce re-entrainment on the cyclone wall are:
The resultant expression of the collection efficiency for particle of any size is given as
where
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 ad- 200ditional following assumptions:
The tangential velocity of a particle is equal to the tan-genital 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
G is a factor related to the configuration of the cyclone, n is related to the vortex and T is the relaxation term.
Lapple Model:
Lapple model was developed based on force balance with-out 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
The efficency of collection of any size particle is given by
Methodology:
There are two different Phases as given below:
Continuous Phase:
It consists of fluid flow within the fluid volume.
Discrete Phase:
It consists of smaller particles interacting with continuous Phase. It can also exchange momentum, mass and energy with Fluid phase or Continuous phase.
Discrete Phase modelling (DPM):
Uncoupled Flow:
Discrete phase will not have any interaction with continuous phase.
Coupled Flow:
Influence the flow of continuous phase.
Formulas:
Separation Efficiency:
It is the ratio of trapped particles to the total number of particles tracked.
Pressure Drop:
It is defined as the difference in total pressure between two points of fluid carrying in network.
Pressure drop = total inlet pressure - total outlet pressure(top)
Geometry:
Import the geometry model in Space Claim and create the volume extract region in prepare option.
Select the inlet and outlets for create the volume region in Space claim using edge selection.
Meshing:
The mesh is generated with the help of cut cell method, where available in Assembly Meshing.
The Maximum size of the element is 7 mm.
Case Setup:
To perform this simulation using steady state simulation with pressure based solver.
Gravity also enable because one of the outlet is positioned used to gravity.
Models:
K-e RNZ model is best suitable for this type of problems.
it capture the Swirl dominated flow.
Enable the Discrete phase model for capturing the smaller particles interacting with continuous Phase.
Next click on the Injections
Next create option in injections.
Boundary Conditions:
Inlet velocity is 3m/s.
Inlet and wall DPM is reflect
Outlet(Top):- Escape
Outlet(Bottom/dustbin) - Trap
Solution Methods:
Initialization:
Part A
1. Particle Diameter = 1 μm and velocity is 3m/s
Residual Plot
Contour:
Vortex core region:
separation efficiency = Trapped particles / total no of particles
= 20/98
= 0.204 or 20.4%
2. Particle Diameter = 2 μm and velocity is 3m/s
Residual Plot:
Contour:
Vortex core region:
separation efficiency = Trapped particles / total no of particles
= 64/98
= 0.653 or 65.3%
3. Particle Diameter = 3 μm and velocity is 3m/s
Residual Plot:
Contour:
Vortex core region:
separation efficiency = Trapped particles / total no of particles
= 70/98
= 0.714 or 71.4%
4. Particle Diameter = 4 μm and velocity is 3m/s
Residual Plot:
Contour:
Vortex core region:
separation efficiency = Trapped particles / total no of particles
= 87/98
= 0.887 or 88.7%
5. Particle Diameter = 5 μm and velocity is 3m/s
Residual Plot:
Contour:
Vortex core region:
separation efficiency = Trapped particles / total no of particles
= 98/98
= 1or 100%
Observations:
If particle diameter increases, Separation efficiency also increases.
Trapped Particles increases when increases in particle diameter.
If increases the diameter of the particle, the particulate at top_outlet also decreases.
Lighter particle will escape at top_outlet because lighter in weight.
Higher particle will trap at bottom_outlet due to heaver in size also due to gravity.
Part B:
1. Particle Diameter = 5 μm and velocity is 1 m/s
Residual Plot:
Inlet Pressure:
Top Outlet Pressure:
Contours:
Pressure and velocity contour:
Pressure drop = total inlet pressure - total outlet pressure(top)
= 2.7443 - 0.3394
= 2.4049 pa
separation efficiency = Trapped particles / total no of particles
=9/98
= 0.0918 or 09.18%
2. Particle Diameter = 5 μm and velocity is 2 m/s
Residual Plot:
Inlet Pressure:
Top oulet Pressure:
Contours:
Pressure and velocity contour:
Pressure drop = total inlet pressure - total outlet pressure(top)
= 13.20362 - 1.6511
= 11.5525 pa
separation efficiency = Trapped particles / total no of particles
=59/98
= 0.6020 or 60.20%
3. Particle Diameter = 5 μm and velocity is 3 m/s
Residual Plot:
Inlet Pressure:
Outlet Pressure:
Contour:
Pressure and velocity contour:
Pressure drop = total inlet pressure - total outlet pressure(top)
= 31.9219 - 3.9342
= 27.9877 pa
separation efficiency = Trapped particles / total no of particles
=98/98
= 1 or 100%
4. Particle Diameter = 5 μm and velocity is 4 m/s
Residual Plot:
Inlet Pressure:
Outlet Pressure:
Contour:
Pressure and velocity contour:
Pressure drop = total inlet pressure - total outlet pressure(top)
= 59.1213 - 7.2283
= 51.893 pa
separation efficiency = Trapped particles / total no of particles
=98/98
= 1 or 100%
5. Particle Diameter = 5 μm and velocity is 5 m/s
Residual Plot:
Inlet Pressure:
Outlet Pressure:
Contour:
Pressure and velocity contour:
Pressure drop = total inlet pressure - total outlet pressure(top)
= 95.4086 -11.6103
= 83.7983 pa
separation efficiency = Trapped particles / total no of particles
=98/98
= 1 or 100%
Observations:
If increases the velocity at inlet, Separation efficiency also increases.
Pressure drop also increases with increases in velocity but particle diameter kept constant.
Solution takes more time to converge for velocity increases.
Lighter particle will escape at top_outlet because lighter in weight.
Higher particle will trap at bottom_outlet due to heaver in size also due to gravity.
Separation efficiency of Cyclone separator depends on both diameter of particles and also velocity of the particles.
Efficiency of a cyclone separator has direct effect on pressure drop.
Higher the velocity, higher the pressure drop and highest the efficiency.
Pressure drop depends on the velocity of the particle. As velocity increases the pressure difference between inlet and outlet increases.